Implement #2871 by matching on outcome

core/lib/src/request/from_request.rs

@@ -521,12 +521,13 @@ impl<'r, T: FromRequest<'r>> FromRequest<'r> for Result<T, T::Error> {
 
 #[crate::async_trait]
 impl<'r, T: FromRequest<'r>> FromRequest<'r> for Option<T> {
-    type Error = Infallible;
+    type Error = T::Error;
 
-    async fn from_request(request: &'r Request<'_>) -> Outcome<Self, Infallible> {
+    async fn from_request(request: &'r Request<'_>) -> Outcome<Self, Self::Error> {
         match T::from_request(request).await {
             Success(val) => Success(Some(val)),
-            Error(_) | Forward(_) => Success(None),
+            Forward(_) => Success(None),
+            Error((status, error)) => Error((status, error)),
         }
     }
 }

core/lib/src/response/flash.rs

@@ -256,7 +256,7 @@ impl<'r> FromRequest<'r> for FlashMessage<'r> {
                 Ok(i) if i <= kv.len() => Ok(Flash::named(&kv[..i], &kv[i..], req)),
                 _ => Err(())
             }
-        }).or_error(Status::BadRequest)
+        }).or_forward(Status::BadRequest)
     }
 }
 

core/lib/tests/refined-from-request.rs

@@ -0,0 +1,83 @@
+#[macro_use]
+extern crate rocket;
+
+use std::num::ParseIntError;
+
+use rocket::{outcome::IntoOutcome, request::{FromRequest, Outcome}, Request};
+use rocket_http::{Header, Status};
+
+pub struct SessionId {
+    session_id: u64,
+}
+
+#[rocket::async_trait]
+impl<'r> FromRequest<'r> for SessionId {
+    type Error = ParseIntError;
+
+    async fn from_request(request: &'r Request<'_>) -> Outcome<Self, ParseIntError> {
+        let session_id_string = request.headers().get("Session-Id").next()
+            .or_forward(Status::BadRequest);
+        session_id_string.and_then(|v| v.parse()
+            .map(|id| SessionId { session_id: id })
+            .or_error(Status::BadRequest))
+    }
+}
+
+#[get("/mandatory")]
+fn get_data_with_mandatory_header(header: SessionId) -> String {
+    format!("GET for session {:}", header.session_id)
+}
+
+#[get("/optional")]
+fn get_data_with_opt_header(opt_header: Option<SessionId>) -> String {
+    if let Some(id) = opt_header {
+        format!("GET for session {:}", id.session_id)
+    } else {
+        format!("GET for new session")
+    }
+}
+
+#[test]
+fn read_optional_header() {
+    let rocket = rocket::build().mount(
+        "/",
+        routes![get_data_with_opt_header, get_data_with_mandatory_header]);
+    let client = rocket::local::blocking::Client::debug(rocket).unwrap();
+
+    // If we supply the header, the handler sees it
+    let response = client.get("/optional")
+        .header(Header::new("session-id", "1234567")).dispatch();
+    assert_eq!(response.into_string().unwrap(), "GET for session 1234567".to_string());
+
+    // If no header, means that the handler sees a None
+    let response = client.get("/optional").dispatch();
+    assert_eq!(response.into_string().unwrap(), "GET for new session".to_string());
+
+    // If we supply a malformed header, the handler will not be called, but the request will fail
+    let response = client.get("/optional")
+        .header(Header::new("session-id", "Xw23")).dispatch();
+    assert_eq!(response.status(), Status::BadRequest);
+}
+
+#[test]
+fn read_mandatory_header() {
+        let rocket = rocket::build().mount(
+            "/",
+            routes![get_data_with_opt_header, get_data_with_mandatory_header]);
+        let client = rocket::local::blocking::Client::debug(rocket).unwrap();
+    
+    // If the header is missing, it's a bad request (extra info would be nice, though)
+    let response = client.get("/mandatory").dispatch();
+    assert_eq!(response.status(), Status::BadRequest);
+
+    // If the header is malformed, it's a bad request too (extra info would be nice, though)
+    let response = client.get("/mandatory")
+        .header(Header::new("session-id", "Xw23")).dispatch();
+    assert_eq!(response.status(), Status::BadRequest);
+
+    // If the header is fine, just do the stuff
+    let response = client.get("/mandatory")
+        .header(Header::new("session-id", "64535")).dispatch();
+    assert_eq!(response.status(), Status::Ok);
+    assert_eq!(response.into_string().unwrap(), "GET for session 64535".to_string());
+}