// Copyright (C) 2018-2019, Cloudflare, Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimer.
//
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//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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//! 🥧 Savoury implementation of the QUIC transport protocol and HTTP/3.
//!
//! [quiche] is an implementation of the QUIC transport protocol and HTTP/3 as
//! specified by the [IETF]. It provides a low level API for processing QUIC
//! packets and handling connection state. The application is responsible for
//! providing I/O (e.g. sockets handling) as well as an event loop with support
//! for timers.
//!
//! [quiche]: https://github.com/cloudflare/quiche/
//! [ietf]: https://quicwg.org/
//!
//! ## Connection setup
//!
//! The first step in establishing a QUIC connection using quiche is creating a
//! configuration object:
//!
//! ```
//! let config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! This is shared among multiple connections and can be used to configure a
//! QUIC endpoint.
//!
//! On the client-side the [`connect()`] utility function can be used to create
//! a new connection, while [`accept()`] is for servers:
//!
//! ```
//! # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # let server_name = "quic.tech";
//! # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
//! # let to = "127.0.0.1:1234".parse().unwrap();
//! // Client connection.
//! let conn = quiche::connect(Some(&server_name), &scid, to, &mut config)?;
//!
//! // Server connection.
//! # let from = "127.0.0.1:1234".parse().unwrap();
//! let conn = quiche::accept(&scid, None, from, &mut config)?;
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! In both cases, the application is responsible for generating a new source
//! connection ID that will be used to identify the new connection.
//!
//! The application also need to pass the address of the remote peer of the
//! connection: in the case of a client that would be the address of the server
//! it is trying to connect to, and for a server that is the address of the
//! client that initiated the connection.
//!
//! ## Handling incoming packets
//!
//! Using the connection's [`recv()`] method the application can process
//! incoming packets that belong to that connection from the network:
//!
//! ```no_run
//! # let mut buf = [0; 512];
//! # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
//! # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
//! # let from = "127.0.0.1:1234".parse().unwrap();
//! # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
//! loop {
//!     let (read, from) = socket.recv_from(&mut buf).unwrap();
//!
//!     let recv_info = quiche::RecvInfo { from };
//!
//!     let read = match conn.recv(&mut buf[..read], recv_info) {
//!         Ok(v) => v,
//!
//!         Err(quiche::Error::Done) => {
//!             // Done reading.
//!             break;
//!         },
//!
//!         Err(e) => {
//!             // An error occurred, handle it.
//!             break;
//!         },
//!     };
//! }
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! The application has to pass a [`RecvInfo`] structure in order to provide
//! additional information about the received packet (such as the address it
//! was received from).
//!
//! ## Generating outgoing packets
//!
//! Outgoing packet are generated using the connection's [`send()`] method
//! instead:
//!
//! ```no_run
//! # let mut out = [0; 512];
//! # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
//! # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
//! # let from = "127.0.0.1:1234".parse().unwrap();
//! # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
//! loop {
//!     let (write, send_info) = match conn.send(&mut out) {
//!         Ok(v) => v,
//!
//!         Err(quiche::Error::Done) => {
//!             // Done writing.
//!             break;
//!         },
//!
//!         Err(e) => {
//!             // An error occurred, handle it.
//!             break;
//!         },
//!     };
//!
//!     socket.send_to(&out[..write], &send_info.to).unwrap();
//! }
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! The application will be provided with a [`SendInfo`] structure providing
//! additional information about the newly created packet (such as the address
//! the packet should be sent to).
//!
//! When packets are sent, the application is responsible for maintaining a
//! timer to react to time-based connection events. The timer expiration can be
//! obtained using the connection's [`timeout()`] method.
//!
//! ```
//! # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
//! # let from = "127.0.0.1:1234".parse().unwrap();
//! # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
//! let timeout = conn.timeout();
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! The application is responsible for providing a timer implementation, which
//! can be specific to the operating system or networking framework used. When
//! a timer expires, the connection's [`on_timeout()`] method should be called,
//! after which additional packets might need to be sent on the network:
//!
//! ```no_run
//! # let mut out = [0; 512];
//! # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
//! # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
//! # let from = "127.0.0.1:1234".parse().unwrap();
//! # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
//! // Timeout expired, handle it.
//! conn.on_timeout();
//!
//! // Send more packets as needed after timeout.
//! loop {
//!     let (write, send_info) = match conn.send(&mut out) {
//!         Ok(v) => v,
//!
//!         Err(quiche::Error::Done) => {
//!             // Done writing.
//!             break;
//!         },
//!
//!         Err(e) => {
//!             // An error occurred, handle it.
//!             break;
//!         },
//!     };
//!
//!     socket.send_to(&out[..write], &send_info.to).unwrap();
//! }
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! ## Sending and receiving stream data
//!
//! After some back and forth, the connection will complete its handshake and
//! will be ready for sending or receiving application data.
//!
//! Data can be sent on a stream by using the [`stream_send()`] method:
//!
//! ```no_run
//! # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
//! # let from = "127.0.0.1:1234".parse().unwrap();
//! # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
//! if conn.is_established() {
//!     // Handshake completed, send some data on stream 0.
//!     conn.stream_send(0, b"hello", true)?;
//! }
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! The application can check whether there are any readable streams by using
//! the connection's [`readable()`] method, which returns an iterator over all
//! the streams that have outstanding data to read.
//!
//! The [`stream_recv()`] method can then be used to retrieve the application
//! data from the readable stream:
//!
//! ```no_run
//! # let mut buf = [0; 512];
//! # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
//! # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
//! # let from = "127.0.0.1:1234".parse().unwrap();
//! # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
//! if conn.is_established() {
//!     // Iterate over readable streams.
//!     for stream_id in conn.readable() {
//!         // Stream is readable, read until there's no more data.
//!         while let Ok((read, fin)) = conn.stream_recv(stream_id, &mut buf) {
//!             println!("Got {} bytes on stream {}", read, stream_id);
//!         }
//!     }
//! }
//! # Ok::<(), quiche::Error>(())
//! ```
//!
//! ## HTTP/3
//!
//! The quiche [HTTP/3 module] provides a high level API for sending and
//! receiving HTTP requests and responses on top of the QUIC transport protocol.
//!
//! [`connect()`]: fn.connect.html
//! [`accept()`]: fn.accept.html
//! [`recv()`]: struct.Connection.html#method.recv
//! [`RecvInfo`]: struct.RecvInfo.html
//! [`send()`]: struct.Connection.html#method.send
//! [`SendInfo`]: struct.SendInfo.html
//! [`timeout()`]: struct.Connection.html#method.timeout
//! [`on_timeout()`]: struct.Connection.html#method.on_timeout
//! [`stream_send()`]: struct.Connection.html#method.stream_send
//! [`readable()`]: struct.Connection.html#method.readable
//! [`stream_recv()`]: struct.Connection.html#method.stream_recv
//! [HTTP/3 module]: h3/index.html
//!
//! ## Congestion Control
//!
//! The quiche library provides a high-level API for configuring which
//! congestion control algorithm to use throughout the QUIC connection.
//!
//! When a QUIC connection is created, the application can optionally choose
//! which CC algorithm to use. See [`CongestionControlAlgorithm`] for currently
//! available congestion control algorithms.
//!
//! For example:
//!
//! ```
//! let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION).unwrap();
//! config.set_cc_algorithm(quiche::CongestionControlAlgorithm::Reno);
//! ```
//!
//! Alternatively, you can configure the congestion control algorithm to use
//! by its name.
//!
//! ```
//! let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION).unwrap();
//! config.set_cc_algorithm_name("reno").unwrap();
//! ```
//!
//! Note that the CC algorithm should be configured before calling [`connect()`]
//! or [`accept()`]. Otherwise the connection will use a default CC algorithm.
//!
//! [`CongestionControlAlgorithm`]: enum.CongestionControlAlgorithm.html

#![allow(improper_ctypes)]
#![allow(clippy::suspicious_operation_groupings)]
#![allow(clippy::upper_case_acronyms)]
#![warn(missing_docs)]

#[macro_use]
extern crate log;

use std::cmp;
use std::time;

use std::net::SocketAddr;

use std::pin::Pin;
use std::str::FromStr;

use std::collections::VecDeque;

/// The current QUIC wire version.
pub const PROTOCOL_VERSION: u32 = PROTOCOL_VERSION_V1;

/// Supported QUIC versions.
///
/// Note that the older ones might not be fully supported.
const PROTOCOL_VERSION_V1: u32 = 0x0000_0001;
const PROTOCOL_VERSION_DRAFT27: u32 = 0xff00_001b;
const PROTOCOL_VERSION_DRAFT28: u32 = 0xff00_001c;
const PROTOCOL_VERSION_DRAFT29: u32 = 0xff00_001d;

/// The maximum length of a connection ID.
pub const MAX_CONN_ID_LEN: usize = crate::packet::MAX_CID_LEN as usize;

/// The minimum length of Initial packets sent by a client.
pub const MIN_CLIENT_INITIAL_LEN: usize = 1200;

#[cfg(not(feature = "fuzzing"))]
const PAYLOAD_MIN_LEN: usize = 4;

#[cfg(feature = "fuzzing")]
// Due to the fact that in fuzzing mode we use a zero-length AEAD tag (which
// would normally be 16 bytes), we need to adjust the minimum payload size to
// account for that.
const PAYLOAD_MIN_LEN: usize = 20;

const MAX_AMPLIFICATION_FACTOR: usize = 3;

// The maximum number of tracked packet number ranges that need to be acked.
//
// This represents more or less how many ack blocks can fit in a typical packet.
const MAX_ACK_RANGES: usize = 68;

// The highest possible stream ID allowed.
const MAX_STREAM_ID: u64 = 1 << 60;

// The default max_datagram_size used in congestion control.
const MAX_SEND_UDP_PAYLOAD_SIZE: usize = 1200;

// The default length of DATAGRAM queues.
const DEFAULT_MAX_DGRAM_QUEUE_LEN: usize = 0;

// The DATAGRAM standard recommends either none or 65536 as maximum DATAGRAM
// frames size. We enforce the recommendation for forward compatibility.
const MAX_DGRAM_FRAME_SIZE: u64 = 65536;

// The length of the payload length field.
const PAYLOAD_LENGTH_LEN: usize = 2;

// The number of undecryptable that can be buffered.
const MAX_UNDECRYPTABLE_PACKETS: usize = 10;

const RESERVED_VERSION_MASK: u32 = 0xfafafafa;

// The default size of the receiver connection flow control window.
const DEFAULT_CONNECTION_WINDOW: u64 = 48 * 1024;

// The maximum size of the receiver connection flow control window.
const MAX_CONNECTION_WINDOW: u64 = 24 * 1024 * 1024;

// How much larger the connection flow control window need to be larger than
// the stream flow control window.
const CONNECTION_WINDOW_FACTOR: f64 = 1.5;

/// A specialized [`Result`] type for quiche operations.
///
/// This type is used throughout quiche's public API for any operation that
/// can produce an error.
///
/// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html
pub type Result<T> = std::result::Result<T, Error>;

/// A QUIC error.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum Error {
    /// There is no more work to do.
    Done,

    /// The provided buffer is too short.
    BufferTooShort,

    /// The provided packet cannot be parsed because its version is unknown.
    UnknownVersion,

    /// The provided packet cannot be parsed because it contains an invalid
    /// frame.
    InvalidFrame,

    /// The provided packet cannot be parsed.
    InvalidPacket,

    /// The operation cannot be completed because the connection is in an
    /// invalid state.
    InvalidState,

    /// The operation cannot be completed because the stream is in an
    /// invalid state.
    ///
    /// The stream ID is provided as associated data.
    InvalidStreamState(u64),

    /// The peer's transport params cannot be parsed.
    InvalidTransportParam,

    /// A cryptographic operation failed.
    CryptoFail,

    /// The TLS handshake failed.
    TlsFail,

    /// The peer violated the local flow control limits.
    FlowControl,

    /// The peer violated the local stream limits.
    StreamLimit,

    /// The specified stream was stopped by the peer.
    ///
    /// The error code sent as part of the `STOP_SENDING` frame is provided as
    /// associated data.
    StreamStopped(u64),

    /// The specified stream was reset by the peer.
    ///
    /// The error code sent as part of the `RESET_STREAM` frame is provided as
    /// associated data.
    StreamReset(u64),

    /// The received data exceeds the stream's final size.
    FinalSize,

    /// Error in congestion control.
    CongestionControl,
}

impl Error {
    fn to_wire(self) -> u64 {
        match self {
            Error::Done => 0x0,
            Error::InvalidFrame => 0x7,
            Error::InvalidStreamState(..) => 0x5,
            Error::InvalidTransportParam => 0x8,
            Error::FlowControl => 0x3,
            Error::StreamLimit => 0x4,
            Error::FinalSize => 0x6,
            _ => 0xa,
        }
    }

    #[cfg(feature = "ffi")]
    fn to_c(self) -> libc::ssize_t {
        match self {
            Error::Done => -1,
            Error::BufferTooShort => -2,
            Error::UnknownVersion => -3,
            Error::InvalidFrame => -4,
            Error::InvalidPacket => -5,
            Error::InvalidState => -6,
            Error::InvalidStreamState(_) => -7,
            Error::InvalidTransportParam => -8,
            Error::CryptoFail => -9,
            Error::TlsFail => -10,
            Error::FlowControl => -11,
            Error::StreamLimit => -12,
            Error::FinalSize => -13,
            Error::CongestionControl => -14,
            Error::StreamStopped { .. } => -15,
            Error::StreamReset { .. } => -16,
        }
    }
}

impl std::fmt::Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{:?}", self)
    }
}

impl std::error::Error for Error {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        None
    }
}

impl std::convert::From<octets::BufferTooShortError> for Error {
    fn from(_err: octets::BufferTooShortError) -> Self {
        Error::BufferTooShort
    }
}

/// Ancillary information about incoming packets.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct RecvInfo {
    /// The address the packet was received from.
    pub from: SocketAddr,
}

/// Ancillary information about outgoing packets.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct SendInfo {
    /// The address the packet should be sent to.
    pub to: SocketAddr,

    /// The time to send the packet out.
    pub at: time::Instant,
}

/// Represents information carried by `CONNECTION_CLOSE` frames.
#[derive(Clone, Debug, PartialEq)]
pub struct ConnectionError {
    /// Whether the error came from the application or the transport layer.
    pub is_app: bool,

    /// The error code carried by the `CONNECTION_CLOSE` frame.
    pub error_code: u64,

    /// The reason carried by the `CONNECTION_CLOSE` frame.
    pub reason: Vec<u8>,
}

/// The stream's side to shutdown.
///
/// This should be used when calling [`stream_shutdown()`].
///
/// [`stream_shutdown()`]: struct.Connection.html#method.stream_shutdown
#[repr(C)]
pub enum Shutdown {
    /// Stop receiving stream data.
    Read  = 0,

    /// Stop sending stream data.
    Write = 1,
}

/// Qlog logging level.
#[repr(C)]
#[cfg(feature = "qlog")]
pub enum QlogLevel {
    /// Logs any events of Core importance.
    Core  = 0,

    /// Logs any events of Core and Base importance.
    Base  = 1,

    /// Logs any events of Core, Base and Extra importance
    Extra = 2,
}

/// Stores configuration shared between multiple connections.
pub struct Config {
    local_transport_params: TransportParams,

    version: u32,

    tls_ctx: tls::Context,

    application_protos: Vec<Vec<u8>>,

    grease: bool,

    cc_algorithm: CongestionControlAlgorithm,

    hystart: bool,

    dgram_recv_max_queue_len: usize,
    dgram_send_max_queue_len: usize,

    max_send_udp_payload_size: usize,

    max_connection_window: u64,
    max_stream_window: u64,
}

// See https://quicwg.org/base-drafts/rfc9000.html#section-15
fn is_reserved_version(version: u32) -> bool {
    version & RESERVED_VERSION_MASK == version
}

impl Config {
    /// Creates a config object with the given version.
    ///
    /// ## Examples:
    ///
    /// ```
    /// let config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn new(version: u32) -> Result<Config> {
        if !is_reserved_version(version) && !version_is_supported(version) {
            return Err(Error::UnknownVersion);
        }

        let tls_ctx = tls::Context::new()?;

        Ok(Config {
            local_transport_params: TransportParams::default(),
            version,
            tls_ctx,
            application_protos: Vec::new(),
            grease: true,
            cc_algorithm: CongestionControlAlgorithm::CUBIC,
            hystart: true,

            dgram_recv_max_queue_len: DEFAULT_MAX_DGRAM_QUEUE_LEN,
            dgram_send_max_queue_len: DEFAULT_MAX_DGRAM_QUEUE_LEN,

            max_send_udp_payload_size: MAX_SEND_UDP_PAYLOAD_SIZE,

            max_connection_window: MAX_CONNECTION_WINDOW,
            max_stream_window: stream::MAX_STREAM_WINDOW,
        })
    }

    /// Configures the given certificate chain.
    ///
    /// The content of `file` is parsed as a PEM-encoded leaf certificate,
    /// followed by optional intermediate certificates.
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut config = quiche::Config::new(0xbabababa)?;
    /// config.load_cert_chain_from_pem_file("/path/to/cert.pem")?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn load_cert_chain_from_pem_file(&mut self, file: &str) -> Result<()> {
        self.tls_ctx.use_certificate_chain_file(file)
    }

    /// Configures the given private key.
    ///
    /// The content of `file` is parsed as a PEM-encoded private key.
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut config = quiche::Config::new(0xbabababa)?;
    /// config.load_priv_key_from_pem_file("/path/to/key.pem")?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn load_priv_key_from_pem_file(&mut self, file: &str) -> Result<()> {
        self.tls_ctx.use_privkey_file(file)
    }

    /// Specifies a file where trusted CA certificates are stored for the
    /// purposes of certificate verification.
    ///
    /// The content of `file` is parsed as a PEM-encoded certificate chain.
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut config = quiche::Config::new(0xbabababa)?;
    /// config.load_verify_locations_from_file("/path/to/cert.pem")?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn load_verify_locations_from_file(&mut self, file: &str) -> Result<()> {
        self.tls_ctx.load_verify_locations_from_file(file)
    }

    /// Specifies a directory where trusted CA certificates are stored for the
    /// purposes of certificate verification.
    ///
    /// The content of `dir` a set of PEM-encoded certificate chains.
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut config = quiche::Config::new(0xbabababa)?;
    /// config.load_verify_locations_from_directory("/path/to/certs")?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn load_verify_locations_from_directory(
        &mut self, dir: &str,
    ) -> Result<()> {
        self.tls_ctx.load_verify_locations_from_directory(dir)
    }

    /// Configures whether to verify the peer's certificate.
    ///
    /// The default value is `true` for client connections, and `false` for
    /// server ones.
    pub fn verify_peer(&mut self, verify: bool) {
        self.tls_ctx.set_verify(verify);
    }

    /// Configures whether to send GREASE values.
    ///
    /// The default value is `true`.
    pub fn grease(&mut self, grease: bool) {
        self.grease = grease;
    }

    /// Enables logging of secrets.
    ///
    /// When logging is enabled, the [`set_keylog()`] method must be called on
    /// the connection for its cryptographic secrets to be logged in the
    /// [keylog] format to the specified writer.
    ///
    /// [`set_keylog()`]: struct.Connection.html#method.set_keylog
    /// [keylog]: https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format
    pub fn log_keys(&mut self) {
        self.tls_ctx.enable_keylog();
    }

    /// Configures the session ticket key material.
    ///
    /// On the server this key will be used to encrypt and decrypt session
    /// tickets, used to perform session resumption without server-side state.
    ///
    /// By default a key is generated internally, and rotated regularly, so
    /// applications don't need to call this unless they need to use a
    /// specific key (e.g. in order to support resumption across multiple
    /// servers), in which case the application is also responsible for
    /// rotating the key to provide forward secrecy.
    pub fn set_ticket_key(&mut self, key: &[u8]) -> Result<()> {
        self.tls_ctx.set_ticket_key(key)
    }

    /// Enables sending or receiving early data.
    pub fn enable_early_data(&mut self) {
        self.tls_ctx.set_early_data_enabled(true);
    }

    /// Configures the list of supported application protocols.
    ///
    /// The list of protocols `protos` must be in wire-format (i.e. a series
    /// of non-empty, 8-bit length-prefixed strings).
    ///
    /// On the client this configures the list of protocols to send to the
    /// server as part of the ALPN extension.
    ///
    /// On the server this configures the list of supported protocols to match
    /// against the client-supplied list.
    ///
    /// Applications must set a value, but no default is provided.
    ///
    /// ## Examples:
    ///
    /// ```
    /// # let mut config = quiche::Config::new(0xbabababa)?;
    /// config.set_application_protos(b"\x08http/1.1\x08http/0.9")?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn set_application_protos(&mut self, protos: &[u8]) -> Result<()> {
        let mut b = octets::Octets::with_slice(protos);

        let mut protos_list = Vec::new();

        while let Ok(proto) = b.get_bytes_with_u8_length() {
            protos_list.push(proto.to_vec());
        }

        self.application_protos = protos_list;

        self.tls_ctx.set_alpn(&self.application_protos)
    }

    /// Sets the `max_idle_timeout` transport parameter, in milliseconds.
    ///
    /// The default value is infinite, that is, no timeout is used.
    pub fn set_max_idle_timeout(&mut self, v: u64) {
        self.local_transport_params.max_idle_timeout = v;
    }

    /// Sets the `max_udp_payload_size transport` parameter.
    ///
    /// The default value is `65527`.
    pub fn set_max_recv_udp_payload_size(&mut self, v: usize) {
        self.local_transport_params.max_udp_payload_size = v as u64;
    }

    /// Sets the maximum outgoing UDP payload size.
    ///
    /// The default and minimum value is `1200`.
    pub fn set_max_send_udp_payload_size(&mut self, v: usize) {
        self.max_send_udp_payload_size = cmp::max(v, MAX_SEND_UDP_PAYLOAD_SIZE);
    }

    /// Sets the `initial_max_data` transport parameter.
    ///
    /// When set to a non-zero value quiche will only allow at most `v` bytes
    /// of incoming stream data to be buffered for the whole connection (that
    /// is, data that is not yet read by the application) and will allow more
    /// data to be received as the buffer is consumed by the application.
    ///
    /// The default value is `0`.
    pub fn set_initial_max_data(&mut self, v: u64) {
        self.local_transport_params.initial_max_data = v;
    }

    /// Sets the `initial_max_stream_data_bidi_local` transport parameter.
    ///
    /// When set to a non-zero value quiche will only allow at most `v` bytes
    /// of incoming stream data to be buffered for each locally-initiated
    /// bidirectional stream (that is, data that is not yet read by the
    /// application) and will allow more data to be received as the buffer is
    /// consumed by the application.
    ///
    /// The default value is `0`.
    pub fn set_initial_max_stream_data_bidi_local(&mut self, v: u64) {
        self.local_transport_params
            .initial_max_stream_data_bidi_local = v;
    }

    /// Sets the `initial_max_stream_data_bidi_remote` transport parameter.
    ///
    /// When set to a non-zero value quiche will only allow at most `v` bytes
    /// of incoming stream data to be buffered for each remotely-initiated
    /// bidirectional stream (that is, data that is not yet read by the
    /// application) and will allow more data to be received as the buffer is
    /// consumed by the application.
    ///
    /// The default value is `0`.
    pub fn set_initial_max_stream_data_bidi_remote(&mut self, v: u64) {
        self.local_transport_params
            .initial_max_stream_data_bidi_remote = v;
    }

    /// Sets the `initial_max_stream_data_uni` transport parameter.
    ///
    /// When set to a non-zero value quiche will only allow at most `v` bytes
    /// of incoming stream data to be buffered for each unidirectional stream
    /// (that is, data that is not yet read by the application) and will allow
    /// more data to be received as the buffer is consumed by the application.
    ///
    /// The default value is `0`.
    pub fn set_initial_max_stream_data_uni(&mut self, v: u64) {
        self.local_transport_params.initial_max_stream_data_uni = v;
    }

    /// Sets the `initial_max_streams_bidi` transport parameter.
    ///
    /// When set to a non-zero value quiche will only allow `v` number of
    /// concurrent remotely-initiated bidirectional streams to be open at any
    /// given time and will increase the limit automatically as streams are
    /// completed.
    ///
    /// A bidirectional stream is considered completed when all incoming data
    /// has been read by the application (up to the `fin` offset) or the
    /// stream's read direction has been shutdown, and all outgoing data has
    /// been acked by the peer (up to the `fin` offset) or the stream's write
    /// direction has been shutdown.
    ///
    /// The default value is `0`.
    pub fn set_initial_max_streams_bidi(&mut self, v: u64) {
        self.local_transport_params.initial_max_streams_bidi = v;
    }

    /// Sets the `initial_max_streams_uni` transport parameter.
    ///
    /// When set to a non-zero value quiche will only allow `v` number of
    /// concurrent remotely-initiated unidirectional streams to be open at any
    /// given time and will increase the limit automatically as streams are
    /// completed.
    ///
    /// A unidirectional stream is considered completed when all incoming data
    /// has been read by the application (up to the `fin` offset) or the
    /// stream's read direction has been shutdown.
    ///
    /// The default value is `0`.
    pub fn set_initial_max_streams_uni(&mut self, v: u64) {
        self.local_transport_params.initial_max_streams_uni = v;
    }

    /// Sets the `ack_delay_exponent` transport parameter.
    ///
    /// The default value is `3`.
    pub fn set_ack_delay_exponent(&mut self, v: u64) {
        self.local_transport_params.ack_delay_exponent = v;
    }

    /// Sets the `max_ack_delay` transport parameter.
    ///
    /// The default value is `25`.
    pub fn set_max_ack_delay(&mut self, v: u64) {
        self.local_transport_params.max_ack_delay = v;
    }

    /// Sets the `disable_active_migration` transport parameter.
    ///
    /// The default value is `false`.
    pub fn set_disable_active_migration(&mut self, v: bool) {
        self.local_transport_params.disable_active_migration = v;
    }

