fix(streamable-http-server): map handler-generated HeaderMismatch to … - #1259
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fix(streamable-http-server): map handler-generated HeaderMismatch to …#1259voidstackloop wants to merge 1 commit into
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…HTTP 400 `jsonrpc_http_status` maps several protocol errors (unsupported protocol version, missing required client capability, invalid params) to HTTP 400 on the modern per-request Streamable HTTP path, but fell through to the default HTTP 200 for `ErrorCode::HEADER_MISMATCH`. When a `ServerHandler` returns `Err(ErrorData::header_mismatch(...))`, RMCP serialized the correct JSON-RPC -32020 error but sent it with HTTP 200. The legacy/transport-generated header validation path (SEP-2243 Mcp-Method/Mcp-Name/Mcp-Param-* mismatches) was unaffected, since `header_mismatch_jsonrpc_response` constructs an HTTP 400 response directly rather than going through `jsonrpc_http_status`. Only handler-generated HeaderMismatch errors on the modern path hit the bug. Add `ErrorCode::HEADER_MISMATCH` to the existing `BAD_REQUEST` match arm, matching the Streamable HTTP server-validation rules in the 2026-07-28 spec. Added unit tests covering the mapper directly (header-mismatch to 400, method-not-found to 404, an unmapped code defaulting to 200). Closes modelcontextprotocol#1225 Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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…HTTP 400
jsonrpc_http_statusmaps several protocol errors (unsupported protocol version, missing required client capability, invalid params) to HTTP 400 on the modern per-request Streamable HTTP path, but fell through to the default HTTP 200 forErrorCode::HEADER_MISMATCH. When aServerHandlerreturnsErr(ErrorData::header_mismatch(...)), RMCP serialized the correct JSON-RPC -32020 error but sent it with HTTP 200.The legacy/transport-generated header validation path (SEP-2243 Mcp-Method/Mcp-Name/Mcp-Param-* mismatches) was unaffected, since
header_mismatch_jsonrpc_responseconstructs an HTTP 400 response directly rather than going throughjsonrpc_http_status. Only handler-generated HeaderMismatch errors on the modern path hit the bug.Add
ErrorCode::HEADER_MISMATCHto the existingBAD_REQUESTmatch arm, matching the Streamable HTTP server-validation rules in the 2026-07-28 spec. Added unit tests covering the mapper directly (header-mismatch to 400, method-not-found to 404, an unmapped code defaulting to 200).Closes #1225
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