Add a separate trait for optional extractors (#2475)

axum-core/src/extract/mod.rs

@@ -13,11 +13,16 @@ pub mod rejection;
 
 mod default_body_limit;
 mod from_ref;
+mod option;
 mod request_parts;
 mod tuple;
 
 pub(crate) use self::default_body_limit::DefaultBodyLimitKind;
-pub use self::{default_body_limit::DefaultBodyLimit, from_ref::FromRef};
+pub use self::{
+    default_body_limit::DefaultBodyLimit,
+    from_ref::FromRef,
+    option::{OptionalFromRequest, OptionalFromRequestParts},
+};
 
 /// Type alias for [`http::Request`] whose body type defaults to [`Body`], the most common body
 /// type used with axum.
@@ -102,33 +107,6 @@ where
     }
 }
 
-impl<S, T> FromRequestParts<S> for Option<T>
-where
-    T: FromRequestParts<S>,
-    S: Send + Sync,
-{
-    type Rejection = Infallible;
-
-    async fn from_request_parts(
-        parts: &mut Parts,
-        state: &S,
-    ) -> Result<Option<T>, Self::Rejection> {
-        Ok(T::from_request_parts(parts, state).await.ok())
-    }
-}
-
-impl<S, T> FromRequest<S> for Option<T>
-where
-    T: FromRequest<S>,
-    S: Send + Sync,
-{
-    type Rejection = Infallible;
-
-    async fn from_request(req: Request, state: &S) -> Result<Option<T>, Self::Rejection> {
-        Ok(T::from_request(req, state).await.ok())
-    }
-}
-
 impl<S, T> FromRequestParts<S> for Result<T, T::Rejection>
 where
     T: FromRequestParts<S>,

axum-core/src/extract/option.rs

@@ -0,0 +1,63 @@
+use std::future::Future;
+
+use http::request::Parts;
+
+use crate::response::IntoResponse;
+
+use super::{private, FromRequest, FromRequestParts, Request};
+
+/// Customize the behavior of `Option<Self>` as a [`FromRequestParts`]
+/// extractor.
+pub trait OptionalFromRequestParts<S>: Sized {
+    /// If the extractor fails, it will use this "rejection" type.
+    ///
+    /// A rejection is a kind of error that can be converted into a response.
+    type Rejection: IntoResponse;
+
+    /// Perform the extraction.
+    fn from_request_parts(
+        parts: &mut Parts,
+        state: &S,
+    ) -> impl Future<Output = Result<Option<Self>, Self::Rejection>> + Send;
+}
+
+/// Customize the behavior of `Option<Self>` as a [`FromRequest`] extractor.
+pub trait OptionalFromRequest<S, M = private::ViaRequest>: Sized {
+    /// If the extractor fails, it will use this "rejection" type.
+    ///
+    /// A rejection is a kind of error that can be converted into a response.
+    type Rejection: IntoResponse;
+
+    /// Perform the extraction.
+    fn from_request(
+        req: Request,
+        state: &S,
+    ) -> impl Future<Output = Result<Option<Self>, Self::Rejection>> + Send;
+}
+
+impl<S, T> FromRequestParts<S> for Option<T>
+where
+    T: OptionalFromRequestParts<S>,
+    S: Send + Sync,
+{
+    type Rejection = T::Rejection;
+
+    fn from_request_parts(
+        parts: &mut Parts,
+        state: &S,
+    ) -> impl Future<Output = Result<Option<T>, Self::Rejection>> {
+        T::from_request_parts(parts, state)
+    }
+}
+
+impl<S, T> FromRequest<S> for Option<T>
+where
+    T: OptionalFromRequest<S>,
+    S: Send + Sync,
+{
+    type Rejection = T::Rejection;
+
+    async fn from_request(req: Request, state: &S) -> Result<Option<T>, Self::Rejection> {
+        T::from_request(req, state).await
+    }
+}