    /// Sets the congestion control algorithm used by string.
    ///
    /// The default value is `cubic`. On error `Error::CongestionControl`
    /// will be returned.
    ///
    /// ## Examples:
    ///
    /// ```
    /// # let mut config = quiche::Config::new(0xbabababa)?;
    /// config.set_cc_algorithm_name("reno");
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn set_cc_algorithm_name(&mut self, name: &str) -> Result<()> {
        self.cc_algorithm = CongestionControlAlgorithm::from_str(name)?;

        Ok(())
    }

    /// Sets the congestion control algorithm used.
    ///
    /// The default value is `CongestionControlAlgorithm::CUBIC`.
    pub fn set_cc_algorithm(&mut self, algo: CongestionControlAlgorithm) {
        self.cc_algorithm = algo;
    }

    /// Configures whether to enable HyStart++.
    ///
    /// The default value is `true`.
    pub fn enable_hystart(&mut self, v: bool) {
        self.hystart = v;
    }

    /// Configures whether to enable receiving DATAGRAM frames.
    ///
    /// When enabled, the `max_datagram_frame_size` transport parameter is set
    /// to 65536 as recommended by draft-ietf-quic-datagram-01.
    ///
    /// The default is `false`.
    pub fn enable_dgram(
        &mut self, enabled: bool, recv_queue_len: usize, send_queue_len: usize,
    ) {
        self.local_transport_params.max_datagram_frame_size = if enabled {
            Some(MAX_DGRAM_FRAME_SIZE)
        } else {
            None
        };
        self.dgram_recv_max_queue_len = recv_queue_len;
        self.dgram_send_max_queue_len = send_queue_len;
    }

    /// Sets the maximum size of the connection window.
    ///
    /// The default value is MAX_CONNECTION_WINDOW (24MBytes).
    pub fn set_max_connection_window(&mut self, v: u64) {
        self.max_connection_window = v;
    }

    /// Sets the maximum size of the stream window.
    ///
    /// The default value is MAX_STREAM_WINDOW (16MBytes).
    pub fn set_max_stream_window(&mut self, v: u64) {
        self.max_stream_window = v;
    }
}

/// A QUIC connection.
pub struct Connection {
    /// QUIC wire version used for the connection.
    version: u32,

    /// Peer's connection ID.
    dcid: ConnectionId<'static>,

    /// Local connection ID.
    scid: ConnectionId<'static>,

    /// Unique opaque ID for the connection that can be used for logging.
    trace_id: String,

    /// Packet number spaces.
    pkt_num_spaces: [packet::PktNumSpace; packet::EPOCH_COUNT],

    /// Peer's transport parameters.
    peer_transport_params: TransportParams,

    /// Local transport parameters.
    local_transport_params: TransportParams,

    /// TLS handshake state.
    handshake: tls::Handshake,

    /// Serialized TLS session buffer.
    ///
    /// This field is populated when a new session ticket is processed on the
    /// client. On the server this is empty.
    session: Option<Vec<u8>>,

    /// Loss recovery and congestion control state.
    recovery: recovery::Recovery,

    peer_addr: SocketAddr,

    /// List of supported application protocols.
    application_protos: Vec<Vec<u8>>,

    /// Total number of received packets.
    recv_count: usize,

    /// Total number of sent packets.
    sent_count: usize,

    /// Total number of packets sent with data retransmitted.
    retrans_count: usize,

    /// Total number of bytes received from the peer.
    rx_data: u64,

    /// Receiver flow controller.
    flow_control: flowcontrol::FlowControl,

    /// Whether we send MAX_DATA frame.
    almost_full: bool,

    /// Number of stream data bytes that can be buffered.
    tx_cap: usize,

    /// Total number of bytes sent to the peer.
    tx_data: u64,

    /// Peer's flow control limit for the connection.
    max_tx_data: u64,

    /// Total number of bytes the server can send before the peer's address
    /// is verified.
    max_send_bytes: usize,

    /// Total number of bytes retransmitted over the connection.
    /// This counts only STREAM and CRYPTO data.
    stream_retrans_bytes: u64,

    /// Total number of bytes sent over the connection.
    sent_bytes: u64,

    /// Total number of bytes recevied over the connection.
    recv_bytes: u64,

    /// Streams map, indexed by stream ID.
    streams: stream::StreamMap,

    /// Peer's original destination connection ID. Used by the client to
    /// validate the server's transport parameter.
    odcid: Option<ConnectionId<'static>>,

    /// Peer's retry source connection ID. Used by the client during stateless
    /// retry to validate the server's transport parameter.
    rscid: Option<ConnectionId<'static>>,

    /// Received address verification token.
    token: Option<Vec<u8>>,

    /// Error code and reason to be sent to the peer in a CONNECTION_CLOSE
    /// frame.
    local_error: Option<ConnectionError>,

    /// Error code and reason received from the peer in a CONNECTION_CLOSE
    /// frame.
    peer_error: Option<ConnectionError>,

    /// Received path challenge.
    challenge: Option<Vec<u8>>,

    /// The connection-level limit at which send blocking occurred.
    blocked_limit: Option<u64>,

    /// Idle timeout expiration time.
    idle_timer: Option<time::Instant>,

    /// Draining timeout expiration time.
    draining_timer: Option<time::Instant>,

    /// List of raw packets that were received before they could be decrypted.
    undecryptable_pkts: VecDeque<(Vec<u8>, RecvInfo)>,

    /// The negotiated ALPN protocol.
    alpn: Vec<u8>,

    /// Whether this is a server-side connection.
    is_server: bool,

    /// Whether the initial secrets have been derived.
    derived_initial_secrets: bool,

    /// Whether a version negotiation packet has already been received. Only
    /// relevant for client connections.
    did_version_negotiation: bool,

    /// Whether stateless retry has been performed.
    did_retry: bool,

    /// Whether the peer already updated its connection ID.
    got_peer_conn_id: bool,

    /// Whether the peer's address has been verified.
    verified_peer_address: bool,

    /// Whether the peer has verified our address.
    peer_verified_address: bool,

    /// Whether the peer's transport parameters were parsed.
    parsed_peer_transport_params: bool,

    /// Whether the connection handshake has been completed.
    handshake_completed: bool,

    /// Whether the HANDSHAKE_DONE frame has been sent.
    handshake_done_sent: bool,

    /// Whether the HANDSHAKE_DONE frame has been acked.
    handshake_done_acked: bool,

    /// Whether the connection handshake has been confirmed.
    handshake_confirmed: bool,

    /// Whether an ack-eliciting packet has been sent since last receiving a
    /// packet.
    ack_eliciting_sent: bool,

    /// Whether the connection is closed.
    closed: bool,

    // Whether the connection was timed out
    timed_out: bool,

    /// Whether to send GREASE.
    grease: bool,

    /// TLS keylog writer.
    keylog: Option<Box<dyn std::io::Write + Send + Sync>>,

    #[cfg(feature = "qlog")]
    qlog: QlogInfo,

    /// DATAGRAM queues.
    dgram_recv_queue: dgram::DatagramQueue,
    dgram_send_queue: dgram::DatagramQueue,

    /// Whether to emit DATAGRAM frames in the next packet.
    emit_dgram: bool,
}

/// Creates a new server-side connection.
///
/// The `scid` parameter represents the server's source connection ID, while
/// the optional `odcid` parameter represents the original destination ID the
/// client sent before a stateless retry (this is only required when using
/// the [`retry()`] function).
///
/// [`retry()`]: fn.retry.html
///
/// ## Examples:
///
/// ```no_run
/// # let mut config = quiche::Config::new(0xbabababa)?;
/// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
/// # let from = "127.0.0.1:1234".parse().unwrap();
/// let conn = quiche::accept(&scid, None, from, &mut config)?;
/// # Ok::<(), quiche::Error>(())
/// ```
#[inline]
pub fn accept(
    scid: &ConnectionId, odcid: Option<&ConnectionId>, from: SocketAddr,
    config: &mut Config,
) -> Result<Pin<Box<Connection>>> {
    let conn = Connection::new(scid, odcid, from, config, true)?;

    Ok(conn)
}

/// Creates a new client-side connection.
///
/// The `scid` parameter is used as the connection's source connection ID,
/// while the optional `server_name` parameter is used to verify the peer's
/// certificate.
///
/// ## Examples:
///
/// ```no_run
/// # let mut config = quiche::Config::new(0xbabababa)?;
/// # let server_name = "quic.tech";
/// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
/// # let to = "127.0.0.1:1234".parse().unwrap();
/// let conn = quiche::connect(Some(&server_name), &scid, to, &mut config)?;
/// # Ok::<(), quiche::Error>(())
/// ```
#[inline]
pub fn connect(
    server_name: Option<&str>, scid: &ConnectionId, to: SocketAddr,
    config: &mut Config,
) -> Result<Pin<Box<Connection>>> {
    let mut conn = Connection::new(scid, None, to, config, false)?;

    if let Some(server_name) = server_name {
        conn.handshake.set_host_name(server_name)?;
    }

    Ok(conn)
}

/// Writes a version negotiation packet.
///
/// The `scid` and `dcid` parameters are the source connection ID and the
/// destination connection ID extracted from the received client's Initial
/// packet that advertises an unsupported version.
///
/// ## Examples:
///
/// ```no_run
/// # let mut buf = [0; 512];
/// # let mut out = [0; 512];
/// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
/// let (len, src) = socket.recv_from(&mut buf).unwrap();
///
/// let hdr =
///     quiche::Header::from_slice(&mut buf[..len], quiche::MAX_CONN_ID_LEN)?;
///
/// if hdr.version != quiche::PROTOCOL_VERSION {
///     let len = quiche::negotiate_version(&hdr.scid, &hdr.dcid, &mut out)?;
///     socket.send_to(&out[..len], &src).unwrap();
/// }
/// # Ok::<(), quiche::Error>(())
/// ```
#[inline]
pub fn negotiate_version(
    scid: &ConnectionId, dcid: &ConnectionId, out: &mut [u8],
) -> Result<usize> {
    packet::negotiate_version(scid, dcid, out)
}

/// Writes a stateless retry packet.
///
/// The `scid` and `dcid` parameters are the source connection ID and the
/// destination connection ID extracted from the received client's Initial
/// packet, while `new_scid` is the server's new source connection ID and
/// `token` is the address validation token the client needs to echo back.
///
/// The application is responsible for generating the address validation
/// token to be sent to the client, and verifying tokens sent back by the
/// client. The generated token should include the `dcid` parameter, such
/// that it can be later extracted from the token and passed to the
/// [`accept()`] function as its `odcid` parameter.
///
/// [`accept()`]: fn.accept.html
///
/// ## Examples:
///
/// ```no_run
/// # let mut config = quiche::Config::new(0xbabababa)?;
/// # let mut buf = [0; 512];
/// # let mut out = [0; 512];
/// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
/// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
/// # fn mint_token(hdr: &quiche::Header, src: &std::net::SocketAddr) -> Vec<u8> {
/// #     vec![]
/// # }
/// # fn validate_token<'a>(src: &std::net::SocketAddr, token: &'a [u8]) -> Option<quiche::ConnectionId<'a>> {
/// #     None
/// # }
/// let (len, src) = socket.recv_from(&mut buf).unwrap();
///
/// let hdr = quiche::Header::from_slice(&mut buf[..len], quiche::MAX_CONN_ID_LEN)?;
///
/// let token = hdr.token.as_ref().unwrap();
///
/// // No token sent by client, create a new one.
/// if token.is_empty() {
///     let new_token = mint_token(&hdr, &src);
///
///     let len = quiche::retry(
///         &hdr.scid, &hdr.dcid, &scid, &new_token, hdr.version, &mut out,
///     )?;
///
///     socket.send_to(&out[..len], &src).unwrap();
///     return Ok(());
/// }
///
/// // Client sent token, validate it.
/// let odcid = validate_token(&src, token);
///
/// if odcid.is_none() {
///     // Invalid address validation token.
///     return Ok(());
/// }
///
/// let conn = quiche::accept(&scid, odcid.as_ref(), src, &mut config)?;
/// # Ok::<(), quiche::Error>(())
/// ```
#[inline]
pub fn retry(
    scid: &ConnectionId, dcid: &ConnectionId, new_scid: &ConnectionId,
    token: &[u8], version: u32, out: &mut [u8],
) -> Result<usize> {
    packet::retry(scid, dcid, new_scid, token, version, out)
}

/// Returns true if the given protocol version is supported.
#[inline]
pub fn version_is_supported(version: u32) -> bool {
    matches!(
        version,
        PROTOCOL_VERSION_V1 |
            PROTOCOL_VERSION_DRAFT27 |
            PROTOCOL_VERSION_DRAFT28 |
            PROTOCOL_VERSION_DRAFT29
    )
}

/// Pushes a frame to the output packet if there is enough space.
///
/// Returns `true` on success, `false` otherwise. In case of failure it means
/// there is no room to add the frame in the packet. You may retry to add the
/// frame later.
macro_rules! push_frame_to_pkt {
    ($out:expr, $frames:expr, $frame:expr, $left:expr) => {{
        if $frame.wire_len() <= $left {
            $left -= $frame.wire_len();

            $frame.to_bytes(&mut $out)?;

            $frames.push($frame);

            true
        } else {
            false
        }
    }};
}

/// Conditional qlog actions.
///
/// Executes the provided body if the qlog feature is enabled and quiche
/// has been configured with a log writer.
macro_rules! qlog_with {
    ($qlog:expr, $qlog_streamer_ref:ident, $body:block) => {{
        #[cfg(feature = "qlog")]
        {
            if let Some($qlog_streamer_ref) = &mut $qlog.streamer {
                $body
            }
        }
    }};
}

/// Executes the provided body if the qlog feature is enabled, quiche has been
/// configured with a log writer, the event's importance is within the
/// confgured level.
macro_rules! qlog_with_type {
    ($ty:expr, $qlog:expr, $qlog_streamer_ref:ident, $body:block) => {{
        #[cfg(feature = "qlog")]
        {
            if qlog::EventImportance::from($ty).is_contained_in(&$qlog.level) {
                if let Some($qlog_streamer_ref) = &mut $qlog.streamer {
                    $body
                }
            }
        }
    }};
}

#[cfg(feature = "qlog")]
const QLOG_PARAMS_SET: qlog::EventType =
    qlog::EventType::TransportEventType(qlog::TransportEventType::ParametersSet);

#[cfg(feature = "qlog")]
const QLOG_PACKET_RX: qlog::EventType =
    qlog::EventType::TransportEventType(qlog::TransportEventType::PacketReceived);

#[cfg(feature = "qlog")]
const QLOG_PACKET_TX: qlog::EventType =
    qlog::EventType::TransportEventType(qlog::TransportEventType::PacketSent);

#[cfg(feature = "qlog")]
const QLOG_DATA_MV: qlog::EventType =
    qlog::EventType::TransportEventType(qlog::TransportEventType::DataMoved);

#[cfg(feature = "qlog")]
const QLOG_METRICS: qlog::EventType =
    qlog::EventType::RecoveryEventType(qlog::RecoveryEventType::MetricsUpdated);

#[cfg(feature = "qlog")]
struct QlogInfo {
    streamer: Option<qlog::QlogStreamer>,
    logged_peer_params: bool,
    level: qlog::EventImportance,
}

#[cfg(feature = "qlog")]
impl Default for QlogInfo {
    fn default() -> Self {
        QlogInfo {
            streamer: None,
            logged_peer_params: false,
            level: qlog::EventImportance::Base,
        }
    }
}

impl Connection {
    fn new(
        scid: &ConnectionId, odcid: Option<&ConnectionId>, peer: SocketAddr,
        config: &mut Config, is_server: bool,
    ) -> Result<Pin<Box<Connection>>> {
        let tls = config.tls_ctx.new_handshake()?;
        Connection::with_tls(scid, odcid, peer, config, tls, is_server)
    }

    fn with_tls(
        scid: &ConnectionId, odcid: Option<&ConnectionId>, peer: SocketAddr,
        config: &mut Config, tls: tls::Handshake, is_server: bool,
    ) -> Result<Pin<Box<Connection>>> {
        let max_rx_data = config.local_transport_params.initial_max_data;

        let scid_as_hex: Vec<String> =
            scid.iter().map(|b| format!("{:02x}", b)).collect();

        let mut conn = Box::pin(Connection {
            version: config.version,

            dcid: ConnectionId::default(),
            scid: scid.to_vec().into(),

            trace_id: scid_as_hex.join(""),

            pkt_num_spaces: [
                packet::PktNumSpace::new(),
                packet::PktNumSpace::new(),
                packet::PktNumSpace::new(),
            ],

            peer_transport_params: TransportParams::default(),

            local_transport_params: config.local_transport_params.clone(),

            handshake: tls,

            session: None,

            recovery: recovery::Recovery::new(config),

            peer_addr: peer,

            application_protos: config.application_protos.clone(),

            recv_count: 0,
            sent_count: 0,
            retrans_count: 0,
            sent_bytes: 0,
            recv_bytes: 0,

            rx_data: 0,
            flow_control: flowcontrol::FlowControl::new(
                max_rx_data,
                cmp::min(max_rx_data / 2 * 3, DEFAULT_CONNECTION_WINDOW),
                config.max_connection_window,
            ),
            almost_full: false,

            tx_cap: 0,

            tx_data: 0,
            max_tx_data: 0,

            stream_retrans_bytes: 0,

            max_send_bytes: 0,

            streams: stream::StreamMap::new(
                config.local_transport_params.initial_max_streams_bidi,
                config.local_transport_params.initial_max_streams_uni,
                config.max_stream_window,
            ),

            odcid: None,

            rscid: None,

            token: None,

            local_error: None,

            peer_error: None,

            challenge: None,

            blocked_limit: None,

            idle_timer: None,

            draining_timer: None,

            undecryptable_pkts: VecDeque::new(),

            alpn: Vec::new(),

            is_server,

            derived_initial_secrets: false,

            did_version_negotiation: false,

            did_retry: false,

            got_peer_conn_id: false,

            // If we did stateless retry assume the peer's address is verified.
            verified_peer_address: odcid.is_some(),

            // Assume clients validate the server's address implicitly.
            peer_verified_address: is_server,

            parsed_peer_transport_params: false,

            handshake_completed: false,

            handshake_done_sent: false,
            handshake_done_acked: false,

            handshake_confirmed: false,

            ack_eliciting_sent: false,

            closed: false,

            timed_out: false,

            grease: config.grease,

            keylog: None,

            #[cfg(feature = "qlog")]
            qlog: Default::default(),

            dgram_recv_queue: dgram::DatagramQueue::new(
                config.dgram_recv_max_queue_len,
            ),

            dgram_send_queue: dgram::DatagramQueue::new(
                config.dgram_send_max_queue_len,
            ),

            emit_dgram: true,
        });

        if let Some(odcid) = odcid {
            conn.local_transport_params
                .original_destination_connection_id = Some(odcid.to_vec().into());

            conn.local_transport_params.retry_source_connection_id =
                Some(scid.to_vec().into());

            conn.did_retry = true;
        }

        conn.local_transport_params.initial_source_connection_id =
            Some(scid.to_vec().into());

        let conn_ptr = &conn as &Connection as *const Connection;
        conn.handshake.init(conn_ptr, is_server)?;

        conn.handshake
            .use_legacy_codepoint(config.version != PROTOCOL_VERSION_V1);

        conn.encode_transport_params()?;

        // Derive initial secrets for the client. We can do this here because
        // we already generated the random destination connection ID.
        if !is_server {
            let mut dcid = [0; 16];
            rand::rand_bytes(&mut dcid[..]);

            let (aead_open, aead_seal) = crypto::derive_initial_key_material(
                &dcid,
                conn.version,
                conn.is_server,
            )?;

            conn.dcid = dcid.to_vec().into();

            conn.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_open =
                Some(aead_open);
            conn.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_seal =
                Some(aead_seal);

            conn.derived_initial_secrets = true;
        }

        Ok(conn)
    }

    /// Sets keylog output to the designated [`Writer`].
    ///
    /// This needs to be called as soon as the connection is created, to avoid
    /// missing some early logs.
    ///
    /// [`Writer`]: https://doc.rust-lang.org/std/io/trait.Write.html
    #[inline]
    pub fn set_keylog(&mut self, writer: Box<dyn std::io::Write + Send + Sync>) {
        self.keylog = Some(writer);
    }

    /// Sets qlog output to the designated [`Writer`].
    ///
    /// Only events included in `QlogLevel::Base` are written.
    ///
    /// This needs to be called as soon as the connection is created, to avoid
    /// missing some early logs.
    ///
    /// [`Writer`]: https://doc.rust-lang.org/std/io/trait.Write.html
    #[cfg(feature = "qlog")]
    pub fn set_qlog(
        &mut self, writer: Box<dyn std::io::Write + Send + Sync>, title: String,
        description: String,
    ) {
        self.set_qlog_with_level(writer, title, description, QlogLevel::Base)
    }

    /// Sets qlog output to the designated [`Writer`].
    ///
    /// Only qlog events included in the specified `QlogLevel` are written
    ///
    /// This needs to be called as soon as the connection is created, to avoid
    /// missing some early logs.
    ///
    /// [`Writer`]: https://doc.rust-lang.org/std/io/trait.Write.html
    #[cfg(feature = "qlog")]
    pub fn set_qlog_with_level(
        &mut self, writer: Box<dyn std::io::Write + Send + Sync>, title: String,
        description: String, qlog_level: QlogLevel,
    ) {
        let vp = if self.is_server {
            qlog::VantagePointType::Server
        } else {
            qlog::VantagePointType::Client
        };

        let level = match qlog_level {
            QlogLevel::Core => qlog::EventImportance::Core,

            QlogLevel::Base => qlog::EventImportance::Base,

            QlogLevel::Extra => qlog::EventImportance::Extra,
        };

        self.qlog.level = level;

        let trace = qlog::Trace::new(
            qlog::VantagePoint {
                name: None,
                ty: vp,
                flow: None,
            },
            Some(title.to_string()),
            Some(description.to_string()),
            Some(qlog::Configuration {
                time_offset: Some(0.0),
                original_uris: None,
            }),
            None,
        );

        let mut streamer = qlog::QlogStreamer::new(
            qlog::QLOG_VERSION.to_string(),
            Some(title),
            Some(description),
            None,
            time::Instant::now(),
            trace,
            self.qlog.level.clone(),
            writer,
        );

        streamer.start_log().ok();

        let ev_data = self
            .local_transport_params
            .to_qlog(qlog::TransportOwner::Local, self.handshake.cipher());

        // This event occurs very early, so just mark the relative time as 0.0.
        streamer
            .add_event(qlog::Event::with_time(0.0, ev_data))
            .ok();

        self.qlog.streamer = Some(streamer);
    }

    /// Configures the given session for resumption.
    ///
    /// On the client, this can be used to offer the given serialized session,
    /// as returned by [`session()`], for resumption.
    ///
    /// This must only be called immediately after creating a connection, that
    /// is, before any packet is sent or received.
    ///
    /// [`session()`]: struct.Connection.html#method.session
    #[inline]
    pub fn set_session(&mut self, session: &[u8]) -> Result<()> {
        let mut b = octets::Octets::with_slice(session);

        let session_len = b.get_u64()? as usize;
        let session_bytes = b.get_bytes(session_len)?;

        self.handshake.set_session(session_bytes.as_ref())?;

        let raw_params_len = b.get_u64()? as usize;
        let raw_params_bytes = b.get_bytes(raw_params_len)?;

        let peer_params =
            TransportParams::decode(raw_params_bytes.as_ref(), self.is_server)?;

        self.process_peer_transport_params(peer_params);

        Ok(())
    }

    /// Processes QUIC packets received from the peer.
    ///
    /// On success the number of bytes processed from the input buffer is
    /// returned. On error the connection will be closed by calling [`close()`]
    /// with the appropriate error code.
    ///
    /// Coalesced packets will be processed as necessary.
    ///
    /// Note that the contents of the input buffer `buf` might be modified by
    /// this function due to, for example, in-place decryption.
    ///
    /// [`close()`]: struct.Connection.html#method.close
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// loop {
    ///     let (read, from) = socket.recv_from(&mut buf).unwrap();
    ///
    ///     let recv_info = quiche::RecvInfo { from };
    ///
    ///     let read = match conn.recv(&mut buf[..read], recv_info) {
    ///         Ok(v) => v,
    ///
    ///         Err(e) => {
    ///             // An error occurred, handle it.
    ///             break;
    ///         },
    ///     };
    /// }
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn recv(&mut self, buf: &mut [u8], info: RecvInfo) -> Result<usize> {
        let len = buf.len();

        if len == 0 {
            return Err(Error::BufferTooShort);
        }

        // Keep track of how many bytes we received from the client, so we
        // can limit bytes sent back before address validation, to a multiple
        // of this. The limit needs to be increased early on, so that if there
        // is an error there is enough credit to send a CONNECTION_CLOSE.
        //
        // It doesn't matter if the packets received were valid or not, we only
        // need to track the total amount of bytes received.
        if !self.verified_peer_address {
            self.max_send_bytes += len * MAX_AMPLIFICATION_FACTOR;
        }

        let mut done = 0;
        let mut left = len;

        // Process coalesced packets.
        while left > 0 {
            let read = match self.recv_single(&mut buf[len - left..len], &info) {
                Ok(v) => v,

                Err(Error::Done) => left,

                Err(e) => {
                    // In case of error processing the incoming packet, close
                    // the connection.
                    self.close(false, e.to_wire(), b"").ok();
                    return Err(e);
                },
            };

            done += read;
            left -= read;
        }

        // Process previously undecryptable 0-RTT packets if the decryption key
        // is now available.
        if self.pkt_num_spaces[packet::EPOCH_APPLICATION]
            .crypto_0rtt_open
            .is_some()
        {
            while let Some((mut pkt, info)) = self.undecryptable_pkts.pop_front()
            {
                if let Err(e) = self.recv(&mut pkt, info) {
                    self.undecryptable_pkts.clear();

                    // Even though the packet was previously "accepted", it
                    // should be safe to forward the error, as it also comes
                    // from the `recv()` method.
                    return Err(e);
                }
            }
        }

