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use core::pin::Pin;
use futures_core::future::{FusedFuture, 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! {
#[project = TryFlattenProj]
#[derive(Debug)]
pub enum TryFlatten<Fut1, Fut2> {
First { #[pin] f: Fut1 },
Second { #[pin] f: Fut2 },
Empty,
}
}
impl<Fut1, Fut2> TryFlatten<Fut1, Fut2> {
pub(crate) fn new(future: Fut1) -> Self {
Self::First { f: future }
}
}
impl<Fut> FusedFuture for TryFlatten<Fut, Fut::Ok>
where
Fut: TryFuture,
Fut::Ok: TryFuture<Error = Fut::Error>,
{
fn is_terminated(&self) -> bool {
match self {
Self::Empty => true,
_ => false,
}
}
}
impl<Fut> Future for TryFlatten<Fut, Fut::Ok>
where
Fut: TryFuture,
Fut::Ok: TryFuture<Error = Fut::Error>,
{
type Output = Result<<Fut::Ok as TryFuture>::Ok, Fut::Error>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
Poll::Ready(loop {
match self.as_mut().project() {
TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
Ok(f) => self.set(Self::Second { f }),
Err(e) => {
self.set(Self::Empty);
break Err(e);
}
},
TryFlattenProj::Second { f } => {
let output = ready!(f.try_poll(cx));
self.set(Self::Empty);
break output;
}
TryFlattenProj::Empty => panic!("TryFlatten polled after completion"),
}
})
}
}
impl<Fut> FusedStream for TryFlatten<Fut, Fut::Ok>
where
Fut: TryFuture,
Fut::Ok: TryStream<Error = Fut::Error>,
{
fn is_terminated(&self) -> bool {
match self {
Self::Empty => true,
_ => false,
}
}
}
impl<Fut> Stream for TryFlatten<Fut, Fut::Ok>
where
Fut: TryFuture,
Fut::Ok: TryStream<Error = Fut::Error>,
{
type Item = Result<<Fut::Ok as TryStream>::Ok, Fut::Error>;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
Poll::Ready(loop {
match self.as_mut().project() {
TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
Ok(f) => self.set(Self::Second { f }),
Err(e) => {
self.set(Self::Empty);
break Some(Err(e));
}
},
TryFlattenProj::Second { f } => {
let output = ready!(f.try_poll_next(cx));
if output.is_none() {
self.set(Self::Empty);
}
break output;
}
TryFlattenProj::Empty => break None,
}
})
}
}
#[cfg(feature = "sink")]
impl<Fut, Item> Sink<Item> for TryFlatten<Fut, Fut::Ok>
where
Fut: TryFuture,
Fut::Ok: Sink<Item, Error = Fut::Error>,
{
type Error = Fut::Error;
fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
Poll::Ready(loop {
match self.as_mut().project() {
TryFlattenProj::First { f } => match ready!(f.try_poll(cx)) {
Ok(f) => self.set(Self::Second { f }),
Err(e) => {
self.set(Self::Empty);
break Err(e);
}
},
TryFlattenProj::Second { f } => {
break ready!(f.poll_ready(cx));
}
TryFlattenProj::Empty => panic!("poll_ready called after eof"),
}
})
}
fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
match self.project() {
TryFlattenProj::First { .. } => panic!("poll_ready not called first"),
TryFlattenProj::Second { f } => f.start_send(item),
TryFlattenProj::Empty => panic!("start_send called after eof"),
}
}
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
match self.project() {
TryFlattenProj::First { .. } => Poll::Ready(Ok(())),
TryFlattenProj::Second { f } => f.poll_flush(cx),
TryFlattenProj::Empty => panic!("poll_flush called after eof"),
}
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
let res = match self.as_mut().project() {
TryFlattenProj::Second { f } => f.poll_close(cx),
_ => Poll::Ready(Ok(())),
};
if res.is_ready() {
self.set(Self::Empty);
}
res
}
}