tokio/io/util/
take.rs

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1use crate::io::{AsyncBufRead, AsyncRead, ReadBuf};
2
3use pin_project_lite::pin_project;
4use std::convert::TryFrom;
5use std::pin::Pin;
6use std::task::{ready, Context, Poll};
7use std::{cmp, io};
8
9pin_project! {
10    /// Stream for the [`take`](super::AsyncReadExt::take) method.
11    #[derive(Debug)]
12    #[must_use = "streams do nothing unless you `.await` or poll them"]
13    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
14    pub struct Take<R> {
15        #[pin]
16        inner: R,
17        // Add '_' to avoid conflicts with `limit` method.
18        limit_: u64,
19    }
20}
21
22pub(super) fn take<R: AsyncRead>(inner: R, limit: u64) -> Take<R> {
23    Take {
24        inner,
25        limit_: limit,
26    }
27}
28
29impl<R: AsyncRead> Take<R> {
30    /// Returns the remaining number of bytes that can be
31    /// read before this instance will return EOF.
32    ///
33    /// # Note
34    ///
35    /// This instance may reach `EOF` after reading fewer bytes than indicated by
36    /// this method if the underlying [`AsyncRead`] instance reaches EOF.
37    pub fn limit(&self) -> u64 {
38        self.limit_
39    }
40
41    /// Sets the number of bytes that can be read before this instance will
42    /// return EOF. This is the same as constructing a new `Take` instance, so
43    /// the amount of bytes read and the previous limit value don't matter when
44    /// calling this method.
45    pub fn set_limit(&mut self, limit: u64) {
46        self.limit_ = limit;
47    }
48
49    /// Gets a reference to the underlying reader.
50    pub fn get_ref(&self) -> &R {
51        &self.inner
52    }
53
54    /// Gets a mutable reference to the underlying reader.
55    ///
56    /// Care should be taken to avoid modifying the internal I/O state of the
57    /// underlying reader as doing so may corrupt the internal limit of this
58    /// `Take`.
59    pub fn get_mut(&mut self) -> &mut R {
60        &mut self.inner
61    }
62
63    /// Gets a pinned mutable reference to the underlying reader.
64    ///
65    /// Care should be taken to avoid modifying the internal I/O state of the
66    /// underlying reader as doing so may corrupt the internal limit of this
67    /// `Take`.
68    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut R> {
69        self.project().inner
70    }
71
72    /// Consumes the `Take`, returning the wrapped reader.
73    pub fn into_inner(self) -> R {
74        self.inner
75    }
76}
77
78impl<R: AsyncRead> AsyncRead for Take<R> {
79    fn poll_read(
80        self: Pin<&mut Self>,
81        cx: &mut Context<'_>,
82        buf: &mut ReadBuf<'_>,
83    ) -> Poll<Result<(), io::Error>> {
84        if self.limit_ == 0 {
85            return Poll::Ready(Ok(()));
86        }
87
88        let me = self.project();
89        let mut b = buf.take(usize::try_from(*me.limit_).unwrap_or(usize::MAX));
90
91        let buf_ptr = b.filled().as_ptr();
92        ready!(me.inner.poll_read(cx, &mut b))?;
93        assert_eq!(b.filled().as_ptr(), buf_ptr);
94
95        let n = b.filled().len();
96
97        // We need to update the original ReadBuf
98        unsafe {
99            buf.assume_init(n);
100        }
101        buf.advance(n);
102        *me.limit_ -= n as u64;
103        Poll::Ready(Ok(()))
104    }
105}
106
107impl<R: AsyncBufRead> AsyncBufRead for Take<R> {
108    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
109        let me = self.project();
110
111        // Don't call into inner reader at all at EOF because it may still block
112        if *me.limit_ == 0 {
113            return Poll::Ready(Ok(&[]));
114        }
115
116        let buf = ready!(me.inner.poll_fill_buf(cx)?);
117        let cap = cmp::min(buf.len() as u64, *me.limit_) as usize;
118        Poll::Ready(Ok(&buf[..cap]))
119    }
120
121    fn consume(self: Pin<&mut Self>, amt: usize) {
122        let me = self.project();
123        // Don't let callers reset the limit by passing an overlarge value
124        let amt = cmp::min(amt as u64, *me.limit_) as usize;
125        *me.limit_ -= amt as u64;
126        me.inner.consume(amt);
127    }
128}
129
130#[cfg(test)]
131mod tests {
132    use super::*;
133
134    #[test]
135    fn assert_unpin() {
136        crate::is_unpin::<Take<()>>();
137    }
138}
tokio/io/util/take.rs

tokio/io/util/
take.rs