        Ok(done)
    }

    /// Processes a single QUIC packet received from the peer.
    ///
    /// On success the number of bytes processed from the input buffer is
    /// returned. When the [`Done`] error is returned, processing of the
    /// remainder of the incoming UDP datagram should be interrupted.
    ///
    /// On error, an error other than [`Done`] is returned.
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    fn recv_single(&mut self, buf: &mut [u8], info: &RecvInfo) -> Result<usize> {
        let now = time::Instant::now();

        if buf.is_empty() {
            return Err(Error::Done);
        }

        if self.is_closed() || self.is_draining() {
            return Err(Error::Done);
        }

        let is_closing = self.local_error.is_some();

        if is_closing {
            return Err(Error::Done);
        }

        let mut b = octets::OctetsMut::with_slice(buf);

        let mut hdr =
            Header::from_bytes(&mut b, self.scid.len()).map_err(|e| {
                drop_pkt_on_err(
                    e,
                    self.recv_count,
                    self.is_server,
                    &self.trace_id,
                )
            })?;

        if hdr.ty == packet::Type::VersionNegotiation {
            // Version negotiation packets can only be sent by the server.
            if self.is_server {
                return Err(Error::Done);
            }

            // Ignore duplicate version negotiation.
            if self.did_version_negotiation {
                return Err(Error::Done);
            }

            // Ignore version negotiation if any other packet has already been
            // successfully processed.
            if self.recv_count > 0 {
                return Err(Error::Done);
            }

            if hdr.dcid != self.scid {
                return Err(Error::Done);
            }

            if hdr.scid != self.dcid {
                return Err(Error::Done);
            }

            trace!("{} rx pkt {:?}", self.trace_id, hdr);

            let versions = hdr.versions.ok_or(Error::Done)?;

            // Ignore version negotiation if the version already selected is
            // listed.
            if versions.iter().any(|&v| v == self.version) {
                return Err(Error::Done);
            }

            let supported_versions =
                versions.iter().filter(|&&v| version_is_supported(v));

            let mut found_version = false;

            for &v in supported_versions {
                found_version = true;

                // The final version takes precedence over draft ones.
                if v == PROTOCOL_VERSION_V1 {
                    self.version = v;
                    break;
                }

                self.version = cmp::max(self.version, v);
            }

            if !found_version {
                // We don't support any of the versions offered.
                //
                // While a man-in-the-middle attacker might be able to
                // inject a version negotiation packet that triggers this
                // failure, the window of opportunity is very small and
                // this error is quite useful for debugging, so don't just
                // ignore the packet.
                return Err(Error::UnknownVersion);
            }

            self.did_version_negotiation = true;

            // Derive Initial secrets based on the new version.
            let (aead_open, aead_seal) = crypto::derive_initial_key_material(
                &self.dcid,
                self.version,
                self.is_server,
            )?;

            // Reset connection state to force sending another Initial packet.
            self.drop_epoch_state(packet::EPOCH_INITIAL, now);
            self.got_peer_conn_id = false;
            self.handshake.clear()?;

            self.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_open =
                Some(aead_open);
            self.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_seal =
                Some(aead_seal);

            self.handshake
                .use_legacy_codepoint(self.version != PROTOCOL_VERSION_V1);

            // Encode transport parameters again, as the new version might be
            // using a different format.
            self.encode_transport_params()?;

            return Err(Error::Done);
        }

        if hdr.ty == packet::Type::Retry {
            // Retry packets can only be sent by the server.
            if self.is_server {
                return Err(Error::Done);
            }

            // Ignore duplicate retry.
            if self.did_retry {
                return Err(Error::Done);
            }

            // Check if Retry packet is valid.
            if packet::verify_retry_integrity(&b, &self.dcid, self.version)
                .is_err()
            {
                return Err(Error::Done);
            }

            trace!("{} rx pkt {:?}", self.trace_id, hdr);

            self.token = hdr.token;
            self.did_retry = true;

            // Remember peer's new connection ID.
            self.odcid = Some(self.dcid.clone());

            self.dcid = hdr.scid.clone();

            self.rscid = Some(self.dcid.clone());

            // Derive Initial secrets using the new connection ID.
            let (aead_open, aead_seal) = crypto::derive_initial_key_material(
                &hdr.scid,
                self.version,
                self.is_server,
            )?;

            // Reset connection state to force sending another Initial packet.
            self.drop_epoch_state(packet::EPOCH_INITIAL, now);
            self.got_peer_conn_id = false;
            self.handshake.clear()?;

            self.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_open =
                Some(aead_open);
            self.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_seal =
                Some(aead_seal);

            return Err(Error::Done);
        }

        if self.is_server && !self.did_version_negotiation {
            if !version_is_supported(hdr.version) {
                return Err(Error::UnknownVersion);
            }

            self.version = hdr.version;
            self.did_version_negotiation = true;

            self.handshake
                .use_legacy_codepoint(self.version != PROTOCOL_VERSION_V1);

            // Encode transport parameters again, as the new version might be
            // using a different format.
            self.encode_transport_params()?;
        }

        if hdr.ty != packet::Type::Short && hdr.version != self.version {
            // At this point version negotiation was already performed, so
            // ignore packets that don't match the connection's version.
            return Err(Error::Done);
        }

        // Long header packets have an explicit payload length, but short
        // packets don't so just use the remaining capacity in the buffer.
        let payload_len = if hdr.ty == packet::Type::Short {
            b.cap()
        } else {
            b.get_varint().map_err(|e| {
                drop_pkt_on_err(
                    e.into(),
                    self.recv_count,
                    self.is_server,
                    &self.trace_id,
                )
            })? as usize
        };

        // Make sure the buffer is same or larger than an explicit
        // payload length.
        if payload_len > b.cap() {
            return Err(drop_pkt_on_err(
                Error::InvalidPacket,
                self.recv_count,
                self.is_server,
                &self.trace_id,
            ));
        }

        // Derive initial secrets on the server.
        if !self.derived_initial_secrets {
            let (aead_open, aead_seal) = crypto::derive_initial_key_material(
                &hdr.dcid,
                self.version,
                self.is_server,
            )?;

            self.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_open =
                Some(aead_open);
            self.pkt_num_spaces[packet::EPOCH_INITIAL].crypto_seal =
                Some(aead_seal);

            self.derived_initial_secrets = true;
        }

        // Select packet number space epoch based on the received packet's type.
        let epoch = hdr.ty.to_epoch()?;

        // Select AEAD context used to open incoming packet.
        let aead = if hdr.ty == packet::Type::ZeroRTT {
            // Only use 0-RTT key if incoming packet is 0-RTT.
            self.pkt_num_spaces[epoch].crypto_0rtt_open.as_ref()
        } else {
            // Otherwise use the packet number space's main key.
            self.pkt_num_spaces[epoch].crypto_open.as_ref()
        };

        // Finally, discard packet if no usable key is available.
        let aead = match aead {
            Some(v) => v,

            None => {
                if hdr.ty == packet::Type::ZeroRTT &&
                    self.undecryptable_pkts.len() < MAX_UNDECRYPTABLE_PACKETS &&
                    !self.is_established()
                {
                    // Buffer 0-RTT packets when the required read key is not
                    // available yet, and process them later.
                    //
                    // TODO: in the future we might want to buffer other types
                    // of undecryptable packets as well.
                    let pkt_len = b.off() + payload_len;
                    let pkt = (b.buf()[..pkt_len]).to_vec();

                    self.undecryptable_pkts.push_back((pkt, *info));
                    return Ok(pkt_len);
                }

                let e = drop_pkt_on_err(
                    Error::CryptoFail,
                    self.recv_count,
                    self.is_server,
                    &self.trace_id,
                );

                return Err(e);
            },
        };

        let aead_tag_len = aead.alg().tag_len();

        packet::decrypt_hdr(&mut b, &mut hdr, aead).map_err(|e| {
            drop_pkt_on_err(e, self.recv_count, self.is_server, &self.trace_id)
        })?;

        let pn = packet::decode_pkt_num(
            self.pkt_num_spaces[epoch].largest_rx_pkt_num,
            hdr.pkt_num,
            hdr.pkt_num_len,
        );

        let pn_len = hdr.pkt_num_len;

        trace!(
            "{} rx pkt {:?} len={} pn={}",
            self.trace_id,
            hdr,
            payload_len,
            pn
        );

        qlog_with_type!(QLOG_PACKET_RX, self.qlog, q, {
            let packet_size = b.len();

            let qlog_pkt_hdr = qlog::PacketHeader::with_type(
                hdr.ty.to_qlog(),
                pn,
                Some(hdr.version),
                Some(&hdr.scid),
                Some(&hdr.dcid),
            );

            let qlog_raw_info = qlog::RawInfo {
                length: Some(packet_size as u64),
                payload_length: Some(payload_len as u64),
                data: None,
            };

            let ev_data = qlog::EventData::PacketReceived {
                header: qlog_pkt_hdr,
                frames: Some(vec![]),
                is_coalesced: None,
                retry_token: None,
                stateless_reset_token: None,
                supported_versions: None,
                raw: Some(qlog_raw_info),
                datagram_id: None,
            };

            q.add_event_data_with_instant(ev_data, now).ok();
        });

        let mut payload = packet::decrypt_pkt(
            &mut b,
            pn,
            pn_len,
            payload_len,
            aead,
        )
        .map_err(|e| {
            drop_pkt_on_err(e, self.recv_count, self.is_server, &self.trace_id)
        })?;

        if self.pkt_num_spaces[epoch].recv_pkt_num.contains(pn) {
            trace!("{} ignored duplicate packet {}", self.trace_id, pn);
            return Err(Error::Done);
        }

        // Packets with no frames are invalid.
        if payload.cap() == 0 {
            return Err(Error::InvalidPacket);
        }

        if !self.is_server && !self.got_peer_conn_id {
            if self.odcid.is_none() {
                self.odcid = Some(self.dcid.clone());
            }

            // Replace the randomly generated destination connection ID with
            // the one supplied by the server.
            self.dcid = hdr.scid.clone();

            self.got_peer_conn_id = true;
        }

        if self.is_server && !self.got_peer_conn_id {
            self.dcid = hdr.scid.clone();

            if !self.did_retry &&
                (self.version >= PROTOCOL_VERSION_DRAFT28 ||
                    self.version == PROTOCOL_VERSION_V1)
            {
                self.local_transport_params
                    .original_destination_connection_id =
                    Some(hdr.dcid.to_vec().into());

                self.encode_transport_params()?;
            }

            self.got_peer_conn_id = true;
        }

        // To avoid sending an ACK in response to an ACK-only packet, we need
        // to keep track of whether this packet contains any frame other than
        // ACK and PADDING.
        let mut ack_elicited = false;

        // Process packet payload.
        while payload.cap() > 0 {
            let frame = frame::Frame::from_bytes(&mut payload, hdr.ty)?;

            qlog_with_type!(QLOG_PACKET_RX, self.qlog, q, {
                q.add_frame(frame.to_qlog(), false).ok();
            });

            if frame.ack_eliciting() {
                ack_elicited = true;
            }

            if let Err(e) = self.process_frame(frame, epoch, now) {
                qlog_with_type!(QLOG_PACKET_RX, self.qlog, q, {
                    // Always conclude frame writing on error.
                    q.finish_frames().ok();
                });

                return Err(e);
            }
        }

        qlog_with_type!(QLOG_PACKET_RX, self.qlog, q, {
            // Always conclude frame writing.
            q.finish_frames().ok();
        });

        qlog_with_type!(QLOG_PACKET_RX, self.qlog, q, {
            if let Some(ev_data) = self.recovery.maybe_qlog() {
                q.add_event_data_with_instant(ev_data, now).ok();
            }
        });

        // Only log the remote transport parameters once the connection is
        // established (i.e. after frames have been fully parsed) and only
        // once per connection.
        if self.is_established() {
            qlog_with_type!(QLOG_PARAMS_SET, self.qlog, q, {
                if !self.qlog.logged_peer_params {
                    let ev_data = self.peer_transport_params.to_qlog(
                        qlog::TransportOwner::Remote,
                        self.handshake.cipher(),
                    );

                    q.add_event_data_with_instant(ev_data, now).ok();

                    self.qlog.logged_peer_params = true;
                }
            });
        }

        // Process acked frames.
        for acked in self.recovery.acked[epoch].drain(..) {
            match acked {
                frame::Frame::ACK { ranges, .. } => {
                    // Stop acknowledging packets less than or equal to the
                    // largest acknowledged in the sent ACK frame that, in
                    // turn, got acked.
                    if let Some(largest_acked) = ranges.last() {
                        self.pkt_num_spaces[epoch]
                            .recv_pkt_need_ack
                            .remove_until(largest_acked);
                    }
                },

                frame::Frame::CryptoHeader { offset, length } => {
                    self.pkt_num_spaces[epoch]
                        .crypto_stream
                        .send
                        .ack_and_drop(offset, length);
                },

                frame::Frame::StreamHeader {
                    stream_id,
                    offset,
                    length,
                    ..
                } => {
                    let stream = match self.streams.get_mut(stream_id) {
                        Some(v) => v,

                        None => continue,
                    };

                    stream.send.ack_and_drop(offset, length);

                    // Only collect the stream if it is complete and not
                    // readable. If it is readable, it will get collected when
                    // stream_recv() is used.
                    if stream.is_complete() && !stream.is_readable() {
                        let local = stream.local;
                        self.streams.collect(stream_id, local);
                    }
                },

                frame::Frame::HandshakeDone => {
                    // Explicitly set this to true, so that if the frame was
                    // already scheduled for retransmission, it is aborted.
                    self.handshake_done_sent = true;

                    self.handshake_done_acked = true;
                },

                frame::Frame::ResetStream { stream_id, .. } => {
                    let stream = match self.streams.get_mut(stream_id) {
                        Some(v) => v,

                        None => continue,
                    };

                    // Only collect the stream if it is complete and not
                    // readable. If it is readable, it will get collected when
                    // stream_recv() is used.
                    if stream.is_complete() && !stream.is_readable() {
                        let local = stream.local;
                        self.streams.collect(stream_id, local);
                    }
                },

                _ => (),
            }
        }

        // We only record the time of arrival of the largest packet number
        // that still needs to be acked, to be used for ACK delay calculation.
        if self.pkt_num_spaces[epoch].recv_pkt_need_ack.last() < Some(pn) {
            self.pkt_num_spaces[epoch].largest_rx_pkt_time = now;
        }

        self.pkt_num_spaces[epoch].recv_pkt_num.insert(pn);

        self.pkt_num_spaces[epoch].recv_pkt_need_ack.push_item(pn);

        self.pkt_num_spaces[epoch].ack_elicited =
            cmp::max(self.pkt_num_spaces[epoch].ack_elicited, ack_elicited);

        self.pkt_num_spaces[epoch].largest_rx_pkt_num =
            cmp::max(self.pkt_num_spaces[epoch].largest_rx_pkt_num, pn);

        if let Some(idle_timeout) = self.idle_timeout() {
            self.idle_timer = Some(now + idle_timeout);
        }

        // Update send capacity.
        self.update_tx_cap();

        self.recv_count += 1;

        let read = b.off() + aead_tag_len;

        self.recv_bytes += read as u64;

        // An Handshake packet has been received from the client and has been
        // successfully processed, so we can drop the initial state and consider
        // the client's address to be verified.
        if self.is_server && hdr.ty == packet::Type::Handshake {
            self.drop_epoch_state(packet::EPOCH_INITIAL, now);

            self.verified_peer_address = true;
        }

        self.ack_eliciting_sent = false;

        Ok(read)
    }

    /// Writes a single QUIC packet to be sent to the peer.
    ///
    /// On success the number of bytes written to the output buffer is
    /// returned, or [`Done`] if there was nothing to write.
    ///
    /// The application should call `send()` multiple times until [`Done`] is
    /// returned, indicating that there are no more packets to send. It is
    /// recommended that `send()` be called in the following cases:
    ///
    ///  * When the application receives QUIC packets from the peer (that is,
    ///    any time [`recv()`] is also called).
    ///
    ///  * When the connection timer expires (that is, any time [`on_timeout()`]
    ///    is also called).
    ///
    ///  * When the application sends data to the peer (for examples, any time
    ///    [`stream_send()`] or [`stream_shutdown()`] are called).
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    /// [`recv()`]: struct.Connection.html#method.recv
    /// [`on_timeout()`]: struct.Connection.html#method.on_timeout
    /// [`stream_send()`]: struct.Connection.html#method.stream_send
    /// [`stream_shutdown()`]: struct.Connection.html#method.stream_shutdown
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut out = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// loop {
    ///     let (write, send_info) = match conn.send(&mut out) {
    ///         Ok(v) => v,
    ///
    ///         Err(quiche::Error::Done) => {
    ///             // Done writing.
    ///             break;
    ///         },
    ///
    ///         Err(e) => {
    ///             // An error occurred, handle it.
    ///             break;
    ///         },
    ///     };
    ///
    ///     socket.send_to(&out[..write], &send_info.to).unwrap();
    /// }
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn send(&mut self, out: &mut [u8]) -> Result<(usize, SendInfo)> {
        if out.is_empty() {
            return Err(Error::BufferTooShort);
        }

        if self.is_closed() || self.is_draining() {
            return Err(Error::Done);
        }

        if self.local_error.is_none() {
            self.do_handshake()?;
        }

        // Process previously undecryptable 0-RTT packets if the decryption key
        // is now available.
        if self.pkt_num_spaces[packet::EPOCH_APPLICATION]
            .crypto_0rtt_open
            .is_some()
        {
            while let Some((mut pkt, info)) = self.undecryptable_pkts.pop_front()
            {
                if self.recv(&mut pkt, info).is_err() {
                    self.undecryptable_pkts.clear();

                    // Forwarding the error value here could confuse
                    // applications, as they may not expect getting a `recv()`
                    // error when calling `send()`.
                    //
                    // We simply fall-through to sending packets, which should
                    // take care of terminating the connection as needed.
                    break;
                }
            }
        }

        // There's no point in trying to send a packet if the Initial secrets
        // have not been derived yet, so return early.
        if !self.derived_initial_secrets {
            return Err(Error::Done);
        }

        let mut has_initial = false;

        let mut done = 0;

        // Limit output packet size to respect the sender and receiver's
        // maximum UDP payload size limit.
        let mut left = cmp::min(out.len(), self.max_send_udp_payload_size());

        // Limit data sent by the server based on the amount of data received
        // from the client before its address is validated.
        if !self.verified_peer_address && self.is_server {
            left = cmp::min(left, self.max_send_bytes);
        }

        // Generate coalesced packets.
        while left > 0 {
            let (ty, written) = match self
                .send_single(&mut out[done..done + left], has_initial)
            {
                Ok(v) => v,

                Err(Error::BufferTooShort) | Err(Error::Done) => break,

                Err(e) => return Err(e),
            };

            done += written;
            left -= written;

            match ty {
                packet::Type::Initial => has_initial = true,

                // No more packets can be coalesced after a 1-RTT.
                packet::Type::Short => break,

                _ => (),
            };

            // When sending multiple PTO probes, don't coalesce them together,
            // so they are sent on separate UDP datagrams.
            if let Ok(epoch) = ty.to_epoch() {
                if self.recovery.loss_probes[epoch] > 0 {
                    break;
                }
            }
        }

        if done == 0 {
            return Err(Error::Done);
        }

        // Pad UDP datagram if it contains a QUIC Initial packet.
        if has_initial && left > 0 && done < MIN_CLIENT_INITIAL_LEN {
            let pad_len = cmp::min(left, MIN_CLIENT_INITIAL_LEN - done);

            // Fill padding area with null bytes, to avoid leaking information
            // in case the application reuses the packet buffer.
            out[done..done + pad_len].fill(0);

            done += pad_len;
        }

        let info = SendInfo {
            to: self.peer_addr,

            at: self
                .recovery
                .get_packet_send_time()
                .unwrap_or_else(time::Instant::now),
        };

        Ok((done, info))
    }

    fn send_single(
        &mut self, out: &mut [u8], has_initial: bool,
    ) -> Result<(packet::Type, usize)> {
        let now = time::Instant::now();

        if out.is_empty() {
            return Err(Error::BufferTooShort);
        }

        if self.is_draining() {
            return Err(Error::Done);
        }

        let is_closing = self.local_error.is_some();

        let mut b = octets::OctetsMut::with_slice(out);

        let pkt_type = self.write_pkt_type()?;

        let epoch = pkt_type.to_epoch()?;

        let stream_retrans_bytes = self.stream_retrans_bytes;

        // Process lost frames.
        for lost in self.recovery.lost[epoch].drain(..) {
            match lost {
                frame::Frame::CryptoHeader { offset, length } => {
                    self.pkt_num_spaces[epoch]
                        .crypto_stream
                        .send
                        .retransmit(offset, length);

                    self.stream_retrans_bytes += length as u64;
                },

                frame::Frame::StreamHeader {
                    stream_id,
                    offset,
                    length,
                    fin,
                } => {
                    let stream = match self.streams.get_mut(stream_id) {
                        Some(v) => v,

                        None => continue,
                    };

                    let was_flushable = stream.is_flushable();

                    let empty_fin = length == 0 && fin;

                    stream.send.retransmit(offset, length);

                    // If the stream is now flushable push it to the flushable
                    // queue, but only if it wasn't already queued.
                    //
                    // Consider the stream flushable also when we are sending a
                    // zero-length frame that has the fin flag set.
                    if (stream.is_flushable() || empty_fin) && !was_flushable {
                        let urgency = stream.urgency;
                        let incremental = stream.incremental;
                        self.streams.push_flushable(
                            stream_id,
                            urgency,
                            incremental,
                        );
                    }

                    self.stream_retrans_bytes += length as u64;
                },

                frame::Frame::ACK { .. } => {
                    self.pkt_num_spaces[epoch].ack_elicited = true;
                },

                frame::Frame::ResetStream {
                    stream_id,
                    error_code,
                    final_size,
                } =>
                    if self.streams.get(stream_id).is_some() {
                        self.streams
                            .mark_reset(stream_id, true, error_code, final_size);
                    },

                // Retransmit HANDSHAKE_DONE only if it hasn't been acked at
                // least once already.
                frame::Frame::HandshakeDone if !self.handshake_done_acked => {
                    self.handshake_done_sent = false;
                },

                frame::Frame::MaxStreamData { stream_id, .. } => {
                    if self.streams.get(stream_id).is_some() {
                        self.streams.mark_almost_full(stream_id, true);
                    }
                },

                frame::Frame::MaxData { .. } => {
                    self.almost_full = true;
                },

                _ => (),
            }
        }

        if stream_retrans_bytes > self.stream_retrans_bytes {
            self.retrans_count += 1;
        }

        let mut left = b.cap();

        // Limit output packet size by congestion window size.
        left = cmp::min(left, self.recovery.cwnd_available());

        let pn = self.pkt_num_spaces[epoch].next_pkt_num;
        let pn_len = packet::pkt_num_len(pn)?;

        // The AEAD overhead at the current encryption level.
        let crypto_overhead = self.pkt_num_spaces[epoch]
            .crypto_overhead()
            .ok_or(Error::Done)?;

        let hdr = Header {
            ty: pkt_type,

            version: self.version,

            dcid: ConnectionId::from_ref(&self.dcid),
            scid: ConnectionId::from_ref(&self.scid),

            pkt_num: 0,
            pkt_num_len: pn_len,

            // Only clone token for Initial packets, as other packets don't have
            // this field (Retry doesn't count, as it's not encoded as part of
            // this code path).
            token: if pkt_type == packet::Type::Initial {
                self.token.clone()
            } else {
                None
            },

            versions: None,
            key_phase: false,
        };

        hdr.to_bytes(&mut b)?;

        // Calculate the space required for the packet, including the header
        // the payload length, the packet number and the AEAD overhead.
        let mut overhead = b.off() + pn_len + crypto_overhead;

        // We assume that the payload length, which is only present in long
        // header packets, can always be encoded with a 2-byte varint.
        if pkt_type != packet::Type::Short {
            overhead += PAYLOAD_LENGTH_LEN;
        }

        // Make sure we have enough space left for the packet overhead.
        match left.checked_sub(overhead) {
            Some(v) => left = v,

            None => {
                // We can't send more because there isn't enough space available
                // in the output buffer.
                //
                // This usually happens when we try to send a new packet but
                // failed because cwnd is almost full. In such case app_limited
                // is set to false here to make cwnd grow when ACK is received.
                self.recovery.update_app_limited(false);
                return Err(Error::Done);
            },
        }

        // Make sure there is enough space for the minimum payload length.
        if left < PAYLOAD_MIN_LEN {
            self.recovery.update_app_limited(false);
            return Err(Error::Done);
        }

        let mut frames: Vec<frame::Frame> = Vec::new();

        let mut ack_eliciting = false;
        let mut in_flight = false;
        let mut has_data = false;

        let header_offset = b.off();

        // Reserve space for payload length in advance. Since we don't yet know
        // what the final length will be, we reserve 2 bytes in all cases.
        //
        // Only long header packets have an explicit length field.
        if pkt_type != packet::Type::Short {
            b.skip(PAYLOAD_LENGTH_LEN)?;
        }

        packet::encode_pkt_num(pn, &mut b)?;

        let payload_offset = b.off();

        // Create ACK frame.
        if self.pkt_num_spaces[epoch].recv_pkt_need_ack.len() > 0 &&
            (self.pkt_num_spaces[epoch].ack_elicited ||
                self.recovery.loss_probes[epoch] > 0) &&
            !is_closing
        {
            let ack_delay =
                self.pkt_num_spaces[epoch].largest_rx_pkt_time.elapsed();

            let ack_delay = ack_delay.as_micros() as u64 /
                2_u64
                    .pow(self.local_transport_params.ack_delay_exponent as u32);

            let frame = frame::Frame::ACK {
                ack_delay,
                ranges: self.pkt_num_spaces[epoch].recv_pkt_need_ack.clone(),
                ecn_counts: None, // sending ECN is not supported at this time
            };

            if push_frame_to_pkt!(b, frames, frame, left) {
                self.pkt_num_spaces[epoch].ack_elicited = false;
            }
        }

        if pkt_type == packet::Type::Short && !is_closing {
            // Create HANDSHAKE_DONE frame.
            if self.should_send_handshake_done() {
                let frame = frame::Frame::HandshakeDone;

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.handshake_done_sent = true;

                    ack_eliciting = true;
                    in_flight = true;
                }
            }

