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use crate::io::AsyncRead;
use crate::stream::Stream;
use bytes::{Bytes, BytesMut};
use pin_project_lite::pin_project;
use std::pin::Pin;
use std::task::{Context, Poll};
pin_project! {
/// Convert an [`AsyncRead`] implementor into a
/// [`Stream`] of Result<[`Bytes`], std::io::Error>.
/// After first error it will stop.
/// Additionally, this stream is fused: after it returns None at some
/// moment, it is guaranteed that further `next()`, `poll_next()` and
/// similar functions will instantly return None.
///
/// This type can be created using the [`reader_stream`] function
///
/// [`AsyncRead`]: crate::io::AsyncRead
/// [`Stream`]: crate::stream::Stream
/// [`Bytes`]: bytes::Bytes
/// [`reader_stream`]: crate::io::reader_stream
#[derive(Debug)]
#[cfg_attr(docsrs, doc(cfg(feature = "stream")))]
#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
pub struct ReaderStream<R> {
// Reader itself.
// None if we had error reading from the `reader` in the past.
#[pin]
reader: Option<R>,
// Working buffer, used to optimize allocations.
// # Capacity behavior
// Initially `buf` is empty. Also it's getting smaller and smaller
// during polls (because its chunks are returned to stream user).
// But when it's capacity reaches 0, it is growed.
buf: BytesMut,
}
}
/// Convert an [`AsyncRead`] implementor into a
/// [`Stream`] of Result<[`Bytes`], std::io::Error>.
///
/// # Example
///
/// ```
/// # #[tokio::main]
/// # async fn main() -> std::io::Result<()> {
/// use tokio::stream::StreamExt;
///
/// let data: &[u8] = b"hello, world!";
/// let mut stream = tokio::io::reader_stream(data);
/// let mut stream_contents = Vec::new();
/// while let Some(chunk) = stream.next().await {
/// stream_contents.extend_from_slice(chunk?.as_ref());
/// }
/// assert_eq!(stream_contents, data);
/// # Ok(())
/// # }
/// ```
///
/// [`AsyncRead`]: crate::io::AsyncRead
/// [`Stream`]: crate::stream::Stream
/// [`Bytes`]: bytes::Bytes
pub fn reader_stream<R>(reader: R) -> ReaderStream<R>
where
R: AsyncRead,
{
ReaderStream {
reader: Some(reader),
buf: BytesMut::new(),
}
}
const CAPACITY: usize = 4096;
impl<R> Stream for ReaderStream<R>
where
R: AsyncRead,
{
type Item = std::io::Result<Bytes>;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
let mut this = self.as_mut().project();
let reader = match this.reader.as_pin_mut() {
Some(r) => r,
None => return Poll::Ready(None),
};
if this.buf.capacity() == 0 {
this.buf.reserve(CAPACITY);
}
match reader.poll_read_buf(cx, &mut this.buf) {
Poll::Pending => Poll::Pending,
Poll::Ready(Err(err)) => {
self.project().reader.set(None);
Poll::Ready(Some(Err(err)))
}
Poll::Ready(Ok(0)) => {
self.project().reader.set(None);
Poll::Ready(None)
}
Poll::Ready(Ok(_)) => {
let chunk = this.buf.split();
Poll::Ready(Some(Ok(chunk.freeze())))
}
}
}
}