broker_tokio/io/util/
empty.rs

1use crate::io::{AsyncBufRead, AsyncRead};
2
3use std::fmt;
4use std::io;
5use std::pin::Pin;
6use std::task::{Context, Poll};
7
8cfg_io_util! {
9    /// An async reader which is always at EOF.
10    ///
11    /// This struct is generally created by calling [`empty`]. Please see
12    /// the documentation of [`empty()`][`empty`] for more details.
13    ///
14    /// This is an asynchronous version of [`std::io::empty`][std].
15    ///
16    /// [`empty`]: fn.empty.html
17    /// [std]: std::io::empty
18    pub struct Empty {
19        _p: (),
20    }
21
22    /// Creates a new empty async reader.
23    ///
24    /// All reads from the returned reader will return `Poll::Ready(Ok(0))`.
25    ///
26    /// This is an asynchronous version of [`std::io::empty`][std].
27    ///
28    /// [std]: std::io::empty
29    ///
30    /// # Examples
31    ///
32    /// A slightly sad example of not reading anything into a buffer:
33    ///
34    /// ```
35    /// use tokio::io::{self, AsyncReadExt};
36    ///
37    /// #[tokio::main]
38    /// async fn main() {
39    ///     let mut buffer = String::new();
40    ///     io::empty().read_to_string(&mut buffer).await.unwrap();
41    ///     assert!(buffer.is_empty());
42    /// }
43    /// ```
44    pub fn empty() -> Empty {
45        Empty { _p: () }
46    }
47}
48
49impl AsyncRead for Empty {
50    #[inline]
51    fn poll_read(
52        self: Pin<&mut Self>,
53        _: &mut Context<'_>,
54        _: &mut [u8],
55    ) -> Poll<io::Result<usize>> {
56        Poll::Ready(Ok(0))
57    }
58}
59
60impl AsyncBufRead for Empty {
61    #[inline]
62    fn poll_fill_buf(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
63        Poll::Ready(Ok(&[]))
64    }
65
66    #[inline]
67    fn consume(self: Pin<&mut Self>, _: usize) {}
68}
69
70impl fmt::Debug for Empty {
71    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
72        f.pad("Empty { .. }")
73    }
74}
75
76#[cfg(test)]
77mod tests {
78    use super::*;
79
80    #[test]
81    fn assert_unpin() {
82        crate::is_unpin::<Empty>();
83    }
84}
broker_tokio/io/util/empty.rs

broker_tokio/io/util/
empty.rs