            // Create MAX_STREAMS_BIDI frame.
            if self.streams.should_update_max_streams_bidi() {
                let frame = frame::Frame::MaxStreamsBidi {
                    max: self.streams.max_streams_bidi_next(),
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.streams.update_max_streams_bidi();

                    ack_eliciting = true;
                    in_flight = true;
                }
            }

            // Create MAX_STREAMS_UNI frame.
            if self.streams.should_update_max_streams_uni() {
                let frame = frame::Frame::MaxStreamsUni {
                    max: self.streams.max_streams_uni_next(),
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.streams.update_max_streams_uni();

                    ack_eliciting = true;
                    in_flight = true;
                }
            }

            // Create DATA_BLOCKED frame.
            if let Some(limit) = self.blocked_limit {
                let frame = frame::Frame::DataBlocked { limit };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.blocked_limit = None;

                    ack_eliciting = true;
                    in_flight = true;
                }
            }

            // Create MAX_STREAM_DATA frames as needed.
            for stream_id in self.streams.almost_full() {
                let stream = match self.streams.get_mut(stream_id) {
                    Some(v) => v,

                    None => {
                        // The stream doesn't exist anymore, so remove it from
                        // the almost full set.
                        self.streams.mark_almost_full(stream_id, false);
                        continue;
                    },
                };

                // Autotune the stream window size.
                stream.recv.autotune_window(now, self.recovery.rtt());

                let frame = frame::Frame::MaxStreamData {
                    stream_id,
                    max: stream.recv.max_data_next(),
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    let recv_win = stream.recv.window();

                    stream.recv.update_max_data(now);

                    self.streams.mark_almost_full(stream_id, false);

                    ack_eliciting = true;
                    in_flight = true;

                    // Make sure the connection window always has some
                    // room compared to the stream window.
                    self.flow_control.ensure_window_lower_bound(
                        (recv_win as f64 * CONNECTION_WINDOW_FACTOR) as u64,
                    );

                    // Also send MAX_DATA when MAX_STREAM_DATA is sent, to avoid a
                    // potential race condition.
                    self.almost_full = true;
                }
            }

            // Create MAX_DATA frame as needed.
            if self.almost_full && self.max_rx_data() < self.max_rx_data_next() {
                // Autotune the connection window size.
                self.flow_control.autotune_window(now, self.recovery.rtt());

                let frame = frame::Frame::MaxData {
                    max: self.max_rx_data_next(),
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.almost_full = false;

                    // Commits the new max_rx_data limit.
                    self.flow_control.update_max_data(now);

                    ack_eliciting = true;
                    in_flight = true;
                }
            }

            // Create STOP_SENDING frames as needed.
            for (stream_id, error_code) in self
                .streams
                .stopped()
                .map(|(&k, &v)| (k, v))
                .collect::<Vec<(u64, u64)>>()
            {
                let frame = frame::Frame::StopSending {
                    stream_id,
                    error_code,
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.streams.mark_stopped(stream_id, false, 0);

                    ack_eliciting = true;
                    in_flight = true;
                }
            }

            // Create RESET_STREAM frames as needed.
            for (stream_id, (error_code, final_size)) in self
                .streams
                .reset()
                .map(|(&k, &v)| (k, v))
                .collect::<Vec<(u64, (u64, u64))>>()
            {
                let frame = frame::Frame::ResetStream {
                    stream_id,
                    error_code,
                    final_size,
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.streams.mark_reset(stream_id, false, 0, 0);

                    ack_eliciting = true;
                    in_flight = true;
                }
            }

            // Create STREAM_DATA_BLOCKED frames as needed.
            for (stream_id, limit) in self
                .streams
                .blocked()
                .map(|(&k, &v)| (k, v))
                .collect::<Vec<(u64, u64)>>()
            {
                let frame = frame::Frame::StreamDataBlocked { stream_id, limit };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.streams.mark_blocked(stream_id, false, 0);

                    ack_eliciting = true;
                    in_flight = true;
                }
            }
        }

        // Create CONNECTION_CLOSE frame.
        if let Some(conn_err) = self.local_error.as_ref() {
            if conn_err.is_app {
                // Create ApplicationClose frame.
                if pkt_type == packet::Type::Short {
                    let frame = frame::Frame::ApplicationClose {
                        error_code: conn_err.error_code,
                        reason: conn_err.reason.clone(),
                    };

                    if push_frame_to_pkt!(b, frames, frame, left) {
                        self.draining_timer =
                            Some(now + (self.recovery.pto() * 3));

                        ack_eliciting = true;
                        in_flight = true;
                    }
                }
            } else {
                // Create ConnectionClose frame.
                let frame = frame::Frame::ConnectionClose {
                    error_code: conn_err.error_code,
                    frame_type: 0,
                    reason: conn_err.reason.clone(),
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    self.draining_timer = Some(now + (self.recovery.pto() * 3));

                    ack_eliciting = true;
                    in_flight = true;
                }
            }
        }

        // Create PATH_RESPONSE frame.
        if let Some(ref challenge) = self.challenge {
            let frame = frame::Frame::PathResponse {
                data: challenge.clone(),
            };

            if push_frame_to_pkt!(b, frames, frame, left) {
                self.challenge = None;

                ack_eliciting = true;
                in_flight = true;
            }
        }

        // Create CRYPTO frame.
        if self.pkt_num_spaces[epoch].crypto_stream.is_flushable() &&
            left > frame::MAX_CRYPTO_OVERHEAD &&
            !is_closing
        {
            let crypto_off =
                self.pkt_num_spaces[epoch].crypto_stream.send.off_front();

            // Encode the frame.
            //
            // Instead of creating a `frame::Frame` object, encode the frame
            // directly into the packet buffer.
            //
            // First we reserve some space in the output buffer for writing the
            // frame header (we assume the length field is always a 2-byte
            // varint as we don't know the value yet).
            //
            // Then we emit the data from the crypto stream's send buffer.
            //
            // Finally we go back and encode the frame header with the now
            // available information.
            let hdr_off = b.off();
            let hdr_len = 1 + // frame type
                octets::varint_len(crypto_off) + // offset
                2; // length, always encode as 2-byte varint

            if let Some(max_len) = left.checked_sub(hdr_len) {
                let (mut crypto_hdr, mut crypto_payload) =
                    b.split_at(hdr_off + hdr_len)?;

                // Write stream data into the packet buffer.
                let (len, _) = self.pkt_num_spaces[epoch]
                    .crypto_stream
                    .send
                    .emit(&mut crypto_payload.as_mut()[..max_len])?;

                // Encode the frame's header.
                //
                // Due to how `OctetsMut::split_at()` works, `crypto_hdr` starts
                // from the initial offset of `b` (rather than the current
                // offset), so it needs to be advanced to the
                // initial frame offset.
                crypto_hdr.skip(hdr_off)?;

                frame::encode_crypto_header(
                    crypto_off,
                    len as u64,
                    &mut crypto_hdr,
                )?;

                // Advance the packet buffer's offset.
                b.skip(hdr_len + len)?;

                let frame = frame::Frame::CryptoHeader {
                    offset: crypto_off,
                    length: len,
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    ack_eliciting = true;
                    in_flight = true;
                    has_data = true;
                }
            }
        }

        // The preference of data-bearing frame to include in a packet
        // is managed by `self.emit_dgram`. However, whether any frames
        // can be sent depends on the state of their buffers. In the case
        // where one type is preferred but its buffer is empty, fall back
        // to the other type in order not to waste this function call.
        let mut dgram_emitted = false;
        let dgrams_to_emit = self.dgram_max_writable_len().is_some();
        let stream_to_emit = self.streams.has_flushable();

        let mut do_dgram = self.emit_dgram && dgrams_to_emit;
        let do_stream = !self.emit_dgram && stream_to_emit;

        if !do_stream && dgrams_to_emit {
            do_dgram = true;
        }

        // Create DATAGRAM frame.
        if (pkt_type == packet::Type::Short || pkt_type == packet::Type::ZeroRTT) &&
            left > frame::MAX_DGRAM_OVERHEAD &&
            !is_closing &&
            do_dgram
        {
            if let Some(max_dgram_payload) = self.dgram_max_writable_len() {
                while let Some(len) = self.dgram_send_queue.peek_front_len() {
                    let hdr_off = b.off();
                    let hdr_len = 1 + // frame type
                        2; // length, always encode as 2-byte varint

                    if (hdr_len + len) <= left {
                        // Front of the queue fits this packet, send it.
                        match self.dgram_send_queue.pop() {
                            Some(data) => {
                                // Encode the frame.
                                //
                                // Instead of creating a `frame::Frame` object,
                                // encode the frame directly into the packet
                                // buffer.
                                //
                                // First we reserve some space in the output
                                // buffer for writing the frame header (we
                                // assume the length field is always a 2-byte
                                // varint as we don't know the value yet).
                                //
                                // Then we emit the data from the DATAGRAM's
                                // buffer.
                                //
                                // Finally we go back and encode the frame
                                // header with the now available information.
                                let (mut dgram_hdr, mut dgram_payload) =
                                    b.split_at(hdr_off + hdr_len)?;

                                dgram_payload.as_mut()[..len]
                                    .copy_from_slice(&data);

                                // Encode the frame's header.
                                //
                                // Due to how `OctetsMut::split_at()` works,
                                // `dgram_hdr` starts from the initial offset
                                // of `b` (rather than the current offset), so
                                // it needs to be advanced to the initial frame
                                // offset.
                                dgram_hdr.skip(hdr_off)?;

                                frame::encode_dgram_header(
                                    len as u64,
                                    &mut dgram_hdr,
                                )?;

                                // Advance the packet buffer's offset.
                                b.skip(hdr_len + len)?;

                                let frame =
                                    frame::Frame::DatagramHeader { length: len };

                                if push_frame_to_pkt!(b, frames, frame, left) {
                                    ack_eliciting = true;
                                    in_flight = true;
                                    dgram_emitted = true;
                                }
                            },

                            None => continue,
                        };
                    } else if len > max_dgram_payload {
                        // This dgram frame will never fit. Let's purge it.
                        self.dgram_send_queue.pop();
                    } else {
                        break;
                    }
                }
            }
        }

        // Create a single STREAM frame for the first stream that is flushable.
        if (pkt_type == packet::Type::Short || pkt_type == packet::Type::ZeroRTT) &&
            left > frame::MAX_STREAM_OVERHEAD &&
            !is_closing &&
            !dgram_emitted
        {
            while let Some(stream_id) = self.streams.pop_flushable() {
                let stream = match self.streams.get_mut(stream_id) {
                    Some(v) => v,

                    None => continue,
                };

                // Avoid sending frames for streams that were already stopped.
                //
                // This might happen if stream data was buffered but not yet
                // flushed on the wire when a STOP_SENDING frame is received.
                if stream.send.is_stopped() {
                    continue;
                }

                let stream_off = stream.send.off_front();

                // Encode the frame.
                //
                // Instead of creating a `frame::Frame` object, encode the frame
                // directly into the packet buffer.
                //
                // First we reserve some space in the output buffer for writing
                // the frame header (we assume the length field is always a
                // 2-byte varint as we don't know the value yet).
                //
                // Then we emit the data from the stream's send buffer.
                //
                // Finally we go back and encode the frame header with the now
                // available information.
                let hdr_off = b.off();
                let hdr_len = 1 + // frame type
                    octets::varint_len(stream_id) + // stream_id
                    octets::varint_len(stream_off) + // offset
                    2; // length, always encode as 2-byte varint

                let max_len = match left.checked_sub(hdr_len) {
                    Some(v) => v,

                    None => continue,
                };

                let (mut stream_hdr, mut stream_payload) =
                    b.split_at(hdr_off + hdr_len)?;

                // Write stream data into the packet buffer.
                let (len, fin) =
                    stream.send.emit(&mut stream_payload.as_mut()[..max_len])?;

                // Encode the frame's header.
                //
                // Due to how `OctetsMut::split_at()` works, `stream_hdr` starts
                // from the initial offset of `b` (rather than the current
                // offset), so it needs to be advanced to the initial frame
                // offset.
                stream_hdr.skip(hdr_off)?;

                frame::encode_stream_header(
                    stream_id,
                    stream_off,
                    len as u64,
                    fin,
                    &mut stream_hdr,
                )?;

                // Advance the packet buffer's offset.
                b.skip(hdr_len + len)?;

                let frame = frame::Frame::StreamHeader {
                    stream_id,
                    offset: stream_off,
                    length: len,
                    fin,
                };

                if push_frame_to_pkt!(b, frames, frame, left) {
                    ack_eliciting = true;
                    in_flight = true;
                    has_data = true;
                }

                // If the stream is still flushable, push it to the back of the
                // queue again.
                if stream.is_flushable() {
                    let urgency = stream.urgency;
                    let incremental = stream.incremental;
                    self.streams.push_flushable(stream_id, urgency, incremental);
                }

                // When fuzzing, try to coalesce multiple STREAM frames in the
                // same packet, so it's easier to generate fuzz corpora.
                if cfg!(feature = "fuzzing") && left > frame::MAX_STREAM_OVERHEAD
                {
                    continue;
                }

                break;
            }
        }

        // Alternate trying to send DATAGRAMs next time.
        self.emit_dgram = !dgram_emitted;

        // Create PING for PTO probe if no other ack-elicitng frame is sent.
        if self.recovery.loss_probes[epoch] > 0 &&
            !ack_eliciting &&
            left >= 1 &&
            !is_closing
        {
            let frame = frame::Frame::Ping;

            if push_frame_to_pkt!(b, frames, frame, left) {
                ack_eliciting = true;
                in_flight = true;
            }
        }

        if ack_eliciting {
            self.recovery.loss_probes[epoch] =
                self.recovery.loss_probes[epoch].saturating_sub(1);
        }

        if frames.is_empty() {
            // When we reach this point we are not able to write more, so set
            // app_limited to false.
            self.recovery.update_app_limited(false);
            return Err(Error::Done);
        }

        // When coalescing a 1-RTT packet, we can't add padding in the UDP
        // datagram, so use PADDING frames instead.
        //
        // This is only needed if an Initial packet has already been written to
        // the UDP datagram, as Initial always requires padding.
        if has_initial && pkt_type == packet::Type::Short && left >= 1 {
            let frame = frame::Frame::Padding { len: left };

            if push_frame_to_pkt!(b, frames, frame, left) {
                in_flight = true;
            }
        }

        // Pad payload so that it's always at least 4 bytes.
        if b.off() - payload_offset < PAYLOAD_MIN_LEN {
            let payload_len = b.off() - payload_offset;

            let frame = frame::Frame::Padding {
                len: PAYLOAD_MIN_LEN - payload_len,
            };

            #[allow(unused_assignments)]
            if push_frame_to_pkt!(b, frames, frame, left) {
                in_flight = true;
            }
        }

        let payload_len = b.off() - payload_offset;

        // Fill in payload length.
        if pkt_type != packet::Type::Short {
            let len = pn_len + payload_len + crypto_overhead;

            let (_, mut payload_with_len) = b.split_at(header_offset)?;
            payload_with_len
                .put_varint_with_len(len as u64, PAYLOAD_LENGTH_LEN)?;
        }

        trace!(
            "{} tx pkt {:?} len={} pn={}",
            self.trace_id,
            hdr,
            payload_len,
            pn
        );

        qlog_with_type!(QLOG_PACKET_TX, self.qlog, q, {
            let qlog_pkt_hdr = qlog::PacketHeader::with_type(
                hdr.ty.to_qlog(),
                pn,
                Some(hdr.version),
                Some(&hdr.scid),
                Some(&hdr.dcid),
            );

            // Qlog packet raw info described at
            // https://datatracker.ietf.org/doc/html/draft-ietf-quic-qlog-main-schema-00#section-5.1
            //
            // `length` includes packet headers and trailers (AEAD tag).
            let length = payload_len + payload_offset + crypto_overhead;
            let qlog_raw_info = qlog::RawInfo {
                length: Some(length as u64),
                payload_length: Some(payload_len as u64),
                data: None,
            };

            let ev_data = qlog::EventData::PacketSent {
                header: qlog_pkt_hdr,
                frames: Some(vec![]),
                is_coalesced: None,
                retry_token: None,
                stateless_reset_token: None,
                supported_versions: None,
                raw: Some(qlog_raw_info),
                datagram_id: None,
            };

            q.add_event_data_with_instant(ev_data, now).ok();
        });

        for frame in &mut frames {
            trace!("{} tx frm {:?}", self.trace_id, frame);

            qlog_with_type!(QLOG_PACKET_TX, self.qlog, q, {
                q.add_frame(frame.to_qlog(), false).ok();
            });
        }

        qlog_with_type!(QLOG_PACKET_TX, self.qlog, q, {
            q.finish_frames().ok();
        });

        let aead = match self.pkt_num_spaces[epoch].crypto_seal {
            Some(ref v) => v,
            None => return Err(Error::InvalidState),
        };

        let written = packet::encrypt_pkt(
            &mut b,
            pn,
            pn_len,
            payload_len,
            payload_offset,
            None,
            aead,
        )?;

        let sent_pkt = recovery::Sent {
            pkt_num: pn,
            frames,
            time_sent: now,
            time_acked: None,
            time_lost: None,
            size: if ack_eliciting { written } else { 0 },
            ack_eliciting,
            in_flight,
            delivered: 0,
            delivered_time: now,
            recent_delivered_packet_sent_time: now,
            is_app_limited: false,
            has_data,
        };

        self.recovery.on_packet_sent(
            sent_pkt,
            epoch,
            self.handshake_status(),
            now,
            &self.trace_id,
        );

        qlog_with_type!(QLOG_METRICS, self.qlog, q, {
            if let Some(ev_data) = self.recovery.maybe_qlog() {
                q.add_event_data_with_instant(ev_data, now).ok();
            }
        });

        self.pkt_num_spaces[epoch].next_pkt_num += 1;

        self.sent_count += 1;
        self.sent_bytes += written as u64;

        if self.dgram_send_queue.byte_size() > self.recovery.cwnd_available() {
            self.recovery.update_app_limited(false);
        }

        // On the client, drop initial state after sending an Handshake packet.
        if !self.is_server && hdr.ty == packet::Type::Handshake {
            self.drop_epoch_state(packet::EPOCH_INITIAL, now);
        }

        self.max_send_bytes = self.max_send_bytes.saturating_sub(written);

        // (Re)start the idle timer if we are sending the first ack-eliciting
        // packet since last receiving a packet.
        if ack_eliciting && !self.ack_eliciting_sent {
            if let Some(idle_timeout) = self.idle_timeout() {
                self.idle_timer = Some(now + idle_timeout);
            }
        }

        if ack_eliciting {
            self.ack_eliciting_sent = true;
        }

        Ok((pkt_type, written))
    }

    /// Reads contiguous data from a stream into the provided slice.
    ///
    /// The slice must be sized by the caller and will be populated up to its
    /// capacity.
    ///
    /// On success the amount of bytes read and a flag indicating the fin state
    /// is returned as a tuple, or [`Done`] if there is no data to read.
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// # let stream_id = 0;
    /// while let Ok((read, fin)) = conn.stream_recv(stream_id, &mut buf) {
    ///     println!("Got {} bytes on stream {}", read, stream_id);
    /// }
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn stream_recv(
        &mut self, stream_id: u64, out: &mut [u8],
    ) -> Result<(usize, bool)> {
        // We can't read on our own unidirectional streams.
        if !stream::is_bidi(stream_id) &&
            stream::is_local(stream_id, self.is_server)
        {
            return Err(Error::InvalidStreamState(stream_id));
        }

        let stream = self
            .streams
            .get_mut(stream_id)
            .ok_or(Error::InvalidStreamState(stream_id))?;

        if !stream.is_readable() {
            return Err(Error::Done);
        }

        let local = stream.local;

        #[cfg(feature = "qlog")]
        let offset = stream.recv.off_front();

        let (read, fin) = match stream.recv.emit(out) {
            Ok(v) => v,

            Err(e) => {
                // Collect the stream if it is now complete. This can happen if
                // we got a `StreamReset` error which will now be propagated to
                // the application, so we don't need to keep the stream's state
                // anymore.
                if stream.is_complete() {
                    self.streams.collect(stream_id, local);
                }

                self.streams.mark_readable(stream_id, false);
                return Err(e);
            },
        };

        self.flow_control.add_consumed(read as u64);

        let readable = stream.is_readable();

        let complete = stream.is_complete();

        if stream.recv.almost_full() {
            self.streams.mark_almost_full(stream_id, true);
        }

        if !readable {
            self.streams.mark_readable(stream_id, false);
        }

        if complete {
            self.streams.collect(stream_id, local);
        }

        qlog_with_type!(QLOG_DATA_MV, self.qlog, q, {
            let ev_data = qlog::EventData::DataMoved {
                stream_id: Some(stream_id),
                offset: Some(offset),
                length: Some(read as u64),
                from: Some(qlog::DataRecipient::Transport),
                to: Some(qlog::DataRecipient::Application),
                data: None,
            };

            let now = time::Instant::now();
            q.add_event_data_with_instant(ev_data, now).ok();
        });

        if self.should_update_max_data() {
            self.almost_full = true;
        }

        Ok((read, fin))
    }

    /// Writes data to a stream.
    ///
    /// On success the number of bytes written is returned, or [`Done`] if no
    /// data was written (e.g. because the stream has no capacity).
    ///
    /// Applications can provide a 0-length buffer with the fin flag set to
    /// true. This will lead to a 0-length FIN STREAM frame being sent at the
    /// latest offset. This is the only case where `Ok(0)` is returned.
    ///
    /// In addition, if the peer has signalled that it doesn't want to receive
    /// any more data from this stream by sending the `STOP_SENDING` frame, the
    /// [`StreamStopped`] error will be returned instead of any data.
    ///
    /// Note that in order to avoid buffering an infinite amount of data in the
    /// stream's send buffer, streams are only allowed to buffer outgoing data
    /// up to the amount that the peer allows it to send (that is, up to the
    /// stream's outgoing flow control capacity).
    ///
    /// This means that the number of written bytes returned can be lower than
    /// the length of the input buffer when the stream doesn't have enough
    /// capacity for the operation to complete. The application should retry the
    /// operation once the stream is reported as writable again.
    ///
    /// Applications should call this method only after the handshake is
    /// completed (whenever [`is_established()`] returns `true`) or during
    /// early data if enabled (whenever [`is_in_early_data()`] returns `true`).
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    /// [`StreamStopped`]: enum.Error.html#variant.StreamStopped
    /// [`is_established()`]: struct.Connection.html#method.is_established
    /// [`is_in_early_data()`]: struct.Connection.html#method.is_in_early_data
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// # let stream_id = 0;
    /// conn.stream_send(stream_id, b"hello", true)?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn stream_send(
        &mut self, stream_id: u64, buf: &[u8], fin: bool,
    ) -> Result<usize> {
        // We can't write on the peer's unidirectional streams.
        if !stream::is_bidi(stream_id) &&
            !stream::is_local(stream_id, self.is_server)
        {
            return Err(Error::InvalidStreamState(stream_id));
        }

        // Mark the connection as blocked if the connection-level flow control
        // limit doesn't let us buffer all the data.
        //
        // Note that this is separate from "send capacity" as that also takes
        // congestion control into consideration.
        if self.max_tx_data - self.tx_data < buf.len() as u64 {
            self.blocked_limit = Some(self.max_tx_data);
        }

        // Truncate the input buffer based on the connection's send capacity if
        // necessary.
        let cap = self.tx_cap;
        if cap == 0 && !fin {
            return Err(Error::Done);
        }

        let (buf, fin) = if cap < buf.len() {
            (&buf[..cap], false)
        } else {
            (buf, fin)
        };

        // Get existing stream or create a new one.
        let stream = self.get_or_create_stream(stream_id, true)?;

        #[cfg(feature = "qlog")]
        let offset = stream.send.off_back();

        let was_flushable = stream.is_flushable();

        let sent = match stream.send.write(buf, fin) {
            Ok(v) => v,

            Err(e) => {
                self.streams.mark_writable(stream_id, false);
                return Err(e);
            },
        };

        let urgency = stream.urgency;
        let incremental = stream.incremental;

        let flushable = stream.is_flushable();

        let writable = stream.is_writable();

        let empty_fin = buf.is_empty() && fin;

        if sent < buf.len() {
            let max_off = stream.send.max_off();

            self.streams.mark_blocked(stream_id, true, max_off);
        } else {
            self.streams.mark_blocked(stream_id, false, 0);
        }

        // If the stream is now flushable push it to the flushable queue, but
        // only if it wasn't already queued.
        //
        // Consider the stream flushable also when we are sending a zero-length
        // frame that has the fin flag set.
        if (flushable || empty_fin) && !was_flushable {
            self.streams.push_flushable(stream_id, urgency, incremental);
        }

        if !writable {
            self.streams.mark_writable(stream_id, false);
        }

        self.tx_cap -= sent;

        self.tx_data += sent as u64;

        self.recovery.rate_check_app_limited();

        qlog_with_type!(QLOG_DATA_MV, self.qlog, q, {
            let ev_data = qlog::EventData::DataMoved {
                stream_id: Some(stream_id),
                offset: Some(offset),
                length: Some(sent as u64),
                from: Some(qlog::DataRecipient::Application),
                to: Some(qlog::DataRecipient::Transport),
                data: None,
            };

            let now = time::Instant::now();
            q.add_event_data_with_instant(ev_data, now).ok();
        });

        Ok(sent)
    }

    /// Sets the priority for a stream.
    ///
    /// A stream's priority determines the order in which stream data is sent
    /// on the wire (streams with lower priority are sent first). Streams are
    /// created with a default priority of `127`.
    ///
    /// The target stream is created if it did not exist before calling this
    /// method.
    pub fn stream_priority(
        &mut self, stream_id: u64, urgency: u8, incremental: bool,
    ) -> Result<()> {
        // Get existing stream or create a new one, but if the stream
        // has already been closed and collected, ignore the prioritization.
        let stream = match self.get_or_create_stream(stream_id, true) {
            Ok(v) => v,

            Err(Error::Done) => return Ok(()),

            Err(e) => return Err(e),
        };

        if stream.urgency == urgency && stream.incremental == incremental {
            return Ok(());
        }

        stream.urgency = urgency;
        stream.incremental = incremental;

