Throw ProtocolError on packet decoding failures - #564
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🟡 Changes recommended
The implementation still surfaces some handshake decode failures as a generic “fail to connect” (not identifying the failed packet) which conflicts with the PR’s stated behavior, and there are a few low-risk allocation inefficiencies to address.
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Pull request overview
This PR improves ClickHouse client robustness by converting packet decode failures into ProtocolError exceptions instead of silently treating corrupted/incomplete responses as successful completion.
Changes:
- Make
ReceivePacket()throwProtocolErroron all packet decoding failures, with packet-specific context in error messages. - Refactor per-packet decoding into helper methods (
ReceiveProgress,ReceiveProfileInfo, etc.) to centralize validation and event emission. - Add unit tests that simulate corrupted server responses/handshake packets via a scripted socket.
File summaries
| File | Description |
|---|---|
clickhouse/client.cpp |
Changes packet decoding to throw ProtocolError on decode failures; refactors decoding logic into helper methods; adjusts exception handling during handshake and query response processing. |
ut/CMakeLists.txt |
Adds the new protocol-focused unit test source file to the UT target. |
ut/client_protocol_ut.cpp |
Adds tests covering malformed packet types and corrupt packet payloads to ensure decode failures raise ProtocolError (and well-formed exception packets still raise ServerException). |
Review details
Suppressed comments (1)
clickhouse/client.cpp:1234
- This pre-allocates an Exception object that is thrown away once ReceiveException succeeds (
error = ServerError(e);), causing an avoidable heap allocation during handshake failures.
ServerError ret{std::make_shared<Exception>()};
- Files reviewed: 3/3 changed files
- Comments generated: 3
- Review effort level: Lite
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| } else if (packet_type == ServerCodes::Exception) { | ||
| ReceiveException(true); | ||
| return false; | ||
| ServerError ret{std::make_shared<Exception>()}; | ||
| if (!ReceiveException(ret)) { | ||
| throw ProtocolError{"server rejected the connection, but its exception packet could not be decoded"}; | ||
| } | ||
| throw ret; | ||
| } |
Contributor
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Hello happens only during the handshake, and yes, in that case the client throws another exception.
| } | ||
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| case ServerCodes::Exception: { | ||
| ServerError ret{std::make_shared<Exception>()}; |
Contributor
Author
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This is okay for this rare exception path.
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| bool Client::Impl::ReceiveException(bool rethrow, ServerError * error) { | ||
| bool Client::Impl::ReceiveException(ServerError & error) { | ||
| std::shared_ptr<Exception> e(new Exception); |
Previously, when a packet payload could not be decoded (e.g. the connection dropped mid-response), ReceivePacket() returned an empty std::monostate variant that callers treated as a clean end of stream: NextBlock() returned std::nullopt as if the query had completed successfully, silently losing data. Now every decoding failure throws ProtocolError with a message identifying the packet that failed to decode, and std::monostate is removed from the DecodedPacket variant. Behavior changes: - A connection broken mid-query now surfaces as ProtocolError instead of a seemingly successful end of stream. This applies regardless of ClientOptions::SetRethrowException(false), which only concerns server-reported exceptions. - QueryEvents::OnServerException is no longer invoked with a partially populated exception when decoding the exception packet fails. - If the server rejects the connection but its exception packet cannot be decoded, the handshake now fails with a descriptive ProtocolError.
Move packet payload decoding out of ReceivePacket() into dedicated ReceiveProfileInfo/ReceiveProgress/ReceiveLog/ReceiveTableColumns/ ReceiveProfileEvents helpers. ReceiveException no longer throws; the throw decision (gated by ClientOptions::SetRethrowException) now lives at the call sites in ReceivePacket() and ReceiveHello().
slabko
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chernser
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Sep 4, 2026
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| if (!WireFormat::ReadVarint64(*input_, &packet_type)) { | ||
| return {}; | ||
| throw ProtocolError{"can't read packet type from input stream"}; |
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may be use different messages to mark point where it is failing?
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actually everything looks ok - never mind.
I usually like to see "read failed: packet type" - so I can grep on "read failed" and see what steps passed.
chernser
approved these changes
Sep 4, 2026
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Summary
Previously, when a packet payload could not be decoded (e.g. the connection dropped mid-response),
ReceivePacket()returned as if the query had completed successfully, silently losing data. Now every decoding failure throwsProtocolErrorwith a message identifying the packet that failed to decode.Behavior changes
QueryEvents::OnServerExceptionis no longer invoked with a partially populated exception when decoding the exception packet fails.ProtocolError.