use std::io::{self, IoSlice};
use std::ops::DerefMut;
use std::pin::Pin;
use std::task::{Context, Poll};
/// Writes bytes asynchronously.
///
/// The trait inherits from [`std::io::Write`] and indicates that an I/O object is
/// **nonblocking**. All non-blocking I/O objects must return an error when
/// bytes cannot be written instead of blocking the current thread.
///
/// Specifically, this means that the [`poll_write`] function will return one of
/// the following:
///
/// * `Poll::Ready(Ok(n))` means that `n` bytes of data was immediately
/// written.
///
/// * `Poll::Pending` means that no data was written from the buffer
/// provided. The I/O object is not currently writable but may become writable
/// in the future. Most importantly, **the current future's task is scheduled
/// to get unparked when the object is writable**. This means that like
/// `Future::poll` you'll receive a notification when the I/O object is
/// writable again.
///
/// * `Poll::Ready(Err(e))` for other errors are standard I/O errors coming from the
/// underlying object.
///
/// This trait importantly means that the [`write`][stdwrite] method only works in
/// the context of a future's task. The object may panic if used outside of a task.
///
/// Note that this trait also represents that the [`Write::flush`][stdflush] method
/// works very similarly to the `write` method, notably that `Ok(())` means that the
/// writer has successfully been flushed, a "would block" error means that the
/// current task is ready to receive a notification when flushing can make more
/// progress, and otherwise normal errors can happen as well.
///
/// Utilities for working with `AsyncWrite` values are provided by
/// [`AsyncWriteExt`].
///
/// [`std::io::Write`]: std::io::Write
/// [`poll_write`]: AsyncWrite::poll_write()
/// [stdwrite]: std::io::Write::write()
/// [stdflush]: std::io::Write::flush()
/// [`AsyncWriteExt`]: crate::io::AsyncWriteExt
pub trait AsyncWrite {
/// Attempt to write bytes from `buf` into the object.
///
/// On success, returns `Poll::Ready(Ok(num_bytes_written))`. If successful,
/// then it must be guaranteed that `n <= buf.len()`. A return value of `0`
/// typically means that the underlying object is no longer able to accept
/// bytes and will likely not be able to in the future as well, or that the
/// buffer provided is empty.
///
/// If the object is not ready for writing, the method returns
/// `Poll::Pending` and arranges for the current task (via
/// `cx.waker()`) to receive a notification when the object becomes
/// writable or is closed.
fn poll_write(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<Result<usize, io::Error>>;
/// Attempts 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()`) to receive a notification when the object can make
/// progress towards flushing.
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>>;
/// Initiates or attempts to shut down this writer, returning success when
/// the I/O connection has completely shut down.
///
/// This method is intended to be used for asynchronous shutdown of I/O
/// connections. For example this is suitable for implementing shutdown of a
/// TLS connection or calling `TcpStream::shutdown` on a proxied connection.
/// Protocols sometimes need to flush out final pieces of data or otherwise
/// perform a graceful shutdown handshake, reading/writing more data as
/// appropriate. This method is the hook for such protocols to implement the
/// graceful shutdown logic.
///
/// This `shutdown` method is required by implementers of the
/// `AsyncWrite` trait. Wrappers typically just want to proxy this call
/// through to the wrapped type, and base types will typically implement
/// shutdown logic here or just return `Ok(().into())`. Note that if you're
/// wrapping an underlying `AsyncWrite` a call to `shutdown` implies that
/// transitively the entire stream has been shut down. After your wrapper's
/// shutdown logic has been executed you should shut down the underlying
/// stream.
///
/// Invocation of a `shutdown` implies an invocation of `flush`. Once this
/// method returns `Ready` it implies that a flush successfully happened
/// before the shutdown happened. That is, callers don't need to call
/// `flush` before calling `shutdown`. They can rely that by calling
/// `shutdown` any pending buffered data will be written out.
///
/// # Return value
///
/// This function returns a `Poll<io::Result<()>>` classified as such:
///
/// * `Poll::Ready(Ok(()))` - indicates that the connection was
/// successfully shut down and is now safe to deallocate/drop/close
/// resources associated with it. This method means that the current task
/// will no longer receive any notifications due to this method and the
/// I/O object itself is likely no longer usable.
///
/// * `Poll::Pending` - indicates that shutdown is initiated but could
/// not complete just yet. This may mean that more I/O needs to happen to
/// continue this shutdown operation. The current task is scheduled to
/// receive a notification when it's otherwise ready to continue the
/// shutdown operation. When woken up this method should be called again.