        // TODO: reprioritization

        Ok(())
    }

    /// Shuts down reading or writing from/to the specified stream.
    ///
    /// When the `direction` argument is set to [`Shutdown::Read`], outstanding
    /// data in the stream's receive buffer is dropped, and no additional data
    /// is added to it. Data received after calling this method is still
    /// validated and acked but not stored, and [`stream_recv()`] will not
    /// return it to the application. In addition, a `STOP_SENDING` frame will
    /// be sent to the peer to signal it to stop sending data.
    ///
    /// When the `direction` argument is set to [`Shutdown::Write`], outstanding
    /// data in the stream's send buffer is dropped, and no additional data
    /// is added to it. Data passed to [`stream_send()`] after calling this
    /// method will be ignored.
    ///
    /// [`Shutdown::Read`]: enum.Shutdown.html#variant.Read
    /// [`Shutdown::Write`]: enum.Shutdown.html#variant.Write
    /// [`stream_recv()`]: struct.Connection.html#method.stream_recv
    /// [`stream_send()`]: struct.Connection.html#method.stream_send
    pub fn stream_shutdown(
        &mut self, stream_id: u64, direction: Shutdown, err: u64,
    ) -> Result<()> {
        // Get existing stream.
        let stream = self.streams.get_mut(stream_id).ok_or(Error::Done)?;

        match direction {
            Shutdown::Read => {
                stream.recv.shutdown()?;

                if !stream.recv.is_fin() {
                    self.streams.mark_stopped(stream_id, true, err);
                }

                // Once shutdown, the stream is guaranteed to be non-readable.
                self.streams.mark_readable(stream_id, false);
            },

            Shutdown::Write => {
                let (final_size, unsent) = stream.send.shutdown()?;

                // Claw back some flow control allowance from data that was
                // buffered but not actually sent before the stream was reset.
                self.tx_data = self.tx_data.saturating_sub(unsent);

                // Update send capacity.
                self.update_tx_cap();

                self.streams.mark_reset(stream_id, true, err, final_size);

                // Once shutdown, the stream is guaranteed to be non-writable.
                self.streams.mark_writable(stream_id, false);
            },
        }

        Ok(())
    }

    /// Returns the stream's send capacity in bytes.
    ///
    /// If the specified stream doesn't exist (including when it has already
    /// been completed and closed), the [`InvalidStreamState`] error will be
    /// returned.
    ///
    /// In addition, if the peer has signalled that it doesn't want to receive
    /// any more data from this stream by sending the `STOP_SENDING` frame, the
    /// [`StreamStopped`] error will be returned.
    ///
    /// [`InvalidStreamState`]: enum.Error.html#variant.InvalidStreamState
    /// [`StreamStopped`]: enum.Error.html#variant.StreamStopped
    #[inline]
    pub fn stream_capacity(&self, stream_id: u64) -> Result<usize> {
        if let Some(stream) = self.streams.get(stream_id) {
            let cap = cmp::min(self.tx_cap, stream.send.cap()?);
            return Ok(cap);
        };

        Err(Error::InvalidStreamState(stream_id))
    }

    /// Returns true if the stream has data that can be read.
    pub fn stream_readable(&self, stream_id: u64) -> bool {
        let stream = match self.streams.get(stream_id) {
            Some(v) => v,

            None => return false,
        };

        stream.is_readable()
    }

    /// Returns true if the stream has enough send capacity.
    ///
    /// When `len` more bytes can be buffered into the given stream's send
    /// buffer, `true` will be returned, `false` otherwise.
    ///
    /// In the latter case, if the additional data can't be buffered due to
    /// flow control limits, the peer will also be notified.
    ///
    /// If the specified stream doesn't exist (including when it has already
    /// been completed and closed), the [`InvalidStreamState`] error will be
    /// returned.
    ///
    /// In addition, if the peer has signalled that it doesn't want to receive
    /// any more data from this stream by sending the `STOP_SENDING` frame, the
    /// [`StreamStopped`] error will be returned.
    ///
    /// [`InvalidStreamState`]: enum.Error.html#variant.InvalidStreamState
    /// [`StreamStopped`]: enum.Error.html#variant.StreamStopped
    #[inline]
    pub fn stream_writable(
        &mut self, stream_id: u64, len: usize,
    ) -> Result<bool> {
        if self.stream_capacity(stream_id)? >= len {
            return Ok(true);
        }

        let stream = match self.streams.get(stream_id) {
            Some(v) => v,

            None => return Err(Error::InvalidStreamState(stream_id)),
        };

        if self.max_tx_data - self.tx_data < len as u64 {
            self.blocked_limit = Some(self.max_tx_data);
        }

        if stream.send.cap()? < len {
            let max_off = stream.send.max_off();
            self.streams.mark_blocked(stream_id, true, max_off);
        }

        Ok(false)
    }

    /// Returns true if all the data has been read from the specified stream.
    ///
    /// This instructs the application that all the data received from the
    /// peer on the stream has been read, and there won't be anymore in the
    /// future.
    ///
    /// Basically this returns true when the peer either set the `fin` flag
    /// for the stream, or sent `RESET_STREAM`.
    #[inline]
    pub fn stream_finished(&self, stream_id: u64) -> bool {
        let stream = match self.streams.get(stream_id) {
            Some(v) => v,

            None => return true,
        };

        stream.recv.is_fin()
    }

    /// Returns the number of bidirectional streams that can be created
    /// before the peer's stream count limit is reached.
    ///
    /// This can be useful to know if it's possible to create a bidirectional
    /// stream without trying it first.
    #[inline]
    pub fn peer_streams_left_bidi(&self) -> u64 {
        self.streams.peer_streams_left_bidi()
    }

    /// Returns the number of unidirectional streams that can be created
    /// before the peer's stream count limit is reached.
    ///
    /// This can be useful to know if it's possible to create a unidirectional
    /// stream without trying it first.
    #[inline]
    pub fn peer_streams_left_uni(&self) -> u64 {
        self.streams.peer_streams_left_uni()
    }

    /// Initializes the stream's application data.
    ///
    /// This can be used by applications to store per-stream information without
    /// having to maintain their own stream map.
    ///
    /// Stream data can only be initialized once. Additional calls to this
    /// method will return [`Done`].
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    pub fn stream_init_application_data<T>(
        &mut self, stream_id: u64, data: T,
    ) -> Result<()>
    where
        T: std::any::Any + Send + Sync,
    {
        // Get existing stream.
        let stream = self.streams.get_mut(stream_id).ok_or(Error::Done)?;

        if stream.data.is_some() {
            return Err(Error::Done);
        }

        stream.data = Some(Box::new(data));

        Ok(())
    }

    /// Returns the stream's application data, if any was initialized.
    ///
    /// This returns a reference to the application data that was initialized
    /// by calling [`stream_init_application_data()`].
    ///
    /// [`stream_init_application_data()`]:
    /// struct.Connection.html#method.stream_init_application_data
    pub fn stream_application_data(
        &mut self, stream_id: u64,
    ) -> Option<&mut dyn std::any::Any> {
        // Get existing stream.
        let stream = self.streams.get_mut(stream_id)?;

        if let Some(ref mut stream_data) = stream.data {
            return Some(stream_data.as_mut());
        }

        None
    }

    /// Returns an iterator over streams that have outstanding data to read.
    ///
    /// Note that the iterator will only include streams that were readable at
    /// the time the iterator itself was created (i.e. when `readable()` was
    /// called). To account for newly readable streams, the iterator needs to
    /// be created again.
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// // Iterate over readable streams.
    /// for stream_id in conn.readable() {
    ///     // Stream is readable, read until there's no more data.
    ///     while let Ok((read, fin)) = conn.stream_recv(stream_id, &mut buf) {
    ///         println!("Got {} bytes on stream {}", read, stream_id);
    ///     }
    /// }
    /// # Ok::<(), quiche::Error>(())
    /// ```
    #[inline]
    pub fn readable(&self) -> StreamIter {
        self.streams.readable()
    }

    /// Returns an iterator over streams that can be written to.
    ///
    /// A "writable" stream is a stream that has enough flow control capacity to
    /// send data to the peer. To avoid buffering an infinite amount of data,
    /// streams are only allowed to buffer outgoing data up to the amount that
    /// the peer allows to send.
    ///
    /// Note that the iterator will only include streams that were writable at
    /// the time the iterator itself was created (i.e. when `writable()` was
    /// called). To account for newly writable streams, the iterator needs to
    /// be created again.
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// // Iterate over writable streams.
    /// for stream_id in conn.writable() {
    ///     // Stream is writable, write some data.
    ///     if let Ok(written) = conn.stream_send(stream_id, &buf, false) {
    ///         println!("Written {} bytes on stream {}", written, stream_id);
    ///     }
    /// }
    /// # Ok::<(), quiche::Error>(())
    /// ```
    #[inline]
    pub fn writable(&self) -> StreamIter {
        // If there is not enough connection-level send capacity, none of the
        // streams are writable, so return an empty iterator.
        if self.tx_cap == 0 {
            return StreamIter::default();
        }

        self.streams.writable()
    }

    /// Returns the maximum possible size of egress UDP payloads.
    ///
    /// This is the maximum size of UDP payloads that can be sent, and depends
    /// on both the configured maximum send payload size of the local endpoint
    /// (as configured with [`set_max_send_udp_payload_size()`]), as well as
    /// the transport parameter advertised by the remote peer.
    ///
    /// Note that this value can change during the lifetime of the connection,
    /// but should remain stable across consecutive calls to [`send()`].
    ///
    /// [`set_max_send_udp_payload_size()`]:
    ///     struct.Config.html#method.set_max_send_udp_payload_size
    /// [`send()`]: struct.Connection.html#method.send
    pub fn max_send_udp_payload_size(&self) -> usize {
        if self.is_established() {
            // We cap the maximum packet size to 16KB or so, so that it can be
            // always encoded with a 2-byte varint.
            cmp::min(16383, self.recovery.max_datagram_size())
        } else {
            // Allow for 1200 bytes (minimum QUIC packet size) during the
            // handshake.
            MIN_CLIENT_INITIAL_LEN
        }
    }

    /// Reads the first received DATAGRAM.
    ///
    /// On success the DATAGRAM's data is returned along with its size.
    ///
    /// [`Done`] is returned if there is no data to read.
    ///
    /// [`BufferTooShort`] is returned if the provided buffer is too small for
    /// the DATAGRAM.
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    /// [`BufferTooShort`]: enum.Error.html#variant.BufferTooShort
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// let mut dgram_buf = [0; 512];
    /// while let Ok((len)) = conn.dgram_recv(&mut dgram_buf) {
    ///     println!("Got {} bytes of DATAGRAM", len);
    /// }
    /// # Ok::<(), quiche::Error>(())
    /// ```
    #[inline]
    pub fn dgram_recv(&mut self, buf: &mut [u8]) -> Result<usize> {
        match self.dgram_recv_queue.pop() {
            Some(d) => {
                if d.len() > buf.len() {
                    return Err(Error::BufferTooShort);
                }

                buf[..d.len()].copy_from_slice(&d);
                Ok(d.len())
            },

            None => Err(Error::Done),
        }
    }

    /// Reads the first received DATAGRAM.
    ///
    /// This is the same as [`dgram_recv()`] but returns the DATAGRAM as a
    /// `Vec<u8>` instead of copying into the provided buffer.
    ///
    /// [`dgram_recv()`]: struct.Connection.html#method.dgram_recv
    #[inline]
    pub fn dgram_recv_vec(&mut self) -> Result<Vec<u8>> {
        match self.dgram_recv_queue.pop() {
            Some(d) => Ok(d),

            None => Err(Error::Done),
        }
    }

    /// Reads the first received DATAGRAM without removing it from the queue.
    ///
    /// On success the DATAGRAM's data is returned along with the actual number
    /// of bytes peeked. The requested length cannot exceed the DATAGRAM's
    /// actual length.
    ///
    /// [`Done`] is returned if there is no data to read.
    ///
    /// [`BufferTooShort`] is returned if the provided buffer is smaller the
    /// number of bytes to peek.
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    /// [`BufferTooShort`]: enum.Error.html#variant.BufferTooShort
    #[inline]
    pub fn dgram_recv_peek(&self, buf: &mut [u8], len: usize) -> Result<usize> {
        self.dgram_recv_queue.peek_front_bytes(buf, len)
    }

    /// Returns the length of the first stored DATAGRAM.
    #[inline]
    pub fn dgram_recv_front_len(&self) -> Option<usize> {
        self.dgram_recv_queue.peek_front_len()
    }

    /// Returns the number of items in the DATAGRAM receive queue.
    #[inline]
    pub fn dgram_recv_queue_len(&self) -> usize {
        self.dgram_recv_queue.len()
    }

    /// Returns the total size of all items in the DATAGRAM receive queue.
    #[inline]
    pub fn dgram_recv_queue_byte_size(&self) -> usize {
        self.dgram_recv_queue.byte_size()
    }

    /// Returns the number of items in the DATAGRAM send queue.
    #[inline]
    pub fn dgram_send_queue_len(&self) -> usize {
        self.dgram_send_queue.len()
    }

    /// Returns the total size of all items in the DATAGRAM send queue.
    #[inline]
    pub fn dgram_send_queue_byte_size(&self) -> usize {
        self.dgram_send_queue.byte_size()
    }

    /// Sends data in a DATAGRAM frame.
    ///
    /// [`Done`] is returned if no data was written.
    /// [`InvalidState`] is returned if the peer does not support DATAGRAM.
    /// [`BufferTooShort`] is returned if the DATAGRAM frame length is larger
    /// than peer's supported DATAGRAM frame length. Use
    /// [`dgram_max_writable_len()`] to get the largest supported DATAGRAM
    /// frame length.
    ///
    /// Note that there is no flow control of DATAGRAM frames, so in order to
    /// avoid buffering an infinite amount of frames we apply an internal
    /// limit.
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    /// [`InvalidState`]: enum.Error.html#variant.InvalidState
    /// [`BufferTooShort`]: enum.Error.html#variant.BufferTooShort
    /// [`dgram_max_writable_len()`]:
    /// struct.Connection.html#method.dgram_max_writable_len
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// conn.dgram_send(b"hello")?;
    /// # Ok::<(), quiche::Error>(())
    /// ```
    pub fn dgram_send(&mut self, buf: &[u8]) -> Result<()> {
        let max_payload_len = match self.dgram_max_writable_len() {
            Some(v) => v,

            None => return Err(Error::InvalidState),
        };

        if buf.len() > max_payload_len {
            return Err(Error::BufferTooShort);
        }

        self.dgram_send_queue.push(buf.to_vec())?;

        if self.dgram_send_queue.byte_size() > self.recovery.cwnd_available() {
            self.recovery.update_app_limited(false);
        }

        Ok(())
    }

    /// Sends data in a DATAGRAM frame.
    ///
    /// This is the same as [`dgram_send()`] but takes a `Vec<u8>` instead of
    /// a slice.
    ///
    /// [`dgram_send()`]: struct.Connection.html#method.dgram_send
    pub fn dgram_send_vec(&mut self, buf: Vec<u8>) -> Result<()> {
        let max_payload_len = match self.dgram_max_writable_len() {
            Some(v) => v,

            None => return Err(Error::InvalidState),
        };

        if buf.len() > max_payload_len {
            return Err(Error::BufferTooShort);
        }

        self.dgram_send_queue.push(buf)?;

        if self.dgram_send_queue.byte_size() > self.recovery.cwnd_available() {
            self.recovery.update_app_limited(false);
        }

        Ok(())
    }

    /// Purges queued outgoing DATAGRAMs matching the predicate.
    ///
    /// In other words, remove all elements `e` such that `f(&e)` returns true.
    ///
    /// ## Examples:
    /// ```no_run
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// conn.dgram_send(b"hello")?;
    /// conn.dgram_purge_outgoing(&|d: &[u8]| -> bool { d[0] == 0 });
    /// # Ok::<(), quiche::Error>(())
    /// ```
    #[inline]
    pub fn dgram_purge_outgoing<F: Fn(&[u8]) -> bool>(&mut self, f: F) {
        self.dgram_send_queue.purge(f);
    }

    /// Returns the maximum DATAGRAM payload that can be sent.
    ///
    /// [`None`] is returned if the peer hasn't advertised a maximum DATAGRAM
    /// frame size.
    ///
    /// ## Examples:
    ///
    /// ```no_run
    /// # let mut buf = [0; 512];
    /// # let socket = std::net::UdpSocket::bind("127.0.0.1:0").unwrap();
    /// # let mut config = quiche::Config::new(quiche::PROTOCOL_VERSION)?;
    /// # let scid = quiche::ConnectionId::from_ref(&[0xba; 16]);
    /// # let from = "127.0.0.1:1234".parse().unwrap();
    /// # let mut conn = quiche::accept(&scid, None, from, &mut config)?;
    /// if let Some(payload_size) = conn.dgram_max_writable_len() {
    ///     if payload_size > 5 {
    ///         conn.dgram_send(b"hello")?;
    ///     }
    /// }
    /// # Ok::<(), quiche::Error>(())
    /// ```
    #[inline]
    pub fn dgram_max_writable_len(&self) -> Option<usize> {
        match self.peer_transport_params.max_datagram_frame_size {
            None => None,
            Some(peer_frame_len) => {
                // Start from the maximum packet size...
                let mut max_len = self.max_send_udp_payload_size();
                // ...subtract the Short packet header overhead...
                // (1 byte of pkt_len + len of dcid)
                max_len = max_len.saturating_sub(1 + self.dcid.len());
                // ...subtract the packet number (max len)...
                max_len = max_len.saturating_sub(packet::MAX_PKT_NUM_LEN);
                // ...subtract the crypto overhead...
                max_len = max_len.saturating_sub(
                    self.pkt_num_spaces[packet::EPOCH_APPLICATION]
                        .crypto_overhead()?,
                );
                // ...clamp to what peer can support...
                max_len = cmp::min(peer_frame_len as usize, max_len);
                // ...subtract frame overhead, checked for underflow.
                // (1 byte of frame type + len of length )
                max_len.checked_sub(1 + frame::MAX_DGRAM_OVERHEAD)
            },
        }
    }

    fn dgram_enabled(&self) -> bool {
        self.local_transport_params
            .max_datagram_frame_size
            .is_some()
    }

    /// Returns the amount of time until the next timeout event.
    ///
    /// Once the given duration has elapsed, the [`on_timeout()`] method should
    /// be called. A timeout of `None` means that the timer should be disarmed.
    ///
    /// [`on_timeout()`]: struct.Connection.html#method.on_timeout
    pub fn timeout(&self) -> Option<time::Duration> {
        if self.is_closed() {
            return None;
        }

        let timeout = if self.is_draining() {
            // Draining timer takes precedence over all other timers. If it is
            // set it means the connection is closing so there's no point in
            // processing the other timers.
            self.draining_timer
        } else {
            // Use the lowest timer value (i.e. "sooner") among idle and loss
            // detection timers. If they are both unset (i.e. `None`) then the
            // result is `None`, but if at least one of them is set then a
            // `Some(...)` value is returned.
            let timers = [self.idle_timer, self.recovery.loss_detection_timer()];

            timers.iter().filter_map(|&x| x).min()
        };

        if let Some(timeout) = timeout {
            let now = time::Instant::now();

            if timeout <= now {
                return Some(time::Duration::new(0, 0));
            }

            return Some(timeout.duration_since(now));
        }

        None
    }

    /// Processes a timeout event.
    ///
    /// If no timeout has occurred it does nothing.
    pub fn on_timeout(&mut self) {
        let now = time::Instant::now();

        if let Some(draining_timer) = self.draining_timer {
            if draining_timer <= now {
                trace!("{} draining timeout expired", self.trace_id);

                qlog_with!(self.qlog, q, {
                    q.finish_log().ok();
                });

                self.closed = true;
            }

            // Draining timer takes precedence over all other timers. If it is
            // set it means the connection is closing so there's no point in
            // processing the other timers.
            return;
        }

        if let Some(timer) = self.idle_timer {
            if timer <= now {
                trace!("{} idle timeout expired", self.trace_id);

                qlog_with!(self.qlog, q, {
                    q.finish_log().ok();
                });

                self.closed = true;
                self.timed_out = true;
                return;
            }
        }

        if let Some(timer) = self.recovery.loss_detection_timer() {
            if timer <= now {
                trace!("{} loss detection timeout expired", self.trace_id);

                self.recovery.on_loss_detection_timeout(
                    self.handshake_status(),
                    now,
                    &self.trace_id,
                );

                qlog_with_type!(QLOG_METRICS, self.qlog, q, {
                    if let Some(ev_data) = self.recovery.maybe_qlog() {
                        q.add_event_data_with_instant(ev_data, now).ok();
                    }
                });

                return;
            }
        }
    }

    /// Closes the connection with the given error and reason.
    ///
    /// The `app` parameter specifies whether an application close should be
    /// sent to the peer. Otherwise a normal connection close is sent.
    ///
    /// Returns [`Done`] if the connection had already been closed.
    ///
    /// Note that the connection will not be closed immediately. An application
    /// should continue calling the [`recv()`], [`send()`], [`timeout()`] and
    /// [`on_timeout()`] methods as normal, until the [`is_closed()`] method
    /// returns `true`.
    ///
    /// [`Done`]: enum.Error.html#variant.Done
    /// [`recv()`]: struct.Connection.html#method.recv
    /// [`send()`]: struct.Connection.html#method.send
    /// [`timeout()`]: struct.Connection.html#method.timeout
    /// [`on_timeout()`]: struct.Connection.html#method.on_timeout
    /// [`is_closed()`]: struct.Connection.html#method.is_closed
    pub fn close(&mut self, app: bool, err: u64, reason: &[u8]) -> Result<()> {
        if self.is_closed() || self.is_draining() {
            return Err(Error::Done);
        }

        if self.local_error.is_some() {
            return Err(Error::Done);
        }

        self.local_error = Some(ConnectionError {
            is_app: app,
            error_code: err,
            reason: reason.to_vec(),
        });

        // When no packet was successfully processed close connection immediately.
        if self.recv_count == 0 {
            self.closed = true;
        }

        Ok(())
    }

    /// Returns a string uniquely representing the connection.
    ///
    /// This can be used for logging purposes to differentiate between multiple
    /// connections.
    #[inline]
    pub fn trace_id(&self) -> &str {
        &self.trace_id
    }

    /// Returns the negotiated ALPN protocol.
    ///
    /// If no protocol has been negotiated, the returned value is empty.
    #[inline]
    pub fn application_proto(&self) -> &[u8] {
        self.alpn.as_ref()
    }

    /// Returns the server name requested by the client.
    #[inline]
    pub fn server_name(&self) -> Option<&str> {
        self.handshake.server_name()
    }

    /// Returns the peer's leaf certificate (if any) as a DER-encoded buffer.
    #[inline]
    pub fn peer_cert(&self) -> Option<Vec<u8>> {
        self.handshake.peer_cert()
    }

    /// Returns the serialized cryptographic session for the connection.
    ///
    /// This can be used by a client to cache a connection's session, and resume
    /// it later using the [`set_session()`] method.
    ///
    /// [`set_session()`]: struct.Connection.html#method.set_session
    #[inline]
    pub fn session(&self) -> Option<Vec<u8>> {
        self.session.clone()
    }

    /// Returns the source connection ID.
    ///
    /// Note that the value returned can change throughout the connection's
    /// lifetime.
    #[inline]
    pub fn source_id(&self) -> ConnectionId {
        ConnectionId::from_ref(self.scid.as_ref())
    }

    /// Returns the destination connection ID.
    ///
    /// Note that the value returned can change throughout the connection's
    /// lifetime.
    #[inline]
    pub fn destination_id(&self) -> ConnectionId {
        ConnectionId::from_ref(self.dcid.as_ref())
    }

    /// Returns true if the connection handshake is complete.
    #[inline]
    pub fn is_established(&self) -> bool {
        self.handshake_completed
    }

    /// Returns true if the connection is resumed.
    #[inline]
    pub fn is_resumed(&self) -> bool {
        self.handshake.is_resumed()
    }

    /// Returns true if the connection has a pending handshake that has
    /// progressed enough to send or receive early data.
    #[inline]
    pub fn is_in_early_data(&self) -> bool {
        self.handshake.is_in_early_data()
    }

    /// Returns whether there is stream or DATAGRAM data available to read.
    #[inline]
    pub fn is_readable(&self) -> bool {
        self.streams.has_readable() || self.dgram_recv_front_len().is_some()
    }

    /// Returns true if the connection is draining.
    ///
    /// If this returns true, the connection object cannot yet be dropped, but
    /// no new application data can be sent or received. An application should
    /// continue calling the [`recv()`], [`send()`], [`timeout()`], and
    /// [`on_timeout()`] methods as normal, until the [`is_closed()`] method
    /// returns `true`.
    ///
    /// [`recv()`]: struct.Connection.html#method.recv
    /// [`send()`]: struct.Connection.html#method.send
    /// [`timeout()`]: struct.Connection.html#method.timeout
    /// [`on_timeout()`]: struct.Connection.html#method.on_timeout
    /// [`is_closed()`]: struct.Connection.html#method.is_closed
    #[inline]
    pub fn is_draining(&self) -> bool {
        self.draining_timer.is_some()
    }

    /// Returns true if the connection is closed.
    ///
    /// If this returns true, the connection object can be dropped.
    #[inline]
    pub fn is_closed(&self) -> bool {
        self.closed
    }

    /// Returns true if the connection was closed due to the idle timeout.
    #[inline]
    pub fn is_timed_out(&self) -> bool {
        self.timed_out
    }

    /// Returns the error received from the peer, if any.
    ///
    /// Note that a `Some` return value does not necessarily imply
    /// [`is_closed()`] or any other connection state.
    ///
    /// [`is_closed()`]: struct.Connection.html#method.is_closed
    #[inline]
    pub fn peer_error(&self) -> Option<&ConnectionError> {
        self.peer_error.as_ref()
    }

