//! Asynchronous I/O
//!
//! This crate contains the `AsyncRead`, `AsyncWrite`, `AsyncSeek`, and
//! `AsyncBufRead` traits, the asynchronous analogs to
//! `std::io::{Read, Write, Seek, BufRead}`. The primary difference is
//! that these traits integrate with the asynchronous task system.
//!
//! All items of this library are only available when the `std` feature of this
//! library is activated, and it is activated by default.
#![cfg_attr(not(feature = "std"), no_std)]
#![warn(missing_debug_implementations, missing_docs, rust_2018_idioms, unreachable_pub)]
// It cannot be included in the published code because this lints have false positives in the minimum required version.
#![cfg_attr(test, warn(single_use_lifetimes))]
#![doc(test(
no_crate_inject,
attr(
deny(warnings, rust_2018_idioms, single_use_lifetimes),
allow(dead_code, unused_assignments, unused_variables)
)
))]
#![cfg_attr(docsrs, feature(doc_cfg))]
#[cfg(feature = "std")]
mod if_std {
use std::io;
use std::ops::DerefMut;
use std::pin::Pin;
use std::task::{Context, Poll};
// Re-export some types from `std::io` so that users don't have to deal
// with conflicts when `use`ing `futures::io` and `std::io`.
#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
#[doc(no_inline)]
pub use io::{Error, ErrorKind, IoSlice, IoSliceMut, Result, SeekFrom};
/// Read bytes asynchronously.
///
/// This trait is analogous to the `std::io::Read` trait, but integrates
/// with the asynchronous task system. In particular, the `poll_read`
/// method, unlike `Read::read`, will automatically queue the current task
/// for wakeup and return if data is not yet available, rather than blocking
/// the calling thread.
pub trait AsyncRead {
/// Attempt to read from the `AsyncRead` into `buf`.
///
/// On success, returns `Poll::Ready(Ok(num_bytes_read))`.
///
/// If no data is available for reading, the method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes
/// readable or is closed.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<Result<usize>>;
/// Attempt to read from the `AsyncRead` into `bufs` using vectored
/// IO operations.
///
/// This method is similar to `poll_read`, but allows data to be read
/// into multiple buffers using a single operation.
///
/// On success, returns `Poll::Ready(Ok(num_bytes_read))`.
///
/// If no data is available for reading, the method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes
/// readable or is closed.
/// By default, this method delegates to using `poll_read` on the first
/// nonempty buffer in `bufs`, or an empty one if none exists. Objects which
/// support vectored IO should override this method.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_read_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &mut [IoSliceMut<'_>],
) -> Poll<Result<usize>> {
for b in bufs {
if !b.is_empty() {
return self.poll_read(cx, b);
}
}
self.poll_read(cx, &mut [])
}
}
/// Write bytes asynchronously.
///
/// This trait is analogous to the `std::io::Write` trait, but integrates
/// with the asynchronous task system. In particular, the `poll_write`
/// method, unlike `Write::write`, will automatically queue the current task
/// for wakeup and return if the writer cannot take more data, rather than blocking
/// the calling thread.
pub trait AsyncWrite {
/// Attempt to write bytes from `buf` into the object.
///
/// On success, returns `Poll::Ready(Ok(num_bytes_written))`.
///
/// If the object is not ready for writing, the method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes
/// writable or is closed.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
///
/// `poll_write` must try to make progress by flushing the underlying object if
/// that is the only way the underlying object can become writable again.
fn poll_write(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<Result<usize>>;
/// Attempt to write bytes from `bufs` into the object using vectored
/// IO operations.
///
/// This method is similar to `poll_write`, but allows data from multiple buffers to be written
/// using a single operation.
///
/// On success, returns `Poll::Ready(Ok(num_bytes_written))`.
///
/// If the object is not ready for writing, the method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes
/// writable or is closed.
///
/// By default, this method delegates to using `poll_write` on the first
/// nonempty buffer in `bufs`, or an empty one if none exists. Objects which
/// support vectored IO should override this method.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_write_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<Result<usize>> {
for b in bufs {
if !b.is_empty() {
return self.poll_write(cx, b);
}
}
self.poll_write(cx, &[])
}
/// Attempt to flush the object, ensuring that any buffered data reach
/// their destination.
