Use RST_STREAM(NO_ERROR) in case server early respond (#633) (#634)

Http2 Server are allowed to early respond without fully
  consuming client input stream, but must respond with an
  error code of NO_ERROR when sending RST_STREAM.
  Nginx treat any other error code as fatal if not done so

  Commit change error code from CANCEL to NO_ERROR, when the
  server is early responding to the client

  https://github.com/hyperium/h2/issues/633
  https://trac.nginx.org/nginx/ticket/2376

src/proto/streams/streams.rs

@@ -1461,9 +1461,21 @@ fn drop_stream_ref(inner: &Mutex<Inner>, key: store::Key) {
 
 fn maybe_cancel(stream: &mut store::Ptr, actions: &mut Actions, counts: &mut Counts) {
     if stream.is_canceled_interest() {
+        // Server is allowed to early respond without fully consuming the client input stream
+        // But per the RFC, must send a RST_STREAM(NO_ERROR) in such cases. https://www.rfc-editor.org/rfc/rfc7540#section-8.1
+        // Some other http2 implementation may interpret other error code as fatal if not respected (i.e: nginx https://trac.nginx.org/nginx/ticket/2376)
+        let reason = if counts.peer().is_server()
+            && stream.state.is_send_closed()
+            && stream.state.is_recv_streaming()
+        {
+            Reason::NO_ERROR
+        } else {
+            Reason::CANCEL
+        };
+
         actions
             .send
-            .schedule_implicit_reset(stream, Reason::CANCEL, counts, &mut actions.task);
+            .schedule_implicit_reset(stream, reason, counts, &mut actions.task);
         actions.recv.enqueue_reset_expiration(stream, counts);
     }
 }

tests/h2-tests/tests/server.rs

@@ -566,7 +566,9 @@ async fn sends_reset_cancel_when_req_body_is_dropped() {
         client
             .recv_frame(frames::headers(1).response(200).eos())
             .await;
-        client.recv_frame(frames::reset(1).cancel()).await;
+        client
+            .recv_frame(frames::reset(1).reason(Reason::NO_ERROR))
+            .await;
     };
 
     let srv = async move {