    /// Returns the error [`close()`] was called with, or internally
    /// created quiche errors, if any.
    ///
    /// Note that a `Some` return value does not necessarily imply
    /// [`is_closed()`] or any other connection state.
    /// `Some` also does not guarantee that the error has been sent to
    /// or recieved by the peer.
    ///
    /// [`close()`]: struct.Connection.html#method.close
    /// [`is_closed()`]: struct.Connection.html#method.is_closed
    #[inline]
    pub fn local_error(&self) -> Option<&ConnectionError> {
        self.local_error.as_ref()
    }

    /// Collects and returns statistics about the connection.
    #[inline]
    pub fn stats(&self) -> Stats {
        Stats {
            recv: self.recv_count,
            sent: self.sent_count,
            lost: self.recovery.lost_count,
            retrans: self.retrans_count,
            cwnd: self.recovery.cwnd(),
            rtt: self.recovery.rtt(),
            sent_bytes: self.sent_bytes,
            lost_bytes: self.recovery.bytes_lost,
            recv_bytes: self.recv_bytes,
            stream_retrans_bytes: self.stream_retrans_bytes,
            pmtu: self.recovery.max_datagram_size(),
            delivery_rate: self.recovery.delivery_rate(),
            peer_max_idle_timeout: self.peer_transport_params.max_idle_timeout,
            peer_max_udp_payload_size: self
                .peer_transport_params
                .max_udp_payload_size,
            peer_initial_max_data: self.peer_transport_params.initial_max_data,
            peer_initial_max_stream_data_bidi_local: self
                .peer_transport_params
                .initial_max_stream_data_bidi_local,
            peer_initial_max_stream_data_bidi_remote: self
                .peer_transport_params
                .initial_max_stream_data_bidi_remote,
            peer_initial_max_stream_data_uni: self
                .peer_transport_params
                .initial_max_stream_data_uni,
            peer_initial_max_streams_bidi: self
                .peer_transport_params
                .initial_max_streams_bidi,
            peer_initial_max_streams_uni: self
                .peer_transport_params
                .initial_max_streams_uni,
            peer_ack_delay_exponent: self
                .peer_transport_params
                .ack_delay_exponent,
            peer_max_ack_delay: self.peer_transport_params.max_ack_delay,
            peer_disable_active_migration: self
                .peer_transport_params
                .disable_active_migration,
            peer_active_conn_id_limit: self
                .peer_transport_params
                .active_conn_id_limit,
            peer_max_datagram_frame_size: self
                .peer_transport_params
                .max_datagram_frame_size,
        }
    }

    fn encode_transport_params(&mut self) -> Result<()> {
        let mut raw_params = [0; 128];

        let raw_params = TransportParams::encode(
            &self.local_transport_params,
            self.is_server,
            &mut raw_params,
        )?;

        self.handshake.set_quic_transport_params(raw_params)?;

        Ok(())
    }

    fn parse_peer_transport_params(
        &mut self, peer_params: TransportParams,
    ) -> Result<()> {
        if self.version >= PROTOCOL_VERSION_DRAFT28 ||
            self.version == PROTOCOL_VERSION_V1
        {
            // Validate initial_source_connection_id.
            match &peer_params.initial_source_connection_id {
                Some(v) if v != &self.dcid =>
                    return Err(Error::InvalidTransportParam),

                Some(_) => (),

                // initial_source_connection_id must be sent by
                // both endpoints.
                None => return Err(Error::InvalidTransportParam),
            }

            // Validate original_destination_connection_id.
            if let Some(odcid) = &self.odcid {
                match &peer_params.original_destination_connection_id {
                    Some(v) if v != odcid =>
                        return Err(Error::InvalidTransportParam),

                    Some(_) => (),

                    // original_destination_connection_id must be
                    // sent by the server.
                    None if !self.is_server =>
                        return Err(Error::InvalidTransportParam),

                    None => (),
                }
            }

            // Validate retry_source_connection_id.
            if let Some(rscid) = &self.rscid {
                match &peer_params.retry_source_connection_id {
                    Some(v) if v != rscid =>
                        return Err(Error::InvalidTransportParam),

                    Some(_) => (),

                    // retry_source_connection_id must be sent by
                    // the server.
                    None => return Err(Error::InvalidTransportParam),
                }
            }
        } else {
            // Legacy validation of the original connection ID when
            // stateless retry is performed, for drafts < 28.
            if self.did_retry &&
                peer_params.original_destination_connection_id != self.odcid
            {
                return Err(Error::InvalidTransportParam);
            }
        }

        self.process_peer_transport_params(peer_params);

        self.parsed_peer_transport_params = true;

        Ok(())
    }

    fn process_peer_transport_params(&mut self, peer_params: TransportParams) {
        self.max_tx_data = peer_params.initial_max_data;

        // Update send capacity.
        self.update_tx_cap();

        self.streams
            .update_peer_max_streams_bidi(peer_params.initial_max_streams_bidi);
        self.streams
            .update_peer_max_streams_uni(peer_params.initial_max_streams_uni);

        self.recovery.max_ack_delay =
            time::Duration::from_millis(peer_params.max_ack_delay);

        self.recovery
            .update_max_datagram_size(peer_params.max_udp_payload_size as usize);

        self.peer_transport_params = peer_params;
    }

    /// Continues the handshake.
    ///
    /// If the connection is already established, it does nothing.
    fn do_handshake(&mut self) -> Result<()> {
        if self.handshake_completed {
            // Handshake is already complete, nothing more to do.
            return Ok(());
        }

        match self.handshake.do_handshake() {
            Ok(_) => (),

            Err(Error::Done) => {
                // Try to parse transport parameters as soon as the first flight
                // of handshake data is processed.
                //
                // This is potentially dangerous as the handshake hasn't been
                // completed yet, though it's required to be able to send data
                // in 0.5 RTT.
                let raw_params = self.handshake.quic_transport_params();

                if !self.parsed_peer_transport_params && !raw_params.is_empty() {
                    let peer_params =
                        TransportParams::decode(raw_params, self.is_server)?;

                    self.parse_peer_transport_params(peer_params)?;
                }

                return Ok(());
            },

            Err(e) => return Err(e),
        };

        self.handshake_completed = self.handshake.is_completed();

        self.alpn = self.handshake.alpn_protocol().to_vec();

        let raw_params = self.handshake.quic_transport_params();

        if !self.parsed_peer_transport_params && !raw_params.is_empty() {
            let peer_params =
                TransportParams::decode(raw_params, self.is_server)?;

            self.parse_peer_transport_params(peer_params)?;
        }

        // Once the handshake is completed there's no point in processing 0-RTT
        // packets anymore, so clear the buffer now.
        if self.handshake_completed {
            self.undecryptable_pkts.clear();
        }

        trace!("{} connection established: proto={:?} cipher={:?} curve={:?} sigalg={:?} resumed={} {:?}",
               &self.trace_id,
               std::str::from_utf8(self.application_proto()),
               self.handshake.cipher(),
               self.handshake.curve(),
               self.handshake.sigalg(),
               self.handshake.is_resumed(),
               self.peer_transport_params);

        Ok(())
    }

    /// Selects the packet type for the next outgoing packet.
    fn write_pkt_type(&self) -> Result<packet::Type> {
        // On error send packet in the latest epoch available, but only send
        // 1-RTT ones when the handshake is completed.
        if self
            .local_error
            .as_ref()
            .map_or(false, |conn_err| !conn_err.is_app)
        {
            let epoch = match self.handshake.write_level() {
                crypto::Level::Initial => packet::EPOCH_INITIAL,
                crypto::Level::ZeroRTT => unreachable!(),
                crypto::Level::Handshake => packet::EPOCH_HANDSHAKE,
                crypto::Level::OneRTT => packet::EPOCH_APPLICATION,
            };

            if epoch == packet::EPOCH_APPLICATION && !self.is_established() {
                // Downgrade the epoch to handshake as the handshake is not
                // completed yet.
                return Ok(packet::Type::Handshake);
            }

            return Ok(packet::Type::from_epoch(epoch));
        }

        for epoch in packet::EPOCH_INITIAL..packet::EPOCH_COUNT {
            // Only send packets in a space when we have the send keys for it.
            if self.pkt_num_spaces[epoch].crypto_seal.is_none() {
                continue;
            }

            // We are ready to send data for this packet number space.
            if self.pkt_num_spaces[epoch].ready() {
                return Ok(packet::Type::from_epoch(epoch));
            }

            // There are lost frames in this packet number space.
            if !self.recovery.lost[epoch].is_empty() {
                return Ok(packet::Type::from_epoch(epoch));
            }

            // We need to send PTO probe packets.
            if self.recovery.loss_probes[epoch] > 0 {
                return Ok(packet::Type::from_epoch(epoch));
            }
        }

        // If there are flushable, almost full or blocked streams, use the
        // Application epoch.
        if (self.is_established() || self.is_in_early_data()) &&
            (self.should_send_handshake_done() ||
                self.almost_full ||
                self.blocked_limit.is_some() ||
                self.dgram_send_queue.has_pending() ||
                self.local_error
                    .as_ref()
                    .map_or(false, |conn_err| conn_err.is_app) ||
                self.streams.should_update_max_streams_bidi() ||
                self.streams.should_update_max_streams_uni() ||
                self.streams.has_flushable() ||
                self.streams.has_almost_full() ||
                self.streams.has_blocked() ||
                self.streams.has_reset() ||
                self.streams.has_stopped())
        {
            // Only clients can send 0-RTT packets.
            if !self.is_server && self.is_in_early_data() {
                return Ok(packet::Type::ZeroRTT);
            }

            return Ok(packet::Type::Short);
        }

        Err(Error::Done)
    }

    /// Returns the mutable stream with the given ID if it exists, or creates
    /// a new one otherwise.
    fn get_or_create_stream(
        &mut self, id: u64, local: bool,
    ) -> Result<&mut stream::Stream> {
        self.streams.get_or_create(
            id,
            &self.local_transport_params,
            &self.peer_transport_params,
            local,
            self.is_server,
        )
    }

    /// Processes an incoming frame.
    fn process_frame(
        &mut self, frame: frame::Frame, epoch: packet::Epoch, now: time::Instant,
    ) -> Result<()> {
        trace!("{} rx frm {:?}", self.trace_id, frame);

        match frame {
            frame::Frame::Padding { .. } => (),

            frame::Frame::Ping => (),

            frame::Frame::ACK {
                ranges, ack_delay, ..
            } => {
                let ack_delay = ack_delay
                    .checked_mul(2_u64.pow(
                        self.peer_transport_params.ack_delay_exponent as u32,
                    ))
                    .ok_or(Error::InvalidFrame)?;

                if epoch == packet::EPOCH_HANDSHAKE {
                    self.peer_verified_address = true;
                }

                // When we receive an ACK for a 1-RTT packet after handshake
                // completion, it means the handshake has been confirmed.
                if epoch == packet::EPOCH_APPLICATION && self.is_established() {
                    self.peer_verified_address = true;

                    self.handshake_confirmed = true;
                }

                self.recovery.on_ack_received(
                    &ranges,
                    ack_delay,
                    epoch,
                    self.handshake_status(),
                    now,
                    &self.trace_id,
                )?;

                // Once the handshake is confirmed, we can drop Handshake keys.
                if self.handshake_confirmed {
                    self.drop_epoch_state(packet::EPOCH_HANDSHAKE, now);
                }
            },

            frame::Frame::ResetStream {
                stream_id,
                error_code,
                final_size,
            } => {
                // Peer can't send on our unidirectional streams.
                if !stream::is_bidi(stream_id) &&
                    stream::is_local(stream_id, self.is_server)
                {
                    return Err(Error::InvalidStreamState(stream_id));
                }

                let max_rx_data_left = self.max_rx_data() - self.rx_data;

                // Get existing stream or create a new one, but if the stream
                // has already been closed and collected, ignore the frame.
                //
                // This can happen if e.g. an ACK frame is lost, and the peer
                // retransmits another frame before it realizes that the stream
                // is gone.
                //
                // Note that it makes it impossible to check if the frame is
                // illegal, since we have no state, but since we ignore the
                // frame, it should be fine.
                let stream = match self.get_or_create_stream(stream_id, false) {
                    Ok(v) => v,

                    Err(Error::Done) => return Ok(()),

                    Err(e) => return Err(e),
                };

                let was_readable = stream.is_readable();

                let max_off_delta =
                    stream.recv.reset(error_code, final_size)? as u64;

                if max_off_delta > max_rx_data_left {
                    return Err(Error::FlowControl);
                }

                if !was_readable && stream.is_readable() {
                    self.streams.mark_readable(stream_id, true);
                }

                self.rx_data += max_off_delta;
            },

            frame::Frame::StopSending {
                stream_id,
                error_code,
            } => {
                // STOP_SENDING on a receive-only stream is a fatal error.
                if !stream::is_local(stream_id, self.is_server) &&
                    !stream::is_bidi(stream_id)
                {
                    return Err(Error::InvalidStreamState(stream_id));
                }

                // Get existing stream or create a new one, but if the stream
                // has already been closed and collected, ignore the frame.
                //
                // This can happen if e.g. an ACK frame is lost, and the peer
                // retransmits another frame before it realizes that the stream
                // is gone.
                //
                // Note that it makes it impossible to check if the frame is
                // illegal, since we have no state, but since we ignore the
                // frame, it should be fine.
                let stream = match self.get_or_create_stream(stream_id, false) {
                    Ok(v) => v,

                    Err(Error::Done) => return Ok(()),

                    Err(e) => return Err(e),
                };

                let was_writable = stream.is_writable();

                // Try stopping the stream.
                if let Ok((final_size, unsent)) = stream.send.stop(error_code) {
                    // Claw back some flow control allowance from data that was
                    // buffered but not actually sent before the stream was
                    // reset.
                    //
                    // Note that `tx_cap` will be updated later on, so no need
                    // to touch it here.
                    self.tx_data = self.tx_data.saturating_sub(unsent);

                    self.streams
                        .mark_reset(stream_id, true, error_code, final_size);

                    if !was_writable {
                        self.streams.mark_writable(stream_id, true);
                    }
                }
            },

            frame::Frame::Crypto { data } => {
                // Push the data to the stream so it can be re-ordered.
                self.pkt_num_spaces[epoch].crypto_stream.recv.write(data)?;

                // Feed crypto data to the TLS state, if there's data
                // available at the expected offset.
                let mut crypto_buf = [0; 512];

                let level = crypto::Level::from_epoch(epoch);

                let stream = &mut self.pkt_num_spaces[epoch].crypto_stream;

                while let Ok((read, _)) = stream.recv.emit(&mut crypto_buf) {
                    let recv_buf = &crypto_buf[..read];
                    self.handshake.provide_data(level, recv_buf)?;
                }

                if self.is_established() {
                    self.handshake.process_post_handshake()?;
                } else {
                    self.do_handshake()?;
                }
            },

            frame::Frame::CryptoHeader { .. } => unreachable!(),

            // TODO: implement stateless retry
            frame::Frame::NewToken { .. } => (),

            frame::Frame::Stream { stream_id, data } => {
                // Peer can't send on our unidirectional streams.
                if !stream::is_bidi(stream_id) &&
                    stream::is_local(stream_id, self.is_server)
                {
                    return Err(Error::InvalidStreamState(stream_id));
                }

                let max_rx_data_left = self.max_rx_data() - self.rx_data;

                // Get existing stream or create a new one, but if the stream
                // has already been closed and collected, ignore the frame.
                //
                // This can happen if e.g. an ACK frame is lost, and the peer
                // retransmits another frame before it realizes that the stream
                // is gone.
                //
                // Note that it makes it impossible to check if the frame is
                // illegal, since we have no state, but since we ignore the
                // frame, it should be fine.
                let stream = match self.get_or_create_stream(stream_id, false) {
                    Ok(v) => v,

                    Err(Error::Done) => return Ok(()),

                    Err(e) => return Err(e),
                };

                // Check for the connection-level flow control limit.
                let max_off_delta =
                    data.max_off().saturating_sub(stream.recv.max_off());

                if max_off_delta > max_rx_data_left {
                    return Err(Error::FlowControl);
                }

                let was_readable = stream.is_readable();

                stream.recv.write(data)?;

                if !was_readable && stream.is_readable() {
                    self.streams.mark_readable(stream_id, true);
                }

                self.rx_data += max_off_delta;
            },

            frame::Frame::StreamHeader { .. } => unreachable!(),

            frame::Frame::MaxData { max } => {
                self.max_tx_data = cmp::max(self.max_tx_data, max);
            },

            frame::Frame::MaxStreamData { stream_id, max } => {
                // Peer can't receive on its own unidirectional streams.
                if !stream::is_bidi(stream_id) &&
                    !stream::is_local(stream_id, self.is_server)
                {
                    return Err(Error::InvalidStreamState(stream_id));
                }

                // Get existing stream or create a new one, but if the stream
                // has already been closed and collected, ignore the frame.
                //
                // This can happen if e.g. an ACK frame is lost, and the peer
                // retransmits another frame before it realizes that the stream
                // is gone.
                //
                // Note that it makes it impossible to check if the frame is
                // illegal, since we have no state, but since we ignore the
                // frame, it should be fine.
                let stream = match self.get_or_create_stream(stream_id, false) {
                    Ok(v) => v,

                    Err(Error::Done) => return Ok(()),

                    Err(e) => return Err(e),
                };

                let was_flushable = stream.is_flushable();

                stream.send.update_max_data(max);

                let writable = stream.is_writable();

                // If the stream is now flushable push it to the flushable queue,
                // but only if it wasn't already queued.
                if stream.is_flushable() && !was_flushable {
                    let urgency = stream.urgency;
                    let incremental = stream.incremental;
                    self.streams.push_flushable(stream_id, urgency, incremental);
                }

                if writable {
                    self.streams.mark_writable(stream_id, true);
                }
            },

            frame::Frame::MaxStreamsBidi { max } => {
                if max > MAX_STREAM_ID {
                    return Err(Error::InvalidFrame);
                }

                self.streams.update_peer_max_streams_bidi(max);
            },

            frame::Frame::MaxStreamsUni { max } => {
                if max > MAX_STREAM_ID {
                    return Err(Error::InvalidFrame);
                }

                self.streams.update_peer_max_streams_uni(max);
            },

            frame::Frame::DataBlocked { .. } => (),

            frame::Frame::StreamDataBlocked { .. } => (),

            frame::Frame::StreamsBlockedBidi { limit } =>
                if limit > MAX_STREAM_ID {
                    return Err(Error::InvalidFrame);
                },

            frame::Frame::StreamsBlockedUni { limit } =>
                if limit > MAX_STREAM_ID {
                    return Err(Error::InvalidFrame);
                },

            // TODO: implement connection migration
            frame::Frame::NewConnectionId { .. } => (),

            // TODO: implement connection migration
            frame::Frame::RetireConnectionId { .. } => (),

            frame::Frame::PathChallenge { data } => {
                self.challenge = Some(data);
            },

            frame::Frame::PathResponse { .. } => (),

            frame::Frame::ConnectionClose {
                error_code, reason, ..
            } => {
                self.peer_error = Some(ConnectionError {
                    is_app: false,
                    error_code,
                    reason,
                });
                self.draining_timer = Some(now + (self.recovery.pto() * 3));
            },

            frame::Frame::ApplicationClose { error_code, reason } => {
                self.peer_error = Some(ConnectionError {
                    is_app: true,
                    error_code,
                    reason,
                });
                self.draining_timer = Some(now + (self.recovery.pto() * 3));
            },

            frame::Frame::HandshakeDone => {
                if self.is_server {
                    return Err(Error::InvalidPacket);
                }

                self.peer_verified_address = true;

                self.handshake_confirmed = true;

                // Once the handshake is confirmed, we can drop Handshake keys.
                self.drop_epoch_state(packet::EPOCH_HANDSHAKE, now);
            },

            frame::Frame::Datagram { data } => {
                // Close the connection if DATAGRAMs are not enabled.
                // quiche always advertises support for 64K sized DATAGRAM
                // frames, as recommended by the standard, so we don't need a
                // size check.
                if !self.dgram_enabled() {
                    return Err(Error::InvalidState);
                }

                // If recv queue is full, discard oldest
                if self.dgram_recv_queue.is_full() {
                    self.dgram_recv_queue.pop();
                }

                self.dgram_recv_queue.push(data)?;
            },

            frame::Frame::DatagramHeader { .. } => unreachable!(),
        }

        Ok(())
    }

    /// Drops the keys and recovery state for the given epoch.
    fn drop_epoch_state(&mut self, epoch: packet::Epoch, now: time::Instant) {
        if self.pkt_num_spaces[epoch].crypto_open.is_none() {
            return;
        }

        self.pkt_num_spaces[epoch].crypto_open = None;
        self.pkt_num_spaces[epoch].crypto_seal = None;
        self.pkt_num_spaces[epoch].clear();

        self.recovery.on_pkt_num_space_discarded(
            epoch,
            self.handshake_status(),
            now,
        );

        trace!("{} dropped epoch {} state", self.trace_id, epoch);
    }

    /// Returns true if the connection-level flow control needs to be updated.
    ///
    /// This happens when the new max data limit is at least double the amount
    /// of data that can be received before blocking.
    fn should_update_max_data(&self) -> bool {
        self.flow_control.should_update_max_data()
    }

    /// Returns the connection level flow control limit.
    fn max_rx_data(&self) -> u64 {
        self.flow_control.max_data()
    }

    /// Returns the updated connection level flow control limit.
    fn max_rx_data_next(&self) -> u64 {
        self.flow_control.max_data_next()
    }

    /// Returns true if the HANDSHAKE_DONE frame needs to be sent.
    fn should_send_handshake_done(&self) -> bool {
        self.is_established() && !self.handshake_done_sent && self.is_server
    }

    /// Returns the idle timeout value.
    ///
    /// `None` is returned if both end-points disabled the idle timeout.
    fn idle_timeout(&mut self) -> Option<time::Duration> {
        // If the transport parameter is set to 0, then the respective endpoint
        // decided to disable the idle timeout. If both are disabled we should
        // not set any timeout.
        if self.local_transport_params.max_idle_timeout == 0 &&
            self.peer_transport_params.max_idle_timeout == 0
        {
            return None;
        }

        // If the local endpoint or the peer disabled the idle timeout, use the
        // other peer's value, otherwise use the minimum of the two values.
        let idle_timeout = if self.local_transport_params.max_idle_timeout == 0 {
            self.peer_transport_params.max_idle_timeout
        } else if self.peer_transport_params.max_idle_timeout == 0 {
            self.local_transport_params.max_idle_timeout
        } else {
            cmp::min(
                self.local_transport_params.max_idle_timeout,
                self.peer_transport_params.max_idle_timeout,
            )
        };

        let idle_timeout = time::Duration::from_millis(idle_timeout);
        let idle_timeout = cmp::max(idle_timeout, 3 * self.recovery.pto());

        Some(idle_timeout)
    }

    /// Returns the connection's handshake status for use in loss recovery.
    fn handshake_status(&self) -> recovery::HandshakeStatus {
        recovery::HandshakeStatus {
            has_handshake_keys: self.pkt_num_spaces[packet::EPOCH_HANDSHAKE]
                .has_keys(),

            peer_verified_address: self.peer_verified_address,

            completed: self.is_established(),
        }
    }

    /// Updates send capacity.
    fn update_tx_cap(&mut self) {
        self.tx_cap = cmp::min(
            self.recovery.cwnd_available() as u64,
            self.max_tx_data - self.tx_data,
        ) as usize;
    }
}

/// Maps an `Error` to `Error::Done`, or itself.
///
/// When a received packet that hasn't yet been authenticated triggers a failure
/// it should, in most cases, be ignored, instead of raising a connection error,
/// to avoid potential man-in-the-middle and man-on-the-side attacks.
///
/// However, if no other packet was previously received, the connection should
/// indeed be closed as the received packet might just be network background
/// noise, and it shouldn't keep resources occupied indefinitely.
///
/// This function maps an error to `Error::Done` to ignore a packet failure
/// without aborting the connection, except when no other packet was previously
/// received, in which case the error itself is returned, but only on the
/// server-side as the client will already have armed the idle timer.
///
/// This must only be used for errors preceding packet authentication. Failures
/// happening after a packet has been authenticated should still cause the
/// connection to be aborted.
fn drop_pkt_on_err(
    e: Error, recv_count: usize, is_server: bool, trace_id: &str,
) -> Error {
    // On the server, if no other packet has been successflully processed, abort
    // the connection to avoid keeping the connection open when only junk is
    // received.
    if is_server && recv_count == 0 {
        return e;
    }

    trace!("{} dropped invalid packet", trace_id);

    // Ignore other invalid packets that haven't been authenticated to prevent
    // man-in-the-middle and man-on-the-side attacks.
    Error::Done
}

/// Statistics about the connection.
///
/// A connection's statistics can be collected using the [`stats()`] method.
///
/// [`stats()`]: struct.Connection.html#method.stats
#[derive(Clone)]
pub struct Stats {
    /// The number of QUIC packets received.
    pub recv: usize,

    /// The number of QUIC packets sent.
    pub sent: usize,

    /// The number of QUIC packets that were lost.
    pub lost: usize,

    /// The number of sent QUIC packets with retransmitted data.
    pub retrans: usize,

    /// The estimated round-trip time of the connection.
    pub rtt: time::Duration,

    /// The size of the connection's congestion window in bytes.
    pub cwnd: usize,

    /// The number of sent bytes.
    pub sent_bytes: u64,

    /// The number of received bytes.
    pub recv_bytes: u64,

    /// The number of bytes lost.
    pub lost_bytes: u64,

    /// The number of stream bytes retranmitted.
    pub stream_retrans_bytes: u64,

    /// The current PMTU for the connection.
    pub pmtu: usize,

    /// The most recent data delivery rate estimate in bytes/s.
    pub delivery_rate: u64,

    /// The maximum idle timeout.
    pub peer_max_idle_timeout: u64,

    /// The maximum UDP payload size.
    pub peer_max_udp_payload_size: u64,

    /// The initial flow control maximum data for the connection.
    pub peer_initial_max_data: u64,

    /// The initial flow control maximum data for local bidirectional streams.
    pub peer_initial_max_stream_data_bidi_local: u64,

    /// The initial flow control maximum data for remote bidirectional streams.
    pub peer_initial_max_stream_data_bidi_remote: u64,

