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use std::prelude::v1::*;
use crate::{clock, Jitter, NotUntil, RateLimiter};
use crate::{
middleware::RateLimitingMiddleware,
state::{DirectStateStore, NotKeyed},
};
use futures_timer::Delay;
use futures_util::task::{Context, Poll};
use futures_util::{Future, Sink, Stream};
use std::pin::Pin;
use std::time::Duration;
/// Allows converting a [`futures_util::Stream`] combinator into a rate-limited stream.
pub trait StreamRateLimitExt<'a>: Stream {
/// Limits the rate at which the stream produces items.
///
/// Note that this combinator limits the rate at which it yields
/// items, not necessarily the rate at which the underlying stream is polled.
/// The combinator will buffer at most one item in order to adhere to the
/// given limiter. I.e. if it already has an item buffered and needs to wait
/// it will not `poll` the underlying stream.
fn ratelimit_stream<
D: DirectStateStore,
C: clock::ReasonablyRealtime,
MW: RateLimitingMiddleware<C::Instant>,
>(
self,
limiter: &'a RateLimiter<NotKeyed, D, C, MW>,
) -> RatelimitedStream<'a, Self, D, C, MW>
where
Self: Sized;
/// Limits the rate at which the stream produces items, with a randomized wait period.
///
/// Note that this combinator limits the rate at which it yields
/// items, not necessarily the rate at which the underlying stream is polled.
/// The combinator will buffer at most one item in order to adhere to the
/// given limiter. I.e. if it already has an item buffered and needs to wait
/// it will not `poll` the underlying stream.
fn ratelimit_stream_with_jitter<
D: DirectStateStore,
C: clock::ReasonablyRealtime,
MW: RateLimitingMiddleware<C::Instant>,
>(
self,
limiter: &'a RateLimiter<NotKeyed, D, C, MW>,
jitter: Jitter,
) -> RatelimitedStream<'a, Self, D, C, MW>
where
Self: Sized;
}
impl<'a, S: Stream> StreamRateLimitExt<'a> for S {
fn ratelimit_stream<
D: DirectStateStore,
C: clock::ReasonablyRealtime,
MW: RateLimitingMiddleware<C::Instant>,
>(
self,
limiter: &'a RateLimiter<NotKeyed, D, C, MW>,
) -> RatelimitedStream<'a, Self, D, C, MW>
where
Self: Sized,
{
self.ratelimit_stream_with_jitter(limiter, Jitter::NONE)
}
fn ratelimit_stream_with_jitter<
D: DirectStateStore,
C: clock::ReasonablyRealtime,
MW: RateLimitingMiddleware<C::Instant>,
>(
self,
limiter: &'a RateLimiter<NotKeyed, D, C, MW>,
jitter: Jitter,
) -> RatelimitedStream<'a, Self, D, C, MW>
where
Self: Sized,
{
RatelimitedStream {
inner: self,
limiter,
buf: None,
delay: Delay::new(Duration::new(0, 0)),
jitter,
state: State::ReadInner,
}
}
}
enum State {
ReadInner,
NotReady,
Wait,
}
/// A [`Stream`][futures_util::Stream] combinator which will limit the rate of items being received.
///
/// This is produced by the [`StreamRateLimitExt::ratelimit_stream`] and
/// [`StreamRateLimitExt::ratelimit_stream_with_jitter`] methods.
pub struct RatelimitedStream<
'a,
S: Stream,
D: DirectStateStore,
C: clock::Clock,
MW: RateLimitingMiddleware<C::Instant>,
> {
inner: S,
limiter: &'a RateLimiter<NotKeyed, D, C, MW>,
delay: Delay,
buf: Option<S::Item>,
jitter: Jitter,
state: State,
}
/// Conversion methods for the stream combinator.
impl<S: Stream, D: DirectStateStore, C: clock::Clock, MW: RateLimitingMiddleware<C::Instant>>
RatelimitedStream<'_, S, D, C, MW>
{
/// Acquires a reference to the underlying stream that this combinator is pulling from.
