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fix(http): update cpp-httplib to v0.63.0 to stop realtime WebSocket drops under load - #73
VitorAMJorge wants to merge 2 commits into
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| Layer / File(s) | Summary |
|---|---|
Dependency update and timeout handling third_party/cpp-httplib, server/http/http_server.cpp, server/http/s2s_realtime.cpp |
The cpp-httplib submodule reference changes. Both realtime WebSocket loops now continue after a read timeout without processing the retained message. |
Buffered-frame regression test tests/cpp/common/test_websocket_frames.cpp, tests/cpp/CMakeLists.txt |
The integration test sends masked frame bursts across varied lead-frame lengths and checks that the server receives all 65 frames. Non-Windows builds register the test with CTest. |
Priority:
Estimated code review effort: 3 (Moderate) | ~20 minutes
Change: Bug fix · Severity of issue fixed: Medium
Merge Risk: 
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No actionable merge-blocking risk remains from the reviewed change.
Pre-merge checks: 
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Check name Status Explanation Description check The description directly explains the cpp-httplib update, the WebSocket frame-drop issue, the Timeout handling, the regression test, and the reported validation results. Title check The title clearly identifies the cpp-httplib update and its purpose of preventing realtime WebSocket drops under load. Linked Issues check Issue #72requires a cpp-httplib update to at least v0.59.0 and a regression test for queued WebSocket frames across all 4 KiB buffer alignments. The submodule updates to v0.63.0. `test_websocket_fram…Out of Scope Changes check The changed files support Issue #72. The submodule update provides the frame-read fix. The read-loop changes support the updated result type. The CMake and integration-test changes verify the required…Docstring Coverage Docstring coverage is inconclusive: files from earlier reviews still need to be rechecked within the check's analysis limits. Not blocking. Full details: Linked Issues check
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Explanation
Issue
#72requires a cpp-httplib update to at least v0.59.0 and a regression test for queued WebSocket frames across all 4 KiB buffer alignments. The submodule updates to v0.63.0.test_websocket_frames.cppsends the required burst and checks all 648 lead-frame alignments. CMake registers the test. Both server read loops handleReadResult::Timeoutwithout processing stale message data. The public WebSocket API and server CMake options remain unchanged.
Full details: Out of Scope Changes check
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Explanation
The changed files support Issue
#72. The submodule update provides the frame-read fix. The read-loop changes support the updated result type. The CMake and integration-test changes verify the required behavior. No unrelated production behavior or public API change is identified.
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Inline comments:
Review comments at @tests/cpp/common/test_websocket_frames.cpp:
- Around line 41-43: Update append_frame to use the shortest RFC 6455
payload-length encoding: encode lengths below 126 in the 7-bit field, or adjust
the lead-payload range to start at 126 while retaining 648 consecutive lengths.
Ensure every generated lead frame has a valid length encoding.
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- Repository: NVIDIA/NeMo-Speech.cpp
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📒 Files selected for processing: 5
server/http/http_server.cppserver/http/s2s_realtime.cpptests/cpp/CMakeLists.txttests/cpp/common/test_websocket_frames.cppthird_party/cpp-httplib
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 [Medium impact] No established issue blocks merging this PR. SummaryUpdates
No new actionable issues were established. Tests were not run, and the updated submodule’s source was unavailable locally. Reviews (3) · Last reviewed commit: "test(http): keep every websocket_frames ..." · Reviewed by Greptile |
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The pre-commit.ci failure is pre-existing on main: license-headers reports missing license header: src/runtime/ggml/llama_log_shim.cpp, which this PR does not touch. The same check fails on main at 2bdfb03 (pre-commit.ci run). The checker requires files under src/runtime/ggml/ to carry the parakeet.cpp-derived notice, and llama_log_shim.cpp (added in #47) only has the NVIDIA header. All other hooks pass on this PR. |
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@VitorAMJorge thanks for the fix! Can you please resolve conflict and rebase on main? |
