# write_all.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.4.0/src/io/util/write_all.rs`.
Keywords: rust, rustlang, rust-lang

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    use crate::io::AsyncWrite;

    use pin_project_lite::pin_project;
    use std::future::Future;
    use std::io;
    use std::marker::PhantomPinned;
    use std::mem;
    use std::pin::Pin;
    use std::task::{Context, Poll};

    pin_project! {
        #[derive(Debug)]
        #[must_use = "futures do nothing unless you `.await` or poll them"]
        pub struct WriteAll<'a, W: ?Sized> {
            writer: &'a mut W,
            buf: &'a [u8],
            // Make this future `!Unpin` for compatibility with async trait methods.
            #[pin]
            _pin: PhantomPinned,
        }
    }

    pub(crate) fn write_all<'a, W>(writer: &'a mut W, buf: &'a [u8]) -> WriteAll<'a, W>
    where
        W: AsyncWrite + Unpin + ?Sized,
    {
        WriteAll {
            writer,
            buf,
            _pin: PhantomPinned,
        }
    }

    impl<W> Future for WriteAll<'_, W>
    where
        W: AsyncWrite + Unpin + ?Sized,
    {
        type Output = io::Result<()>;

        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
            let me = self.project();
            while !me.buf.is_empty() {
                let n = ready!(Pin::new(&mut *me.writer).poll_write(cx, me.buf))?;
                {
                    let (_, rest) = mem::replace(&mut *me.buf, &[]).split_at(n);
                    *me.buf = rest;
                }
                if n == 0 {
                    return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
                }
            }

            Poll::Ready(Ok(()))
        }
    }