vendor/futures-util/src/io/repeat.rs

   1 use futures_core::ready;
   2 use futures_core::task::{Context, Poll};
   3 use futures_io::{AsyncRead, IoSliceMut};
   4 use std::fmt;
   5 use std::io;
   6 use std::pin::Pin;
   7
   8 /// Reader for the [`repeat()`] function.
   9 #[must_use = "readers do nothing unless polled"]
  10 pub struct Repeat {
  11     byte: u8,
  12 }
  13
  14 /// Creates an instance of a reader that infinitely repeats one byte.
  15 ///
  16 /// All reads from this reader will succeed by filling the specified buffer with
  17 /// the given byte.
  18 ///
  19 /// # Examples
  20 ///
  21 /// ```
  22 /// # futures::executor::block_on(async {
  23 /// use futures::io::{self, AsyncReadExt};
  24 ///
  25 /// let mut buffer = [0; 3];
  26 /// let mut reader = io::repeat(0b101);
  27 /// reader.read_exact(&mut buffer).await.unwrap();
  28 /// assert_eq!(buffer, [0b101, 0b101, 0b101]);
  29 /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
  30 /// ```
  31 pub fn repeat(byte: u8) -> Repeat {
  32     Repeat { byte }
  33 }
  34
  35 impl AsyncRead for Repeat {
  36     #[inline]
  37     fn poll_read(
  38         self: Pin<&mut Self>,
  39         _: &mut Context<'_>,
  40         buf: &mut [u8],
  41     ) -> Poll<io::Result<usize>> {
  42         for slot in &mut *buf {
  43             *slot = self.byte;
  44         }
  45         Poll::Ready(Ok(buf.len()))
  46     }
  47
  48     #[inline]
  49     fn poll_read_vectored(
  50         mut self: Pin<&mut Self>,
  51         cx: &mut Context<'_>,
  52         bufs: &mut [IoSliceMut<'_>],
  53     ) -> Poll<io::Result<usize>> {
  54         let mut nwritten = 0;
  55         for buf in bufs {
  56             nwritten += ready!(self.as_mut().poll_read(cx, buf))?;
  57         }
  58         Poll::Ready(Ok(nwritten))
  59     }
  60 }
  61
  62 impl fmt::Debug for Repeat {
  63     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  64         f.pad("Repeat { .. }")
  65     }
  66 }