Fix WebTransportImpl session flow control granting too frequently#613
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afrind wants to merge 1 commit intofacebook:mainfrom
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Fix WebTransportImpl session flow control granting too frequently#613afrind wants to merge 1 commit intofacebook:mainfrom
afrind wants to merge 1 commit intofacebook:mainfrom
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shouldGrantFlowControl() was checking (getCurrentOffset() - bytesRead_) i.e. bytes buffered but not yet consumed by the app. After every read this drops to ~0, satisfying the < window/2 condition unconditionally and sending WT_MAX_DATA after every tiny read regardless of how much window the peer actually had remaining. Fix: check (getMaxOffset() - bytesRead_) < window/2 instead — only grant when the app has consumed enough that the peer is within half a window of their limit. Also guard sendWTMaxData on the return value of recvFlowController_.grant() to avoid sending capsules when the flow controller is initialized to kMaxVarInt (no configured FC). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
joanna-jo
approved these changes
Apr 20, 2026
| .WillRepeatedly(Return(folly::unit)); | ||
| } | ||
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| TEST_F(HTTPTransactionWebTransportTest, FrequentFlowControlGrants) { |
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redundant test? i think this is already tested above?
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@joanna-jo has imported this pull request. If you are a Meta employee, you can view this in D101809433. |
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shouldGrantFlowControl() was checking (getCurrentOffset() - bytesRead_) i.e. bytes buffered but not yet consumed by the app. After every read this drops to ~0, satisfying the < window/2 condition unconditionally and sending WT_MAX_DATA after every tiny read regardless of how much window the peer actually had remaining.
Fix: check (getMaxOffset() - bytesRead_) < window/2 instead — only grant when the app has consumed enough that the peer is within half a window of their limit. Also guard sendWTMaxData on the return value of recvFlowController_.grant() to avoid sending capsules when the flow controller is initialized to kMaxVarInt (no configured FC).