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//! Slow down a stream by enforcing a delay between items.
use {clock, Delay, Error};
use futures::future::Either;
use futures::{Async, Future, Poll, Stream};
use std::{
error::Error as StdError,
fmt::{Display, Formatter, Result as FmtResult},
time::Duration,
};
/// Slow down a stream by enforcing a delay between items.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Throttle<T> {
delay: Option<Delay>,
duration: Duration,
stream: T,
}
/// Either the error of the underlying stream, or an error within
/// tokio's timing machinery.
#[derive(Debug)]
pub struct ThrottleError<T>(Either<T, Error>);
impl<T> Throttle<T> {
/// Slow down a stream by enforcing a delay between items.
pub fn new(stream: T, duration: Duration) -> Self {
Self {
delay: None,
duration: duration,
stream: stream,
}
}
/// Acquires a reference to the underlying stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &T {
&self.stream
}
/// Acquires a mutable reference to the underlying stream that this combinator
/// is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the stream
/// which may otherwise confuse this combinator.
pub fn get_mut(&mut self) -> &mut T {
&mut self.stream
}
/// Consumes this combinator, returning the underlying stream.
///
/// 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) -> T {
self.stream
}
}
impl<T: Stream> Stream for Throttle<T> {
type Item = T::Item;
type Error = ThrottleError<T::Error>;
fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
if let Some(ref mut delay) = self.delay {
try_ready!({ delay.poll().map_err(ThrottleError::from_timer_err) });
}
self.delay = None;
let value = try_ready!({ self.stream.poll().map_err(ThrottleError::from_stream_err) });
if value.is_some() {
self.delay = Some(Delay::new(clock::now() + self.duration));
}
Ok(Async::Ready(value))
}
}
impl<T> ThrottleError<T> {
/// Creates a new `ThrottleError` from the given stream error.
pub fn from_stream_err(err: T) -> Self {
ThrottleError(Either::A(err))
}
/// Creates a new `ThrottleError` from the given tokio timer error.
pub fn from_timer_err(err: Error) -> Self {
ThrottleError(Either::B(err))
}
/// Attempts to get the underlying stream error, if it is present.
pub fn get_stream_error(&self) -> Option<&T> {
match self.0 {
Either::A(ref x) => Some(x),
_ => None,
}
}
/// Attempts to get the underlying timer error, if it is present.
pub fn get_timer_error(&self) -> Option<&Error> {
match self.0 {
Either::B(ref x) => Some(x),
_ => None,
}
}
/// Attempts to extract the underlying stream error, if it is present.
pub fn into_stream_error(self) -> Option<T> {
match self.0 {
Either::A(x) => Some(x),
_ => None,
}
}
/// Attempts to extract the underlying timer error, if it is present.
pub fn into_timer_error(self) -> Option<Error> {
match self.0 {
Either::B(x) => Some(x),
_ => None,
}
}
/// Returns whether the throttle error has occured because of an error
/// in the underlying stream.
pub fn is_stream_error(&self) -> bool {
!self.is_timer_error()
}
/// Returns whether the throttle error has occured because of an error
/// in tokio's timer system.
pub fn is_timer_error(&self) -> bool {
match self.0 {
Either::A(_) => false,
Either::B(_) => true,
}
}
}
impl<T: StdError> Display for ThrottleError<T> {
fn fmt(&self, f: &mut Formatter) -> FmtResult {
match self.0 {
Either::A(ref err) => write!(f, "stream error: {}", err),
Either::B(ref err) => write!(f, "timer error: {}", err),
}
}
}
impl<T: StdError + 'static> StdError for ThrottleError<T> {
fn description(&self) -> &str {
match self.0 {
Either::A(_) => "stream error",
Either::B(_) => "timer error",
}
}
// FIXME(taiki-e): When the minimum support version of tokio reaches Rust 1.30,
// replace this with Error::source.
#[allow(deprecated)]
fn cause(&self) -> Option<&dyn StdError> {
match self.0 {
Either::A(ref err) => Some(err),
Either::B(ref err) => Some(err),
}
}
}