1 use crate::stream::{Fuse, FuturesOrdered, StreamExt, IntoStream}; 2 use crate::future::{IntoFuture, TryFutureExt}; 3 use futures_core::future::TryFuture; 4 use futures_core::stream::{Stream, TryStream}; 5 use futures_core::task::{Context, Poll}; 6 #[cfg(feature = "sink")] 7 use futures_sink::Sink; 8 use pin_project_lite::pin_project; 9 use core::pin::Pin; 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( 51 self: Pin<&mut Self>, 52 cx: &mut Context<'_>, 53 ) -> Poll<Option<Self::Item>> { 54 let mut this = self.project(); 55 56 // First up, try to spawn off as many futures as possible by filling up 57 // our queue of futures. Propagate errors from the stream immediately. 58 while this.in_progress_queue.len() < *this.max { 59 match this.stream.as_mut().poll_next(cx)? { 60 Poll::Ready(Some(fut)) => this.in_progress_queue.push(fut.into_future()), 61 Poll::Ready(None) | Poll::Pending => break, 62 } 63 } 64 65 // Attempt to pull the next value from the in_progress_queue 66 match this.in_progress_queue.poll_next_unpin(cx) { 67 x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x, 68 Poll::Ready(None) => {} 69 } 70 71 // If more values are still coming from the stream, we're not done yet 72 if this.stream.is_done() { 73 Poll::Ready(None) 74 } else { 75 Poll::Pending 76 } 77 } 78 } 79 80 // Forwarding impl of Sink from the underlying stream 81 #[cfg(feature = "sink")] 82 impl<S, Item, E> Sink<Item> for TryBuffered<S> 83 where 84 S: TryStream + Sink<Item, Error = E>, 85 S::Ok: TryFuture<Error = E>, 86 { 87 type Error = E; 88 89 delegate_sink!(stream, Item); 90 } 91