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QuicWtSession: refresh stale stream window before waiting on write callback #660

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QuicWtSession: refresh stale stream window before waiting on write callback #660

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7 changes: 6 additions & 1 deletion proxygen/lib/http/webtransport/QuicWtSession.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -373,7 +373,12 @@ void QuicWtSessionBase::StreamManagerCallback::eventsAvailableImpl() noexcept {
if (streamData.fin) {
sock->setStopSendingCallback(streamId, nullptr);
} else if (isWtStreamEgressFcBlocked(sess.sm_, *wh)) {
sess.quicSocket_->notifyPendingWriteOnStream(streamId, &sess);
// The cached window may lag the peer's MAX_STREAM_DATA; refreshing it
// here saves a loop iteration through notifyPendingWriteOnStream.
grantMaxData(*sock, sess.sm_, *wh);
if (isWtStreamEgressFcBlocked(sess.sm_, *wh)) {
sess.quicSocket_->notifyPendingWriteOnStream(streamId, &sess);
}
}
}
}
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21 changes: 21 additions & 0 deletions proxygen/lib/http/webtransport/test/QuicWtSessionTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -846,6 +846,27 @@ TEST_F(QuicWtSessionTest, WriteFlowControlBlocked) {
EXPECT_TRUE(stream.writeEOF);
}

TEST_F(QuicWtSessionTest, WriteRefreshesStaleFlowControl) {
auto handle = session_->createUniStream();
ASSERT_TRUE(handle.hasValue());
const auto id = handle.value()->getID();
socketDriver_.setConnectionFlowControlWindow(
std::numeric_limits<uint64_t>::max());

// Peer raised MAX_STREAM_DATA after creation; the cached window is stale.
constexpr size_t kDataLength = 65'537;
socketDriver_.setStreamFlowControlWindow(id, kDataLength);

handle.value()->writeStreamData(
folly::IOBuf::copyBuffer(std::string(kDataLength, 'a')), true, nullptr);
eventBase_.loopOnce();

auto& stream = socketDriver_.streams_[id];
EXPECT_EQ(stream.writeBuf.chainLength(), kDataLength);
EXPECT_TRUE(stream.writeEOF);
EXPECT_EQ(stream.pendingWriteCb.stream, nullptr);
}

/**
* Unsure if the following is possible in production (i.e. QuicTransportBase) --
* but it tests when a ::writeChain fails without a prior ::readError or
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