/// ```rust
/// # use futures_util::{Stream, stream};
/// # use governor::{prelude::*, Quota, RateLimiter};
/// # use nonzero_ext::nonzero;
/// let inner = stream::repeat(());
/// let lim = RateLimiter::direct(Quota::per_second(nonzero!(10u32)));
/// let outer = inner.clone().ratelimit_stream(&lim);
/// assert!(outer.get_ref().size_hint().1.is_none());
/// assert_eq!(outer.size_hint(), outer.get_ref().size_hint());
/// ```
pub fn get_ref(&self) -> &S {
&self.inner
}
/// Acquires a mutable reference to the underlying stream that this combinator is pulling from.
/// ```rust
/// # use futures_util::{stream, StreamExt};
/// # use futures_executor::block_on;
/// # use governor::{prelude::*, Quota, RateLimiter};
/// # use nonzero_ext::nonzero;
/// let inner = stream::repeat(());
/// let lim = RateLimiter::direct(Quota::per_second(nonzero!(10u32)));
/// let mut outer = inner.clone().ratelimit_stream(&lim);
/// assert_eq!(block_on(outer.get_mut().next()), Some(()));
/// ```
pub fn get_mut(&mut self) -> &mut S {
&mut self.inner
}
/// Consumes this combinator, returning the underlying stream and any item
/// which it has already produced but which is still being held back
/// in order to abide by the limiter.
/// ```rust
/// # use futures_util::{stream, StreamExt};
/// # use futures_executor::block_on;
/// # use governor::{prelude::*, Quota, RateLimiter};
/// # use nonzero_ext::nonzero;
/// let inner = stream::repeat(());
/// let lim = RateLimiter::direct(Quota::per_second(nonzero!(10u32)));
/// let mut outer = inner.clone().ratelimit_stream(&lim);
/// let (mut inner_again, _) = outer.into_inner();
/// assert_eq!(block_on(inner_again.next()), Some(()));
/// ```
pub fn into_inner(self) -> (S, Option<S::Item>) {
(self.inner, self.buf)
}
}
/// Implements the [`futures_util::Stream`] combinator.
impl<S: Stream, D: DirectStateStore, C: clock::Clock, MW> Stream
for RatelimitedStream<'_, S, D, C, MW>
where
S: Unpin,
S::Item: Unpin,
Self: Unpin,
C: clock::ReasonablyRealtime,
MW: RateLimitingMiddleware<C::Instant, NegativeOutcome = NotUntil<C::Instant>>,
{
type Item = S::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
loop {
match self.state {
State::ReadInner => {
let inner = Pin::new(&mut self.inner);
match inner.poll_next(cx) {
Poll::Pending => return Poll::Pending,
Poll::Ready(None) => {
// never talk tome or my inner again
return Poll::Ready(None);
}
Poll::Ready(Some(x)) => {
self.buf.replace(x);
self.state = State::NotReady;
}
}
}
State::NotReady => {
let reference = self.limiter.reference_reading();
if let Err(negative) = self.limiter.check() {
let earliest = negative.wait_time_with_offset(reference, self.jitter);
self.delay.reset(earliest);
let future = Pin::new(&mut self.delay);
match future.poll(cx) {
Poll::Pending => {
self.state = State::Wait;
return Poll::Pending;
}
Poll::Ready(_) => {}
}
} else {
self.state = State::ReadInner;
return Poll::Ready(self.buf.take());
}
}
State::Wait => {
let future = Pin::new(&mut self.delay);
match future.poll(cx) {
Poll::Pending => {
return Poll::Pending;
}
Poll::Ready(_) => {
self.state = State::NotReady;
}
}
}
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.inner.size_hint()
}
}
/// Pass-through implementation for [`futures_util::Sink`] if the Stream also implements it.
impl<
Item,
S: Stream + Sink<Item>,
D: DirectStateStore,
C: clock::Clock,
MW: RateLimitingMiddleware<C::Instant>,
> Sink<Item> for RatelimitedStream<'_, S, D, C, MW>
where
S: Unpin,
S::Item: Unpin,
{
type Error = <S as Sink<Item>>::Error;
fn poll_ready(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
let inner = Pin::new(&mut self.inner);
inner.poll_ready(cx)
}
fn start_send(mut self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> {
let inner = Pin::new(&mut self.inner);
inner.start_send(item)
}
fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
let inner = Pin::new(&mut self.inner);
inner.poll_flush(cx)
}
fn poll_close(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
let inner = Pin::new(&mut self.inner);
inner.poll_close(cx)
}
}