1 | use super::ReadBuf; |
2 | use std::io; |
3 | use std::ops::DerefMut; |
4 | use std::pin::Pin; |
5 | use std::task::{Context, Poll}; |
6 | |
7 | /// Reads bytes from a source. |
8 | /// |
9 | /// This trait is analogous to the [`std::io::Read`] trait, but integrates with |
10 | /// the asynchronous task system. In particular, the [`poll_read`] method, |
11 | /// unlike [`Read::read`], will automatically queue the current task for wakeup |
12 | /// and return if data is not yet available, rather than blocking the calling |
13 | /// thread. |
14 | /// |
15 | /// Specifically, this means that the `poll_read` function will return one of |
16 | /// the following: |
17 | /// |
18 | /// * `Poll::Ready(Ok(()))` means that data was immediately read and placed into |
19 | /// the output buffer. The amount of data read can be determined by the |
20 | /// increase in the length of the slice returned by `ReadBuf::filled`. If the |
21 | /// difference is 0, EOF has been reached. |
22 | /// |
23 | /// * `Poll::Pending` means that no data was read into the buffer |
24 | /// provided. The I/O object is not currently readable but may become readable |
25 | /// in the future. Most importantly, **the current future's task is scheduled |
26 | /// to get unparked when the object is readable**. This means that like |
27 | /// `Future::poll` you'll receive a notification when the I/O object is |
28 | /// readable again. |
29 | /// |
30 | /// * `Poll::Ready(Err(e))` for other errors are standard I/O errors coming from the |
31 | /// underlying object. |
32 | /// |
33 | /// This trait importantly means that the `read` method only works in the |
34 | /// context of a future's task. The object may panic if used outside of a task. |
35 | /// |
36 | /// Utilities for working with `AsyncRead` values are provided by |
37 | /// [`AsyncReadExt`]. |
38 | /// |
39 | /// [`poll_read`]: AsyncRead::poll_read |
40 | /// [`std::io::Read`]: std::io::Read |
41 | /// [`Read::read`]: std::io::Read::read |
42 | /// [`AsyncReadExt`]: crate::io::AsyncReadExt |
43 | pub trait AsyncRead { |
44 | /// Attempts to read from the `AsyncRead` into `buf`. |
45 | /// |
46 | /// On success, returns `Poll::Ready(Ok(()))` and places data in the |
47 | /// unfilled portion of `buf`. If no data was read (`buf.filled().len()` is |
48 | /// unchanged), it implies that EOF has been reached. |
49 | /// |
50 | /// If no data is available for reading, the method returns `Poll::Pending` |
51 | /// and arranges for the current task (via `cx.waker()`) to receive a |
52 | /// notification when the object becomes readable or is closed. |
53 | fn poll_read( |
54 | self: Pin<&mut Self>, |
55 | cx: &mut Context<'_>, |
56 | buf: &mut ReadBuf<'_>, |
57 | ) -> Poll<io::Result<()>>; |
58 | } |
59 | |
60 | macro_rules! deref_async_read { |
61 | () => { |
62 | fn poll_read( |
63 | mut self: Pin<&mut Self>, |
64 | cx: &mut Context<'_>, |
65 | buf: &mut ReadBuf<'_>, |
66 | ) -> Poll<io::Result<()>> { |
67 | Pin::new(&mut **self).poll_read(cx, buf) |
68 | } |
69 | }; |
70 | } |
71 | |
72 | impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for Box<T> { |
73 | deref_async_read!(); |
74 | } |
75 | |
76 | impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for &mut T { |
77 | deref_async_read!(); |
78 | } |
79 | |
80 | impl<P> AsyncRead for Pin<P> |
81 | where |
82 | P: DerefMut + Unpin, |
83 | P::Target: AsyncRead, |
84 | { |
85 | fn poll_read( |
86 | self: Pin<&mut Self>, |
87 | cx: &mut Context<'_>, |
88 | buf: &mut ReadBuf<'_>, |
89 | ) -> Poll<io::Result<()>> { |
90 | self.get_mut().as_mut().poll_read(cx, buf) |
91 | } |
92 | } |
93 | |
94 | impl AsyncRead for &[u8] { |
95 | fn poll_read( |
96 | mut self: Pin<&mut Self>, |
97 | _cx: &mut Context<'_>, |
98 | buf: &mut ReadBuf<'_>, |
99 | ) -> Poll<io::Result<()>> { |
100 | let amt: usize = std::cmp::min(self.len(), v2:buf.remaining()); |
101 | let (a: &[u8], b: &[u8]) = self.split_at(mid:amt); |
102 | buf.put_slice(buf:a); |
103 | *self = b; |
104 | Poll::Ready(Ok(())) |
105 | } |
106 | } |
107 | |
108 | impl<T: AsRef<[u8]> + Unpin> AsyncRead for io::Cursor<T> { |
109 | fn poll_read( |
110 | mut self: Pin<&mut Self>, |
111 | _cx: &mut Context<'_>, |
112 | buf: &mut ReadBuf<'_>, |
113 | ) -> Poll<io::Result<()>> { |
114 | let pos: u64 = self.position(); |
115 | let slice: &[u8] = (*self).get_ref().as_ref(); |
116 | |
117 | // The position could technically be out of bounds, so don't panic... |
118 | if pos > slice.len() as u64 { |
119 | return Poll::Ready(Ok(())); |
120 | } |
121 | |
122 | let start: usize = pos as usize; |
123 | let amt: usize = std::cmp::min(v1:slice.len() - start, v2:buf.remaining()); |
124 | // Add won't overflow because of pos check above. |
125 | let end: usize = start + amt; |
126 | buf.put_slice(&slice[start..end]); |
127 | self.set_position(pos:end as u64); |
128 | |
129 | Poll::Ready(Ok(())) |
130 | } |
131 | } |
132 | |