# conn.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/hyper-0.14.5/src/client/conn.rs`.
Keywords: rust, rustlang, rust-lang

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    //! Lower-level client connection API.
    //!
    //! The types in this module are to provide a lower-level API based around a
    //! single connection. Connecting to a host, pooling connections, and the like
    //! are not handled at this level. This module provides the building blocks to
    //! customize those things externally.
    //!
    //! If don't have need to manage connections yourself, consider using the
    //! higher-level [Client](super) API.
    //!
    //! ## Example
    //! A simple example that uses the `SendRequest` struct to talk HTTP over a Tokio TCP stream
    //! ```no_run
    //! # #[cfg(all(feature = "client", feature = "http1", feature = "runtime"))]
    //! # mod rt {
    //! use http::{Request, StatusCode};
    //! use hyper::{client::conn::Builder, Body};
    //! use tokio::net::TcpStream;
    //!
    //! #[tokio::main]
    //! async fn main() -> Result<(), Box<dyn std::error::Error>> {
    //!     let target_stream = TcpStream::connect("example.com:80").await?;
    //!
    //!     let (mut request_sender, connection) = Builder::new()
    //!         .handshake::<TcpStream, Body>(target_stream)
    //!         .await?;
    //!
    //!     // spawn a task to poll the connection and drive the HTTP state
    //!     tokio::spawn(async move {
    //!         if let Err(e) = connection.await {
    //!             eprintln!("Error in connection: {}", e);
    //!         }
    //!     });
    //!
    //!     let request = Request::builder()
    //!     // We need to manually add the host header because SendRequest does not
    //!         .header("Host", "example.com")
    //!         .method("GET")
    //!         .body(Body::from(""))?;
    //!
    //!     let response = request_sender.send_request(request).await?;
    //!     assert!(response.status() == StatusCode::OK);
    //!     Ok(())
    //! }
    //!
    //! # }
    //! ```

    use std::error::Error as StdError;
    use std::fmt;
    #[cfg(feature = "http2")]
    use std::marker::PhantomData;
    use std::sync::Arc;
    #[cfg(all(feature = "runtime", feature = "http2"))]
    use std::time::Duration;

    use bytes::Bytes;
    use futures_util::future::{self, Either, FutureExt as _};
    use pin_project::pin_project;
    use tokio::io::{AsyncRead, AsyncWrite};
    use tower_service::Service;

    use super::dispatch;
    use crate::body::HttpBody;
    use crate::common::{
        exec::{BoxSendFuture, Exec},
        task, Future, Pin, Poll,
    };
    use crate::proto;
    use crate::rt::Executor;
    #[cfg(feature = "http1")]
    use crate::upgrade::Upgraded;
    use crate::{Body, Request, Response};

    #[cfg(feature = "http1")]
    type Http1Dispatcher<T, B, R> = proto::dispatch::Dispatcher<proto::dispatch::Client<B>, B, T, R>;

    #[pin_project(project = ProtoClientProj)]
    enum ProtoClient<T, B>
    where
        B: HttpBody,
    {
        #[cfg(feature = "http1")]
        H1(#[pin] Http1Dispatcher<T, B, proto::h1::ClientTransaction>),
        #[cfg(feature = "http2")]
        H2(#[pin] proto::h2::ClientTask<B>, PhantomData<fn(T)>),
    }

    /// Returns a handshake future over some IO.
    ///
    /// This is a shortcut for `Builder::new().handshake(io)`.
    pub async fn handshake<T>(
        io: T,
    ) -> crate::Result<(SendRequest<crate::Body>, Connection<T, crate::Body>)>
    where
        T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
    {
        Builder::new().handshake(io).await
    }

    /// The sender side of an established connection.
    pub struct SendRequest<B> {
        dispatch: dispatch::Sender<Request<B>, Response<Body>>,
    }

    /// A future that processes all HTTP state for the IO object.
    ///
    /// In most cases, this should just be spawned into an executor, so that it
    /// can process incoming and outgoing messages, notice hangups, and the like.
    #[must_use = "futures do nothing unless polled"]
    pub struct Connection<T, B>
    where
        T: AsyncRead + AsyncWrite + Send + 'static,
        B: HttpBody + 'static,
    {
        inner: Option<ProtoClient<T, B>>,
    }

