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    use std::borrow::Cow;
    #[cfg(feature = "stream")]
    use std::error::Error as StdError;
    use std::fmt;

    use bytes::Bytes;
    use futures_channel::mpsc;
    use futures_channel::oneshot;
    use futures_core::Stream; // for mpsc::Receiver
    #[cfg(feature = "stream")]
    use futures_util::TryStreamExt;
    use http::HeaderMap;
    use http_body::{Body as HttpBody, SizeHint};

    use super::DecodedLength;
    #[cfg(feature = "stream")]
    use crate::common::sync_wrapper::SyncWrapper;
    use crate::common::Future;
    #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
    use crate::common::Never;
    use crate::common::{task, watch, Pin, Poll};
    #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
    use crate::proto::h2::ping;

    type BodySender = mpsc::Sender<Result<Bytes, crate::Error>>;
    type TrailersSender = oneshot::Sender<HeaderMap>;

    /// A stream of `Bytes`, used when receiving bodies.
    ///
    /// A good default [`HttpBody`](crate::body::HttpBody) to use in many
    /// applications.
    #[must_use = "streams do nothing unless polled"]
    pub struct Body {
        kind: Kind,
        /// Keep the extra bits in an `Option<Box<Extra>>`, so that
        /// Body stays small in the common case (no extras needed).
        extra: Option<Box<Extra>>,
    }

    enum Kind {
        Once(Option<Bytes>),
        Chan {
            content_length: DecodedLength,
            want_tx: watch::Sender,
            data_rx: mpsc::Receiver<Result<Bytes, crate::Error>>,
            trailers_rx: oneshot::Receiver<HeaderMap>,
        },
        #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
        H2 {
            ping: ping::Recorder,
            content_length: DecodedLength,
            recv: h2::RecvStream,
        },
        #[cfg(feature = "ffi")]
        Ffi(crate::ffi::UserBody),
        #[cfg(feature = "stream")]
        Wrapped(
            SyncWrapper<
                Pin<Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>>,
            >,
        ),
    }

    struct Extra {
        /// Allow the client to pass a future to delay the `Body` from returning
        /// EOF. This allows the `Client` to try to put the idle connection
        /// back into the pool before the body is "finished".
        ///
        /// The reason for this is so that creating a new request after finishing
        /// streaming the body of a response could sometimes result in creating
        /// a brand new connection, since the pool didn't know about the idle
        /// connection yet.
        delayed_eof: Option<DelayEof>,
    }

    #[cfg(all(feature = "client", any(feature = "http1", feature = "http2")))]
    type DelayEofUntil = oneshot::Receiver<Never>;

    enum DelayEof {
        /// Initial state, stream hasn't seen EOF yet.
        #[cfg(any(feature = "http1", feature = "http2"))]
        #[cfg(feature = "client")]
        NotEof(DelayEofUntil),
        /// Transitions to this state once we've seen `poll` try to
        /// return EOF (`None`). This future is then polled, and
        /// when it completes, the Body finally returns EOF (`None`).
        #[cfg(any(feature = "http1", feature = "http2"))]
        #[cfg(feature = "client")]
        Eof(DelayEofUntil),
    }

    /// A sender half created through [`Body::channel()`].
    ///
    /// Useful when wanting to stream chunks from another thread.
    ///
    /// ## Body Closing
    ///
    /// Note that the request body will always be closed normally when the sender is dropped (meaning
    /// that the empty terminating chunk will be sent to the remote). If you desire to close the
    /// connection with an incomplete response (e.g. in the case of an error during asynchronous
    /// processing), call the [`Sender::abort()`] method to abort the body in an abnormal fashion.
    ///
    /// [`Body::channel()`]: struct.Body.html#method.channel
    /// [`Sender::abort()`]: struct.Sender.html#method.abort
    #[must_use = "Sender does nothing unless sent on"]
    pub struct Sender {
        want_rx: watch::Receiver,
        data_tx: BodySender,
        trailers_tx: Option<TrailersSender>,
    }

    const WANT_PENDING: usize = 1;
    const WANT_READY: usize = 2;

    impl Body {
        /// Create an empty `Body` stream.
        ///
        /// # Example
        ///
        /// ```
        /// use hyper::{Body, Request};
        ///
        /// // create a `GET /` request
        /// let get = Request::new(Body::empty());
        /// ```
        #[inline]
        pub fn empty() -> Body {
            Body::new(Kind::Once(None))
        }

