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use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
use std::future::Future;
use std::io;
use std::pin::Pin;
use std::task::{Context, Poll};
#[derive(Debug)]
pub(super) struct CopyBuffer {
read_done: bool,
need_flush: bool,
pos: usize,
cap: usize,
amt: u64,
buf: Box<[u8]>,
}
impl CopyBuffer {
pub(super) fn new() -> Self {
Self {
read_done: false,
need_flush: false,
pos: 0,
cap: 0,
amt: 0,
buf: vec![0; super::DEFAULT_BUF_SIZE].into_boxed_slice(),
}
}
pub(super) fn poll_copy<R, W>(
&mut self,
cx: &mut Context<'_>,
mut reader: Pin<&mut R>,
mut writer: Pin<&mut W>,
) -> Poll<io::Result<u64>>
where
R: AsyncRead + ?Sized,
W: AsyncWrite + ?Sized,
{
loop {
// If our buffer is empty, then we need to read some data to
// continue.
if self.pos == self.cap && !self.read_done {
let me = &mut *self;
let mut buf = ReadBuf::new(&mut me.buf);
match reader.as_mut().poll_read(cx, &mut buf) {
Poll::Ready(Ok(_)) => (),
Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
Poll::Pending => {
// Try flushing when the reader has no progress to avoid deadlock
// when the reader depends on buffered writer.
if self.need_flush {
ready!(writer.as_mut().poll_flush(cx))?;
self.need_flush = false;
}
return Poll::Pending;
}
}
let n = buf.filled().len();
if n == 0 {
self.read_done = true;
} else {
self.pos = 0;
self.cap = n;
}
}
// If our buffer has some data, let's write it out!
while self.pos < self.cap {
let me = &mut *self;
let i = ready!(writer.as_mut().poll_write(cx, &me.buf[me.pos..me.cap]))?;
if i == 0 {
return Poll::Ready(Err(io::Error::new(
io::ErrorKind::WriteZero,
"write zero byte into writer",
)));
} else {
self.pos += i;
self.amt += i as u64;
self.need_flush = true;
}
}
// If pos larger than cap, this loop will never stop.
// In particular, user's wrong poll_write implementation returning
// incorrect written length may lead to thread blocking.
debug_assert!(
self.pos <= self.cap,
"writer returned length larger than input slice"
);
// If we've written all the data and we've seen EOF, flush out the
// data and finish the transfer.
if self.pos == self.cap && self.read_done {
ready!(writer.as_mut().poll_flush(cx))?;
return Poll::Ready(Ok(self.amt));
}
}
}
}
/// A future that asynchronously copies the entire contents of a reader into a
/// writer.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
struct Copy<'a, R: ?Sized, W: ?Sized> {
reader: &'a mut R,
writer: &'a mut W,
buf: CopyBuffer,
}
cfg_io_util! {
/// Asynchronously copies the entire contents of a reader into a writer.
///
/// This function returns a future that will continuously read data from
/// `reader` and then write it into `writer` in a streaming fashion until
/// `reader` returns EOF.
///
/// On success, the total number of bytes that were copied from `reader` to
/// `writer` is returned.
///
/// This is an asynchronous version of [`std::io::copy`][std].
///
/// [std]: std::io::copy
///
/// # Errors
///
/// The returned future will return an error immediately if any call to
/// `poll_read` or `poll_write` returns an error.
///
/// # Examples
///
/// ```
/// use tokio::io;
///
/// # async fn dox() -> std::io::Result<()> {
/// let mut reader: &[u8] = b"hello";
/// let mut writer: Vec<u8> = vec![];
///
/// io::copy(&mut reader, &mut writer).await?;
///
/// assert_eq!(&b"hello"[..], &writer[..]);
/// # Ok(())
/// # }
/// ```
pub async fn copy<'a, R, W>(reader: &'a mut R, writer: &'a mut W) -> io::Result<u64>
where
R: AsyncRead + Unpin + ?Sized,
W: AsyncWrite + Unpin + ?Sized,
{
Copy {
reader,
writer,
buf: CopyBuffer::new()
}.await
}
}
impl<R, W> Future for Copy<'_, R, W>
where
R: AsyncRead + Unpin + ?Sized,
W: AsyncWrite + Unpin + ?Sized,
{
type Output = io::Result<u64>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
let me = &mut *self;
me.buf
.poll_copy(cx, Pin::new(&mut *me.reader), Pin::new(&mut *me.writer))
}
}