axum-extra: implement FromRequest for Either*

axum-extra/src/either.rs

@@ -1,6 +1,6 @@
 //! `Either*` types for combining extractors or responses into a single type.
 //!
-//! # As an extractor
+//! # As an `FromRequestParts` extractor
 //!
 //! ```
 //! use axum_extra::either::Either3;
@@ -54,6 +54,42 @@
 //! Note that if all the inner extractors reject the request, the rejection from the last
 //! extractor will be returned. For the example above that would be [`BytesRejection`].
 //!
+//! # As an `FromRequest` extractor
+//!
+//! In the following example, we can first try to deserialize the payload as JSON, if that fails try
+//! to interpret it as a UTF-8 string, and lastly just take the raw bytes.
+//!
+//! It might be preferable to instead extract `Bytes` directly and then fallibly convert them to
+//! `String` and then deserialize the data inside the handler.
+//!
+//! ```
+//! use axum_extra::either::Either3;
+//! use axum::{
+//!     body::Bytes,
+//!     Json,
+//!     Router,
+//!     routing::get,
+//!     extract::FromRequestParts,
+//! };
+//!
+//! #[derive(serde::Deserialize)]
+//! struct Payload {
+//!     user: String,
+//!     request_id: u32,
+//! }
+//!
+//! async fn handler(
+//!     body: Either3<Json<Payload>, String, Bytes>,
+//! ) {
+//!     match body {
+//!         Either3::E1(json) => { /* ... */ }
+//!         Either3::E2(string) => { /* ... */ }
+//!         Either3::E3(bytes) => { /* ... */ }
+//!     }
+//! }
+//! #
+//! # let _: axum::routing::MethodRouter = axum::routing::get(handler);
+//! ```
 //! # As a response
 //!
 //! ```
@@ -93,9 +129,10 @@
 use std::task::{Context, Poll};
 
 use axum::{
-    extract::FromRequestParts,
+    extract::{rejection::BytesRejection, FromRequest, FromRequestParts, Request},
     response::{IntoResponse, Response},
 };
+use bytes::Bytes;
 use http::request::Parts;
 use tower_layer::Layer;
 use tower_service::Service;
@@ -226,6 +263,28 @@ pub enum Either8<E1, E2, E3, E4, E5, E6, E7, E8> {
     E8(E8),
 }
 
+/// Rejection used for [`Either`], [`Either3`], etc.
+///
+/// Contains one variant for a case when the whole request could not be loaded and one variant
+/// containing the rejection of the last variant if all extractors failed..
+#[derive(Debug)]
+pub enum EitherRejection<E> {
+    /// Buffering of the request body failed.
+    Bytes(BytesRejection),
+
+    /// All extractors failed. This contains the error returned by the last extractor.
+    LastRejection(E),
+}
+
+impl<E: IntoResponse> IntoResponse for EitherRejection<E> {
+    fn into_response(self) -> Response {
+        match self {
+            EitherRejection::Bytes(rejection) => rejection.into_response(),
+            EitherRejection::LastRejection(rejection) => rejection.into_response(),
+        }
+    }
+}
+
 macro_rules! impl_traits_for_either {
     (
         $either:ident =>
@@ -251,6 +310,43 @@ macro_rules! impl_traits_for_either {
             }
         }
 
+        impl<S, $($ident),*, $last> FromRequest<S> for $either<$($ident),*, $last>
+        where
+            S: Send + Sync,
+            $($ident: FromRequest<S>),*,
+            $last: FromRequest<S>,
+            $($ident::Rejection: Send),*,
+            $last::Rejection: IntoResponse + Send,
+        {
+            type Rejection = EitherRejection<$last::Rejection>;
+
+            async fn from_request(req: Request, state: &S) -> Result<Self, Self::Rejection> {
+                let (parts, body) = req.into_parts();
+                let bytes = Bytes::from_request(Request::from_parts(parts.clone(), body), state)
+                    .await
+                    .map_err(EitherRejection::Bytes)?;
+
+                $(
+                    let req = Request::from_parts(
+                        parts.clone(),
+                        axum::body::Body::new(http_body_util::Full::new(bytes.clone())),
+                    );
+                    if let Ok(extracted) = $ident::from_request(req, state).await {
+                        return Ok(Self::$ident(extracted));
+                    }
+                )*
+
+                let req = Request::from_parts(
+                    parts.clone(),
+                    axum::body::Body::new(http_body_util::Full::new(bytes.clone())),
+                );
+                match $last::from_request(req, state).await {
+                    Ok(extracted) => Ok(Self::$last(extracted)),
+                    Err(error) => Err(EitherRejection::LastRejection(error)),
+                }
+            }
+        }
+
         impl<$($ident),*, $last> IntoResponse for $either<$($ident),*, $last>
         where
             $($ident: IntoResponse),*,
@@ -312,3 +408,67 @@ where
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::future::Future;
+
+    use axum::body::Body;
+    use axum::extract::rejection::StringRejection;
+    use axum::extract::{FromRequest, Request, State};
+    use bytes::Bytes;
+    use http_body_util::Full;
+
+    use super::*;
+
+    struct False;
+
+    impl<S> FromRequestParts<S> for False {
+        type Rejection = ();
+
+        fn from_request_parts(
+            _parts: &mut Parts,
+            _state: &S,
+        ) -> impl Future<Output = Result<Self, Self::Rejection>> + Send {
+            std::future::ready(Err(()))
+        }
+    }
+
+    #[tokio::test]
+    async fn either_from_request() {
+        // The body is by design not valid UTF-8.
+        let request = Request::new(Body::new(Full::new(Bytes::from_static(&[255]))));
+
+        let either = Either4::<String, String, Request, Bytes>::from_request(request, &())
+            .await
+            .unwrap();
+
+        assert!(matches!(either, Either4::E3(_)));
+    }
+
+    #[tokio::test]
+    async fn either_from_request_rejection() {
+        // The body is by design not valid UTF-8.
+        let request = Request::new(Body::new(Full::new(Bytes::from_static(&[255]))));
+
+        let either = Either::<String, String>::from_request(request, &())
+            .await
+            .unwrap_err();
+
+        assert!(matches!(
+            either,
+            EitherRejection::LastRejection(StringRejection::InvalidUtf8(_))
+        ));
+    }
+
+    #[tokio::test]
+    async fn either_from_request_parts() {
+        let (mut parts, _) = Request::new(Body::empty()).into_parts();
+
+        let either = Either3::<False, False, State<()>>::from_request_parts(&mut parts, &())
+            .await
+            .unwrap();
+
+        assert!(matches!(either, Either3::E3(State(()))));
+    }
+}