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use futures_core::ready;
use futures_core::task::{Context, Poll};
use futures_io::AsyncWrite;
use futures_sink::Sink;
use pin_project_lite::pin_project;
use std::io;
use std::pin::Pin;
#[derive(Debug)]
struct Block<Item> {
offset: usize,
bytes: Item,
}
pin_project! {
/// Sink for the [`into_sink`](super::AsyncWriteExt::into_sink) method.
#[must_use = "sinks do nothing unless polled"]
#[derive(Debug)]
#[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
pub struct IntoSink<W, Item> {
#[pin]
writer: W,
// An outstanding block for us to push into the underlying writer, along with an offset of how
// far into this block we have written already.
buffer: Option<Block<Item>>,
}
}
impl<W: AsyncWrite, Item: AsRef<[u8]>> IntoSink<W, Item> {
pub(super) fn new(writer: W) -> Self {
Self { writer, buffer: None }
}
/// If we have an outstanding block in `buffer` attempt to push it into the writer, does _not_
/// flush the writer after it succeeds in pushing the block into it.
fn poll_flush_buffer(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Result<(), io::Error>> {
let mut this = self.project();
if let Some(buffer) = this.buffer {
loop {
let bytes = buffer.bytes.as_ref();
let written = ready!(this.writer.as_mut().poll_write(cx, &bytes[buffer.offset..]))?;
buffer.offset += written;
if buffer.offset == bytes.len() {
break;
}
}
}
*this.buffer = None;
Poll::Ready(Ok(()))
}
}
impl<W: AsyncWrite, Item: AsRef<[u8]>> Sink<Item> for IntoSink<W, Item> {
type Error = io::Error;
fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
ready!(self.poll_flush_buffer(cx))?;
Poll::Ready(Ok(()))
}
fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
debug_assert!(self.buffer.is_none());
*self.project().buffer = Some(Block { offset: 0, bytes: item });
Ok(())
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
ready!(self.as_mut().poll_flush_buffer(cx))?;
ready!(self.project().writer.poll_flush(cx))?;
Poll::Ready(Ok(()))
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
ready!(self.as_mut().poll_flush_buffer(cx))?;
ready!(self.project().writer.poll_close(cx))?;
Poll::Ready(Ok(()))
}
}