    /// A builder to configure an HTTP connection.
    ///
    /// After setting options, the builder is used to create a handshake future.
    #[derive(Clone, Debug)]
    pub struct Builder {
        pub(super) exec: Exec,
        h09_responses: bool,
        h1_title_case_headers: bool,
        h1_read_buf_exact_size: Option<usize>,
        h1_max_buf_size: Option<usize>,
        #[cfg(feature = "http2")]
        h2_builder: proto::h2::client::Config,
        version: Proto,
    }

    #[derive(Clone, Debug)]
    enum Proto {
        #[cfg(feature = "http1")]
        Http1,
        #[cfg(feature = "http2")]
        Http2,
    }

    /// A future returned by `SendRequest::send_request`.
    ///
    /// Yields a `Response` if successful.
    #[must_use = "futures do nothing unless polled"]
    pub struct ResponseFuture {
        inner: ResponseFutureState,
    }

    enum ResponseFutureState {
        Waiting(dispatch::Promise<Response<Body>>),
        // Option is to be able to `take()` it in `poll`
        Error(Option<crate::Error>),
    }

    /// Deconstructed parts of a `Connection`.
    ///
    /// This allows taking apart a `Connection` at a later time, in order to
    /// reclaim the IO object, and additional related pieces.
    #[derive(Debug)]
    pub struct Parts<T> {
        /// The original IO object used in the handshake.
        pub io: T,
        /// A buffer of bytes that have been read but not processed as HTTP.
        ///
        /// For instance, if the `Connection` is used for an HTTP upgrade request,
        /// it is possible the server sent back the first bytes of the new protocol
        /// along with the response upgrade.
        ///
        /// You will want to check for any existing bytes if you plan to continue
        /// communicating on the IO object.
        pub read_buf: Bytes,
        _inner: (),
    }

    // ========== internal client api

    // A `SendRequest` that can be cloned to send HTTP2 requests.
    // private for now, probably not a great idea of a type...
    #[must_use = "futures do nothing unless polled"]
    #[cfg(feature = "http2")]
    pub(super) struct Http2SendRequest<B> {
        dispatch: dispatch::UnboundedSender<Request<B>, Response<Body>>,
    }

    // ===== impl SendRequest

    impl<B> SendRequest<B> {
        /// Polls to determine whether this sender can be used yet for a request.
        ///
        /// If the associated connection is closed, this returns an Error.
        pub fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
            self.dispatch.poll_ready(cx)
        }

        pub(super) async fn when_ready(self) -> crate::Result<Self> {
            let mut me = Some(self);
            future::poll_fn(move |cx| {
                ready!(me.as_mut().unwrap().poll_ready(cx))?;
                Poll::Ready(Ok(me.take().unwrap()))
            })
            .await
        }

        pub(super) fn is_ready(&self) -> bool {
            self.dispatch.is_ready()
        }

        pub(super) fn is_closed(&self) -> bool {
            self.dispatch.is_closed()
        }

        #[cfg(feature = "http2")]
        pub(super) fn into_http2(self) -> Http2SendRequest<B> {
            Http2SendRequest {
                dispatch: self.dispatch.unbound(),
            }
        }
    }

    impl<B> SendRequest<B>
    where
        B: HttpBody + 'static,
    {
        /// Sends a `Request` on the associated connection.
        ///
        /// Returns a future that if successful, yields the `Response`.
        ///
        /// # Note
        ///
        /// There are some key differences in what automatic things the `Client`
        /// does for you that will not be done here:
        ///
        /// - `Client` requires absolute-form `Uri`s, since the scheme and
        ///   authority are needed to connect. They aren't required here.
        /// - Since the `Client` requires absolute-form `Uri`s, it can add
        ///   the `Host` header based on it. You must add a `Host` header yourself
        ///   before calling this method.
        /// - Since absolute-form `Uri`s are not required, if received, they will
        ///   be serialized as-is.
        ///
        /// # Example
        ///
        /// ```
        /// # use http::header::HOST;
        /// # use hyper::client::conn::SendRequest;
        /// # use hyper::Body;
        /// use hyper::Request;
        ///
        /// # async fn doc(mut tx: SendRequest<Body>) -> hyper::Result<()> {
        /// // build a Request
        /// let req = Request::builder()
        ///     .uri("/foo/bar")
        ///     .header(HOST, "hyper.rs")
        ///     .body(Body::empty())
        ///     .unwrap();
        ///
        /// // send it and await a Response
        /// let res = tx.send_request(req).await?;
        /// // assert the Response
        /// assert!(res.status().is_success());
        /// # Ok(())
        /// # }
        /// # fn main() {}
        /// ```
        pub fn send_request(&mut self, req: Request<B>) -> ResponseFuture {
            let inner = match self.dispatch.send(req) {
                Ok(rx) => ResponseFutureState::Waiting(rx),
                Err(_req) => {
                    debug!("connection was not ready");
                    let err = crate::Error::new_canceled().with("connection was not ready");
                    ResponseFutureState::Error(Some(err))
                }
            };

