diff options
Diffstat (limited to 'third_party/rust/tokio-stream/src/stream_ext/take_while.rs')
-rw-r--r-- | third_party/rust/tokio-stream/src/stream_ext/take_while.rs | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/third_party/rust/tokio-stream/src/stream_ext/take_while.rs b/third_party/rust/tokio-stream/src/stream_ext/take_while.rs new file mode 100644 index 0000000000..5ce4dd98a9 --- /dev/null +++ b/third_party/rust/tokio-stream/src/stream_ext/take_while.rs @@ -0,0 +1,79 @@ +use crate::Stream; + +use core::fmt; +use core::pin::Pin; +use core::task::{Context, Poll}; +use pin_project_lite::pin_project; + +pin_project! { + /// Stream for the [`take_while`](super::StreamExt::take_while) method. + #[must_use = "streams do nothing unless polled"] + pub struct TakeWhile<St, F> { + #[pin] + stream: St, + predicate: F, + done: bool, + } +} + +impl<St, F> fmt::Debug for TakeWhile<St, F> +where + St: fmt::Debug, +{ + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("TakeWhile") + .field("stream", &self.stream) + .field("done", &self.done) + .finish() + } +} + +impl<St, F> TakeWhile<St, F> { + pub(super) fn new(stream: St, predicate: F) -> Self { + Self { + stream, + predicate, + done: false, + } + } +} + +impl<St, F> Stream for TakeWhile<St, F> +where + St: Stream, + F: FnMut(&St::Item) -> bool, +{ + type Item = St::Item; + + fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { + if !*self.as_mut().project().done { + self.as_mut().project().stream.poll_next(cx).map(|ready| { + let ready = ready.and_then(|item| { + if !(self.as_mut().project().predicate)(&item) { + None + } else { + Some(item) + } + }); + + if ready.is_none() { + *self.as_mut().project().done = true; + } + + ready + }) + } else { + Poll::Ready(None) + } + } + + fn size_hint(&self) -> (usize, Option<usize>) { + if self.done { + return (0, Some(0)); + } + + let (_, upper) = self.stream.size_hint(); + + (0, upper) + } +} |