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The POST handler answered a body that is not valid JSON with Invalid Request (-32600). JSON-RPC 2.0 section 5.1 reserves -32700 for invalid JSON and -32600 for JSON that is not a valid request object. Parse the body as JSON first and answer -32700 when that fails, then deserialize the JSON-RPC message and keep -32600 for envelope failures such as an explicit null request id. Fixes modelcontextprotocol#1918
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Fixes #1918
The Streamable HTTP POST handler caught every
JsonExceptionfrom reading the body in one place and answeredInvalidRequest(-32600). That catch covered two different failures: a body that is not valid JSON, and valid JSON that theJsonRpcMessageconverter rejects (for example"id": null). JSON-RPC 2.0 §5.1 assigns -32700 (Parse error) to the first and -32600 to the second.The handler now reads the body as a
JsonElementfirst and answersParseError(-32700) if that fails, then deserializes theJsonRpcMessagefrom the element and keepsInvalidRequest(-32600) for envelope failures. HTTP status stays 400 and the error id stays null.SseHandler, which sharesReadJsonRpcMessageAsync, is unchanged. This matches the stdio transport, which already answersParseErrorsince #1629.Tests:
PostMalformedJson_Returns400_InvalidRequest_WithNullIdasserted -32600 for malformed JSON; it is nowPostMalformedJson_Returns400_ParseError_WithNullId, a theory over{ this is not valid jsonand the issue's truncated{"jsonrpc":. Both cases fail on main (expected -32700, actual -32600) and pass with this change.PostRequestWithExplicitNullId_Returns400_InvalidRequest_WithNullIdstill passes, pinning -32600 for valid JSON that is not a valid request. Builds on net8.0/net9.0/net10.0 with 0 warnings; tests run on net10.0.Reproduced against
samples/AspNetCoreMcpServerby POSTing{"jsonrpc":: main answers -32600, this branch answers -32700 (recording below).Notes: overlaps the
catchblock edited in #1844, so whichever lands second needs a small rebase. Valid requests now parse once into aJsonElementbefore deserializing; happy to measure if that's a concern. Opened as a draft so the approach can be confirmed on the issue first.AI disclosure: this change was written with Claude Code (investigation, code and tests). I reviewed the diff and ran the build and tests locally.
Evidence: real MCP clients against the SDK's own
samples/AspNetCoreMcpServer. Left pane: the sample server, built from main (before) or this branch (after), with its request log. Right: the official MCP Inspector connects over Streamable HTTP and callsechonormally, then a small "buggy client" page POSTs (1) a normalinitialize, (2) a body cut off mid-write ({"jsonrpc":), and (3) valid JSON with"id": null, showing the error code it gets back and what that code tells a client developer.Before (main): the cut-off body gets -32600 Invalid Request.
video-narrow.mp4
After (this branch): the cut-off body gets -32700 Parse error; the null-id request still gets -32600.
video-narrow.mp4