feat(middleware): return request ID in response header (#214)

crates/router/src/middleware.rs

@@ -0,0 +1,61 @@
+/// Middleware to include request ID in response header.
+pub(crate) struct RequestId;
+
+impl<S, B> actix_web::dev::Transform<S, actix_web::dev::ServiceRequest> for RequestId
+where
+    S: actix_web::dev::Service<
+        actix_web::dev::ServiceRequest,
+        Response = actix_web::dev::ServiceResponse<B>,
+        Error = actix_web::Error,
+    >,
+    S::Future: 'static,
+    B: 'static,
+{
+    type Response = actix_web::dev::ServiceResponse<B>;
+    type Error = actix_web::Error;
+    type Transform = RequestIdMiddleware<S>;
+    type InitError = ();
+    type Future = std::future::Ready<Result<Self::Transform, Self::InitError>>;
+
+    fn new_transform(&self, service: S) -> Self::Future {
+        std::future::ready(Ok(RequestIdMiddleware { service }))
+    }
+}
+
+pub(crate) struct RequestIdMiddleware<S> {
+    service: S,
+}
+
+impl<S, B> actix_web::dev::Service<actix_web::dev::ServiceRequest> for RequestIdMiddleware<S>
+where
+    S: actix_web::dev::Service<
+        actix_web::dev::ServiceRequest,
+        Response = actix_web::dev::ServiceResponse<B>,
+        Error = actix_web::Error,
+    >,
+    S::Future: 'static,
+    B: 'static,
+{
+    type Response = actix_web::dev::ServiceResponse<B>;
+    type Error = actix_web::Error;
+    type Future = futures::future::LocalBoxFuture<'static, Result<Self::Response, Self::Error>>;
+
+    actix_web::dev::forward_ready!(service);
+
+    fn call(&self, req: actix_web::dev::ServiceRequest) -> Self::Future {
+        let mut req = req;
+        let request_id_fut = req.extract::<router_env::tracing_actix_web::RequestId>();
+        let response_fut = self.service.call(req);
+
+        Box::pin(async move {
+            let request_id = request_id_fut.await?;
+            let mut response = response_fut.await?;
+            response.headers_mut().append(
+                http::header::HeaderName::from_static("x-request-id"),
+                http::HeaderValue::from_str(&request_id.as_hyphenated().to_string())?,
+            );
+
+            Ok(response)
+        })
+    }
+}