        /// Create a `Body` stream with an associated sender half.
        ///
        /// Useful when wanting to stream chunks from another thread.
        #[inline]
        pub fn channel() -> (Sender, Body) {
            Self::new_channel(DecodedLength::CHUNKED, /*wanter =*/ false)
        }

        pub(crate) fn new_channel(content_length: DecodedLength, wanter: bool) -> (Sender, Body) {
            let (data_tx, data_rx) = mpsc::channel(0);
            let (trailers_tx, trailers_rx) = oneshot::channel();

            // If wanter is true, `Sender::poll_ready()` won't becoming ready
            // until the `Body` has been polled for data once.
            let want = if wanter { WANT_PENDING } else { WANT_READY };

            let (want_tx, want_rx) = watch::channel(want);

            let tx = Sender {
                want_rx,
                data_tx,
                trailers_tx: Some(trailers_tx),
            };
            let rx = Body::new(Kind::Chan {
                content_length,
                want_tx,
                data_rx,
                trailers_rx,
            });

            (tx, rx)
        }

        /// Wrap a futures `Stream` in a box inside `Body`.
        ///
        /// # Example
        ///
        /// ```
        /// # use hyper::Body;
        /// let chunks: Vec<Result<_, std::io::Error>> = vec![
        ///     Ok("hello"),
        ///     Ok(" "),
        ///     Ok("world"),
        /// ];
        ///
        /// let stream = futures_util::stream::iter(chunks);
        ///
        /// let body = Body::wrap_stream(stream);
        /// ```
        ///
        /// # Optional
        ///
        /// This function requires enabling the `stream` feature in your
        /// `Cargo.toml`.
        #[cfg(feature = "stream")]
        #[cfg_attr(docsrs, doc(cfg(feature = "stream")))]
        pub fn wrap_stream<S, O, E>(stream: S) -> Body
        where
            S: Stream<Item = Result<O, E>> + Send + 'static,
            O: Into<Bytes> + 'static,
            E: Into<Box<dyn StdError + Send + Sync>> + 'static,
        {
            let mapped = stream.map_ok(Into::into).map_err(Into::into);
            Body::new(Kind::Wrapped(SyncWrapper::new(Box::pin(mapped))))
        }

        fn new(kind: Kind) -> Body {
            Body { kind, extra: None }
        }

        #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
        pub(crate) fn h2(
            recv: h2::RecvStream,
            content_length: DecodedLength,
            ping: ping::Recorder,
        ) -> Self {
            let body = Body::new(Kind::H2 {
                ping,
                content_length,
                recv,
            });

            body
        }

        #[cfg(any(feature = "http1", feature = "http2"))]
        #[cfg(feature = "client")]
        pub(crate) fn delayed_eof(&mut self, fut: DelayEofUntil) {
            self.extra_mut().delayed_eof = Some(DelayEof::NotEof(fut));
        }

        fn take_delayed_eof(&mut self) -> Option<DelayEof> {
            self.extra
                .as_mut()
                .and_then(|extra| extra.delayed_eof.take())
        }

        #[cfg(any(feature = "http1", feature = "http2"))]
        fn extra_mut(&mut self) -> &mut Extra {
            self.extra
                .get_or_insert_with(|| Box::new(Extra { delayed_eof: None }))
        }

