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
use crate::io::{AsyncBufRead, AsyncRead, ReadBuf};

use pin_project_lite::pin_project;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::{cmp, io};

pin_project! {
    /// Stream for the [`take`](super::AsyncReadExt::take) method.
    #[derive(Debug)]
    #[must_use = "streams do nothing unless you `.await` or poll them"]
    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
    pub struct Take<R> {
        #[pin]
        inner: R,
        // Add '_' to avoid conflicts with `limit` method.
        limit_: u64,
    }
}

pub(super) fn take<R: AsyncRead>(inner: R, limit: u64) -> Take<R> {
    Take {
        inner,
        limit_: limit,
    }
}

impl<R: AsyncRead> Take<R> {
    /// Returns the remaining number of bytes that can be
    /// read before this instance will return EOF.
    ///
    /// # Note
    ///
    /// This instance may reach `EOF` after reading fewer bytes than indicated by
    /// this method if the underlying [`AsyncRead`] instance reaches EOF.
    pub fn limit(&self) -> u64 {
        self.limit_
    }

    /// Sets the number of bytes that can be read before this instance will
    /// return EOF. This is the same as constructing a new `Take` instance, so
    /// the amount of bytes read and the previous limit value don't matter when
    /// calling this method.
    pub fn set_limit(&mut self, limit: u64) {
        self.limit_ = limit
    }

    /// Gets a reference to the underlying reader.
    pub fn get_ref(&self) -> &R {
        &self.inner
    }

    /// Gets a mutable reference to the underlying reader.
    ///
    /// Care should be taken to avoid modifying the internal I/O state of the
    /// underlying reader as doing so may corrupt the internal limit of this
    /// `Take`.
    pub fn get_mut(&mut self) -> &mut R {
        &mut self.inner
    }

    /// Gets a pinned mutable reference to the underlying reader.
    ///
    /// Care should be taken to avoid modifying the internal I/O state of the
    /// underlying reader as doing so may corrupt the internal limit of this
    /// `Take`.
    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut R> {
        self.project().inner
    }

    /// Consumes the `Take`, returning the wrapped reader.
    pub fn into_inner(self) -> R {
        self.inner
    }
}

impl<R: AsyncRead> AsyncRead for Take<R> {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<Result<(), io::Error>> {
        if self.limit_ == 0 {
            return Poll::Ready(Ok(()));
        }

        let me = self.project();
        let mut b = buf.take(*me.limit_ as usize);
        ready!(me.inner.poll_read(cx, &mut b))?;
        let n = b.filled().len();

        // We need to update the original ReadBuf
        unsafe {
            buf.assume_init(n);
        }
        buf.advance(n);
        *me.limit_ -= n as u64;
        Poll::Ready(Ok(()))
    }
}

impl<R: AsyncBufRead> AsyncBufRead for Take<R> {
    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
        let me = self.project();

        // Don't call into inner reader at all at EOF because it may still block
        if *me.limit_ == 0 {
            return Poll::Ready(Ok(&[]));
        }

        let buf = ready!(me.inner.poll_fill_buf(cx)?);
        let cap = cmp::min(buf.len() as u64, *me.limit_) as usize;
        Poll::Ready(Ok(&buf[..cap]))
    }

    fn consume(self: Pin<&mut Self>, amt: usize) {
        let me = self.project();
        // Don't let callers reset the limit by passing an overlarge value
        let amt = cmp::min(amt as u64, *me.limit_) as usize;
        *me.limit_ -= amt as u64;
        me.inner.consume(amt);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn assert_unpin() {
        crate::is_unpin::<Take<()>>();
    }
}