Echo request id in post-parse Streamable HTTP error responses#1687
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tarekgh merged 1 commit intoJul 2, 2026
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On the Streamable HTTP transport, several JSON-RPC error responses were emitted with id null even after the request body had been parsed and its id was readable. This violates the base protocol responses rule (error responses must include the same id as the request, except when the id could not be read due to a malformed request) and SEP-2243's error response format for header validation failures. Thread the parsed request id through every post-parse error site on the POST path: the header validation failure (-32020 HeaderMismatch), the 2026-07-28 session-id rejection, the unsupported protocol version fallback, the new-session-only-via-initialize rejection, the stateless session-id rejection, and the session not found and forbidden cases. Pre-parse and malformed cases still return id null, which is correct. Add and strengthen conformance tests to assert the echoed id, while keeping the existing null-id guards for malformed and explicit-null-id requests. Fixes modelcontextprotocol#1677
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CC @cclabadmin |
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CC @jeffhandley |
jeffhandley
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Jul 2, 2026
halter73
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Jul 2, 2026
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Summary
On the Streamable HTTP transport, several JSON-RPC error responses were emitted with
"id": nulleven after the request body had been successfully parsed and its id was readable. This violates the base protocol responses rule (error responses MUST include the same id as the request they correspond to, except when the id could not be read due to a malformed request) and SEP-2243's error response format for header validation failures, which echoes the request id.Fix
Thread the parsed request id through every post-parse error site on the POST path in
StreamableHttpHandler:-32020HeaderMismatch) - the reported caseMcp-Session-Idrejection (SEP-2567)-32001) and forbidden casesPre-parse failures (protocol version and accept header checks) and malformed requests (invalid JSON, explicit
id: null) still returnid: null, which is correct per the base protocol.Tests
Mcp-Nametest to assert the echoed id.All
ModelContextProtocol.AspNetCore.Testspass on net8.0, net9.0, and net10.0.Fixes #1677