      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155

    use std::marker::Unpin;
    use std::{cmp, io};

    use bytes::{Buf, Bytes};
    use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};

    use crate::common::{task, Pin, Poll};

    /// Combine a buffer with an IO, rewinding reads to use the buffer.
    #[derive(Debug)]
    pub(crate) struct Rewind<T> {
        pre: Option<Bytes>,
        inner: T,
    }

    impl<T> Rewind<T> {
        #[cfg(any(all(feature = "http2", feature = "server"), test))]
        pub(crate) fn new(io: T) -> Self {
            Rewind {
                pre: None,
                inner: io,
            }
        }

        pub(crate) fn new_buffered(io: T, buf: Bytes) -> Self {
            Rewind {
                pre: Some(buf),
                inner: io,
            }
        }

        #[cfg(any(all(feature = "http1", feature = "http2", feature = "server"), test))]
        pub(crate) fn rewind(&mut self, bs: Bytes) {
            debug_assert!(self.pre.is_none());
            self.pre = Some(bs);
        }

        pub(crate) fn into_inner(self) -> (T, Bytes) {
            (self.inner, self.pre.unwrap_or_else(Bytes::new))
        }

        // pub(crate) fn get_mut(&mut self) -> &mut T {
        //     &mut self.inner
        // }
    }

    impl<T> AsyncRead for Rewind<T>
    where
        T: AsyncRead + Unpin,
    {
        fn poll_read(
            mut self: Pin<&mut Self>,
            cx: &mut task::Context<'_>,
            buf: &mut ReadBuf<'_>,
        ) -> Poll<io::Result<()>> {
            if let Some(mut prefix) = self.pre.take() {
                // If there are no remaining bytes, let the bytes get dropped.
                if !prefix.is_empty() {
                    let copy_len = cmp::min(prefix.len(), buf.remaining());
                    // TODO: There should be a way to do following two lines cleaner...
                    buf.put_slice(&prefix[..copy_len]);
                    prefix.advance(copy_len);
                    // Put back whats left
                    if !prefix.is_empty() {
                        self.pre = Some(prefix);
                    }

                    return Poll::Ready(Ok(()));
                }
            }
            Pin::new(&mut self.inner).poll_read(cx, buf)
        }
    }

    impl<T> AsyncWrite for Rewind<T>
    where
        T: AsyncWrite + Unpin,
    {
        fn poll_write(
            mut self: Pin<&mut Self>,
            cx: &mut task::Context<'_>,
            buf: &[u8],
        ) -> Poll<io::Result<usize>> {
            Pin::new(&mut self.inner).poll_write(cx, buf)
        }

        fn poll_write_vectored(
            mut self: Pin<&mut Self>,
            cx: &mut task::Context<'_>,
            bufs: &[io::IoSlice<'_>],
        ) -> Poll<io::Result<usize>> {
            Pin::new(&mut self.inner).poll_write_vectored(cx, bufs)
        }

        fn poll_flush(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<io::Result<()>> {
            Pin::new(&mut self.inner).poll_flush(cx)
        }

        fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<io::Result<()>> {
            Pin::new(&mut self.inner).poll_shutdown(cx)
        }

        fn is_write_vectored(&self) -> bool {
            self.inner.is_write_vectored()
        }
    }

    #[cfg(test)]
    mod tests {
        // FIXME: re-implement tests with `async/await`, this import should
        // trigger a warning to remind us
        use super::Rewind;
        use bytes::Bytes;
        use tokio::io::AsyncReadExt;

        #[tokio::test]
        async fn partial_rewind() {
            let underlying = [104, 101, 108, 108, 111];

            let mock = tokio_test::io::Builder::new().read(&underlying).build();

            let mut stream = Rewind::new(mock);

            // Read off some bytes, ensure we filled o1
            let mut buf = [0; 2];
            stream.read_exact(&mut buf).await.expect("read1");

            // Rewind the stream so that it is as if we never read in the first place.
            stream.rewind(Bytes::copy_from_slice(&buf[..]));

            let mut buf = [0; 5];
            stream.read_exact(&mut buf).await.expect("read1");

            // At this point we should have read everything that was in the MockStream
            assert_eq!(&buf, &underlying);
        }

        #[tokio::test]
        async fn full_rewind() {
            let underlying = [104, 101, 108, 108, 111];

            let mock = tokio_test::io::Builder::new().read(&underlying).build();

            let mut stream = Rewind::new(mock);

            let mut buf = [0; 5];
            stream.read_exact(&mut buf).await.expect("read1");

            // Rewind the stream so that it is as if we never read in the first place.
            stream.rewind(Bytes::copy_from_slice(&buf[..]));

            let mut buf = [0; 5];
            stream.read_exact(&mut buf).await.expect("read1");
        }
    }