1use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
2
3use bytes::{Buf, BufMut};
4use std::io::{self, IoSlice};
5use std::pin::Pin;
6use std::task::{ready, Context, Poll};
7
8/// Try to read data from an `AsyncRead` into an implementer of the [`BufMut`] trait.
9///
10/// [`BufMut`]: bytes::Buf
11///
12/// # Example
13///
14/// ```
15/// use bytes::{Bytes, BytesMut};
16/// use tokio_stream as stream;
17/// use tokio::io::Result;
18/// use tokio_util::io::{StreamReader, poll_read_buf};
19/// use std::future::poll_fn;
20/// use std::pin::Pin;
21/// # #[tokio::main]
22/// # async fn main() -> std::io::Result<()> {
23///
24/// // Create a reader from an iterator. This particular reader will always be
25/// // ready.
26/// let mut read = StreamReader::new(stream::iter(vec![Result::Ok(Bytes::from_static(&[0, 1, 2, 3]))]));
27///
28/// let mut buf = BytesMut::new();
29/// let mut reads = 0;
30///
31/// loop {
32/// reads += 1;
33/// let n = poll_fn(|cx| poll_read_buf(Pin::new(&mut read), cx, &mut buf)).await?;
34///
35/// if n == 0 {
36/// break;
37/// }
38/// }
39///
40/// // one or more reads might be necessary.
41/// assert!(reads >= 1);
42/// assert_eq!(&buf[..], &[0, 1, 2, 3]);
43/// # Ok(())
44/// # }
45/// ```
46#[cfg_attr(not(feature = "io"), allow(unreachable_pub))]
47pub fn poll_read_buf<T: AsyncRead + ?Sized, B: BufMut>(
48 io: Pin<&mut T>,
49 cx: &mut Context<'_>,
50 buf: &mut B,
51) -> Poll<io::Result<usize>> {
52 if !buf.has_remaining_mut() {
53 return Poll::Ready(Ok(0));
54 }
55
56 let n = {
57 let dst = buf.chunk_mut();
58
59 // Safety: `chunk_mut()` returns a `&mut UninitSlice`, and `UninitSlice` is a
60 // transparent wrapper around `[MaybeUninit<u8>]`.
61 let dst = unsafe { dst.as_uninit_slice_mut() };
62 let mut buf = ReadBuf::uninit(dst);
63 let ptr = buf.filled().as_ptr();
64 ready!(io.poll_read(cx, &mut buf)?);
65
66 // Ensure the pointer does not change from under us
67 assert_eq!(ptr, buf.filled().as_ptr());
68 buf.filled().len()
69 };
70
71 // Safety: This is guaranteed to be the number of initialized (and read)
72 // bytes due to the invariants provided by `ReadBuf::filled`.
73 unsafe {
74 buf.advance_mut(n);
75 }
76
77 Poll::Ready(Ok(n))
78}
79
80/// Try to write data from an implementer of the [`Buf`] trait to an
81/// [`AsyncWrite`], advancing the buffer's internal cursor.
82///
83/// This function will use [vectored writes] when the [`AsyncWrite`] supports
84/// vectored writes.
85///
86/// # Examples
87///
88/// [`File`] implements [`AsyncWrite`] and [`Cursor<&[u8]>`] implements
89/// [`Buf`]:
90///
91/// ```no_run
92/// use tokio_util::io::poll_write_buf;
93/// use tokio::io;
94/// use tokio::fs::File;
95///
96/// use bytes::Buf;
97/// use std::future::poll_fn;
98/// use std::io::Cursor;
99/// use std::pin::Pin;
100///
101/// #[tokio::main]
102/// async fn main() -> io::Result<()> {
103/// let mut file = File::create("foo.txt").await?;
104/// let mut buf = Cursor::new(b"data to write");
105///
106/// // Loop until the entire contents of the buffer are written to
107/// // the file.
108/// while buf.has_remaining() {
109/// poll_fn(|cx| poll_write_buf(Pin::new(&mut file), cx, &mut buf)).await?;
110/// }
111///
112/// Ok(())
113/// }
114/// ```
115///
116/// [`Buf`]: bytes::Buf
117/// [`AsyncWrite`]: tokio::io::AsyncWrite
118/// [`File`]: tokio::fs::File
119/// [vectored writes]: tokio::io::AsyncWrite::poll_write_vectored
120#[cfg_attr(not(feature = "io"), allow(unreachable_pub))]
121pub fn poll_write_buf<T: AsyncWrite + ?Sized, B: Buf>(
122 io: Pin<&mut T>,
123 cx: &mut Context<'_>,
124 buf: &mut B,
125) -> Poll<io::Result<usize>> {
126 const MAX_BUFS: usize = 64;
127
128 if !buf.has_remaining() {
129 return Poll::Ready(Ok(0));
130 }
131
132 let n: usize = if io.is_write_vectored() {
133 let mut slices: [IoSlice<'_>; 64] = [IoSlice::new(&[]); MAX_BUFS];
134 let cnt: usize = buf.chunks_vectored(&mut slices);
135 ready!(io.poll_write_vectored(cx, &slices[..cnt]))?
136 } else {
137 ready!(io.poll_write(cx, buf.chunk()))?
138 };
139
140 buf.advance(cnt:n);
141
142 Poll::Ready(Ok(n))
143}
144