    /// The initial flow control maximum data for unidirectional streams.
    pub peer_initial_max_stream_data_uni: u64,

    /// The initial maximum bidirectional streams.
    pub peer_initial_max_streams_bidi: u64,

    /// The initial maximum unidirectional streams.
    pub peer_initial_max_streams_uni: u64,

    /// The ACK delay exponent.
    pub peer_ack_delay_exponent: u64,

    /// The max ACK delay.
    pub peer_max_ack_delay: u64,

    /// Whether active migration is disabled.
    pub peer_disable_active_migration: bool,

    /// The active connection ID limit.
    pub peer_active_conn_id_limit: u64,

    /// DATAGRAM frame extension parameter, if any.
    pub peer_max_datagram_frame_size: Option<u64>,
}

impl std::fmt::Debug for Stats {
    #[inline]
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(
            f,
            "recv={} sent={} lost={} rtt={:?} cwnd={}",
            self.recv, self.sent, self.lost, self.rtt, self.cwnd,
        )?;

        write!(f, " peer_tps={{")?;

        write!(f, " max_idle_timeout={},", self.peer_max_idle_timeout,)?;

        write!(
            f,
            " max_udp_payload_size={},",
            self.peer_max_udp_payload_size,
        )?;

        write!(f, " initial_max_data={},", self.peer_initial_max_data,)?;

        write!(
            f,
            " initial_max_stream_data_bidi_local={},",
            self.peer_initial_max_stream_data_bidi_local,
        )?;

        write!(
            f,
            " initial_max_stream_data_bidi_remote={},",
            self.peer_initial_max_stream_data_bidi_remote,
        )?;

        write!(
            f,
            " initial_max_stream_data_uni={},",
            self.peer_initial_max_stream_data_uni,
        )?;

        write!(
            f,
            " initial_max_streams_bidi={},",
            self.peer_initial_max_streams_bidi,
        )?;

        write!(
            f,
            " initial_max_streams_uni={},",
            self.peer_initial_max_streams_uni,
        )?;

        write!(f, " ack_delay_exponent={},", self.peer_ack_delay_exponent,)?;

        write!(f, " max_ack_delay={},", self.peer_max_ack_delay,)?;

        write!(
            f,
            " disable_active_migration={},",
            self.peer_disable_active_migration,
        )?;

        write!(
            f,
            " active_conn_id_limit={},",
            self.peer_active_conn_id_limit,
        )?;

        write!(
            f,
            " max_datagram_frame_size={:?}",
            self.peer_max_datagram_frame_size,
        )?;

        write!(f, " }}")
    }
}

#[derive(Clone, Debug, PartialEq)]
struct TransportParams {
    pub original_destination_connection_id: Option<ConnectionId<'static>>,
    pub max_idle_timeout: u64,
    pub stateless_reset_token: Option<Vec<u8>>,
    pub max_udp_payload_size: u64,
    pub initial_max_data: u64,
    pub initial_max_stream_data_bidi_local: u64,
    pub initial_max_stream_data_bidi_remote: u64,
    pub initial_max_stream_data_uni: u64,
    pub initial_max_streams_bidi: u64,
    pub initial_max_streams_uni: u64,
    pub ack_delay_exponent: u64,
    pub max_ack_delay: u64,
    pub disable_active_migration: bool,
    // pub preferred_address: ...,
    pub active_conn_id_limit: u64,
    pub initial_source_connection_id: Option<ConnectionId<'static>>,
    pub retry_source_connection_id: Option<ConnectionId<'static>>,
    pub max_datagram_frame_size: Option<u64>,
}

impl Default for TransportParams {
    fn default() -> TransportParams {
        TransportParams {
            original_destination_connection_id: None,
            max_idle_timeout: 0,
            stateless_reset_token: None,
            max_udp_payload_size: 65527,
            initial_max_data: 0,
            initial_max_stream_data_bidi_local: 0,
            initial_max_stream_data_bidi_remote: 0,
            initial_max_stream_data_uni: 0,
            initial_max_streams_bidi: 0,
            initial_max_streams_uni: 0,
            ack_delay_exponent: 3,
            max_ack_delay: 25,
            disable_active_migration: false,
            active_conn_id_limit: 2,
            initial_source_connection_id: None,
            retry_source_connection_id: None,
            max_datagram_frame_size: None,
        }
    }
}

impl TransportParams {
    fn decode(buf: &[u8], is_server: bool) -> Result<TransportParams> {
        let mut params = octets::Octets::with_slice(buf);

        let mut tp = TransportParams::default();

        while params.cap() > 0 {
            let id = params.get_varint()?;

            let mut val = params.get_bytes_with_varint_length()?;

            // TODO: forbid duplicated param

            match id {
                0x0000 => {
                    if is_server {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.original_destination_connection_id =
                        Some(val.to_vec().into());
                },

                0x0001 => {
                    tp.max_idle_timeout = val.get_varint()?;
                },

                0x0002 => {
                    if is_server {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.stateless_reset_token = Some(val.get_bytes(16)?.to_vec());
                },

                0x0003 => {
                    tp.max_udp_payload_size = val.get_varint()?;

                    if tp.max_udp_payload_size < 1200 {
                        return Err(Error::InvalidTransportParam);
                    }
                },

                0x0004 => {
                    tp.initial_max_data = val.get_varint()?;
                },

                0x0005 => {
                    tp.initial_max_stream_data_bidi_local = val.get_varint()?;
                },

                0x0006 => {
                    tp.initial_max_stream_data_bidi_remote = val.get_varint()?;
                },

                0x0007 => {
                    tp.initial_max_stream_data_uni = val.get_varint()?;
                },

                0x0008 => {
                    let max = val.get_varint()?;

                    if max > MAX_STREAM_ID {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.initial_max_streams_bidi = max;
                },

                0x0009 => {
                    let max = val.get_varint()?;

                    if max > MAX_STREAM_ID {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.initial_max_streams_uni = max;
                },

                0x000a => {
                    let ack_delay_exponent = val.get_varint()?;

                    if ack_delay_exponent > 20 {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.ack_delay_exponent = ack_delay_exponent;
                },

                0x000b => {
                    let max_ack_delay = val.get_varint()?;

                    if max_ack_delay >= 2_u64.pow(14) {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.max_ack_delay = max_ack_delay;
                },

                0x000c => {
                    tp.disable_active_migration = true;
                },

                0x000d => {
                    if is_server {
                        return Err(Error::InvalidTransportParam);
                    }

                    // TODO: decode preferred_address
                },

                0x000e => {
                    let limit = val.get_varint()?;

                    if limit < 2 {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.active_conn_id_limit = limit;
                },

                0x000f => {
                    tp.initial_source_connection_id = Some(val.to_vec().into());
                },

                0x00010 => {
                    if is_server {
                        return Err(Error::InvalidTransportParam);
                    }

                    tp.retry_source_connection_id = Some(val.to_vec().into());
                },

                0x0020 => {
                    tp.max_datagram_frame_size = Some(val.get_varint()?);
                },

                // Ignore unknown parameters.
                _ => (),
            }
        }

        Ok(tp)
    }

    fn encode_param(
        b: &mut octets::OctetsMut, ty: u64, len: usize,
    ) -> Result<()> {
        b.put_varint(ty)?;
        b.put_varint(len as u64)?;

        Ok(())
    }

    fn encode<'a>(
        tp: &TransportParams, is_server: bool, out: &'a mut [u8],
    ) -> Result<&'a mut [u8]> {
        let mut b = octets::OctetsMut::with_slice(out);

        if is_server {
            if let Some(ref odcid) = tp.original_destination_connection_id {
                TransportParams::encode_param(&mut b, 0x0000, odcid.len())?;
                b.put_bytes(odcid)?;
            }
        };

        if tp.max_idle_timeout != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0001,
                octets::varint_len(tp.max_idle_timeout),
            )?;
            b.put_varint(tp.max_idle_timeout)?;
        }

        if is_server {
            if let Some(ref token) = tp.stateless_reset_token {
                TransportParams::encode_param(&mut b, 0x0002, token.len())?;
                b.put_bytes(token)?;
            }
        }

        if tp.max_udp_payload_size != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0003,
                octets::varint_len(tp.max_udp_payload_size),
            )?;
            b.put_varint(tp.max_udp_payload_size)?;
        }

        if tp.initial_max_data != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0004,
                octets::varint_len(tp.initial_max_data),
            )?;
            b.put_varint(tp.initial_max_data)?;
        }

        if tp.initial_max_stream_data_bidi_local != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0005,
                octets::varint_len(tp.initial_max_stream_data_bidi_local),
            )?;
            b.put_varint(tp.initial_max_stream_data_bidi_local)?;
        }

        if tp.initial_max_stream_data_bidi_remote != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0006,
                octets::varint_len(tp.initial_max_stream_data_bidi_remote),
            )?;
            b.put_varint(tp.initial_max_stream_data_bidi_remote)?;
        }

        if tp.initial_max_stream_data_uni != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0007,
                octets::varint_len(tp.initial_max_stream_data_uni),
            )?;
            b.put_varint(tp.initial_max_stream_data_uni)?;
        }

        if tp.initial_max_streams_bidi != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0008,
                octets::varint_len(tp.initial_max_streams_bidi),
            )?;
            b.put_varint(tp.initial_max_streams_bidi)?;
        }

        if tp.initial_max_streams_uni != 0 {
            TransportParams::encode_param(
                &mut b,
                0x0009,
                octets::varint_len(tp.initial_max_streams_uni),
            )?;
            b.put_varint(tp.initial_max_streams_uni)?;
        }

        if tp.ack_delay_exponent != 0 {
            TransportParams::encode_param(
                &mut b,
                0x000a,
                octets::varint_len(tp.ack_delay_exponent),
            )?;
            b.put_varint(tp.ack_delay_exponent)?;
        }

        if tp.max_ack_delay != 0 {
            TransportParams::encode_param(
                &mut b,
                0x000b,
                octets::varint_len(tp.max_ack_delay),
            )?;
            b.put_varint(tp.max_ack_delay)?;
        }

        if tp.disable_active_migration {
            TransportParams::encode_param(&mut b, 0x000c, 0)?;
        }

        // TODO: encode preferred_address

        if tp.active_conn_id_limit != 2 {
            TransportParams::encode_param(
                &mut b,
                0x000e,
                octets::varint_len(tp.active_conn_id_limit),
            )?;
            b.put_varint(tp.active_conn_id_limit)?;
        }

        if let Some(scid) = &tp.initial_source_connection_id {
            TransportParams::encode_param(&mut b, 0x000f, scid.len())?;
            b.put_bytes(scid)?;
        }

        if is_server {
            if let Some(scid) = &tp.retry_source_connection_id {
                TransportParams::encode_param(&mut b, 0x0010, scid.len())?;
                b.put_bytes(scid)?;
            }
        }

        if let Some(max_datagram_frame_size) = tp.max_datagram_frame_size {
            TransportParams::encode_param(
                &mut b,
                0x0020,
                octets::varint_len(max_datagram_frame_size),
            )?;
            b.put_varint(max_datagram_frame_size)?;
        }

        let out_len = b.off();

        Ok(&mut out[..out_len])
    }

    /// Creates a qlog event for connection transport parameters and TLS fields
    #[cfg(feature = "qlog")]
    pub fn to_qlog(
        &self, owner: qlog::TransportOwner, cipher: Option<crypto::Algorithm>,
    ) -> qlog::EventData {
        let original_destination_connection_id = qlog::HexSlice::maybe_string(
            self.original_destination_connection_id.as_ref(),
        );

        let stateless_reset_token = Some(qlog::Token {
            ty: Some(qlog::TokenType::StatelessReset),
            length: None,
            data: qlog::HexSlice::maybe_string(
                self.stateless_reset_token.as_ref(),
            ),
            details: None,
        });

        qlog::EventData::TransportParametersSet {
            owner: Some(owner),
            resumption_allowed: None,
            early_data_enabled: None,
            tls_cipher: Some(format!("{:?}", cipher)),
            aead_tag_length: None,
            original_destination_connection_id,
            initial_source_connection_id: None,
            retry_source_connection_id: None,
            stateless_reset_token,
            disable_active_migration: Some(self.disable_active_migration),
            max_idle_timeout: Some(self.max_idle_timeout),
            max_udp_payload_size: Some(self.max_udp_payload_size as u32),
            ack_delay_exponent: Some(self.ack_delay_exponent as u16),
            max_ack_delay: Some(self.max_ack_delay as u16),
            active_connection_id_limit: Some(self.active_conn_id_limit as u32),

            initial_max_data: Some(self.initial_max_data),
            initial_max_stream_data_bidi_local: Some(
                self.initial_max_stream_data_bidi_local,
            ),
            initial_max_stream_data_bidi_remote: Some(
                self.initial_max_stream_data_bidi_remote,
            ),
            initial_max_stream_data_uni: Some(self.initial_max_stream_data_uni),
            initial_max_streams_bidi: Some(self.initial_max_streams_bidi),
            initial_max_streams_uni: Some(self.initial_max_streams_uni),

            preferred_address: None,
        }
    }
}

#[doc(hidden)]
pub mod testing {
    use super::*;

    pub struct Pipe {
        pub client: Pin<Box<Connection>>,
        pub server: Pin<Box<Connection>>,
    }

    impl Pipe {
        pub fn default() -> Result<Pipe> {
            let mut config = Config::new(crate::PROTOCOL_VERSION)?;
            config.load_cert_chain_from_pem_file("examples/cert.crt")?;
            config.load_priv_key_from_pem_file("examples/cert.key")?;
            config.set_application_protos(b"\x06proto1\x06proto2")?;
            config.set_initial_max_data(30);
            config.set_initial_max_stream_data_bidi_local(15);
            config.set_initial_max_stream_data_bidi_remote(15);
            config.set_initial_max_stream_data_uni(10);
            config.set_initial_max_streams_bidi(3);
            config.set_initial_max_streams_uni(3);
            config.set_max_idle_timeout(180_000);
            config.verify_peer(false);
            config.set_ack_delay_exponent(8);

            Pipe::with_config(&mut config)
        }

        pub fn with_config(config: &mut Config) -> Result<Pipe> {
            let mut client_scid = [0; 16];
            rand::rand_bytes(&mut client_scid[..]);
            let client_scid = ConnectionId::from_ref(&client_scid);
            let client_addr = "127.0.0.1:1234".parse().unwrap();

            let mut server_scid = [0; 16];
            rand::rand_bytes(&mut server_scid[..]);
            let server_scid = ConnectionId::from_ref(&server_scid);
            let server_addr = "127.0.0.1:4321".parse().unwrap();

            Ok(Pipe {
                client: connect(
                    Some("quic.tech"),
                    &client_scid,
                    client_addr,
                    config,
                )?,
                server: accept(&server_scid, None, server_addr, config)?,
            })
        }

        pub fn with_client_config(client_config: &mut Config) -> Result<Pipe> {
            let mut client_scid = [0; 16];
            rand::rand_bytes(&mut client_scid[..]);
            let client_scid = ConnectionId::from_ref(&client_scid);
            let client_addr = "127.0.0.1:1234".parse().unwrap();

            let mut server_scid = [0; 16];
            rand::rand_bytes(&mut server_scid[..]);
            let server_scid = ConnectionId::from_ref(&server_scid);
            let server_addr = "127.0.0.1:4321".parse().unwrap();

            let mut config = Config::new(crate::PROTOCOL_VERSION)?;
            config.load_cert_chain_from_pem_file("examples/cert.crt")?;
            config.load_priv_key_from_pem_file("examples/cert.key")?;
            config.set_application_protos(b"\x06proto1\x06proto2")?;
            config.set_initial_max_data(30);
            config.set_initial_max_stream_data_bidi_local(15);
            config.set_initial_max_stream_data_bidi_remote(15);
            config.set_initial_max_streams_bidi(3);
            config.set_initial_max_streams_uni(3);
            config.set_ack_delay_exponent(8);

            Ok(Pipe {
                client: connect(
                    Some("quic.tech"),
                    &client_scid,
                    client_addr,
                    client_config,
                )?,
                server: accept(&server_scid, None, server_addr, &mut config)?,
            })
        }

        pub fn with_server_config(server_config: &mut Config) -> Result<Pipe> {
            let mut client_scid = [0; 16];
            rand::rand_bytes(&mut client_scid[..]);
            let client_scid = ConnectionId::from_ref(&client_scid);
            let client_addr = "127.0.0.1:1234".parse().unwrap();

            let mut server_scid = [0; 16];
            rand::rand_bytes(&mut server_scid[..]);
            let server_scid = ConnectionId::from_ref(&server_scid);
            let server_addr = "127.0.0.1:4321".parse().unwrap();

            let mut config = Config::new(crate::PROTOCOL_VERSION)?;
            config.set_application_protos(b"\x06proto1\x06proto2")?;
            config.set_initial_max_data(30);
            config.set_initial_max_stream_data_bidi_local(15);
            config.set_initial_max_stream_data_bidi_remote(15);
            config.set_initial_max_streams_bidi(3);
            config.set_initial_max_streams_uni(3);
            config.set_ack_delay_exponent(8);

            Ok(Pipe {
                client: connect(
                    Some("quic.tech"),
                    &client_scid,
                    client_addr,
                    &mut config,
                )?,
                server: accept(&server_scid, None, server_addr, server_config)?,
            })
        }

        pub fn handshake(&mut self) -> Result<()> {
            while !self.client.is_established() || !self.server.is_established() {
                let flight = emit_flight(&mut self.client)?;
                process_flight(&mut self.server, flight)?;

                let flight = emit_flight(&mut self.server)?;
                process_flight(&mut self.client, flight)?;
            }

            Ok(())
        }

        pub fn advance(&mut self) -> Result<()> {
            let mut client_done = false;
            let mut server_done = false;

            while !client_done || !server_done {
                match emit_flight(&mut self.client) {
                    Ok(flight) => process_flight(&mut self.server, flight)?,

                    Err(Error::Done) => client_done = true,

                    Err(e) => return Err(e),
                };

                match emit_flight(&mut self.server) {
                    Ok(flight) => process_flight(&mut self.client, flight)?,

                    Err(Error::Done) => server_done = true,

                    Err(e) => return Err(e),
                };
            }

            Ok(())
        }

        pub fn client_recv(&mut self, buf: &mut [u8]) -> Result<usize> {
            let info = RecvInfo {
                from: self.client.peer_addr,
            };

            self.client.recv(buf, info)
        }

        pub fn server_recv(&mut self, buf: &mut [u8]) -> Result<usize> {
            let info = RecvInfo {
                from: self.server.peer_addr,
            };

            self.server.recv(buf, info)
        }

        pub fn send_pkt_to_server(
            &mut self, pkt_type: packet::Type, frames: &[frame::Frame],
            buf: &mut [u8],
        ) -> Result<usize> {
            let written = encode_pkt(&mut self.client, pkt_type, frames, buf)?;
            recv_send(&mut self.server, buf, written)
        }
    }

    pub fn recv_send(
        conn: &mut Connection, buf: &mut [u8], len: usize,
    ) -> Result<usize> {
        let info = RecvInfo {
            from: conn.peer_addr,
        };

        conn.recv(&mut buf[..len], info)?;

        let mut off = 0;

        match conn.send(&mut buf[off..]) {
            Ok((write, _)) => off += write,

            Err(Error::Done) => (),

            Err(e) => return Err(e),
        }

        Ok(off)
    }

    pub fn process_flight(
        conn: &mut Connection, flight: Vec<Vec<u8>>,
    ) -> Result<()> {
        for mut pkt in flight {
            let info = RecvInfo {
                from: conn.peer_addr,
            };

            conn.recv(&mut pkt, info)?;
        }

        Ok(())
    }

    pub fn emit_flight(conn: &mut Connection) -> Result<Vec<Vec<u8>>> {
        let mut flight = Vec::new();

        loop {
            let mut out = vec![0u8; 65535];

            match conn.send(&mut out) {
                Ok((written, _)) => out.truncate(written),

                Err(Error::Done) => break,

                Err(e) => return Err(e),
            };

            flight.push(out);
        }

        if flight.is_empty() {
            return Err(Error::Done);
        }

        Ok(flight)
    }

    pub fn encode_pkt(
        conn: &mut Connection, pkt_type: packet::Type, frames: &[frame::Frame],
        buf: &mut [u8],
    ) -> Result<usize> {
        let mut b = octets::OctetsMut::with_slice(buf);

        let epoch = pkt_type.to_epoch()?;

        let space = &mut conn.pkt_num_spaces[epoch];

        let pn = space.next_pkt_num;
        let pn_len = 4;

        let hdr = Header {
            ty: pkt_type,
            version: conn.version,
            dcid: ConnectionId::from_ref(&conn.dcid),
            scid: ConnectionId::from_ref(&conn.scid),
            pkt_num: 0,
            pkt_num_len: pn_len,
            token: conn.token.clone(),
            versions: None,
            key_phase: false,
        };

        hdr.to_bytes(&mut b)?;

        let payload_len = frames.iter().fold(0, |acc, x| acc + x.wire_len());

        if pkt_type != packet::Type::Short {
            let len = pn_len + payload_len + space.crypto_overhead().unwrap();
            b.put_varint(len as u64)?;
        }

        // Always encode packet number in 4 bytes, to allow encoding packets
        // with empty payloads.
        b.put_u32(pn as u32)?;

        let payload_offset = b.off();

        for frame in frames {
            frame.to_bytes(&mut b)?;
        }

        let aead = match space.crypto_seal {
            Some(ref v) => v,
            None => return Err(Error::InvalidState),
        };

        let written = packet::encrypt_pkt(
            &mut b,
            pn,
            pn_len,
            payload_len,
            payload_offset,
            None,
            aead,
        )?;

        space.next_pkt_num += 1;

        Ok(written)
    }

    pub fn decode_pkt(
        conn: &mut Connection, buf: &mut [u8], len: usize,
    ) -> Result<Vec<frame::Frame>> {
        let mut b = octets::OctetsMut::with_slice(&mut buf[..len]);

        let mut hdr = Header::from_bytes(&mut b, conn.scid.len()).unwrap();

        let epoch = hdr.ty.to_epoch()?;

        let aead = conn.pkt_num_spaces[epoch].crypto_open.as_ref().unwrap();

        let payload_len = b.cap();

        packet::decrypt_hdr(&mut b, &mut hdr, aead).unwrap();

        let pn = packet::decode_pkt_num(
            conn.pkt_num_spaces[epoch].largest_rx_pkt_num,
            hdr.pkt_num,
            hdr.pkt_num_len,
        );

        let mut payload =
            packet::decrypt_pkt(&mut b, pn, hdr.pkt_num_len, payload_len, aead)
                .unwrap();

        let mut frames = Vec::new();

        while payload.cap() > 0 {
            let frame = frame::Frame::from_bytes(&mut payload, hdr.ty)?;
            frames.push(frame);
        }

        Ok(frames)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn transport_params() {
        // Server encodes, client decodes.
        let tp = TransportParams {
            original_destination_connection_id: None,
            max_idle_timeout: 30,
            stateless_reset_token: Some(vec![0xba; 16]),
            max_udp_payload_size: 23_421,
            initial_max_data: 424_645_563,
            initial_max_stream_data_bidi_local: 154_323_123,
            initial_max_stream_data_bidi_remote: 6_587_456,
            initial_max_stream_data_uni: 2_461_234,
            initial_max_streams_bidi: 12_231,
            initial_max_streams_uni: 18_473,
            ack_delay_exponent: 20,
            max_ack_delay: 2_u64.pow(14) - 1,
            disable_active_migration: true,
            active_conn_id_limit: 8,
            initial_source_connection_id: Some(b"woot woot".to_vec().into()),
            retry_source_connection_id: Some(b"retry".to_vec().into()),
            max_datagram_frame_size: Some(32),
        };

        let mut raw_params = [42; 256];
        let raw_params =
            TransportParams::encode(&tp, true, &mut raw_params).unwrap();
        assert_eq!(raw_params.len(), 94);

        let new_tp = TransportParams::decode(&raw_params, false).unwrap();

        assert_eq!(new_tp, tp);

        // Client encodes, server decodes.
        let tp = TransportParams {
            original_destination_connection_id: None,
            max_idle_timeout: 30,
            stateless_reset_token: None,
            max_udp_payload_size: 23_421,
            initial_max_data: 424_645_563,
            initial_max_stream_data_bidi_local: 154_323_123,
            initial_max_stream_data_bidi_remote: 6_587_456,
            initial_max_stream_data_uni: 2_461_234,
            initial_max_streams_bidi: 12_231,
            initial_max_streams_uni: 18_473,
            ack_delay_exponent: 20,
            max_ack_delay: 2_u64.pow(14) - 1,
            disable_active_migration: true,
            active_conn_id_limit: 8,
            initial_source_connection_id: Some(b"woot woot".to_vec().into()),
            retry_source_connection_id: None,
            max_datagram_frame_size: Some(32),
        };

        let mut raw_params = [42; 256];
        let raw_params =
            TransportParams::encode(&tp, false, &mut raw_params).unwrap();
        assert_eq!(raw_params.len(), 69);

        let new_tp = TransportParams::decode(&raw_params, true).unwrap();

        assert_eq!(new_tp, tp);
    }

    #[test]
    fn unknown_version() {
        let mut config = Config::new(0xbabababa).unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.verify_peer(false);

        let mut pipe = testing::Pipe::with_client_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Err(Error::UnknownVersion));
    }

    #[test]
    fn config_version_reserved() {
        Config::new(0xbabababa).unwrap();
        Config::new(0x1a2a3a4a).unwrap();
    }

    #[test]
    fn config_version_invalid() {
        assert_eq!(
            Config::new(0xb1bababa).err().unwrap(),
            Error::UnknownVersion
        );
    }

    #[test]
    fn version_negotiation() {
        let mut buf = [0; 65535];

        let mut config = Config::new(0xbabababa).unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.verify_peer(false);

        let mut pipe = testing::Pipe::with_client_config(&mut config).unwrap();

        let (mut len, _) = pipe.client.send(&mut buf).unwrap();

        let hdr = packet::Header::from_slice(&mut buf[..len], 0).unwrap();
        len = crate::negotiate_version(&hdr.scid, &hdr.dcid, &mut buf).unwrap();

        assert_eq!(pipe.client_recv(&mut buf[..len]), Ok(len));

