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//! Contains [`Either`] and related types and functions.
//!
//! See [`Either`] documentation for more details.
use pin_project_lite::pin_project;
use std::{
future::Future,
pin::Pin,
task::{Context, Poll},
};
use tower_layer::Layer;
use tower_service::Service;
/// Combine two different service types into a single type.
///
/// Both services must be of the same request, response, and error types.
/// [`Either`] is useful for handling conditional branching in service middleware
/// to different inner service types.
#[derive(Clone, Copy, Debug)]
pub enum Either<A, B> {
#[allow(missing_docs)]
Left(A),
#[allow(missing_docs)]
Right(B),
}
impl<A, B, Request> Service<Request> for Either<A, B>
where
A: Service<Request>,
B: Service<Request, Response = A::Response, Error = A::Error>,
{
type Response = A::Response;
type Error = A::Error;
type Future = EitherResponseFuture<A::Future, B::Future>;
fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
match self {
Either::Left(service) => service.poll_ready(cx),
Either::Right(service) => service.poll_ready(cx),
}
}
fn call(&mut self, request: Request) -> Self::Future {
match self {
Either::Left(service) => EitherResponseFuture {
kind: Kind::Left {
inner: service.call(request),
},
},
Either::Right(service) => EitherResponseFuture {
kind: Kind::Right {
inner: service.call(request),
},
},
}
}
}
pin_project! {
/// Response future for [`Either`].
pub struct EitherResponseFuture<A, B> {
#[pin]
kind: Kind<A, B>
}
}
pin_project! {
#[project = KindProj]
enum Kind<A, B> {
Left { #[pin] inner: A },
Right { #[pin] inner: B },
}
}
impl<A, B> Future for EitherResponseFuture<A, B>
where
A: Future,
B: Future<Output = A::Output>,
{
type Output = A::Output;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
match self.project().kind.project() {
KindProj::Left { inner } => inner.poll(cx),
KindProj::Right { inner } => inner.poll(cx),
}
}
}
impl<S, A, B> Layer<S> for Either<A, B>
where
A: Layer<S>,
B: Layer<S>,
{
type Service = Either<A::Service, B::Service>;
fn layer(&self, inner: S) -> Self::Service {
match self {
Either::Left(layer) => Either::Left(layer.layer(inner)),
Either::Right(layer) => Either::Right(layer.layer(inner)),
}
}
}
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