Add an absolute cork (min) threshold for WINDOW_UPDATE

Summary: Changed HTTPTransaction logic to check whether the minimum of 128KB and half the recv FC window has been delivered to the application/handler, effectively resulting in more frequent WINDOW_UPDATE frames.

Reviewed By: afrind

Differential Revision: D66999563

fbshipit-source-id: e5dac20bdfa8c4a6ae3e9879348bfba765d7169e

proxygen/lib/http/session/HTTPTransaction.cpp

@@ -27,6 +27,7 @@ namespace {
 const int64_t kApproximateMTU = 1400;
 const std::chrono::seconds kRateLimitMaxDelay(10);
 const uint64_t kMaxBufferPerTxn = 65536;
+constexpr uint32_t kMinThreshold = 128 * 1024;
 
 using namespace proxygen;
 HTTPException stateMachineError(HTTPException::Direction dir, std::string msg) {
@@ -298,6 +299,7 @@ bool HTTPTransaction::updateContentLengthRemaining(size_t len) {
 void HTTPTransaction::onIngressBody(unique_ptr<IOBuf> chain, uint16_t padding) {
   FOLLY_SCOPED_TRACE_SECTION("HTTPTransaction - onIngressBody");
   DestructorGuard g(this);
+  VLOG(6) << __func__ << " chain_length=" << chain->computeChainDataLength();
   if (isIngressEOMSeen()) {
     std::stringstream ss;
     // Use stringstream to invoke operator << for this
@@ -369,7 +371,8 @@ void HTTPTransaction::processIngressBody(unique_ptr<IOBuf> chain, size_t len) {
           // closed
           divisor = 1;
         }
-        if (uint32_t(recvToAck_) >= (recvWindow_.getCapacity() / divisor)) {
+        if (uint32_t(recvToAck_) >= kMinThreshold ||
+            uint32_t(recvToAck_) >= (recvWindow_.getCapacity() / divisor)) {
           flushWindowUpdate();
         }
       }

proxygen/lib/http/session/test/HTTPSessionMocks.h

@@ -355,6 +355,16 @@ class MockHTTPHandler
     }
   }
 
+  void expectBodyRepeatedly(
+      const std::function<void()>& callback = std::function<void()>()) {
+    if (callback) {
+      EXPECT_CALL(*this, _onBodyWithOffset(testing::_, testing::_))
+          .WillRepeatedly(testing::InvokeWithoutArgs(callback));
+    } else {
+      EXPECT_CALL(*this, _onBodyWithOffset(testing::_, testing::_));
+    }
+  }
+
   void expectBody(
       std::function<void(uint64_t, std::shared_ptr<folly::IOBuf>)> callback) {
     EXPECT_CALL(*this, _onBodyWithOffset(testing::_, testing::_))

proxygen/lib/http/session/test/HTTPUpstreamSessionTest.cpp

@@ -3163,6 +3163,74 @@ TEST_F(HTTP2UpstreamSessionTest, TestPingPreserveData) {
   httpSession_->destroy();
 }
 
+class H2LargeFlowControl : public HTTP2UpstreamSessionTest {
+  void SetUp() override {
+    constexpr uint32_t kCapacity = 1024 * 1024;
+    flowControl_ = {kCapacity, kCapacity, kCapacity};
+    HTTP2UpstreamSessionTest::SetUp();
+  }
+};
+
+/*
+ * Verifies that WINDOW_UPDATE is sent when at least kMinThreshold bytes are
+ * read.
+ */
+TEST_F(H2LargeFlowControl, WindowUpdateThresholdTest) {
+  auto handler = openTransaction();
+  handler->txn_->pauseIngress(); // buffer incoming bytes
+  handler->sendRequest();        // getRequest, sends request and eom
+  eventBase_.loopOnce();
+  eventBase_.loopOnce();
+
+  auto serverCodec = makeServerCodec();
+  folly::IOBufQueue output(folly::IOBufQueue::cacheChainLength());
+  serverCodec->generateConnectionPreface(output);
+  serverCodec->generateSettings(output);
+
+  // enqueue 1MB of data into txn
+  auto resp = makeResponse(200);
+  serverCodec->generateHeader(output, handler->txn_->getID(), *resp, false);
+  serverCodec->generateBody(output,
+                            handler->txn_->getID(),
+                            makeBuf(1024 * 1024),
+                            folly::none /* padding */,
+                            false /* eom */);
+
+  auto input = output.move();
+  input->coalesce();
+  readAndLoop(input->data(),
+              input->length()); // buffers server's headers and body to txn
+
+  uint32_t bytesReadSoFar = 0;
+  constexpr uint32_t kMinThreshold = 128 * 1024;
+
+  handler->expectHeaders();
+  // setting up expectation, pause ingress after reading 128KB in callback
+  handler->expectBodyRepeatedly([&] {
+    bytesReadSoFar += input->computeChainDataLength();
+    if (bytesReadSoFar >= kMinThreshold) {
+      handler->txn_->pauseIngress();
+    }
+  });
+
+  handler->txn_->resumeIngress(); // only sent to the handler after this point
+  handler->expectBodyRepeatedly([&] {});
+  handler->expectDetachTransaction();
+
+  // expect window update here
+  NiceMock<MockHTTPCodecCallback> callbacks;
+  serverCodec->setCallback(&callbacks);
+  EXPECT_CALL(callbacks, onWindowUpdate(0, _)).Times(AnyNumber());
+  EXPECT_CALL(callbacks, onWindowUpdate(handler->txn_->getID(), kMinThreshold))
+      .Times(AtLeast(1));
+
+  handler->txn_->resumeIngress();
+  eventBase_.loop();
+  handler->txn_->sendAbort();
+  parseOutput(*serverCodec); // client's buffer -> serverCodec
+  httpSession_->destroy();
+}
+
 TEST_F(HTTP2UpstreamSessionTest, TestConnectionToken) {
   auto handler = openTransaction();
   handler->expectError();