tower/util/call_all/ordered.rs
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//! [`Stream<Item = Request>`][stream] + [`Service<Request>`] => [`Stream<Item = Response>`][stream].
//!
//! [`Service<Request>`]: crate::Service
//! [stream]: https://docs.rs/futures/latest/futures/stream/trait.Stream.html
use super::common;
use futures_core::Stream;
use futures_util::stream::FuturesOrdered;
use pin_project_lite::pin_project;
use std::{
future::Future,
pin::Pin,
task::{Context, Poll},
};
use tower_service::Service;
pin_project! {
/// This is a [`Stream`] of responses resulting from calling the wrapped [`Service`] for each
/// request received on the wrapped [`Stream`].
///
/// ```rust
/// # use std::task::{Poll, Context};
/// # use std::cell::Cell;
/// # use std::error::Error;
/// # use std::rc::Rc;
/// #
/// use futures::future::{ready, Ready};
/// use futures::StreamExt;
/// use futures::channel::mpsc;
/// use tower_service::Service;
/// use tower::util::ServiceExt;
///
/// // First, we need to have a Service to process our requests.
/// #[derive(Debug, Eq, PartialEq)]
/// struct FirstLetter;
/// impl Service<&'static str> for FirstLetter {
/// type Response = &'static str;
/// type Error = Box<dyn Error + Send + Sync>;
/// type Future = Ready<Result<Self::Response, Self::Error>>;
///
/// fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
/// Poll::Ready(Ok(()))
/// }
///
/// fn call(&mut self, req: &'static str) -> Self::Future {
/// ready(Ok(&req[..1]))
/// }
/// }
///
/// #[tokio::main]
/// async fn main() {
/// // Next, we need a Stream of requests.
// TODO(eliza): when `tokio-util` has a nice way to convert MPSCs to streams,
// tokio::sync::mpsc again?
/// let (mut reqs, rx) = mpsc::unbounded();
/// // Note that we have to help Rust out here by telling it what error type to use.
/// // Specifically, it has to be From<Service::Error> + From<Stream::Error>.
/// let mut rsps = FirstLetter.call_all(rx);
///
/// // Now, let's send a few requests and then check that we get the corresponding responses.
/// reqs.unbounded_send("one").unwrap();
/// reqs.unbounded_send("two").unwrap();
/// reqs.unbounded_send("three").unwrap();
/// drop(reqs);
///
/// // We then loop over the response Strem that we get back from call_all.
/// let mut i = 0usize;
/// while let Some(rsp) = rsps.next().await {
/// // Each response is a Result (we could also have used TryStream::try_next)
/// match (i + 1, rsp.unwrap()) {
/// (1, "o") |
/// (2, "t") |
/// (3, "t") => {}
/// (n, i) => {
/// unreachable!("{}. response was '{}'", n, i);
/// }
/// }
/// i += 1;
/// }
///
/// // And at the end, we can get the Service back when there are no more requests.
/// assert_eq!(rsps.into_inner(), FirstLetter);
/// }
/// ```
///
/// [`Stream`]: https://docs.rs/futures/latest/futures/stream/trait.Stream.html
#[derive(Debug)]
pub struct CallAll<Svc, S>
where
Svc: Service<S::Item>,
S: Stream,
{
#[pin]
inner: common::CallAll<Svc, S, FuturesOrdered<Svc::Future>>,
}
}
impl<Svc, S> CallAll<Svc, S>
where
Svc: Service<S::Item>,
Svc::Error: Into<crate::BoxError>,
S: Stream,
{
/// Create new [`CallAll`] combinator.
///
/// Each request yielded by `stream` is passed to `svc`, and the resulting responses are
/// yielded in the same order by the implementation of [`Stream`] for [`CallAll`].
///
/// [`Stream`]: https://docs.rs/futures/latest/futures/stream/trait.Stream.html
pub fn new(service: Svc, stream: S) -> CallAll<Svc, S> {
CallAll {
inner: common::CallAll::new(service, stream, FuturesOrdered::new()),
}
}
/// Extract the wrapped [`Service`].
///
/// # Panics
///
/// Panics if [`take_service`] was already called.
///
/// [`take_service`]: crate::util::CallAll::take_service
pub fn into_inner(self) -> Svc {
self.inner.into_inner()
}
/// Extract the wrapped [`Service`].
///
/// This [`CallAll`] can no longer be used after this function has been called.
///
/// # Panics
///
/// Panics if [`take_service`] was already called.
///
/// [`take_service`]: crate::util::CallAll::take_service
pub fn take_service(self: Pin<&mut Self>) -> Svc {
self.project().inner.take_service()
}
/// Return responses as they are ready, regardless of the initial order.
///
/// This function must be called before the stream is polled.
///
/// # Panics
///
/// Panics if [`poll`] was called.
///
/// [`poll`]: std::future::Future::poll
pub fn unordered(self) -> super::CallAllUnordered<Svc, S> {
self.inner.unordered()
}
}
impl<Svc, S> Stream for CallAll<Svc, S>
where
Svc: Service<S::Item>,
Svc::Error: Into<crate::BoxError>,
S: Stream,
{
type Item = Result<Svc::Response, crate::BoxError>;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
self.project().inner.poll_next(cx)
}
}
impl<F: Future> common::Drive<F> for FuturesOrdered<F> {
fn is_empty(&self) -> bool {
FuturesOrdered::is_empty(self)
}
fn push(&mut self, future: F) {
FuturesOrdered::push(self, future)
}
fn poll(&mut self, cx: &mut Context<'_>) -> Poll<Option<F::Output>> {
Stream::poll_next(Pin::new(self), cx)
}
}