1 | use crate::io::{AsyncBufRead, AsyncRead, ReadBuf}; |
2 | |
3 | use pin_project_lite::pin_project; |
4 | use std::convert::TryFrom; |
5 | use std::pin::Pin; |
6 | use std::task::{Context, Poll}; |
7 | use std::{cmp, io}; |
8 | |
9 | pin_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 | |
22 | pub(super) fn take<R: AsyncRead>(inner: R, limit: u64) -> Take<R> { |
23 | Take { |
24 | inner, |
25 | limit_: limit, |
26 | } |
27 | } |
28 | |
29 | impl<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 | |
78 | impl<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 | |
107 | impl<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)] |
131 | mod tests { |
132 | use super::*; |
133 | |
134 | #[test] |
135 | fn assert_unpin() { |
136 | crate::is_unpin::<Take<()>>(); |
137 | } |
138 | } |
139 | |