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Treat JSON-null MCP result/error members as omitted - #337
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parse_response treated a present JSON-null member as a real result or error, so serializers that emit "error": null on success (or "result": null on error) threw. Client::rpc counted that as a parse failure and killed the MCP subprocess after five such lines. Match A2A: null means omitted; dual non-null members still reject. Co-authored-by: Tyler Reckart <tylerreckart@users.noreply.github.com>
This was referenced Sep 14, 2026
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Problem
parse_responsetreated a present JSON-nullresultorerrormember as a real value. A serializer (or proxy) that emits{"jsonrpc":"2.0","id":1,"result":{...},"error":null}on success — or"result":nullon error — threwresponse has both 'result' and 'error'.Client::rpccounts that throw as a parse failure, skips the line, and kills the MCP subprocess after five such envelopes./mcptools then fail until the session is rebuilt. A2A already treats JSON-null as omitted (rpc_response_from_json); MCP did not.Fix
Treat JSON-null
result/erroras omitted for the exclusivity check. Dual non-null members still reject. A successful method that returns JSONnullstill keepsresult(distinct from a notification with no result member).Tests
unit_mcp— success +error:null, error +result:null, successfulresult:null,error:nullonly, and the existing dual-object reject. Parse cases 4/4 locally; fullunit_mcp49/49.Independently mergeable against
main(0456350). Code hunks (src/mcp/types.cpp,tests/test_mcp.cpp) do not overlap #321–#336. CHANGELOG[Unreleased]will need a rebase after whichever sibling merges first.