        fn poll_eof(&mut self, cx: &mut task::Context<'_>) -> Poll<Option<crate::Result<Bytes>>> {
            match self.take_delayed_eof() {
                #[cfg(any(feature = "http1", feature = "http2"))]
                #[cfg(feature = "client")]
                Some(DelayEof::NotEof(mut delay)) => match self.poll_inner(cx) {
                    ok @ Poll::Ready(Some(Ok(..))) | ok @ Poll::Pending => {
                        self.extra_mut().delayed_eof = Some(DelayEof::NotEof(delay));
                        ok
                    }
                    Poll::Ready(None) => match Pin::new(&mut delay).poll(cx) {
                        Poll::Ready(Ok(never)) => match never {},
                        Poll::Pending => {
                            self.extra_mut().delayed_eof = Some(DelayEof::Eof(delay));
                            Poll::Pending
                        }
                        Poll::Ready(Err(_done)) => Poll::Ready(None),
                    },
                    Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e))),
                },
                #[cfg(any(feature = "http1", feature = "http2"))]
                #[cfg(feature = "client")]
                Some(DelayEof::Eof(mut delay)) => match Pin::new(&mut delay).poll(cx) {
                    Poll::Ready(Ok(never)) => match never {},
                    Poll::Pending => {
                        self.extra_mut().delayed_eof = Some(DelayEof::Eof(delay));
                        Poll::Pending
                    }
                    Poll::Ready(Err(_done)) => Poll::Ready(None),
                },
                #[cfg(any(
                    not(any(feature = "http1", feature = "http2")),
                    not(feature = "client")
                ))]
                Some(delay_eof) => match delay_eof {},
                None => self.poll_inner(cx),
            }
        }

        #[cfg(feature = "ffi")]
        pub(crate) fn as_ffi_mut(&mut self) -> &mut crate::ffi::UserBody {
            match self.kind {
                Kind::Ffi(ref mut body) => return body,
                _ => {
                    self.kind = Kind::Ffi(crate::ffi::UserBody::new());
                }
            }

            match self.kind {
                Kind::Ffi(ref mut body) => body,
                _ => unreachable!(),
            }
        }

        fn poll_inner(&mut self, cx: &mut task::Context<'_>) -> Poll<Option<crate::Result<Bytes>>> {
            match self.kind {
                Kind::Once(ref mut val) => Poll::Ready(val.take().map(Ok)),
                Kind::Chan {
                    content_length: ref mut len,
                    ref mut data_rx,
                    ref mut want_tx,
                    ..
                } => {
                    want_tx.send(WANT_READY);

                    match ready!(Pin::new(data_rx).poll_next(cx)?) {
                        Some(chunk) => {
                            len.sub_if(chunk.len() as u64);
                            Poll::Ready(Some(Ok(chunk)))
                        }
                        None => Poll::Ready(None),
                    }
                }
                #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
                Kind::H2 {
                    ref ping,
                    recv: ref mut h2,
                    content_length: ref mut len,
                } => match ready!(h2.poll_data(cx)) {
                    Some(Ok(bytes)) => {
                        let _ = h2.flow_control().release_capacity(bytes.len());
                        len.sub_if(bytes.len() as u64);
                        ping.record_data(bytes.len());
                        Poll::Ready(Some(Ok(bytes)))
                    }
                    Some(Err(e)) => Poll::Ready(Some(Err(crate::Error::new_body(e)))),
                    None => Poll::Ready(None),
                },

                #[cfg(feature = "ffi")]
                Kind::Ffi(ref mut body) => body.poll_data(cx),

                #[cfg(feature = "stream")]
                Kind::Wrapped(ref mut s) => match ready!(s.get_mut().as_mut().poll_next(cx)) {
                    Some(res) => Poll::Ready(Some(res.map_err(crate::Error::new_body))),
                    None => Poll::Ready(None),
                },
            }
        }

        #[cfg(feature = "http1")]
        pub(super) fn take_full_data(&mut self) -> Option<Bytes> {
            if let Kind::Once(ref mut chunk) = self.kind {
                chunk.take()
            } else {
                None
            }
        }
    }

    impl Default for Body {
        /// Returns `Body::empty()`.
        #[inline]
        fn default() -> Body {
            Body::empty()
        }
    }

    impl HttpBody for Body {
        type Data = Bytes;
        type Error = crate::Error;

        fn poll_data(
            mut self: Pin<&mut Self>,
            cx: &mut task::Context<'_>,
        ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
            self.poll_eof(cx)
        }

