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    //! An asynchronous, HTTP/2.0 server and client implementation.
    //!
    //! This library implements the [HTTP/2.0] specification. The implementation is
    //! asynchronous, using [futures] as the basis for the API. The implementation
    //! is also decoupled from TCP or TLS details. The user must handle ALPN and
    //! HTTP/1.1 upgrades themselves.
    //!
    //! # Getting started
    //!
    //! Add the following to your `Cargo.toml` file:
    //!
    //! ```toml
    //! [dependencies]
    //! h2 = "0.3"
    //! ```
    //!
    //! # Layout
    //!
    //! The crate is split into [`client`] and [`server`] modules. Types that are
    //! common to both clients and servers are located at the root of the crate.
    //!
    //! See module level documentation for more details on how to use `h2`.
    //!
    //! # Handshake
    //!
    //! Both the client and the server require a connection to already be in a state
    //! ready to start the HTTP/2.0 handshake. This library does not provide
    //! facilities to do this.
    //!
    //! There are three ways to reach an appropriate state to start the HTTP/2.0
    //! handshake.
    //!
    //! * Opening an HTTP/1.1 connection and performing an [upgrade].
    //! * Opening a connection with TLS and use ALPN to negotiate the protocol.
    //! * Open a connection with prior knowledge, i.e. both the client and the
    //!   server assume that the connection is immediately ready to start the
    //!   HTTP/2.0 handshake once opened.
    //!
    //! Once the connection is ready to start the HTTP/2.0 handshake, it can be
    //! passed to [`server::handshake`] or [`client::handshake`]. At this point, the
    //! library will start the handshake process, which consists of:
    //!
    //! * The client sends the connection preface (a predefined sequence of 24
    //! octets).
    //! * Both the client and the server sending a SETTINGS frame.
    //!
    //! See the [Starting HTTP/2] in the specification for more details.
    //!
    //! # Flow control
    //!
    //! [Flow control] is a fundamental feature of HTTP/2.0. The `h2` library
    //! exposes flow control to the user.
    //!
    //! An HTTP/2.0 client or server may not send unlimited data to the peer. When a
    //! stream is initiated, both the client and the server are provided with an
    //! initial window size for that stream.  A window size is the number of bytes
    //! the endpoint can send to the peer. At any point in time, the peer may
    //! increase this window size by sending a `WINDOW_UPDATE` frame. Once a client
    //! or server has sent data filling the window for a stream, no further data may
    //! be sent on that stream until the peer increases the window.
    //!
    //! There is also a **connection level** window governing data sent across all
    //! streams.
    //!
    //! Managing flow control for inbound data is done through [`FlowControl`].
    //! Managing flow control for outbound data is done through [`SendStream`]. See
    //! the struct level documentation for those two types for more details.
    //!
    //! [HTTP/2.0]: https://http2.github.io/
    //! [futures]: https://docs.rs/futures/
    //! [`client`]: client/index.html
    //! [`server`]: server/index.html
    //! [Flow control]: http://httpwg.org/specs/rfc7540.html#FlowControl
    //! [`FlowControl`]: struct.FlowControl.html
    //! [`SendStream`]: struct.SendStream.html
    //! [Starting HTTP/2]: http://httpwg.org/specs/rfc7540.html#starting
    //! [upgrade]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Protocol_upgrade_mechanism
    //! [`server::handshake`]: server/fn.handshake.html
    //! [`client::handshake`]: client/fn.handshake.html

    #![doc(html_root_url = "https://docs.rs/h2/0.3.1")]
    #![deny(missing_debug_implementations, missing_docs)]
    #![cfg_attr(test, deny(warnings))]

    macro_rules! proto_err {
        (conn: $($msg:tt)+) => {
            tracing::debug!("connection error PROTOCOL_ERROR -- {};", format_args!($($msg)+))
        };
        (stream: $($msg:tt)+) => {
            tracing::debug!("stream error PROTOCOL_ERROR -- {};", format_args!($($msg)+))
        };
    }

    macro_rules! ready {
        ($e:expr) => {
            match $e {
                ::std::task::Poll::Ready(r) => r,
                ::std::task::Poll::Pending => return ::std::task::Poll::Pending,
            }
        };
    }

    #[cfg_attr(feature = "unstable", allow(missing_docs))]
    mod codec;
    mod error;
    mod hpack;
    mod proto;

    #[cfg(not(feature = "unstable"))]
    mod frame;

    #[cfg(feature = "unstable")]
    #[allow(missing_docs)]
    pub mod frame;

    pub mod client;
    pub mod server;
    mod share;

    pub use crate::error::{Error, Reason};
    pub use crate::share::{FlowControl, Ping, PingPong, Pong, RecvStream, SendStream, StreamId};

    #[cfg(feature = "unstable")]
    pub use codec::{Codec, RecvError, SendError, UserError};

    use std::task::Poll;

    // TODO: Get rid of this trait once https://github.com/rust-lang/rust/pull/63512
    // is stabilized.
    trait PollExt<T, E> {
        /// Changes the success value of this `Poll` with the closure provided.
        fn map_ok_<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>
        where
            F: FnOnce(T) -> U;
        /// Changes the error value of this `Poll` with the closure provided.
        fn map_err_<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>
        where
            F: FnOnce(E) -> U;
    }

    impl<T, E> PollExt<T, E> for Poll<Option<Result<T, E>>> {
        fn map_ok_<U, F>(self, f: F) -> Poll<Option<Result<U, E>>>
        where
            F: FnOnce(T) -> U,
        {
            match self {
                Poll::Ready(Some(Ok(t))) => Poll::Ready(Some(Ok(f(t)))),
                Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e))),
                Poll::Ready(None) => Poll::Ready(None),
                Poll::Pending => Poll::Pending,
            }
        }

        fn map_err_<U, F>(self, f: F) -> Poll<Option<Result<T, U>>>
        where
            F: FnOnce(E) -> U,
        {
            match self {
                Poll::Ready(Some(Ok(t))) => Poll::Ready(Some(Ok(t))),
                Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(f(e)))),
                Poll::Ready(None) => Poll::Ready(None),
                Poll::Pending => Poll::Pending,
            }
        }
    }