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use crate::stream::{PollRecv, Stream};
use pin_project::pin_project;
use std::pin::Pin;
use crate::Context;
#[derive(Copy, Clone)]
enum State {
Left,
Right,
}
impl State {
pub fn swap(&self) -> Self {
match self {
Self::Left => Self::Right,
Self::Right => Self::Left,
}
}
}
#[pin_project]
pub struct MergeStream<Left, Right> {
state: State,
#[pin]
left: Left,
#[pin]
right: Right,
}
impl<Left, Right> MergeStream<Left, Right>
where
Left: Stream,
Right: Stream<Item = Left::Item>,
{
pub fn new(left: Left, right: Right) -> Self {
Self {
state: State::Left,
left,
right,
}
}
}
impl<Left, Right> Stream for MergeStream<Left, Right>
where
Left: Stream,
Right: Stream<Item = Left::Item>,
{
type Item = Left::Item;
fn poll_recv(self: Pin<&mut Self>, cx: &mut Context<'_>) -> PollRecv<Self::Item> {
let this = self.project();
let poll = match this.state {
State::Left => poll(this.left, this.right, cx),
State::Right => poll(this.right, this.left, cx),
};
if poll.swap() {
*this.state = this.state.swap();
}
poll.into_recv()
}
}
enum MergePoll<T> {
First(PollRecv<T>),
Second(PollRecv<T>),
}
impl<T> MergePoll<T> {
pub fn into_recv(self) -> PollRecv<T> {
match self {
MergePoll::First(p) => p,
MergePoll::Second(p) => p,
}
}
pub fn swap(&self) -> bool {
match self {
MergePoll::First(_) => true,
MergePoll::Second(PollRecv::Ready(_)) => true,
MergePoll::Second(PollRecv::Pending) => true,
MergePoll::Second(PollRecv::Closed) => false,
}
}
}
fn poll<A, B>(first: Pin<&mut A>, second: Pin<&mut B>, cx: &mut Context<'_>) -> MergePoll<A::Item>
where
A: Stream,
B: Stream<Item = A::Item>,
{
match first.poll_recv(cx) {
PollRecv::Ready(v) => MergePoll::First(PollRecv::Ready(v)),
PollRecv::Pending => MergePoll::Second(second.poll_recv(cx)),
PollRecv::Closed => MergePoll::Second(second.poll_recv(cx)),
}
}
#[cfg(test)]
mod tests {
use std::pin::Pin;
use crate::test::stream::*;
use crate::{
stream::{PollRecv, Stream},
Context,
};
use super::MergeStream;
#[test]
fn simple_merge() {
let left = from_poll_iter(vec![PollRecv::Ready(1), PollRecv::Ready(3)]);
let right = from_poll_iter(vec![PollRecv::Ready(2), PollRecv::Ready(4)]);
let mut find = MergeStream::new(left, right);
let mut cx = Context::empty();
assert_eq!(PollRecv::Ready(1), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Ready(2), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Ready(3), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Ready(4), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut find).poll_recv(&mut cx));
}
#[test]
fn swap_ready() {
let left = from_poll_iter(vec![PollRecv::Ready(1), PollRecv::Ready(3)]);
let right = from_poll_iter(vec![PollRecv::Ready(2)]);
let mut find = MergeStream::new(left, right);
let mut cx = Context::empty();
assert_eq!(PollRecv::Ready(1), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Ready(2), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Ready(3), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut find).poll_recv(&mut cx));
}
#[test]
fn swap_pending() {
let left = from_poll_iter(vec![PollRecv::Pending, PollRecv::Ready(2)]);
let right = from_poll_iter(vec![PollRecv::Ready(1)]);
let mut find = MergeStream::new(left, right);
let mut cx = Context::empty();
assert_eq!(PollRecv::Ready(1), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Ready(2), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut find).poll_recv(&mut cx));
}
#[test]
fn swap_closed() {
let left = from_poll_iter(vec![PollRecv::Closed, PollRecv::Closed]);
let right = from_poll_iter(vec![PollRecv::Ready(1), PollRecv::Ready(2)]);
let mut find = MergeStream::new(left, right);
let mut cx = Context::empty();
assert_eq!(PollRecv::Ready(1), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Ready(2), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut find).poll_recv(&mut cx));
}
#[test]
fn pending_uses_right() {
let left = from_poll_iter(vec![PollRecv::Pending]);
let right = from_poll_iter(vec![PollRecv::Ready(1)]);
let mut find = MergeStream::new(left, right);
let mut cx = Context::empty();
assert_eq!(PollRecv::Ready(1), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut find).poll_recv(&mut cx));
}
#[test]
fn pending_uses_left() {
let left = from_poll_iter(vec![PollRecv::Ready(1)]);
let right = from_poll_iter(vec![PollRecv::Pending]);
let mut find = MergeStream::new(left, right);
let mut cx = Context::empty();
assert_eq!(PollRecv::Ready(1), Pin::new(&mut find).poll_recv(&mut cx));
assert_eq!(PollRecv::Closed, Pin::new(&mut find).poll_recv(&mut cx));
}
}