///
/// On success, returns `Poll::Ready(Ok(()))`.
///
/// If flushing cannot immediately complete, this method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object can make
/// progress towards flushing.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
///
/// It only makes sense to do anything here if you actually buffer data.
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>;
/// Attempt to close the object.
///
/// On success, returns `Poll::Ready(Ok(()))`.
///
/// If closing cannot immediately complete, this function returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object can make
/// progress towards closing.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>;
}
/// Seek bytes asynchronously.
///
/// This trait is analogous to the `std::io::Seek` trait, but integrates
/// with the asynchronous task system. In particular, the `poll_seek`
/// method, unlike `Seek::seek`, will automatically queue the current task
/// for wakeup and return if data is not yet available, rather than blocking
/// the calling thread.
pub trait AsyncSeek {
/// Attempt to seek to an offset, in bytes, in a stream.
///
/// A seek beyond the end of a stream is allowed, but behavior is defined
/// by the implementation.
///
/// If the seek operation completed successfully,
/// this method returns the new position from the start of the stream.
/// That position can be used later with [`SeekFrom::Start`].
///
/// # Errors
///
/// Seeking to a negative offset is considered an error.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_seek(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<Result<u64>>;
}
/// Read bytes asynchronously.
///
/// This trait is analogous to the `std::io::BufRead` trait, but integrates
/// with the asynchronous task system. In particular, the `poll_fill_buf`
/// method, unlike `BufRead::fill_buf`, will automatically queue the current task
/// for wakeup and return if data is not yet available, rather than blocking
/// the calling thread.
pub trait AsyncBufRead: AsyncRead {
/// Attempt to return the contents of the internal buffer, filling it with more data
/// from the inner reader if it is empty.
///
/// On success, returns `Poll::Ready(Ok(buf))`.
///
/// If no data is available for reading, the method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes
/// readable or is closed.
///
/// This function is a lower-level call. It needs to be paired with the
/// [`consume`] method to function properly. When calling this
/// method, none of the contents will be "read" in the sense that later
/// calling [`poll_read`] may return the same contents. As such, [`consume`] must
/// be called with the number of bytes that are consumed from this buffer to
/// ensure that the bytes are never returned twice.
///
/// [`poll_read`]: AsyncRead::poll_read
/// [`consume`]: AsyncBufRead::consume
///
/// An empty buffer returned indicates that the stream has reached EOF.
///
/// # Implementation
///
/// This function may not return errors of kind `WouldBlock` or
/// `Interrupted`. Implementations must convert `WouldBlock` into
/// `Poll::Pending` and either internally retry or convert
/// `Interrupted` into another error kind.
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>>;
/// Tells this buffer that `amt` bytes have been consumed from the buffer,
/// so they should no longer be returned in calls to [`poll_read`].
///
/// This function is a lower-level call. It needs to be paired with the
/// [`poll_fill_buf`] method to function properly. This function does
/// not perform any I/O, it simply informs this object that some amount of
/// its buffer, returned from [`poll_fill_buf`], has been consumed and should
/// no longer be returned. As such, this function may do odd things if
/// [`poll_fill_buf`] isn't called before calling it.
///
/// The `amt` must be `<=` the number of bytes in the buffer returned by
/// [`poll_fill_buf`].
