refactor WebTransportImpl::StreamReadHandle::dataAvailable

Summary: refactor WebTransportImpl::StreamReadHandle::dataAvailable for simplicity

Reviewed By: joanna-jo

Differential Revision: D83162391

fbshipit-source-id: b996269470123525c4d54bb2e42310f48e59cb86

Author: hanidamlaj

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

@@ -206,8 +206,12 @@ TEST_F(HTTPTransactionWebTransportTest, ReadStream) {
   EXPECT_CALL(transport_, readWebTransportData(_, _)).WillOnce(Invoke([] {
     return std::make_pair(makeBuf(32768), false);
   }));
+  // hmm, should WebTransportImpl ensure this isn't invoked if we've rx'd eof or
+  // is it the transport's responsiblity to not send WTMaxData capsule in this
+  // case – leaning towards the latter
   EXPECT_CALL(transport_, sendWTMaxData(kDefaultWTReceiveWindow + 10 + 65536))
-      .WillOnce(Return(folly::unit));
+      .Times(2)
+      .WillRepeatedly(Return(folly::unit));
   implHandle->readAvailable(0);
   EXPECT_CALL(transport_, resumeWebTransportIngress(0));
   fut = readHandle->readStreamData()

proxygen/lib/http/webtransport/WebTransportImpl.cpp

@@ -410,19 +410,14 @@ WebTransport::FCState WebTransportImpl::StreamReadHandle::dataAvailable(
       << "dataAvailable buflen=" << (data ? data->computeChainDataLength() : 0)
       << " eof=" << uint64_t(eof);
 
-  if (data) {
-    auto dataLen = data->computeChainDataLength();
-    if (!impl_.recvFlowController_.reserve(dataLen)) {
-      return WebTransport::FCState::SESSION_CLOSED;
-    }
+  auto len = data ? data->computeChainDataLength() : 0;
+  if (!impl_.recvFlowController_.reserve(len)) {
+    return WebTransport::FCState::SESSION_CLOSED;
   }
 
   if (readPromise_.valid()) {
-    if (data) {
-      auto dataLen = data->computeChainDataLength();
-      impl_.bytesRead_ += dataLen;
-      impl_.maybeGrantFlowControl();
-    }
+    impl_.bytesRead_ += len;
+    impl_.maybeGrantFlowControl();
     readPromise_.setValue(StreamData({.data = std::move(data), .fin = eof}));
     readPromise_ = emptyReadPromise();
     if (eof) {
@@ -431,7 +426,7 @@ WebTransport::FCState WebTransportImpl::StreamReadHandle::dataAvailable(
       return WebTransport::FCState::UNBLOCKED;
     }
   } else {
-    buf_.append(std::move(data));
+    buf_.append(std::move(data)); // ok if nullptr
     eof_ = eof;
   }
   VLOG(4) << "dataAvailable buflen=" << buf_.chainLength();