        fn poll_trailers(
            #[cfg_attr(not(feature = "http2"), allow(unused_mut))] mut self: Pin<&mut Self>,
            #[cfg_attr(not(feature = "http2"), allow(unused))] cx: &mut task::Context<'_>,
        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
            match self.kind {
                #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
                Kind::H2 {
                    recv: ref mut h2,
                    ref ping,
                    ..
                } => match ready!(h2.poll_trailers(cx)) {
                    Ok(t) => {
                        ping.record_non_data();
                        Poll::Ready(Ok(t))
                    }
                    Err(e) => Poll::Ready(Err(crate::Error::new_h2(e))),
                },
                Kind::Chan {
                    ref mut trailers_rx,
                    ..
                } => match ready!(Pin::new(trailers_rx).poll(cx)) {
                    Ok(t) => Poll::Ready(Ok(Some(t))),
                    Err(_) => Poll::Ready(Ok(None)),
                },
                #[cfg(feature = "ffi")]
                Kind::Ffi(ref mut body) => body.poll_trailers(cx),
                _ => Poll::Ready(Ok(None)),
            }
        }

        fn is_end_stream(&self) -> bool {
            match self.kind {
                Kind::Once(ref val) => val.is_none(),
                Kind::Chan { content_length, .. } => content_length == DecodedLength::ZERO,
                #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
                Kind::H2 { recv: ref h2, .. } => h2.is_end_stream(),
                #[cfg(feature = "ffi")]
                Kind::Ffi(..) => false,
                #[cfg(feature = "stream")]
                Kind::Wrapped(..) => false,
            }
        }

        fn size_hint(&self) -> SizeHint {
            macro_rules! opt_len {
                ($content_length:expr) => {{
                    let mut hint = SizeHint::default();

                    if let Some(content_length) = $content_length.into_opt() {
                        hint.set_exact(content_length);
                    }

                    hint
                }};
            }

            match self.kind {
                Kind::Once(Some(ref val)) => SizeHint::with_exact(val.len() as u64),
                Kind::Once(None) => SizeHint::with_exact(0),
                #[cfg(feature = "stream")]
                Kind::Wrapped(..) => SizeHint::default(),
                Kind::Chan { content_length, .. } => opt_len!(content_length),
                #[cfg(all(feature = "http2", any(feature = "client", feature = "server")))]
                Kind::H2 { content_length, .. } => opt_len!(content_length),
                #[cfg(feature = "ffi")]
                Kind::Ffi(..) => SizeHint::default(),
            }
        }
    }

    impl fmt::Debug for Body {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            #[derive(Debug)]
            struct Streaming;
            #[derive(Debug)]
            struct Empty;
            #[derive(Debug)]
            struct Full<'a>(&'a Bytes);

            let mut builder = f.debug_tuple("Body");
            match self.kind {
                Kind::Once(None) => builder.field(&Empty),
                Kind::Once(Some(ref chunk)) => builder.field(&Full(chunk)),
                _ => builder.field(&Streaming),
            };

            builder.finish()
        }
    }

    /// # Optional
    ///
    /// This function requires enabling the `stream` feature in your
    /// `Cargo.toml`.
    #[cfg(feature = "stream")]
    impl Stream for Body {
        type Item = crate::Result<Bytes>;

        fn poll_next(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Option<Self::Item>> {
            HttpBody::poll_data(self, cx)
        }
    }

    /// # Optional
    ///
    /// This function requires enabling the `stream` feature in your
    /// `Cargo.toml`.
    #[cfg(feature = "stream")]
    impl From<Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>> for Body {
        #[inline]
        fn from(
            stream: Box<dyn Stream<Item = Result<Bytes, Box<dyn StdError + Send + Sync>>> + Send>,
        ) -> Body {
            Body::new(Kind::Wrapped(SyncWrapper::new(stream.into())))
        }
    }

    impl From<Bytes> for Body {
        #[inline]
        fn from(chunk: Bytes) -> Body {
            if chunk.is_empty() {
                Body::empty()
            } else {
                Body::new(Kind::Once(Some(chunk)))
            }
        }
    }

    impl From<Vec<u8>> for Body {
        #[inline]
        fn from(vec: Vec<u8>) -> Body {
            Body::from(Bytes::from(vec))
        }
    }

