60 lines
1.4 KiB
Rust
60 lines
1.4 KiB
Rust
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use futures_core::task::{Context, Poll};
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use futures_io::{AsyncBufRead, AsyncRead};
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use std::fmt;
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use std::io;
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use std::pin::Pin;
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/// Reader for the [`empty()`] function.
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#[must_use = "readers do nothing unless polled"]
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pub struct Empty {
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_priv: (),
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}
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/// Constructs a new handle to an empty reader.
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///
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/// All reads from the returned reader will return `Poll::Ready(Ok(0))`.
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///
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/// # Examples
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///
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/// A slightly sad example of not reading anything into a buffer:
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///
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/// ```
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/// # futures::executor::block_on(async {
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/// use futures::io::{self, AsyncReadExt};
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///
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/// let mut buffer = String::new();
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/// let mut reader = io::empty();
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/// reader.read_to_string(&mut buffer).await?;
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/// assert!(buffer.is_empty());
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/// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
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/// ```
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pub fn empty() -> Empty {
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Empty { _priv: () }
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}
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impl AsyncRead for Empty {
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#[inline]
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fn poll_read(
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self: Pin<&mut Self>,
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_: &mut Context<'_>,
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_: &mut [u8],
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) -> Poll<io::Result<usize>> {
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Poll::Ready(Ok(0))
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}
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}
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impl AsyncBufRead for Empty {
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#[inline]
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fn poll_fill_buf(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
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Poll::Ready(Ok(&[]))
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}
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#[inline]
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fn consume(self: Pin<&mut Self>, _: usize) {}
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}
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impl fmt::Debug for Empty {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.pad("Empty { .. }")
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}
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}
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