| use core::fmt; |
| use core::pin::Pin; |
| use futures_core::future::TryFuture; |
| use futures_core::ready; |
| use futures_core::stream::{FusedStream, Stream, TryStream}; |
| use futures_core::task::{Context, Poll}; |
| #[cfg(feature = "sink")] |
| use futures_sink::Sink; |
| use pin_project_lite::pin_project; |
| |
| pin_project! { |
| /// Stream for the [`try_take_while`](super::TryStreamExt::try_take_while) |
| /// method. |
| #[must_use = "streams do nothing unless polled"] |
| pub struct TryTakeWhile<St, Fut, F> |
| where |
| St: TryStream, |
| { |
| #[pin] |
| stream: St, |
| f: F, |
| #[pin] |
| pending_fut: Option<Fut>, |
| pending_item: Option<St::Ok>, |
| done_taking: bool, |
| } |
| } |
| |
| impl<St, Fut, F> fmt::Debug for TryTakeWhile<St, Fut, F> |
| where |
| St: TryStream + fmt::Debug, |
| St::Ok: fmt::Debug, |
| Fut: fmt::Debug, |
| { |
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| f.debug_struct("TryTakeWhile") |
| .field("stream", &self.stream) |
| .field("pending_fut", &self.pending_fut) |
| .field("pending_item", &self.pending_item) |
| .field("done_taking", &self.done_taking) |
| .finish() |
| } |
| } |
| |
| impl<St, Fut, F> TryTakeWhile<St, Fut, F> |
| where |
| St: TryStream, |
| F: FnMut(&St::Ok) -> Fut, |
| Fut: TryFuture<Ok = bool, Error = St::Error>, |
| { |
| pub(super) fn new(stream: St, f: F) -> Self { |
| Self { stream, f, pending_fut: None, pending_item: None, done_taking: false } |
| } |
| |
| delegate_access_inner!(stream, St, ()); |
| } |
| |
| impl<St, Fut, F> Stream for TryTakeWhile<St, Fut, F> |
| where |
| St: TryStream, |
| F: FnMut(&St::Ok) -> Fut, |
| Fut: TryFuture<Ok = bool, Error = St::Error>, |
| { |
| type Item = Result<St::Ok, St::Error>; |
| |
| fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { |
| let mut this = self.project(); |
| |
| if *this.done_taking { |
| return Poll::Ready(None); |
| } |
| |
| Poll::Ready(loop { |
| if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() { |
| let res = ready!(fut.try_poll(cx)); |
| this.pending_fut.set(None); |
| let take = res?; |
| let item = this.pending_item.take(); |
| if take { |
| break item.map(Ok); |
| } else { |
| *this.done_taking = true; |
| break None; |
| } |
| } else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) { |
| this.pending_fut.set(Some((this.f)(&item))); |
| *this.pending_item = Some(item); |
| } else { |
| break None; |
| } |
| }) |
| } |
| |
| fn size_hint(&self) -> (usize, Option<usize>) { |
| if self.done_taking { |
| return (0, Some(0)); |
| } |
| |
| let pending_len = usize::from(self.pending_item.is_some()); |
| let (_, upper) = self.stream.size_hint(); |
| let upper = match upper { |
| Some(x) => x.checked_add(pending_len), |
| None => None, |
| }; |
| (0, upper) // can't know a lower bound, due to the predicate |
| } |
| } |
| |
| impl<St, Fut, F> FusedStream for TryTakeWhile<St, Fut, F> |
| where |
| St: TryStream + FusedStream, |
| F: FnMut(&St::Ok) -> Fut, |
| Fut: TryFuture<Ok = bool, Error = St::Error>, |
| { |
| fn is_terminated(&self) -> bool { |
| self.done_taking || self.pending_item.is_none() && self.stream.is_terminated() |
| } |
| } |
| |
| // Forwarding impl of Sink from the underlying stream |
| #[cfg(feature = "sink")] |
| impl<S, Fut, F, Item, E> Sink<Item> for TryTakeWhile<S, Fut, F> |
| where |
| S: TryStream + Sink<Item, Error = E>, |
| { |
| type Error = E; |
| |
| delegate_sink!(stream, Item); |
| } |