            ResponseFuture { inner }
        }

        pub(super) fn send_request_retryable(
            &mut self,
            req: Request<B>,
        ) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>> + Unpin
        where
            B: Send,
        {
            match self.dispatch.try_send(req) {
                Ok(rx) => {
                    Either::Left(rx.then(move |res| {
                        match res {
                            Ok(Ok(res)) => future::ok(res),
                            Ok(Err(err)) => future::err(err),
                            // this is definite bug if it happens, but it shouldn't happen!
                            Err(_) => panic!("dispatch dropped without returning error"),
                        }
                    }))
                }
                Err(req) => {
                    debug!("connection was not ready");
                    let err = crate::Error::new_canceled().with("connection was not ready");
                    Either::Right(future::err((err, Some(req))))
                }
            }
        }
    }

    impl<B> Service<Request<B>> for SendRequest<B>
    where
        B: HttpBody + 'static,
    {
        type Response = Response<Body>;
        type Error = crate::Error;
        type Future = ResponseFuture;

        fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<Result<(), Self::Error>> {
            self.poll_ready(cx)
        }

        fn call(&mut self, req: Request<B>) -> Self::Future {
            self.send_request(req)
        }
    }

    impl<B> fmt::Debug for SendRequest<B> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("SendRequest").finish()
        }
    }

    // ===== impl Http2SendRequest

    #[cfg(feature = "http2")]
    impl<B> Http2SendRequest<B> {
        pub(super) fn is_ready(&self) -> bool {
            self.dispatch.is_ready()
        }

        pub(super) fn is_closed(&self) -> bool {
            self.dispatch.is_closed()
        }
    }

    #[cfg(feature = "http2")]
    impl<B> Http2SendRequest<B>
    where
        B: HttpBody + 'static,
    {
        pub(super) fn send_request_retryable(
            &mut self,
            req: Request<B>,
        ) -> impl Future<Output = Result<Response<Body>, (crate::Error, Option<Request<B>>)>>
        where
            B: Send,
        {
            match self.dispatch.try_send(req) {
                Ok(rx) => {
                    Either::Left(rx.then(move |res| {
                        match res {
                            Ok(Ok(res)) => future::ok(res),
                            Ok(Err(err)) => future::err(err),
                            // this is definite bug if it happens, but it shouldn't happen!
                            Err(_) => panic!("dispatch dropped without returning error"),
                        }
                    }))
                }
                Err(req) => {
                    debug!("connection was not ready");
                    let err = crate::Error::new_canceled().with("connection was not ready");
                    Either::Right(future::err((err, Some(req))))
                }
            }
        }
    }

    #[cfg(feature = "http2")]
    impl<B> fmt::Debug for Http2SendRequest<B> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("Http2SendRequest").finish()
        }
    }

    #[cfg(feature = "http2")]
    impl<B> Clone for Http2SendRequest<B> {
        fn clone(&self) -> Self {
            Http2SendRequest {
                dispatch: self.dispatch.clone(),
            }
        }
    }

    // ===== impl Connection

    impl<T, B> Connection<T, B>
    where
        T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
        B: HttpBody + Unpin + Send + 'static,
        B::Data: Send,
        B::Error: Into<Box<dyn StdError + Send + Sync>>,
    {
        /// Return the inner IO object, and additional information.
        ///
        /// Only works for HTTP/1 connections. HTTP/2 connections will panic.
        pub fn into_parts(self) -> Parts<T> {
            match self.inner.expect("already upgraded") {
                #[cfg(feature = "http1")]
                ProtoClient::H1(h1) => {
                    let (io, read_buf, _) = h1.into_inner();
                    Parts {
                        io,
                        read_buf,
                        _inner: (),
                    }
                }
                #[cfg(feature = "http2")]
                ProtoClient::H2(..) => {
                    panic!("http2 cannot into_inner");
                }
            }
        }