    impl From<&'static [u8]> for Body {
        #[inline]
        fn from(slice: &'static [u8]) -> Body {
            Body::from(Bytes::from(slice))
        }
    }

    impl From<Cow<'static, [u8]>> for Body {
        #[inline]
        fn from(cow: Cow<'static, [u8]>) -> Body {
            match cow {
                Cow::Borrowed(b) => Body::from(b),
                Cow::Owned(o) => Body::from(o),
            }
        }
    }

    impl From<String> for Body {
        #[inline]
        fn from(s: String) -> Body {
            Body::from(Bytes::from(s.into_bytes()))
        }
    }

    impl From<&'static str> for Body {
        #[inline]
        fn from(slice: &'static str) -> Body {
            Body::from(Bytes::from(slice.as_bytes()))
        }
    }

    impl From<Cow<'static, str>> for Body {
        #[inline]
        fn from(cow: Cow<'static, str>) -> Body {
            match cow {
                Cow::Borrowed(b) => Body::from(b),
                Cow::Owned(o) => Body::from(o),
            }
        }
    }

    impl Sender {
        /// Check to see if this `Sender` can send more data.
        pub fn poll_ready(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
            // Check if the receiver end has tried polling for the body yet
            ready!(self.poll_want(cx)?);
            self.data_tx
                .poll_ready(cx)
                .map_err(|_| crate::Error::new_closed())
        }

        fn poll_want(&mut self, cx: &mut task::Context<'_>) -> Poll<crate::Result<()>> {
            match self.want_rx.load(cx) {
                WANT_READY => Poll::Ready(Ok(())),
                WANT_PENDING => Poll::Pending,
                watch::CLOSED => Poll::Ready(Err(crate::Error::new_closed())),
                unexpected => unreachable!("want_rx value: {}", unexpected),
            }
        }

        async fn ready(&mut self) -> crate::Result<()> {
            futures_util::future::poll_fn(|cx| self.poll_ready(cx)).await
        }

        /// Send data on data channel when it is ready.
        pub async fn send_data(&mut self, chunk: Bytes) -> crate::Result<()> {
            self.ready().await?;
            self.data_tx
                .try_send(Ok(chunk))
                .map_err(|_| crate::Error::new_closed())
        }

        /// Send trailers on trailers channel.
        pub async fn send_trailers(&mut self, trailers: HeaderMap) -> crate::Result<()> {
            let tx = match self.trailers_tx.take() {
                Some(tx) => tx,
                None => return Err(crate::Error::new_closed()),
            };
            tx.send(trailers).map_err(|_| crate::Error::new_closed())
        }

        /// Try to send data on this channel.
        ///
        /// # Errors
        ///
        /// Returns `Err(Bytes)` if the channel could not (currently) accept
        /// another `Bytes`.
        ///
        /// # Note
        ///
        /// This is mostly useful for when trying to send from some other thread
        /// that doesn't have an async context. If in an async context, prefer
        /// `send_data()` instead.
        pub fn try_send_data(&mut self, chunk: Bytes) -> Result<(), Bytes> {
            self.data_tx
                .try_send(Ok(chunk))
                .map_err(|err| err.into_inner().expect("just sent Ok"))
        }

        /// Aborts the body in an abnormal fashion.
        pub fn abort(self) {
            let _ = self
                .data_tx
                // clone so the send works even if buffer is full
                .clone()
                .try_send(Err(crate::Error::new_body_write_aborted()));
        }

        #[cfg(feature = "http1")]
        pub(crate) fn send_error(&mut self, err: crate::Error) {
            let _ = self.data_tx.try_send(Err(err));
        }
    }

    impl fmt::Debug for Sender {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            #[derive(Debug)]
            struct Open;
            #[derive(Debug)]
            struct Closed;

            let mut builder = f.debug_tuple("Sender");
            match self.want_rx.peek() {
                watch::CLOSED => builder.field(&Closed),
                _ => builder.field(&Open),
            };

            builder.finish()
        }
    }

    #[cfg(test)]
    mod tests {
        use std::mem;
        use std::task::Poll;

        use super::{Body, DecodedLength, HttpBody, Sender, SizeHint};

        #[test]
        fn test_size_of() {
            // These are mostly to help catch *accidentally* increasing
            // the size by too much.

