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use core::mem;
use core::marker::PhantomData;
use {IntoFuture, Future, Poll, Async, StartSend, AsyncSink};
use sink::Sink;
use stream::Stream;
/// Sink for the `Sink::with` combinator, chaining a computation to run *prior*
/// to pushing a value into the underlying sink.
#[derive(Clone, Debug)]
#[must_use = "sinks do nothing unless polled"]
pub struct With<S, U, F, Fut>
where S: Sink,
F: FnMut(U) -> Fut,
Fut: IntoFuture,
{
sink: S,
f: F,
state: State<Fut::Future, S::SinkItem>,
_phantom: PhantomData<fn(U)>,
}
#[derive(Clone, Debug)]
enum State<Fut, T> {
Empty,
Process(Fut),
Buffered(T),
}
impl<Fut, T> State<Fut, T> {
fn is_empty(&self) -> bool {
if let State::Empty = *self {
true
} else {
false
}
}
}
pub fn new<S, U, F, Fut>(sink: S, f: F) -> With<S, U, F, Fut>
where S: Sink,
F: FnMut(U) -> Fut,
Fut: IntoFuture<Item = S::SinkItem>,
Fut::Error: From<S::SinkError>,
{
With {
state: State::Empty,
sink: sink,
f: f,
_phantom: PhantomData,
}
}
// Forwarding impl of Stream from the underlying sink
impl<S, U, F, Fut> Stream for With<S, U, F, Fut>
where S: Stream + Sink,
F: FnMut(U) -> Fut,
Fut: IntoFuture
{
type Item = S::Item;
type Error = S::Error;
fn poll(&mut self) -> Poll<Option<S::Item>, S::Error> {
self.sink.poll()
}
}
impl<S, U, F, Fut> With<S, U, F, Fut>
where S: Sink,
F: FnMut(U) -> Fut,
Fut: IntoFuture<Item = S::SinkItem>,
Fut::Error: From<S::SinkError>,
{
/// Get a shared reference to the inner sink.
pub fn get_ref(&self) -> &S {
&self.sink
}
/// Get a mutable reference to the inner sink.
pub fn get_mut(&mut self) -> &mut S {
&mut self.sink
}
/// Consumes this combinator, returning the underlying sink.
///
/// Note that this may discard intermediate state of this combinator, so
/// care should be taken to avoid losing resources when this is called.
pub fn into_inner(self) -> S {
self.sink
}
fn poll(&mut self) -> Poll<(), Fut::Error> {
loop {
match mem::replace(&mut self.state, State::Empty) {
State::Empty => break,
State::Process(mut fut) => {
match fut.poll()? {
Async::Ready(item) => {
self.state = State::Buffered(item);
}
Async::NotReady => {
self.state = State::Process(fut);
break
}
}
}
State::Buffered(item) => {
if let AsyncSink::NotReady(item) = self.sink.start_send(item)? {
self.state = State::Buffered(item);
break
}
}
}
}
if self.state.is_empty() {
Ok(Async::Ready(()))
} else {
Ok(Async::NotReady)
}
}
}
impl<S, U, F, Fut> Sink for With<S, U, F, Fut>
where S: Sink,
F: FnMut(U) -> Fut,
Fut: IntoFuture<Item = S::SinkItem>,
Fut::Error: From<S::SinkError>,
{
type SinkItem = U;
type SinkError = Fut::Error;
fn start_send(&mut self, item: Self::SinkItem) -> StartSend<Self::SinkItem, Fut::Error> {
if self.poll()?.is_not_ready() {
return Ok(AsyncSink::NotReady(item))
}
self.state = State::Process((self.f)(item).into_future());
Ok(AsyncSink::Ready)
}
fn poll_complete(&mut self) -> Poll<(), Fut::Error> {
// poll ourselves first, to push data downward
let me_ready = self.poll()?;
// always propagate `poll_complete` downward to attempt to make progress
try_ready!(self.sink.poll_complete());
Ok(me_ready)
}
fn close(&mut self) -> Poll<(), Fut::Error> {
try_ready!(self.poll());
Ok(self.sink.close()?)
}
}
|