        /// Poll the connection for completion, but without calling `shutdown`
        /// on the underlying IO.
        ///
        /// This is useful to allow running a connection while doing an HTTP
        /// upgrade. Once the upgrade is completed, the connection would be "done",
        /// but it is not desired to actually shutdown the IO object. Instead you
        /// would take it back using `into_parts`.
        ///
        /// Use [`poll_fn`](https://docs.rs/futures/0.1.25/futures/future/fn.poll_fn.html)
        /// and [`try_ready!`](https://docs.rs/futures/0.1.25/futures/macro.try_ready.html)
        /// to work with this function; or use the `without_shutdown` wrapper.
        pub fn poll_without_shutdown(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
            match *self.inner.as_mut().expect("already upgraded") {
                #[cfg(feature = "http1")]
                ProtoClient::H1(ref mut h1) => h1.poll_without_shutdown(cx),
                #[cfg(feature = "http2")]
                ProtoClient::H2(ref mut h2, _) => Pin::new(h2).poll(cx).map_ok(|_| ()),
            }
        }

        /// Prevent shutdown of the underlying IO object at the end of service the request,
        /// instead run `into_parts`. This is a convenience wrapper over `poll_without_shutdown`.
        pub fn without_shutdown(self) -> impl Future<Output = crate::Result<Parts<T>>> {
            let mut conn = Some(self);
            future::poll_fn(move |cx| -> Poll<crate::Result<Parts<T>>> {
                ready!(conn.as_mut().unwrap().poll_without_shutdown(cx))?;
                Poll::Ready(Ok(conn.take().unwrap().into_parts()))
            })
        }
    }

    impl<T, B> Future for Connection<T, B>
    where
        T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
        B: HttpBody + Send + 'static,
        B::Data: Send,
        B::Error: Into<Box<dyn StdError + Send + Sync>>,
    {
        type Output = crate::Result<()>;

        fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
            match ready!(Pin::new(self.inner.as_mut().unwrap()).poll(cx))? {
                proto::Dispatched::Shutdown => Poll::Ready(Ok(())),
                #[cfg(feature = "http1")]
                proto::Dispatched::Upgrade(pending) => match self.inner.take() {
                    Some(ProtoClient::H1(h1)) => {
                        let (io, buf, _) = h1.into_inner();
                        pending.fulfill(Upgraded::new(io, buf));
                        Poll::Ready(Ok(()))
                    }
                    _ => {
                        drop(pending);
                        unreachable!("Upgrade expects h1");
                    }
                },
            }
        }
    }

    impl<T, B> fmt::Debug for Connection<T, B>
    where
        T: AsyncRead + AsyncWrite + fmt::Debug + Send + 'static,
        B: HttpBody + 'static,
    {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("Connection").finish()
        }
    }

    // ===== impl Builder

    impl Builder {
        /// Creates a new connection builder.
        #[inline]
        pub fn new() -> Builder {
            Builder {
                exec: Exec::Default,
                h09_responses: false,
                h1_read_buf_exact_size: None,
                h1_title_case_headers: false,
                h1_max_buf_size: None,
                #[cfg(feature = "http2")]
                h2_builder: Default::default(),
                #[cfg(feature = "http1")]
                version: Proto::Http1,
                #[cfg(not(feature = "http1"))]
                version: Proto::Http2,
            }
        }

        /// Provide an executor to execute background HTTP2 tasks.
        pub fn executor<E>(&mut self, exec: E) -> &mut Builder
        where
            E: Executor<BoxSendFuture> + Send + Sync + 'static,
        {
            self.exec = Exec::Executor(Arc::new(exec));
            self
        }

        pub(super) fn h09_responses(&mut self, enabled: bool) -> &mut Builder {
            self.h09_responses = enabled;
            self
        }

        pub(super) fn h1_title_case_headers(&mut self, enabled: bool) -> &mut Builder {
            self.h1_title_case_headers = enabled;
            self
        }

        pub(super) fn h1_read_buf_exact_size(&mut self, sz: Option<usize>) -> &mut Builder {
            self.h1_read_buf_exact_size = sz;
            self.h1_max_buf_size = None;
            self
        }

