blob: 96e657663bfef38b1335d4be3663fddf1d9e343d [file] [log] [blame]
use {Async, Poll};
use stream::{Stream, Fuse};
/// A `Stream` that implements a `peek` method.
///
/// The `peek` method can be used to retrieve a reference
/// to the next `Stream::Item` if available. A subsequent
/// call to `poll` will return the owned item.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Peekable<S: Stream> {
stream: Fuse<S>,
peeked: Option<S::Item>,
}
pub fn new<S: Stream>(stream: S) -> Peekable<S> {
Peekable {
stream: stream.fuse(),
peeked: None
}
}
// Forwarding impl of Sink from the underlying stream
impl<S> ::sink::Sink for Peekable<S>
where S: ::sink::Sink + Stream
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
fn start_send(&mut self, item: S::SinkItem) -> ::StartSend<S::SinkItem, S::SinkError> {
self.stream.start_send(item)
}
fn poll_complete(&mut self) -> Poll<(), S::SinkError> {
self.stream.poll_complete()
}
fn close(&mut self) -> Poll<(), S::SinkError> {
self.stream.close()
}
}
impl<S: Stream> Stream for Peekable<S> {
type Item = S::Item;
type Error = S::Error;
fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
if let Some(item) = self.peeked.take() {
return Ok(Async::Ready(Some(item)))
}
self.stream.poll()
}
}
impl<S: Stream> Peekable<S> {
/// Peek retrieves a reference to the next item in the stream.
///
/// This method polls the underlying stream and return either a reference
/// to the next item if the stream is ready or passes through any errors.
pub fn peek(&mut self) -> Poll<Option<&S::Item>, S::Error> {
if self.peeked.is_some() {
return Ok(Async::Ready(self.peeked.as_ref()))
}
match try_ready!(self.poll()) {
None => Ok(Async::Ready(None)),
Some(item) => {
self.peeked = Some(item);
Ok(Async::Ready(self.peeked.as_ref()))
}
}
}
}