Add a 'status::NotFound' responder.

CHANGELOG.md

@@ -48,6 +48,8 @@ This release includes the following new features:
   * Log coloring is disabled when `stdout` is not a TTY.
   * [`FromForm`] is implemented for `Option<T: FromForm>`, `Result<T: FromForm,
     T::Error>`.
+  * The [`NotFound`] responder was added for simple **404** response
+    construction.
 
 [Fairings]: #FIXME
 [Native TLS support]: #FIXME
@@ -73,6 +75,7 @@ This release includes the following new features:
 [`Config::get_datetime()`]: https://api.rocket.rs/rocket/struct.Config.html#method.get_datetime
 [`LenientForm`]: https://api.rocket.rs/rocket/request/struct.LenientForm.html
 [configuration parameters]: https://api.rocket.rs/rocket/config/index.html#environment-variables
+[`NotFound`]: https://api.rocket.rs/rocket/response/status/struct.NotFound.html
 
 ## Breaking Changes
 

lib/src/response/status.rs

@@ -155,6 +155,30 @@ impl Responder<'static> for Reset {
     }
 }
 
+/// Sets the status of the response to 404 (Not Found).
+///
+/// The remainder of the response is delegated to the wrapped `Responder`.
+///
+/// # Example
+///
+/// ```rust
+/// use rocket::response::status;
+///
+/// # #[allow(unused_variables)]
+/// let response = status::NotFound("Sorry, I couldn't find it!");
+/// ```
+#[derive(Debug, Clone, PartialEq)]
+pub struct NotFound<R>(pub R);
+
+/// Sets the status code of the response to 404 Not Found.
+impl<'r, R: Responder<'r>> Responder<'r> for NotFound<R> {
+    fn respond_to(self, req: &Request) -> Result<Response<'r>, Status> {
+        Response::build_from(self.0.respond_to(req)?)
+            .status(Status::NotFound)
+            .ok()
+    }
+}
+
 /// Creates a response with the given status code and underyling responder.
 ///
 /// # Example