        #[cfg(feature = "http1")]
        pub(super) fn h1_max_buf_size(&mut self, max: usize) -> &mut Self {
            assert!(
                max >= proto::h1::MINIMUM_MAX_BUFFER_SIZE,
                "the max_buf_size cannot be smaller than the minimum that h1 specifies."
            );

            self.h1_max_buf_size = Some(max);
            self.h1_read_buf_exact_size = None;
            self
        }

        /// Sets whether HTTP2 is required.
        ///
        /// Default is false.
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_only(&mut self, enabled: bool) -> &mut Builder {
            if enabled {
                self.version = Proto::Http2
            }
            self
        }

        /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
        /// stream-level flow control.
        ///
        /// Passing `None` will do nothing.
        ///
        /// If not set, hyper will use a default.
        ///
        /// [spec]: https://http2.github.io/http2-spec/#SETTINGS_INITIAL_WINDOW_SIZE
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
            if let Some(sz) = sz.into() {
                self.h2_builder.adaptive_window = false;
                self.h2_builder.initial_stream_window_size = sz;
            }
            self
        }

        /// Sets the max connection-level flow control for HTTP2
        ///
        /// Passing `None` will do nothing.
        ///
        /// If not set, hyper will use a default.
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_initial_connection_window_size(
            &mut self,
            sz: impl Into<Option<u32>>,
        ) -> &mut Self {
            if let Some(sz) = sz.into() {
                self.h2_builder.adaptive_window = false;
                self.h2_builder.initial_conn_window_size = sz;
            }
            self
        }

        /// Sets whether to use an adaptive flow control.
        ///
        /// Enabling this will override the limits set in
        /// `http2_initial_stream_window_size` and
        /// `http2_initial_connection_window_size`.
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_adaptive_window(&mut self, enabled: bool) -> &mut Self {
            use proto::h2::SPEC_WINDOW_SIZE;

            self.h2_builder.adaptive_window = enabled;
            if enabled {
                self.h2_builder.initial_conn_window_size = SPEC_WINDOW_SIZE;
                self.h2_builder.initial_stream_window_size = SPEC_WINDOW_SIZE;
            }
            self
        }

        /// Sets the maximum frame size to use for HTTP2.
        ///
        /// Passing `None` will do nothing.
        ///
        /// If not set, hyper will use a default.
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_max_frame_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
            if let Some(sz) = sz.into() {
                self.h2_builder.max_frame_size = sz;
            }
            self
        }

        /// Sets an interval for HTTP2 Ping frames should be sent to keep a
        /// connection alive.
        ///
        /// Pass `None` to disable HTTP2 keep-alive.
        ///
        /// Default is currently disabled.
        ///
        /// # Cargo Feature
        ///
        /// Requires the `runtime` cargo feature to be enabled.
        #[cfg(feature = "runtime")]
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_keep_alive_interval(
            &mut self,
            interval: impl Into<Option<Duration>>,
        ) -> &mut Self {
            self.h2_builder.keep_alive_interval = interval.into();
            self
        }

        /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
        ///
        /// If the ping is not acknowledged within the timeout, the connection will
        /// be closed. Does nothing if `http2_keep_alive_interval` is disabled.
        ///
        /// Default is 20 seconds.
        ///
        /// # Cargo Feature
        ///
        /// Requires the `runtime` cargo feature to be enabled.
        #[cfg(feature = "runtime")]
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_keep_alive_timeout(&mut self, timeout: Duration) -> &mut Self {
            self.h2_builder.keep_alive_timeout = timeout;
            self
        }

        /// Sets whether HTTP2 keep-alive should apply while the connection is idle.
        ///
        /// If disabled, keep-alive pings are only sent while there are open
        /// request/responses streams. If enabled, pings are also sent when no
        /// streams are active. Does nothing if `http2_keep_alive_interval` is
        /// disabled.
        ///
        /// Default is `false`.
        ///
        /// # Cargo Feature
        ///
        /// Requires the `runtime` cargo feature to be enabled.
        #[cfg(feature = "runtime")]
        #[cfg(feature = "http2")]
        #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
        pub fn http2_keep_alive_while_idle(&mut self, enabled: bool) -> &mut Self {
            self.h2_builder.keep_alive_while_idle = enabled;
            self
        }

