tokio/io/
stderr.rs

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1use crate::io::blocking::Blocking;
2use crate::io::stdio_common::SplitByUtf8BoundaryIfWindows;
3use crate::io::AsyncWrite;
4
5use std::io;
6use std::pin::Pin;
7use std::task::Context;
8use std::task::Poll;
9
10cfg_io_std! {
11    /// A handle to the standard error stream of a process.
12    ///
13    /// Concurrent writes to stderr must be executed with care: Only individual
14    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular
15    /// you should be aware that writes using [`write_all`] are not guaranteed
16    /// to occur as a single write, so multiple threads writing data with
17    /// [`write_all`] may result in interleaved output.
18    ///
19    /// Created by the [`stderr`] function.
20    ///
21    /// [`stderr`]: stderr()
22    /// [`AsyncWrite`]: AsyncWrite
23    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()
24    ///
25    /// # Examples
26    ///
27    /// ```
28    /// use tokio::io::{self, AsyncWriteExt};
29    ///
30    /// #[tokio::main]
31    /// async fn main() -> io::Result<()> {
32    ///     let mut stderr = io::stdout();
33    ///     stderr.write_all(b"Print some error here.").await?;
34    ///     Ok(())
35    /// }
36    /// ```
37    #[derive(Debug)]
38    pub struct Stderr {
39        std: SplitByUtf8BoundaryIfWindows<Blocking<std::io::Stderr>>,
40    }
41
42    /// Constructs a new handle to the standard error of the current process.
43    ///
44    /// The returned handle allows writing to standard error from the within the
45    /// Tokio runtime.
46    ///
47    /// Concurrent writes to stderr must be executed with care: Only individual
48    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular
49    /// you should be aware that writes using [`write_all`] are not guaranteed
50    /// to occur as a single write, so multiple threads writing data with
51    /// [`write_all`] may result in interleaved output.
52    ///
53    /// [`AsyncWrite`]: AsyncWrite
54    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()
55    ///
56    /// # Examples
57    ///
58    /// ```
59    /// use tokio::io::{self, AsyncWriteExt};
60    ///
61    /// #[tokio::main]
62    /// async fn main() -> io::Result<()> {
63    ///     let mut stderr = io::stderr();
64    ///     stderr.write_all(b"Print some error here.").await?;
65    ///     Ok(())
66    /// }
67    /// ```
68    pub fn stderr() -> Stderr {
69        let std = io::stderr();
70        // SAFETY: The `Read` implementation of `std` does not read from the
71        // buffer it is borrowing and correctly reports the length of the data
72        // written into the buffer.
73        let blocking = unsafe { Blocking::new(std) };
74        Stderr {
75            std: SplitByUtf8BoundaryIfWindows::new(blocking),
76        }
77    }
78}
79
80#[cfg(unix)]
81mod sys {
82    use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd};
83
84    use super::Stderr;
85
86    impl AsRawFd for Stderr {
87        fn as_raw_fd(&self) -> RawFd {
88            std::io::stderr().as_raw_fd()
89        }
90    }
91
92    impl AsFd for Stderr {
93        fn as_fd(&self) -> BorrowedFd<'_> {
94            unsafe { BorrowedFd::borrow_raw(self.as_raw_fd()) }
95        }
96    }
97}
98
99cfg_windows! {
100    use crate::os::windows::io::{AsHandle, BorrowedHandle, AsRawHandle, RawHandle};
101
102    impl AsRawHandle for Stderr {
103        fn as_raw_handle(&self) -> RawHandle {
104            std::io::stderr().as_raw_handle()
105        }
106    }
107
108    impl AsHandle for Stderr {
109        fn as_handle(&self) -> BorrowedHandle<'_> {
110            unsafe { BorrowedHandle::borrow_raw(self.as_raw_handle()) }
111        }
112    }
113}
114
115impl AsyncWrite for Stderr {
116    fn poll_write(
117        mut self: Pin<&mut Self>,
118        cx: &mut Context<'_>,
119        buf: &[u8],
120    ) -> Poll<io::Result<usize>> {
121        Pin::new(&mut self.std).poll_write(cx, buf)
122    }
123
124    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
125        Pin::new(&mut self.std).poll_flush(cx)
126    }
127
128    fn poll_shutdown(
129        mut self: Pin<&mut Self>,
130        cx: &mut Context<'_>,
131    ) -> Poll<Result<(), io::Error>> {
132        Pin::new(&mut self.std).poll_shutdown(cx)
133    }
134}
tokio/io/stderr.rs

tokio/io/
stderr.rs
