1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164
use crate::io::util::poll_proceed_and_make_progress;
use crate::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
use std::fmt;
use std::io::{self, SeekFrom};
use std::pin::Pin;
use std::task::{ready, Context, Poll};
cfg_io_util! {
/// `Empty` ignores any data written via [`AsyncWrite`], and will always be empty
/// (returning zero bytes) when read via [`AsyncRead`].
///
/// This struct is generally created by calling [`empty`]. Please see
/// the documentation of [`empty()`][`empty`] for more details.
///
/// This is an asynchronous version of [`std::io::empty`][std].
///
/// [`empty`]: fn@empty
/// [std]: std::io::empty
pub struct Empty {
_p: (),
}
/// Creates a value that is always at EOF for reads, and ignores all data written.
///
/// All writes on the returned instance will return `Poll::Ready(Ok(buf.len()))`
/// and the contents of the buffer will not be inspected.
///
/// All reads from the returned instance will return `Poll::Ready(Ok(0))`.
///
/// This is an asynchronous version of [`std::io::empty`][std].
///
/// [std]: std::io::empty
///
/// # Examples
///
/// A slightly sad example of not reading anything into a buffer:
///
/// ```
/// use tokio::io::{self, AsyncReadExt};
///
/// #[tokio::main]
/// async fn main() {
/// let mut buffer = String::new();
/// io::empty().read_to_string(&mut buffer).await.unwrap();
/// assert!(buffer.is_empty());
/// }
/// ```
///
/// A convoluted way of getting the length of a buffer:
///
/// ```
/// use tokio::io::{self, AsyncWriteExt};
///
/// #[tokio::main]
/// async fn main() {
/// let buffer = vec![1, 2, 3, 5, 8];
/// let num_bytes = io::empty().write(&buffer).await.unwrap();
/// assert_eq!(num_bytes, 5);
/// }
/// ```
pub fn empty() -> Empty {
Empty { _p: () }
}
}
impl AsyncRead for Empty {
#[inline]
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
_: &mut ReadBuf<'_>,
) -> Poll<io::Result<()>> {
ready!(crate::trace::trace_leaf(cx));
ready!(poll_proceed_and_make_progress(cx));
Poll::Ready(Ok(()))
}
}
impl AsyncBufRead for Empty {
#[inline]
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
ready!(crate::trace::trace_leaf(cx));
ready!(poll_proceed_and_make_progress(cx));
Poll::Ready(Ok(&[]))
}
#[inline]
fn consume(self: Pin<&mut Self>, _: usize) {}
}
impl AsyncWrite for Empty {
#[inline]
fn poll_write(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
ready!(crate::trace::trace_leaf(cx));
ready!(poll_proceed_and_make_progress(cx));
Poll::Ready(Ok(buf.len()))
}
#[inline]
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
ready!(crate::trace::trace_leaf(cx));
ready!(poll_proceed_and_make_progress(cx));
Poll::Ready(Ok(()))
}
#[inline]
fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
ready!(crate::trace::trace_leaf(cx));
ready!(poll_proceed_and_make_progress(cx));
Poll::Ready(Ok(()))
}
#[inline]
fn is_write_vectored(&self) -> bool {
true
}
#[inline]
fn poll_write_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[io::IoSlice<'_>],
) -> Poll<Result<usize, io::Error>> {
ready!(crate::trace::trace_leaf(cx));
ready!(poll_proceed_and_make_progress(cx));
let num_bytes = bufs.iter().map(|b| b.len()).sum();
Poll::Ready(Ok(num_bytes))
}
}
impl AsyncSeek for Empty {
#[inline]
fn start_seek(self: Pin<&mut Self>, _position: SeekFrom) -> io::Result<()> {
Ok(())
}
#[inline]
fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
ready!(crate::trace::trace_leaf(cx));
ready!(poll_proceed_and_make_progress(cx));
Poll::Ready(Ok(0))
}
}
impl fmt::Debug for Empty {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Empty { .. }")
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn assert_unpin() {
crate::is_unpin::<Empty>();
}
}