        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(pipe.client.version, PROTOCOL_VERSION);
        assert_eq!(pipe.server.version, PROTOCOL_VERSION);
    }

    #[test]
    fn verify_custom_root() {
        let mut config = Config::new(PROTOCOL_VERSION).unwrap();
        config.verify_peer(true);
        config
            .load_verify_locations_from_file("examples/rootca.crt")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();

        let mut pipe = testing::Pipe::with_client_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));
    }

    #[test]
    fn missing_initial_source_connection_id() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();

        // Reset initial_source_connection_id.
        pipe.client
            .local_transport_params
            .initial_source_connection_id = None;
        assert_eq!(pipe.client.encode_transport_params(), Ok(()));

        // Client sends initial flight.
        let (len, _) = pipe.client.send(&mut buf).unwrap();

        // Server rejects transport parameters.
        assert_eq!(
            pipe.server_recv(&mut buf[..len]),
            Err(Error::InvalidTransportParam)
        );
    }

    #[test]
    fn invalid_initial_source_connection_id() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();

        // Scramble initial_source_connection_id.
        pipe.client
            .local_transport_params
            .initial_source_connection_id = Some(b"bogus value".to_vec().into());
        assert_eq!(pipe.client.encode_transport_params(), Ok(()));

        // Client sends initial flight.
        let (len, _) = pipe.client.send(&mut buf).unwrap();

        // Server rejects transport parameters.
        assert_eq!(
            pipe.server_recv(&mut buf[..len]),
            Err(Error::InvalidTransportParam)
        );
    }

    #[test]
    fn handshake() {
        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(
            pipe.client.application_proto(),
            pipe.server.application_proto()
        );

        assert_eq!(pipe.server.server_name(), Some("quic.tech"));
    }

    #[test]
    fn handshake_done() {
        let mut pipe = testing::Pipe::default().unwrap();

        // Disable session tickets on the server (SSL_OP_NO_TICKET) to avoid
        // triggering 1-RTT packet send with a CRYPTO frame.
        pipe.server.handshake.set_options(0x0000_4000);

        assert_eq!(pipe.handshake(), Ok(()));

        assert!(pipe.server.handshake_done_sent);
    }

    #[test]
    fn handshake_confirmation() {
        let mut pipe = testing::Pipe::default().unwrap();

        // Client sends initial flight.
        let flight = testing::emit_flight(&mut pipe.client).unwrap();
        testing::process_flight(&mut pipe.server, flight).unwrap();

        // Server sends initial flight.
        let flight = testing::emit_flight(&mut pipe.server).unwrap();

        assert!(!pipe.client.is_established());
        assert!(!pipe.client.handshake_confirmed);

        assert!(!pipe.server.is_established());
        assert!(!pipe.server.handshake_confirmed);

        testing::process_flight(&mut pipe.client, flight).unwrap();

        // Client sends Handshake packet and completes handshake.
        let flight = testing::emit_flight(&mut pipe.client).unwrap();

        assert!(pipe.client.is_established());
        assert!(!pipe.client.handshake_confirmed);

        assert!(!pipe.server.is_established());
        assert!(!pipe.server.handshake_confirmed);

        testing::process_flight(&mut pipe.server, flight).unwrap();

        // Server completes handshake and sends HANDSHAKE_DONE.
        let flight = testing::emit_flight(&mut pipe.server).unwrap();

        assert!(pipe.client.is_established());
        assert!(!pipe.client.handshake_confirmed);

        assert!(pipe.server.is_established());
        assert!(!pipe.server.handshake_confirmed);

        testing::process_flight(&mut pipe.client, flight).unwrap();

        // Client acks 1-RTT packet, and confirms handshake.
        let flight = testing::emit_flight(&mut pipe.client).unwrap();

        assert!(pipe.client.is_established());
        assert!(pipe.client.handshake_confirmed);

        assert!(pipe.server.is_established());
        assert!(!pipe.server.handshake_confirmed);

        testing::process_flight(&mut pipe.server, flight).unwrap();

        // Server handshake is confirmed.
        assert!(pipe.client.is_established());
        assert!(pipe.client.handshake_confirmed);

        assert!(pipe.server.is_established());
        assert!(pipe.server.handshake_confirmed);
    }

    #[test]
    fn handshake_resumption() {
        const SESSION_TICKET_KEY: [u8; 48] = [0xa; 48];

        let mut config = Config::new(crate::PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.set_initial_max_data(30);
        config.set_initial_max_stream_data_bidi_local(15);
        config.set_initial_max_stream_data_bidi_remote(15);
        config.set_initial_max_streams_bidi(3);
        config.set_ticket_key(&SESSION_TICKET_KEY).unwrap();

        // Perform initial handshake.
        let mut pipe = testing::Pipe::with_server_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(pipe.client.is_established(), true);
        assert_eq!(pipe.server.is_established(), true);

        assert_eq!(pipe.client.is_resumed(), false);
        assert_eq!(pipe.server.is_resumed(), false);

        // Extract session,
        let session = pipe.client.session().unwrap();

        // Configure session on new connection and perform handshake.
        let mut config = Config::new(crate::PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.set_initial_max_data(30);
        config.set_initial_max_stream_data_bidi_local(15);
        config.set_initial_max_stream_data_bidi_remote(15);
        config.set_initial_max_streams_bidi(3);
        config.set_ticket_key(&SESSION_TICKET_KEY).unwrap();

        let mut pipe = testing::Pipe::with_server_config(&mut config).unwrap();

        assert_eq!(pipe.client.set_session(&session), Ok(()));
        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(pipe.client.is_established(), true);
        assert_eq!(pipe.server.is_established(), true);

        assert_eq!(pipe.client.is_resumed(), true);
        assert_eq!(pipe.server.is_resumed(), true);
    }

    #[test]
    fn handshake_alpn_mismatch() {
        let mut buf = [0; 65535];

        let mut config = Config::new(PROTOCOL_VERSION).unwrap();
        config
            .set_application_protos(b"\x06proto3\x06proto4")
            .unwrap();
        config.verify_peer(false);

        let mut pipe = testing::Pipe::with_client_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Err(Error::TlsFail));

        assert_eq!(pipe.client.application_proto(), b"");
        assert_eq!(pipe.server.application_proto(), b"");

        // Server should only send one packet in response to ALPN mismatch.
        let (len, _) = pipe.server.send(&mut buf).unwrap();
        assert_eq!(len, 1200);

        assert_eq!(pipe.server.send(&mut buf), Err(Error::Done));
        assert_eq!(pipe.server.sent_count, 1);
    }

    #[test]
    fn handshake_0rtt() {
        let mut buf = [0; 65535];

        let mut config = Config::new(crate::PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.set_initial_max_data(30);
        config.set_initial_max_stream_data_bidi_local(15);
        config.set_initial_max_stream_data_bidi_remote(15);
        config.set_initial_max_streams_bidi(3);
        config.enable_early_data();
        config.verify_peer(false);

        // Perform initial handshake.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // Extract session,
        let session = pipe.client.session().unwrap();

        // Configure session on new connection.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.client.set_session(&session), Ok(()));

        // Client sends initial flight.
        let (len, _) = pipe.client.send(&mut buf).unwrap();
        assert_eq!(pipe.server_recv(&mut buf[..len]), Ok(len));

        // Client sends 0-RTT packet.
        let pkt_type = packet::Type::ZeroRTT;

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"aaaaa", 0, true),
        }];

        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Ok(1200)
        );

        assert_eq!(pipe.server.undecryptable_pkts.len(), 0);

        // 0-RTT stream data is readable.
        let mut r = pipe.server.readable();
        assert_eq!(r.next(), Some(4));
        assert_eq!(r.next(), None);

        let mut b = [0; 15];
        assert_eq!(pipe.server.stream_recv(4, &mut b), Ok((5, true)));
        assert_eq!(&b[..5], b"aaaaa");
    }

    #[test]
    fn handshake_0rtt_reordered() {
        let mut buf = [0; 65535];

        let mut config = Config::new(crate::PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.set_initial_max_data(30);
        config.set_initial_max_stream_data_bidi_local(15);
        config.set_initial_max_stream_data_bidi_remote(15);
        config.set_initial_max_streams_bidi(3);
        config.enable_early_data();
        config.verify_peer(false);

        // Perform initial handshake.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // Extract session,
        let session = pipe.client.session().unwrap();

        // Configure session on new connection.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.client.set_session(&session), Ok(()));

        // Client sends initial flight.
        let (len, _) = pipe.client.send(&mut buf).unwrap();
        let mut initial = (&buf[..len]).to_vec();

        // Client sends 0-RTT packet.
        let pkt_type = packet::Type::ZeroRTT;

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"aaaaa", 0, true),
        }];

        let len =
            testing::encode_pkt(&mut pipe.client, pkt_type, &frames, &mut buf)
                .unwrap();
        let mut zrtt = (&buf[..len]).to_vec();

        // 0-RTT packet is received before the Initial one.
        assert_eq!(pipe.server_recv(&mut zrtt), Ok(zrtt.len()));

        assert_eq!(pipe.server.undecryptable_pkts.len(), 1);
        assert_eq!(pipe.server.undecryptable_pkts[0].0.len(), zrtt.len());

        let mut r = pipe.server.readable();
        assert_eq!(r.next(), None);

        // Initial packet is also received.
        assert_eq!(pipe.server_recv(&mut initial), Ok(initial.len()));

        // 0-RTT stream data is readable.
        let mut r = pipe.server.readable();
        assert_eq!(r.next(), Some(4));
        assert_eq!(r.next(), None);

        let mut b = [0; 15];
        assert_eq!(pipe.server.stream_recv(4, &mut b), Ok((5, true)));
        assert_eq!(&b[..5], b"aaaaa");
    }

    #[test]
    fn handshake_0rtt_truncated() {
        let mut buf = [0; 65535];

        let mut config = Config::new(crate::PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.set_initial_max_data(30);
        config.set_initial_max_stream_data_bidi_local(15);
        config.set_initial_max_stream_data_bidi_remote(15);
        config.set_initial_max_streams_bidi(3);
        config.enable_early_data();
        config.verify_peer(false);

        // Perform initial handshake.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // Extract session,
        let session = pipe.client.session().unwrap();

        // Configure session on new connection.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.client.set_session(&session), Ok(()));

        // Client sends initial flight.
        pipe.client.send(&mut buf).unwrap();

        // Client sends 0-RTT packet.
        let pkt_type = packet::Type::ZeroRTT;

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"aaaaa", 0, true),
        }];

        let len =
            testing::encode_pkt(&mut pipe.client, pkt_type, &frames, &mut buf)
                .unwrap();

        // Simulate a truncated packet by sending one byte less.
        let mut zrtt = (&buf[..len - 1]).to_vec();

        // 0-RTT packet is received before the Initial one.
        assert_eq!(pipe.server_recv(&mut zrtt), Err(Error::InvalidPacket));

        assert_eq!(pipe.server.undecryptable_pkts.len(), 0);

        assert!(pipe.server.is_closed());
    }

    #[test]
    /// Tests that a pre-v1 client can connect to a v1-enabled server, by making
    /// the server downgrade to the pre-v1 version.
    fn handshake_downgrade_v1() {
        let mut config = Config::new(PROTOCOL_VERSION_DRAFT29).unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.verify_peer(false);

        let mut pipe = testing::Pipe::with_client_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(pipe.client.version, PROTOCOL_VERSION_DRAFT29);
        assert_eq!(pipe.server.version, PROTOCOL_VERSION_DRAFT29);
    }

    #[test]
    fn limit_handshake_data() {
        let mut config = Config::new(PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert-big.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();

        let mut pipe = testing::Pipe::with_server_config(&mut config).unwrap();

        let flight = testing::emit_flight(&mut pipe.client).unwrap();
        let client_sent = flight.iter().fold(0, |out, p| out + p.len());
        testing::process_flight(&mut pipe.server, flight).unwrap();

        let flight = testing::emit_flight(&mut pipe.server).unwrap();
        let server_sent = flight.iter().fold(0, |out, p| out + p.len());

        assert_eq!(server_sent, client_sent * MAX_AMPLIFICATION_FACTOR);
    }

    #[test]
    fn stream() {
        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(pipe.client.stream_send(4, b"hello, world", true), Ok(12));
        assert_eq!(pipe.advance(), Ok(()));

        assert!(!pipe.server.stream_finished(4));

        let mut r = pipe.server.readable();
        assert_eq!(r.next(), Some(4));
        assert_eq!(r.next(), None);

        let mut b = [0; 15];
        assert_eq!(pipe.server.stream_recv(4, &mut b), Ok((12, true)));
        assert_eq!(&b[..12], b"hello, world");

        assert!(pipe.server.stream_finished(4));
    }

    #[test]
    fn zero_rtt() {
        let mut buf = [0; 65535];

        let mut config = Config::new(crate::PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.set_initial_max_data(30);
        config.set_initial_max_stream_data_bidi_local(15);
        config.set_initial_max_stream_data_bidi_remote(15);
        config.set_initial_max_streams_bidi(3);
        config.enable_early_data();
        config.verify_peer(false);

        // Perform initial handshake.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // Extract session,
        let session = pipe.client.session().unwrap();

        // Configure session on new connection.
        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.client.set_session(&session), Ok(()));

        // Client sends initial flight.
        let (len, _) = pipe.client.send(&mut buf).unwrap();
        let mut initial = (&buf[..len]).to_vec();

        assert_eq!(pipe.client.is_in_early_data(), true);

        // Client sends 0-RTT data.
        assert_eq!(pipe.client.stream_send(4, b"hello, world", true), Ok(12));

        let (len, _) = pipe.client.send(&mut buf).unwrap();
        let mut zrtt = (&buf[..len]).to_vec();

        // Server receives packets.
        assert_eq!(pipe.server_recv(&mut initial), Ok(initial.len()));
        assert_eq!(pipe.server.is_in_early_data(), true);

        assert_eq!(pipe.server_recv(&mut zrtt), Ok(zrtt.len()));

        // 0-RTT stream data is readable.
        let mut r = pipe.server.readable();
        assert_eq!(r.next(), Some(4));
        assert_eq!(r.next(), None);

        let mut b = [0; 15];
        assert_eq!(pipe.server.stream_recv(4, &mut b), Ok((12, true)));
        assert_eq!(&b[..12], b"hello, world");
    }

    #[test]
    fn stream_send_on_32bit_arch() {
        let mut config = Config::new(crate::PROTOCOL_VERSION).unwrap();
        config
            .load_cert_chain_from_pem_file("examples/cert.crt")
            .unwrap();
        config
            .load_priv_key_from_pem_file("examples/cert.key")
            .unwrap();
        config
            .set_application_protos(b"\x06proto1\x06proto2")
            .unwrap();
        config.set_initial_max_data(2_u64.pow(32) + 5);
        config.set_initial_max_stream_data_bidi_local(15);
        config.set_initial_max_stream_data_bidi_remote(15);
        config.set_initial_max_stream_data_uni(10);
        config.set_initial_max_streams_bidi(3);
        config.set_initial_max_streams_uni(0);
        config.verify_peer(false);

        let mut pipe = testing::Pipe::with_config(&mut config).unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // In 32bit arch, send_capacity() should be min(2^32+5, cwnd),
        // not min(5, cwnd)
        assert_eq!(pipe.client.stream_send(4, b"hello, world", true), Ok(12));

        assert_eq!(pipe.advance(), Ok(()));

        assert!(!pipe.server.stream_finished(4));
    }

    #[test]
    fn empty_stream_frame() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"aaaaa", 0, false),
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf), Ok(39));

        let mut readable = pipe.server.readable();
        assert_eq!(readable.next(), Some(4));

        assert_eq!(pipe.server.stream_recv(4, &mut buf), Ok((5, false)));

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"", 5, true),
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf), Ok(39));

        let mut readable = pipe.server.readable();
        assert_eq!(readable.next(), Some(4));

        assert_eq!(pipe.server.stream_recv(4, &mut buf), Ok((0, true)));

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"", 15, true),
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::FinalSize)
        );
    }

    #[test]
    /// Tests that receiving a MAX_STREAM_DATA frame for a receive-only
    /// unidirectional stream is forbidden.
    fn max_stream_data_receive_uni() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // Client opens unidirectional stream.
        assert_eq!(pipe.client.stream_send(2, b"hello", false), Ok(5));
        assert_eq!(pipe.advance(), Ok(()));

        // Client sends MAX_STREAM_DATA on local unidirectional stream.
        let frames = [frame::Frame::MaxStreamData {
            stream_id: 2,
            max: 1024,
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::InvalidStreamState(2)),
        );
    }

    #[test]
    fn empty_payload() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // Send a packet with no frames.
        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &[], &mut buf),
            Err(Error::InvalidPacket)
        );
    }

    #[test]
    fn min_payload() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();

        // Send a non-ack-eliciting packet.
        let frames = [frame::Frame::Padding { len: 4 }];

        let pkt_type = packet::Type::Initial;
        let written =
            testing::encode_pkt(&mut pipe.client, pkt_type, &frames, &mut buf)
                .unwrap();
        assert_eq!(pipe.server_recv(&mut buf[..written]), Ok(written));

        assert_eq!(pipe.server.max_send_bytes, 195);

        // Force server to send a single PING frame.
        pipe.server.recovery.loss_probes[packet::EPOCH_INITIAL] = 1;

        // Artifically limit the amount of bytes the server can send.
        pipe.server.max_send_bytes = 60;

        assert_eq!(pipe.server.send(&mut buf), Err(Error::Done));
    }

    #[test]
    fn flow_control_limit() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [
            frame::Frame::Stream {
                stream_id: 4,
                data: stream::RangeBuf::from(b"aaaaaaaaaaaaaaa", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 8,
                data: stream::RangeBuf::from(b"aaaaaaaaaaaaaaa", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 12,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
        ];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::FlowControl),
        );
    }

    #[test]
    fn flow_control_limit_dup() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [
            // One byte less than stream limit.
            frame::Frame::Stream {
                stream_id: 4,
                data: stream::RangeBuf::from(b"aaaaaaaaaaaaaa", 0, false),
            },
            // Same stream, but one byte more.
            frame::Frame::Stream {
                stream_id: 4,
                data: stream::RangeBuf::from(b"aaaaaaaaaaaaaaa", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 12,
                data: stream::RangeBuf::from(b"aaaaaaaaaaaaaaa", 0, false),
            },
        ];

        let pkt_type = packet::Type::Short;
        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());
    }

    #[test]
    fn flow_control_update() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [
            frame::Frame::Stream {
                stream_id: 4,
                data: stream::RangeBuf::from(b"aaaaaaaaaaaaaaa", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 8,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
        ];

        let pkt_type = packet::Type::Short;

        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        pipe.server.stream_recv(4, &mut buf).unwrap();
        pipe.server.stream_recv(8, &mut buf).unwrap();

        let frames = [frame::Frame::Stream {
            stream_id: 8,
            data: stream::RangeBuf::from(b"a", 1, false),
        }];

        let len = pipe
            .send_pkt_to_server(pkt_type, &frames, &mut buf)
            .unwrap();

        assert!(len > 0);

        let frames =
            testing::decode_pkt(&mut pipe.client, &mut buf, len).unwrap();
        let mut iter = frames.iter();

        // Ignore ACK.
        iter.next().unwrap();

        assert_eq!(
            iter.next(),
            Some(&frame::Frame::MaxStreamData {
                stream_id: 4,
                max: 30
            })
        );
        assert_eq!(iter.next(), Some(&frame::Frame::MaxData { max: 61 }));
    }

    #[test]
    /// Tests that flow control is properly updated even when a stream is shut
    /// down.
    fn flow_control_drain() {
        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        // Client opens a stream and sends some data.
        assert_eq!(pipe.client.stream_send(4, b"aaaaa", false), Ok(5));
        assert_eq!(pipe.advance(), Ok(()));

        // Server receives data, without reading it.
        let mut r = pipe.server.readable();
        assert_eq!(r.next(), Some(4));
        assert_eq!(r.next(), None);

        // In the meantime, client sends more data.
        assert_eq!(pipe.client.stream_send(4, b"aaaaa", false), Ok(5));
        assert_eq!(pipe.client.stream_send(4, b"aaaaa", true), Ok(5));

        assert_eq!(pipe.client.stream_send(8, b"aaaaa", false), Ok(5));
        assert_eq!(pipe.client.stream_send(8, b"aaaaa", false), Ok(5));
        assert_eq!(pipe.client.stream_send(8, b"aaaaa", true), Ok(5));

        // Server shuts down one stream.
        assert_eq!(pipe.server.stream_shutdown(4, Shutdown::Read, 42), Ok(()));

        let mut r = pipe.server.readable();
        assert_eq!(r.next(), None);

        // Flush connection.
        assert_eq!(pipe.advance(), Ok(()));
    }

    #[test]
    fn stream_flow_control_limit_bidi() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"aaaaaaaaaaaaaaaa", 0, true),
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::FlowControl),
        );
    }

    #[test]
    fn stream_flow_control_limit_uni() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::Stream {
            stream_id: 2,
            data: stream::RangeBuf::from(b"aaaaaaaaaaa", 0, true),
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::FlowControl),
        );
    }

    #[test]
    fn stream_flow_control_update() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"aaaaaaaaa", 0, false),
        }];

        let pkt_type = packet::Type::Short;

        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        pipe.server.stream_recv(4, &mut buf).unwrap();

        let frames = [frame::Frame::Stream {
            stream_id: 4,
            data: stream::RangeBuf::from(b"a", 9, false),
        }];

        let len = pipe
            .send_pkt_to_server(pkt_type, &frames, &mut buf)
            .unwrap();

        assert!(len > 0);

        let frames =
            testing::decode_pkt(&mut pipe.client, &mut buf, len).unwrap();
        let mut iter = frames.iter();

        // Ignore ACK.
        iter.next().unwrap();

        assert_eq!(
            iter.next(),
            Some(&frame::Frame::MaxStreamData {
                stream_id: 4,
                max: 24,
            })
        );
    }

    #[test]
    fn stream_left_bidi() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(3, pipe.client.peer_streams_left_bidi());
        assert_eq!(3, pipe.server.peer_streams_left_bidi());

        pipe.server.stream_send(1, b"a", false).ok();
        assert_eq!(2, pipe.server.peer_streams_left_bidi());
        pipe.server.stream_send(5, b"a", false).ok();
        assert_eq!(1, pipe.server.peer_streams_left_bidi());

        pipe.server.stream_send(9, b"a", false).ok();
        assert_eq!(0, pipe.server.peer_streams_left_bidi());

        let frames = [frame::Frame::MaxStreamsBidi { max: MAX_STREAM_ID }];

        let pkt_type = packet::Type::Short;
        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        assert_eq!(MAX_STREAM_ID - 3, pipe.server.peer_streams_left_bidi());
    }

    #[test]
    fn stream_left_uni() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        assert_eq!(3, pipe.client.peer_streams_left_uni());
        assert_eq!(3, pipe.server.peer_streams_left_uni());

        pipe.server.stream_send(3, b"a", false).ok();
        assert_eq!(2, pipe.server.peer_streams_left_uni());
        pipe.server.stream_send(7, b"a", false).ok();
        assert_eq!(1, pipe.server.peer_streams_left_uni());

        pipe.server.stream_send(11, b"a", false).ok();
        assert_eq!(0, pipe.server.peer_streams_left_uni());

        let frames = [frame::Frame::MaxStreamsUni { max: MAX_STREAM_ID }];

        let pkt_type = packet::Type::Short;
        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        assert_eq!(MAX_STREAM_ID - 3, pipe.server.peer_streams_left_uni());
    }

    #[test]
    fn stream_limit_bidi() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [
            frame::Frame::Stream {
                stream_id: 4,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 8,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 12,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 16,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 20,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 24,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 28,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
        ];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::StreamLimit),
        );
    }

    #[test]
    fn stream_limit_max_bidi() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::MaxStreamsBidi { max: MAX_STREAM_ID }];

        let pkt_type = packet::Type::Short;
        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        let frames = [frame::Frame::MaxStreamsBidi {
            max: MAX_STREAM_ID + 1,
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::InvalidFrame),
        );
    }

    #[test]
    fn stream_limit_uni() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [
            frame::Frame::Stream {
                stream_id: 2,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 6,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 10,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 14,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 18,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 22,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
            frame::Frame::Stream {
                stream_id: 26,
                data: stream::RangeBuf::from(b"a", 0, false),
            },
        ];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::StreamLimit),
        );
    }

    #[test]
    fn stream_limit_max_uni() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::MaxStreamsUni { max: MAX_STREAM_ID }];

        let pkt_type = packet::Type::Short;
        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        let frames = [frame::Frame::MaxStreamsUni {
            max: MAX_STREAM_ID + 1,
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::InvalidFrame),
        );
    }

    #[test]
    fn streams_blocked_max_bidi() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::StreamsBlockedBidi {
            limit: MAX_STREAM_ID,
        }];

        let pkt_type = packet::Type::Short;
        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        let frames = [frame::Frame::StreamsBlockedBidi {
            limit: MAX_STREAM_ID + 1,
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::InvalidFrame),
        );
    }

    #[test]
    fn streams_blocked_max_uni() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [frame::Frame::StreamsBlockedUni {
            limit: MAX_STREAM_ID,
        }];

        let pkt_type = packet::Type::Short;
        assert!(pipe.send_pkt_to_server(pkt_type, &frames, &mut buf).is_ok());

        let frames = [frame::Frame::StreamsBlockedUni {
            limit: MAX_STREAM_ID + 1,
        }];

        let pkt_type = packet::Type::Short;
        assert_eq!(
            pipe.send_pkt_to_server(pkt_type, &frames, &mut buf),
            Err(Error::InvalidFrame),
        );
    }

    #[test]
    fn stream_data_overlap() {
        let mut buf = [0; 65535];

        let mut pipe = testing::Pipe::default().unwrap();
        assert_eq!(pipe.handshake(), Ok(()));

        let frames = [
            frame::Frame::Stream {
                stream_id: 0,
                data: stream::RangeBuf::from(b"aaaaa"</