tokio/tokio-futures/src/io/write.rs

use std::future::Future;
use std::io;
use std::pin::Pin;
use std::task::{self, Poll};
use tokio_io::AsyncWrite;

/// A future used to write data.
#[derive(Debug)]
pub struct Write<'a, T: ?Sized> {
    writer: &'a mut T,
    buf: &'a [u8],
}

// Pinning is never projected to fields
impl<'a, T: ?Sized> Unpin for Write<'a, T> {}

impl<'a, T: AsyncWrite + ?Sized> Write<'a, T> {
    pub(super) fn new(writer: &'a mut T, buf: &'a [u8]) -> Write<'a, T> {
        Write { writer, buf }
    }
}

impl<'a, T: AsyncWrite + ?Sized> Future for Write<'a, T> {
    type Output = io::Result<usize>;

    fn poll(mut self: Pin<&mut Self>, _context: &mut task::Context<'_>) -> Poll<io::Result<usize>> {
        use crate::compat::forward::convert_poll;

        let this = &mut *self;
        convert_poll(this.writer.poll_write(this.buf))
    }
}