1 use crate::future::{IntoFuture, TryFutureExt}; 2 use crate::stream::{Fuse, FuturesOrdered, IntoStream, StreamExt}; 3 use core::pin::Pin; 4 use futures_core::future::TryFuture; 5 use futures_core::stream::{Stream, TryStream}; 6 use futures_core::task::{Context, Poll}; 7 #[cfg(feature = "sink")] 8 use futures_sink::Sink; 9 use pin_project_lite::pin_project; 10 11 pin_project! { 12 /// Stream for the [`try_buffered`](super::TryStreamExt::try_buffered) method. 13 #[derive(Debug)] 14 #[must_use = "streams do nothing unless polled"] 15 pub struct TryBuffered<St> 16 where 17 St: TryStream, 18 St::Ok: TryFuture, 19 { 20 #[pin] 21 stream: Fuse<IntoStream<St>>, 22 in_progress_queue: FuturesOrdered<IntoFuture<St::Ok>>, 23 max: usize, 24 } 25 } 26 27 impl<St> TryBuffered<St> 28 where 29 St: TryStream, 30 St::Ok: TryFuture, 31 { new(stream: St, n: usize) -> Self32 pub(super) fn new(stream: St, n: usize) -> Self { 33 Self { 34 stream: IntoStream::new(stream).fuse(), 35 in_progress_queue: FuturesOrdered::new(), 36 max: n, 37 } 38 } 39 40 delegate_access_inner!(stream, St, (. .)); 41 } 42 43 impl<St> Stream for TryBuffered<St> 44 where 45 St: TryStream, 46 St::Ok: TryFuture<Error = St::Error>, 47 { 48 type Item = Result<<St::Ok as TryFuture>::Ok, St::Error>; 49 poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>50 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { 51 let mut this = self.project(); 52 53 // First up, try to spawn off as many futures as possible by filling up 54 // our queue of futures. Propagate errors from the stream immediately. 55 while this.in_progress_queue.len() < *this.max { 56 match this.stream.as_mut().poll_next(cx)? { 57 Poll::Ready(Some(fut)) => this.in_progress_queue.push_back(fut.into_future()), 58 Poll::Ready(None) | Poll::Pending => break, 59 } 60 } 61 62 // Attempt to pull the next value from the in_progress_queue 63 match this.in_progress_queue.poll_next_unpin(cx) { 64 x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x, 65 Poll::Ready(None) => {} 66 } 67 68 // If more values are still coming from the stream, we're not done yet 69 if this.stream.is_done() { 70 Poll::Ready(None) 71 } else { 72 Poll::Pending 73 } 74 } 75 } 76 77 // Forwarding impl of Sink from the underlying stream 78 #[cfg(feature = "sink")] 79 impl<S, Item, E> Sink<Item> for TryBuffered<S> 80 where 81 S: TryStream + Sink<Item, Error = E>, 82 S::Ok: TryFuture<Error = E>, 83 { 84 type Error = E; 85 86 delegate_sink!(stream, Item); 87 } 88