///
/// * `Poll::Ready(Err(e))` - indicates a fatal error has happened with shutdown,
/// indicating that the shutdown operation did not complete successfully.
/// This typically means that the I/O object is no longer usable.
///
/// # Errors
///
/// This function can return normal I/O errors through `Err`, described
/// above. Additionally this method may also render the underlying
/// `Write::write` method no longer usable (e.g. will return errors in the
/// future). It's recommended that once `shutdown` is called the
/// `write` method is no longer called.
///
/// # Panics
///
/// This function will panic if not called within the context of a future's
/// task.
fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>>;
/// Like [`poll_write`], except that it writes from a slice of buffers.
///
/// Data is copied from each buffer in order, with the final buffer
/// read from possibly being only partially consumed. This method must
/// behave as a call to [`write`] with the buffers concatenated would.
///
/// The default implementation calls [`poll_write`] with either the first nonempty
/// buffer provided, or an empty one if none exists.
///
/// 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()`) to receive a notification when the object becomes
/// writable or is closed.
///
/// # Note
///
/// This should be implemented as a single "atomic" write action. If any
/// data has been partially written, it is wrong to return an error or
/// pending.
///
/// [`poll_write`]: AsyncWrite::poll_write
fn poll_write_vectored(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<Result<usize, io::Error>> {
let buf = bufs
.iter()
.find(|b| !b.is_empty())
.map_or(&[][..], |b| &**b);
self.poll_write(cx, buf)
}
/// Determines if this writer has an efficient [`poll_write_vectored`]
/// implementation.
///
/// If a writer does not override the default [`poll_write_vectored`]
/// implementation, code using it may want to avoid the method all together
/// and coalesce writes into a single buffer for higher performance.
///
/// The default implementation returns `false`.
///
/// [`poll_write_vectored`]: AsyncWrite::poll_write_vectored
fn is_write_vectored(&self) -> bool {
false
}
}
macro_rules! deref_async_write {
() => {
fn poll_write(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::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<io::Result<usize>> {
Pin::new(&mut **self).poll_write_vectored(cx, bufs)
}
fn is_write_vectored(&self) -> bool {
(**self).is_write_vectored()
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
Pin::new(&mut **self).poll_flush(cx)
}
fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
Pin::new(&mut **self).poll_shutdown(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<io::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<io::Result<usize>> {
self.get_mut().as_mut().poll_write_vectored(cx, bufs)
}
fn is_write_vectored(&self) -> bool {
(**self).is_write_vectored()
}
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
self.get_mut().as_mut().poll_flush(cx)
}
fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
self.get_mut().as_mut().poll_shutdown(cx)
}
}
impl AsyncWrite for Vec<u8> {
fn poll_write(
self: Pin<&mut Self>,
_cx: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
self.get_mut().extend_from_slice(buf);
Poll::Ready(Ok(buf.len()))
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
}
fn is_write_vectored(&self) -> bool {
true
}
fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
Poll::Ready(Ok(()))
}
fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
Poll::Ready(Ok(()))
}
}
impl AsyncWrite for io::Cursor<&mut [u8]> {
fn poll_write(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write(&mut *self, buf))
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
}
fn is_write_vectored(&self) -> bool {
true
}
fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
Poll::Ready(io::Write::flush(&mut *self))
}
fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
self.poll_flush(cx)
}
}
impl AsyncWrite for io::Cursor<&mut Vec<u8>> {
fn poll_write(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write(&mut *self, buf))
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
}
fn is_write_vectored(&self) -> bool {
true
}
fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
Poll::Ready(io::Write::flush(&mut *self))
}
fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
self.poll_flush(cx)
}
}
impl AsyncWrite for io::Cursor<Vec<u8>> {
fn poll_write(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write(&mut *self, buf))
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
}
fn is_write_vectored(&self) -> bool {
true
}
fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
Poll::Ready(io::Write::flush(&mut *self))
}
fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
self.poll_flush(cx)
}
}
impl AsyncWrite for io::Cursor<Box<[u8]>> {
fn poll_write(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
buf: &[u8],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write(&mut *self, buf))
}
fn poll_write_vectored(
mut self: Pin<&mut Self>,
_: &mut Context<'_>,
bufs: &[IoSlice<'_>],
) -> Poll<io::Result<usize>> {
Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
}
fn is_write_vectored(&self) -> bool {
true
}
fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
Poll::Ready(io::Write::flush(&mut *self))
}
fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
self.poll_flush(cx)
}
}
