jk gating for paused priority

Summary: As lnicco raised, this feature can raise possible "overload" concerns so for safety, add a JK knob to easily disable it if needed.

Reviewed By: mjoras, lnicco

Differential Revision: D70417454

fbshipit-source-id: b79fe59d09f8c547e55d7703ac1438cbded011cb

quic/api/test/QuicPacketSchedulerTest.cpp

@@ -2635,7 +2635,7 @@ TEST_F(QuicPacketSchedulerTest, RstStreamSchedulerReliableReset) {
   EXPECT_FALSE(conn.pendingEvents.resets.contains(stream->id));
 }
 
-TEST_F(QuicPacketSchedulerTest, PausedPriorityInitial) {
+TEST_F(QuicPacketSchedulerTest, PausedPriorityEnabled) {
   static const auto kSequentialPriority = Priority(3, false);
   static const auto kPausedPriority = Priority(0, false, 0, true /* paused */);
 
@@ -2669,6 +2669,26 @@ TEST_F(QuicPacketSchedulerTest, PausedPriorityInitial) {
   ASSERT_FALSE(conn.streamManager->hasWritable());
 }
 
+TEST_F(QuicPacketSchedulerTest, PausedPriorityDisabled) {
+  static const auto kSequentialPriority = Priority(3, false);
+  static const auto kPausedPriority = Priority(0, false, 0, true /* paused */);
+
+  auto connPtr = createConn(10, 100000, 100000);
+  auto& conn = *connPtr;
+  conn.transportSettings.disablePausedPriority = true;
+  StreamFrameScheduler scheduler(conn);
+
+  auto pausedStreamId = createStream(conn, kPausedPriority);
+  auto regularStreamId = createStream(conn, kSequentialPriority);
+
+  auto pausedFrame = writeDataToStream(conn, pausedStreamId, "paused_data");
+  auto regularFrame = writeDataToStream(conn, regularStreamId, "regular_data");
+
+  auto builder = setupMockPacketBuilder();
+  scheduler.writeStreams(*builder);
+  verifyStreamFrames(*builder, {pausedFrame, regularFrame});
+}
+
 TEST_F(QuicPacketSchedulerTest, FixedShortHeaderPadding) {
   QuicServerConnectionState conn(
       FizzServerQuicHandshakeContext::Builder().build());

quic/state/QuicPriorityQueue.h

@@ -213,13 +213,11 @@ struct PriorityQueue {
   void updateIfExist(StreamId id, Priority priority) {
     auto iter = writableStreamsToLevel_.find(id);
     if (iter != writableStreamsToLevel_.end()) {
-      CHECK(!priority.paused);
       updateExistingStreamPriority(iter, priority);
     }
   }
 
   void insertOrUpdate(StreamId id, Priority pri) {
-    CHECK(!pri.paused);
     auto it = writableStreamsToLevel_.find(id);
     auto index = priority2index(pri);
     if (it != writableStreamsToLevel_.end()) {

quic/state/QuicStreamManager.cpp

@@ -646,7 +646,7 @@ void QuicStreamManager::updateWritableStreams(QuicStreamState& stream) {
     removeWritable(stream);
     return;
   }
-  if (stream.priority.paused) {
+  if (stream.priority.paused && !transportSettings_->disablePausedPriority) {
     removeWritable(stream);
     return;
   }

quic/state/TransportSettings.h

@@ -458,6 +458,10 @@ struct TransportSettings {
   // Ceiling of packets to receive from signaled socket per evb loop on the
   // server side.
   uint16_t maxServerRecvPacketsPerLoop{1};
+
+  // Support "paused" requests which buffer on the server without streaming back
+  // to the client.
+  bool disablePausedPriority{false};
 };
 
 } // namespace quic