cpp-httplib v0.50.1 reads each WebSocket frame header field (the 2-byte header, the extended length, the 4-byte mask) with a single Stream::read. The server reads its socket through a 4 KiB buffer, so once frames queue up behind a busy server a field can straddle the end of the buffer; the read comes back short, the frame is rejected, and the connection is dropped without a close frame. Realtime clients see it as a transport drop under load. v0.59.0 reads each field in full (read_exact); v0.63.0 is the current release and adds further WebSocket hardening. The public API the servers use (ws::WebSocket, read(), close(), CloseStatus) and the CMake options are unchanged. ws::ReadResult gains Timeout, returned only after a read timeout set on the socket itself, which neither server sets; both read loops now skip it rather than re-handling the previous message. The idle backstop is still 300 s. test_websocket_frames: a real server and a raw TCP client that writes a burst of masked 640-byte binary frames at every alignment of the 4 KiB buffer. v0.50.1 drops a frame at 50 of 648 alignments; v0.63.0 receives every frame. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Vitor A. M. Jorge <vitor.jorge@widelabs.com.br>
…th form The lead frame's payload ran from 0 to 647 bytes but was always written with the 16-bit extended length. RFC 6455 requires the shortest encoding, so the 126 leads below 126 bytes were malformed frames that a strict parser could reject for a reason unrelated to short reads. The sweep now uses 648 consecutive payload lengths from 126, covering the same alignments of the 4 KiB buffer with valid frames. Results are unchanged: v0.50.1 drops frames at 50 of 648 alignments, v0.63.0 at none. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Signed-off-by: Vitor A. M. Jorge <vitor.jorge@widelabs.com.br>
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@pskrunner14 done. had force push. |
| // httplib listens with a backlog of 5 pending connections: a burst of clients beyond that is | ||
| // reset before a worker sees it. Queue as many as the server has workers (Linux caps it at | ||
| // net.core.somaxconn); listening again on a listening socket changes only its backlog. | ||
| return ::listen(impl_->listen_socket, std::max(5, impl_->config.threads)) == 0; |
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One small follow-on from the version bump, here we call listen() a second time with std::max(5, threads), because cpp-httplib v0.50.1 used a listen backlog of only 5. v0.63.0 raised that default to 128, and the second listen() replaces it, so a default 4-thread server ends up at 5 instead of 128. That's not worse than today, but the comment becomes wrong and the workaround now partly cancels the upgrade. Can you change it to std::max(CPPHTTPLIB_LISTEN_BACKLOG, impl_->config.threads) and update the comment to match?
Fixes #72
The core idea of this PR is to update the behavior of websockets under load to use the new cpp-httplib.
The library cpp-httplib v0.50.1 reads each WebSocket frame header field (2-byte header, extended length, 4-byte mask) with a single Stream::read. The server reads its socket through a 4 KiB buffer, so once frames queue up at a busy server a field can cros the end of the buffer; the read comes back short, the frame is rejected, and the connection is dropped without the closing frame. Realtime clients see it as a transport drop under load. v0.59.0 reads each field in full (read_exact); v0.63.0 is the current release and adds useful WebSocket hardening.
The public API servers use and the CMake options are unchanged. However, ws::ReadResult gains Timeout, returned only after a read timeout set on the socket itself, which neither server sets; both read loops now skip it rather than re-handling the previous message. The idle backstop remains 300 s.
test_websocket_frames: consists of a real server and a raw TCP client that writes a burst of masked 640-byte binary frames at every alignment of the 4 KiB buffer. v0.50.1 drops a frame at 50 of 648 alignments; v0.63.0 receives every frame.
Testing
Fresh clone of this branch, submodules from
.gitmodules, Ubuntu 24.04.2, g++ 13.3.0:scripts/configure.sh cpu-server -DNEMO_SPEECH_BUILD_TESTS=ON, thencmake --build --preset cpu-server: builds cleanly, no warnings in changed files. (cpu-serverrather thancpu-asr, sincecpu-asrdoes not build the HTTP server.)ctest --test-dir build/cpu-server --output-on-failure: 17/17 passed.pre-commit run --all-files: all hooks pass exceptlicense-headers, whichalso fails on
main(src/runtime/ggml/llama_log_shim.cpp, added in feat(runtime): mmap-backed zero-copy ASR weight loading #47);unrelated to this change.
Important
cpp-httplib intends Timeout as a way to get control back periodically, to send something or check a deadline; continue simply ignores it. That is correct as long as no read timeout is set on the WebSocket, and I checked that nothing in the repository sets one (the server's HTTP set_read_timeout does not apply to upgraded WebSocket connections). Whoever adds one later should replace the continue with the periodic work they need.
AI use
An AI assistant (Claude Opus 5.5) helped investigate and fix the bug. I reviewed the changes and tested them on my application