tower_util/
either.rs

1//! Contains `Either` and related types and functions.
2//!
3//! See `Either` documentation for more details.
4
5use futures_core::ready;
6use pin_project::{pin_project, project};
7use std::{
8    future::Future,
9    pin::Pin,
10    task::{Context, Poll},
11};
12use tower_service::Service;
13
14/// Combine two different service types into a single type.
15///
16/// Both services must be of the same request, response, and error types.
17/// `Either` is useful for handling conditional branching in service middleware
18/// to different inner service types.
19#[pin_project]
20#[derive(Clone, Debug)]
21pub enum Either<A, B> {
22    /// One type of backing `Service`.
23    A(#[pin] A),
24    /// The other type of backing `Service`.
25    B(#[pin] B),
26}
27
28type Error = Box<dyn std::error::Error + Send + Sync>;
29
30impl<A, B, Request> Service<Request> for Either<A, B>
31where
32    A: Service<Request>,
33    A::Error: Into<Error>,
34    B: Service<Request, Response = A::Response>,
35    B::Error: Into<Error>,
36{
37    type Response = A::Response;
38    type Error = Error;
39    type Future = Either<A::Future, B::Future>;
40
41    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
42        use self::Either::*;
43
44        match self {
45            A(service) => Poll::Ready(Ok(ready!(service.poll_ready(cx)).map_err(Into::into)?)),
46            B(service) => Poll::Ready(Ok(ready!(service.poll_ready(cx)).map_err(Into::into)?)),
47        }
48    }
49
50    fn call(&mut self, request: Request) -> Self::Future {
51        use self::Either::*;
52
53        match self {
54            A(service) => A(service.call(request)),
55            B(service) => B(service.call(request)),
56        }
57    }
58}
59
60impl<A, B, T, AE, BE> Future for Either<A, B>
61where
62    A: Future<Output = Result<T, AE>>,
63    AE: Into<Error>,
64    B: Future<Output = Result<T, BE>>,
65    BE: Into<Error>,
66{
67    type Output = Result<T, Error>;
68
69    #[project]
70    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
71        #[project]
72        match self.project() {
73            Either::A(fut) => Poll::Ready(Ok(ready!(fut.poll(cx)).map_err(Into::into)?)),
74            Either::B(fut) => Poll::Ready(Ok(ready!(fut.poll(cx)).map_err(Into::into)?)),
75        }
76    }
77}
tower_util/either.rs

tower_util/
either.rs
