1 use crate::io::AsyncRead; 2 3 use std::io; 4 use std::ops::DerefMut; 5 use std::pin::Pin; 6 use std::task::{Context, Poll}; 7 8 /// Reads bytes asynchronously. 9 /// 10 /// This trait is analogous to [`std::io::BufRead`], but integrates with 11 /// the asynchronous task system. In particular, the [`poll_fill_buf`] method, 12 /// unlike [`BufRead::fill_buf`], will automatically queue the current task for wakeup 13 /// and return if data is not yet available, rather than blocking the calling 14 /// thread. 15 /// 16 /// Utilities for working with `AsyncBufRead` values are provided by 17 /// [`AsyncBufReadExt`]. 18 /// 19 /// [`std::io::BufRead`]: std::io::BufRead 20 /// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf 21 /// [`BufRead::fill_buf`]: std::io::BufRead::fill_buf 22 /// [`AsyncBufReadExt`]: crate::io::AsyncBufReadExt 23 pub trait AsyncBufRead: AsyncRead { 24 /// Attempts to return the contents of the internal buffer, filling it with more data 25 /// from the inner reader if it is empty. 26 /// 27 /// On success, returns `Poll::Ready(Ok(buf))`. 28 /// 29 /// If no data is available for reading, the method returns 30 /// `Poll::Pending` and arranges for the current task (via 31 /// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes 32 /// readable or is closed. 33 /// 34 /// This function is a lower-level call. It needs to be paired with the 35 /// [`consume`] method to function properly. When calling this 36 /// method, none of the contents will be "read" in the sense that later 37 /// calling [`poll_read`] may return the same contents. As such, [`consume`] must 38 /// be called with the number of bytes that are consumed from this buffer to 39 /// ensure that the bytes are never returned twice. 40 /// 41 /// An empty buffer returned indicates that the stream has reached EOF. 42 /// 43 /// [`poll_read`]: AsyncRead::poll_read 44 /// [`consume`]: AsyncBufRead::consume poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>45 fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>; 46 47 /// Tells this buffer that `amt` bytes have been consumed from the buffer, 48 /// so they should no longer be returned in calls to [`poll_read`]. 49 /// 50 /// This function is a lower-level call. It needs to be paired with the 51 /// [`poll_fill_buf`] method to function properly. This function does 52 /// not perform any I/O, it simply informs this object that some amount of 53 /// its buffer, returned from [`poll_fill_buf`], has been consumed and should 54 /// no longer be returned. As such, this function may do odd things if 55 /// [`poll_fill_buf`] isn't called before calling it. 56 /// 57 /// The `amt` must be `<=` the number of bytes in the buffer returned by 58 /// [`poll_fill_buf`]. 59 /// 60 /// [`poll_read`]: AsyncRead::poll_read 61 /// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf consume(self: Pin<&mut Self>, amt: usize)62 fn consume(self: Pin<&mut Self>, amt: usize); 63 } 64 65 macro_rules! deref_async_buf_read { 66 () => { 67 fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> { 68 Pin::new(&mut **self.get_mut()).poll_fill_buf(cx) 69 } 70 71 fn consume(mut self: Pin<&mut Self>, amt: usize) { 72 Pin::new(&mut **self).consume(amt) 73 } 74 }; 75 } 76 77 impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for Box<T> { 78 deref_async_buf_read!(); 79 } 80 81 impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for &mut T { 82 deref_async_buf_read!(); 83 } 84 85 impl<P> AsyncBufRead for Pin<P> 86 where 87 P: DerefMut + Unpin, 88 P::Target: AsyncBufRead, 89 { poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>90 fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> { 91 self.get_mut().as_mut().poll_fill_buf(cx) 92 } 93 consume(self: Pin<&mut Self>, amt: usize)94 fn consume(self: Pin<&mut Self>, amt: usize) { 95 self.get_mut().as_mut().consume(amt) 96 } 97 } 98 99 impl AsyncBufRead for &[u8] { poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>100 fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> { 101 Poll::Ready(Ok(*self)) 102 } 103 consume(mut self: Pin<&mut Self>, amt: usize)104 fn consume(mut self: Pin<&mut Self>, amt: usize) { 105 *self = &self[amt..]; 106 } 107 } 108 109 impl<T: AsRef<[u8]> + Unpin> AsyncBufRead for io::Cursor<T> { poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>110 fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> { 111 Poll::Ready(io::BufRead::fill_buf(self.get_mut())) 112 } 113 consume(self: Pin<&mut Self>, amt: usize)114 fn consume(self: Pin<&mut Self>, amt: usize) { 115 io::BufRead::consume(self.get_mut(), amt) 116 } 117 } 118