///
/// [`poll_read`]: AsyncRead::poll_read
/// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf
fn consume(self: Pin<&mut Self>, amt: usize);
}
macro_rules! deref_async_read {
() => {
fn poll_read(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<Result<usize>> {
Pin::new(&mut **self).poll_read(cx, buf)
}
fn poll_read_vectored(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &mut [IoSliceMut<'_>],
) -> Poll<Result<usize>> {
Pin::new(&mut **self).poll_read_vectored(cx, bufs)
}
};
}
impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for Box<T> {
deref_async_read!();
}
impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for &mut T {
deref_async_read!();
}
impl<P> AsyncRead for Pin<P>
where
P: DerefMut + Unpin,
P::Target: AsyncRead,
{
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<Result<usize>> {
self.get_mut().as_mut().poll_read(cx, buf)
}
fn poll_read_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &mut [IoSliceMut<'_>],
) -> Poll<Result<usize>> {
self.get_mut().as_mut().poll_read_vectored(cx, bufs)
}
}
macro_rules! delegate_async_read_to_stdio {
() => {
fn poll_read(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
buf: &mut [u8],
) -> Poll<Result<usize>> {
Poll::Ready(io::Read::read(&mut *self, buf))
}
fn poll_read_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &mut [IoSliceMut<'_>],
) -> Poll<Result<usize>> {
Poll::Ready(io::Read::read_vectored(&mut *self, bufs))
}
};
}
impl AsyncRead for &[u8] {
delegate_async_read_to_stdio!();
}
macro_rules! deref_async_write {
() => {
fn poll_write(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<Result<usize>> {
Pin::new(&mut **self).poll_write(cx, buf)
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<Result<usize>> {
Pin::new(&mut **self).poll_write_vectored(cx, bufs)
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
Pin::new(&mut **self).poll_flush(cx)
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
Pin::new(&mut **self).poll_close(cx)
}
};
}
impl<T: ?Sized + AsyncWrite + Unpin> AsyncWrite for Box<T> {
deref_async_write!();
}
impl<T: ?Sized + AsyncWrite + Unpin> AsyncWrite for &mut T {
deref_async_write!();
}
impl<P> AsyncWrite for Pin<P>
where
P: DerefMut + Unpin,
P::Target: AsyncWrite,
{
fn poll_write(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<Result<usize>> {
self.get_mut().as_mut().poll_write(cx, buf)
}
fn poll_write_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<Result<usize>> {
self.get_mut().as_mut().poll_write_vectored(cx, bufs)
}
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
self.get_mut().as_mut().poll_flush(cx)
}
fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
self.get_mut().as_mut().poll_close(cx)
}
}
macro_rules! delegate_async_write_to_stdio {
() => {
fn poll_write(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
buf: &[u8],
) -> Poll<Result<usize>> {
Poll::Ready(io::Write::write(&mut *self, buf))
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<Result<usize>> {
Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
}
fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<()>> {
Poll::Ready(io::Write::flush(&mut *self))
}
fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>> {
self.poll_flush(cx)
}
};
}
impl AsyncWrite for Vec<u8> {
delegate_async_write_to_stdio!();
}
macro_rules! deref_async_seek {
() => {
fn poll_seek(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<Result<u64>> {
Pin::new(&mut **self).poll_seek(cx, pos)
}
};
}
impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for Box<T> {
deref_async_seek!();
}
impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for &mut T {
deref_async_seek!();
}
impl<P> AsyncSeek for Pin<P>
where
P: DerefMut + Unpin,
P::Target: AsyncSeek,
{
fn poll_seek(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<Result<u64>> {
self.get_mut().as_mut().poll_seek(cx, pos)
}
}
macro_rules! deref_async_buf_read {
() => {
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>> {
Pin::new(&mut **self.get_mut()).poll_fill_buf(cx)
}
fn consume(mut self: Pin<&mut Self>, amt: usize) {
Pin::new(&mut **self).consume(amt)
}
};
}
impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for Box<T> {
deref_async_buf_read!();
}
impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for &mut T {
deref_async_buf_read!();
}
impl<P> AsyncBufRead for Pin<P>
where
P: DerefMut + Unpin,
P::Target: AsyncBufRead,
{
fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<&[u8]>> {
self.get_mut().as_mut().poll_fill_buf(cx)
}
fn consume(self: Pin<&mut Self>, amt: usize) {
self.get_mut().as_mut().consume(amt)
}
}
macro_rules! delegate_async_buf_read_to_stdio {
() => {
fn poll_fill_buf(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<&[u8]>> {
Poll::Ready(io::BufRead::fill_buf(self.get_mut()))
}
fn consume(self: Pin<&mut Self>, amt: usize) {
io::BufRead::consume(self.get_mut(), amt)
}
};
}
impl AsyncBufRead for &[u8] {
delegate_async_buf_read_to_stdio!();
}
}
#[cfg(feature = "std")]
pub use self::if_std::*;