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    #![doc(html_root_url = "https://docs.rs/http-body/0.4.0")]
    #![deny(missing_debug_implementations, missing_docs, unreachable_pub)]
    #![cfg_attr(test, deny(warnings))]

    //! Asynchronous HTTP request or response body.
    //!
    //! See [`Body`] for more details.
    //!
    //! [`Body`]: trait.Body.html

    mod next;
    mod size_hint;

    pub use self::next::{Data, Trailers};
    pub use self::size_hint::SizeHint;

    use bytes::Buf;
    use http::HeaderMap;
    use std::ops;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    /// Trait representing a streaming body of a Request or Response.
    ///
    /// Data is streamed via the `poll_data` function, which asynchronously yields `T: Buf` values. The
    /// `size_hint` function provides insight into the total number of bytes that will be streamed.
    ///
    /// The `poll_trailers` function returns an optional set of trailers used to finalize the request /
    /// response exchange. This is mostly used when using the HTTP/2.0 protocol.
    ///
    pub trait Body {
        /// Values yielded by the `Body`.
        type Data: Buf;

        /// The error type this `Body` might generate.
        type Error;

        /// Attempt to pull out the next data buffer of this stream.
        fn poll_data(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Option<Result<Self::Data, Self::Error>>>;

        /// Poll for an optional **single** `HeaderMap` of trailers.
        ///
        /// This function should only be called once `poll_data` returns `None`.
        fn poll_trailers(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Result<Option<HeaderMap>, Self::Error>>;

        /// Returns `true` when the end of stream has been reached.
        ///
        /// An end of stream means that both `poll_data` and `poll_trailers` will
        /// return `None`.
        ///
        /// A return value of `false` **does not** guarantee that a value will be
        /// returned from `poll_stream` or `poll_trailers`.
        fn is_end_stream(&self) -> bool {
            false
        }

        /// Returns the bounds on the remaining length of the stream.
        ///
        /// When the **exact** remaining length of the stream is known, the upper bound will be set and
        /// will equal the lower bound.
        fn size_hint(&self) -> SizeHint {
            SizeHint::default()
        }

        /// Returns future that resolves to next data chunk, if any.
        fn data(&mut self) -> Data<'_, Self>
        where
            Self: Unpin + Sized,
        {
            Data(self)
        }

        /// Returns future that resolves to trailers, if any.
        fn trailers(&mut self) -> Trailers<'_, Self>
        where
            Self: Unpin + Sized,
        {
            Trailers(self)
        }
    }

    impl<T: Body + Unpin + ?Sized> Body for &mut T {
        type Data = T::Data;
        type Error = T::Error;

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

        fn poll_trailers(
            mut self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
            Pin::new(&mut **self).poll_trailers(cx)
        }

        fn is_end_stream(&self) -> bool {
            Pin::new(&**self).is_end_stream()
        }

        fn size_hint(&self) -> SizeHint {
            Pin::new(&**self).size_hint()
        }
    }

    impl<P> Body for Pin<P>
    where
        P: Unpin + ops::DerefMut,
        P::Target: Body,
    {
        type Data = <<P as ops::Deref>::Target as Body>::Data;
        type Error = <<P as ops::Deref>::Target as Body>::Error;

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

        fn poll_trailers(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
            Pin::get_mut(self).as_mut().poll_trailers(cx)
        }

        fn is_end_stream(&self) -> bool {
            self.as_ref().is_end_stream()
        }

        fn size_hint(&self) -> SizeHint {
            self.as_ref().size_hint()
        }
    }

    impl<T: Body + Unpin + ?Sized> Body for Box<T> {
        type Data = T::Data;
        type Error = T::Error;

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

        fn poll_trailers(
            mut self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
            Pin::new(&mut **self).poll_trailers(cx)
        }

        fn is_end_stream(&self) -> bool {
            self.as_ref().is_end_stream()
        }

        fn size_hint(&self) -> SizeHint {
            self.as_ref().size_hint()
        }
    }

    impl<B: Body> Body for http::Request<B> {
        type Data = B::Data;
        type Error = B::Error;

        fn poll_data(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
            unsafe {
                self.map_unchecked_mut(http::Request::body_mut)
                    .poll_data(cx)
            }
        }

        fn poll_trailers(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
            unsafe {
                self.map_unchecked_mut(http::Request::body_mut)
                    .poll_trailers(cx)
            }
        }

        fn is_end_stream(&self) -> bool {
            self.body().is_end_stream()
        }

        fn size_hint(&self) -> SizeHint {
            self.body().size_hint()
        }
    }

    impl<B: Body> Body for http::Response<B> {
        type Data = B::Data;
        type Error = B::Error;

        fn poll_data(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
            unsafe {
                self.map_unchecked_mut(http::Response::body_mut)
                    .poll_data(cx)
            }
        }

        fn poll_trailers(
            self: Pin<&mut Self>,
            cx: &mut Context<'_>,
        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
            unsafe {
                self.map_unchecked_mut(http::Response::body_mut)
                    .poll_trailers(cx)
            }
        }

        fn is_end_stream(&self) -> bool {
            self.body().is_end_stream()
        }

        fn size_hint(&self) -> SizeHint {
            self.body().size_hint()
        }
    }

    #[cfg(test)]
    fn _assert_bounds() {
        fn can_be_trait_object(_: &dyn Body<Data = std::io::Cursor<Vec<u8>>, Error = std::io::Error>) {}
    }