            let body_size = mem::size_of::<Body>();
            let body_expected_size = mem::size_of::<u64>() * 6;
            assert!(
                body_size <= body_expected_size,
                "Body size = {} <= {}",
                body_size,
                body_expected_size,
            );

            assert_eq!(body_size, mem::size_of::<Option<Body>>(), "Option<Body>");

            assert_eq!(
                mem::size_of::<Sender>(),
                mem::size_of::<usize>() * 5,
                "Sender"
            );

            assert_eq!(
                mem::size_of::<Sender>(),
                mem::size_of::<Option<Sender>>(),
                "Option<Sender>"
            );
        }

        #[test]
        fn size_hint() {
            fn eq(body: Body, b: SizeHint, note: &str) {
                let a = body.size_hint();
                assert_eq!(a.lower(), b.lower(), "lower for {:?}", note);
                assert_eq!(a.upper(), b.upper(), "upper for {:?}", note);
            }

            eq(Body::from("Hello"), SizeHint::with_exact(5), "from str");

            eq(Body::empty(), SizeHint::with_exact(0), "empty");

            eq(Body::channel().1, SizeHint::new(), "channel");

            eq(
                Body::new_channel(DecodedLength::new(4), /*wanter =*/ false).1,
                SizeHint::with_exact(4),
                "channel with length",
            );
        }

        #[tokio::test]
        async fn channel_abort() {
            let (tx, mut rx) = Body::channel();

            tx.abort();

            let err = rx.data().await.unwrap().unwrap_err();
            assert!(err.is_body_write_aborted(), "{:?}", err);
        }

        #[tokio::test]
        async fn channel_abort_when_buffer_is_full() {
            let (mut tx, mut rx) = Body::channel();

            tx.try_send_data("chunk 1".into()).expect("send 1");
            // buffer is full, but can still send abort
            tx.abort();

            let chunk1 = rx.data().await.expect("item 1").expect("chunk 1");
            assert_eq!(chunk1, "chunk 1");

            let err = rx.data().await.unwrap().unwrap_err();
            assert!(err.is_body_write_aborted(), "{:?}", err);
        }

        #[test]
        fn channel_buffers_one() {
            let (mut tx, _rx) = Body::channel();

            tx.try_send_data("chunk 1".into()).expect("send 1");

            // buffer is now full
            let chunk2 = tx.try_send_data("chunk 2".into()).expect_err("send 2");
            assert_eq!(chunk2, "chunk 2");
        }

        #[tokio::test]
        async fn channel_empty() {
            let (_, mut rx) = Body::channel();

            assert!(rx.data().await.is_none());
        }

        #[test]
        fn channel_ready() {
            let (mut tx, _rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ false);

            let mut tx_ready = tokio_test::task::spawn(tx.ready());

            assert!(tx_ready.poll().is_ready(), "tx is ready immediately");
        }

        #[test]
        fn channel_wanter() {
            let (mut tx, mut rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ true);

            let mut tx_ready = tokio_test::task::spawn(tx.ready());
            let mut rx_data = tokio_test::task::spawn(rx.data());

            assert!(
                tx_ready.poll().is_pending(),
                "tx isn't ready before rx has been polled"
            );

            assert!(rx_data.poll().is_pending(), "poll rx.data");
            assert!(tx_ready.is_woken(), "rx poll wakes tx");

            assert!(
                tx_ready.poll().is_ready(),
                "tx is ready after rx has been polled"
            );
        }

        #[test]
        fn channel_notices_closure() {
            let (mut tx, rx) = Body::new_channel(DecodedLength::CHUNKED, /*wanter = */ true);

            let mut tx_ready = tokio_test::task::spawn(tx.ready());

            assert!(
                tx_ready.poll().is_pending(),
                "tx isn't ready before rx has been polled"
            );

            drop(rx);
            assert!(tx_ready.is_woken(), "dropping rx wakes tx");

            match tx_ready.poll() {
                Poll::Ready(Err(ref e)) if e.is_closed() => (),
                unexpected => panic!("tx poll ready unexpected: {:?}", unexpected),
            }
        }
    }