        /// Constructs a connection with the configured options and IO.
        pub fn handshake<T, B>(
            &self,
            io: T,
        ) -> impl Future<Output = crate::Result<(SendRequest<B>, Connection<T, B>)>>
        where
            T: AsyncRead + AsyncWrite + Unpin + Send + 'static,
            B: HttpBody + 'static,
            B::Data: Send,
            B::Error: Into<Box<dyn StdError + Send + Sync>>,
        {
            let opts = self.clone();

            async move {
                trace!("client handshake {:?}", opts.version);

                let (tx, rx) = dispatch::channel();
                let proto = match opts.version {
                    #[cfg(feature = "http1")]
                    Proto::Http1 => {
                        let mut conn = proto::Conn::new(io);
                        if opts.h1_title_case_headers {
                            conn.set_title_case_headers();
                        }
                        if opts.h09_responses {
                            conn.set_h09_responses();
                        }
                        if let Some(sz) = opts.h1_read_buf_exact_size {
                            conn.set_read_buf_exact_size(sz);
                        }
                        if let Some(max) = opts.h1_max_buf_size {
                            conn.set_max_buf_size(max);
                        }
                        let cd = proto::h1::dispatch::Client::new(rx);
                        let dispatch = proto::h1::Dispatcher::new(cd, conn);
                        ProtoClient::H1(dispatch)
                    }
                    #[cfg(feature = "http2")]
                    Proto::Http2 => {
                        let h2 =
                            proto::h2::client::handshake(io, rx, &opts.h2_builder, opts.exec.clone())
                                .await?;
                        ProtoClient::H2(h2, PhantomData)
                    }
                };

                Ok((
                    SendRequest { dispatch: tx },
                    Connection { inner: Some(proto) },
                ))
            }
        }
    }

    // ===== impl ResponseFuture

    impl Future for ResponseFuture {
        type Output = crate::Result<Response<Body>>;

        fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
            match self.inner {
                ResponseFutureState::Waiting(ref mut rx) => {
                    Pin::new(rx).poll(cx).map(|res| match res {
                        Ok(Ok(resp)) => Ok(resp),
                        Ok(Err(err)) => Err(err),
                        // this is definite bug if it happens, but it shouldn't happen!
                        Err(_canceled) => panic!("dispatch dropped without returning error"),
                    })
                }
                ResponseFutureState::Error(ref mut err) => {
                    Poll::Ready(Err(err.take().expect("polled after ready")))
                }
            }
        }
    }

    impl fmt::Debug for ResponseFuture {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.debug_struct("ResponseFuture").finish()
        }
    }

    // ===== impl ProtoClient

    impl<T, B> Future for ProtoClient<T, B>
    where
        T: AsyncRead + AsyncWrite + Send + Unpin + 'static,
        B: HttpBody + Send + 'static,
        B::Data: Send,
        B::Error: Into<Box<dyn StdError + Send + Sync>>,
    {
        type Output = crate::Result<proto::Dispatched>;

        fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
            match self.project() {
                #[cfg(feature = "http1")]
                ProtoClientProj::H1(c) => c.poll(cx),
                #[cfg(feature = "http2")]
                ProtoClientProj::H2(c, _) => c.poll(cx),
            }
        }
    }

    // assert trait markers

    trait AssertSend: Send {}
    trait AssertSendSync: Send + Sync {}

    #[doc(hidden)]
    impl<B: Send> AssertSendSync for SendRequest<B> {}

    #[doc(hidden)]
    impl<T: Send, B: Send> AssertSend for Connection<T, B>
    where
        T: AsyncRead + AsyncWrite + Send + 'static,
        B: HttpBody + 'static,
        B::Data: Send,
    {
    }

    #[doc(hidden)]
    impl<T: Send + Sync, B: Send + Sync> AssertSendSync for Connection<T, B>
    where
        T: AsyncRead + AsyncWrite + Send + 'static,
        B: HttpBody + 'static,
        B::Data: Send + Sync + 'static,
    {
    }

    #[doc(hidden)]
    impl AssertSendSync for Builder {}

    #[doc(hidden)]
    impl AssertSend for ResponseFuture {}