fix: reject duplicate JSON-RPC request IDs with 409 Conflict (fixes #2655)#2944
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When a client reuses a JSON-RPC request id while the original request is still in flight, StreamableHTTPServerTransport now checks for a collision in _request_streams before registering a new stream slot. Previously the assignment was unconditional, which silently overwrote the prior (send, receive) pair — the original request's caller would hang until timeout and the response could be routed to the wrong caller. The fix mirrors the existing GET_STREAM_KEY collision guard at line 695. Also adds an optional request_id parameter to _create_error_response so the JSON-RPC error envelope carries the offending id instead of always using null. Fixes modelcontextprotocol#2655 Co-Authored-By: Claude <noreply@anthropic.com>
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Summary
Fixes #2655:
StreamableHTTPServerTransportnow detects and rejects duplicate JSON-RPC request IDs before overwriting the in-flight stream slot.Before: A client sending two requests with the same
idon the same session would silently overwrite the first request's(send, receive)stream pair in_request_streams. The original caller hangs until timeout; the response may route to the wrong caller.After: The server returns HTTP 409 Conflict with a JSON-RPC
-32600 Invalid Requesterror, preserving the original in-flight stream.Changes
_handle_post_request— added collision check before stream registration, mirroring the existingGET_STREAM_KEYguard at line 695_create_error_response— added optional keyword-onlyrequest_idparameter so the JSON-RPC error envelope carries the offending id instead ofnullAI Assistance Disclosure
This contribution was developed with AI assistance (Claude / Anthropic Claude Code).
Verification Process
uv sync --no-group docsinstalled all dependenciesstreamable_http.py, +1noqa: C901)test_duplicate_request_id_rejected_with_409:_request_streamswith an in-flight requestruff format+ruff check: all cleanCross-Validation
idfieldnull🤖 Generated with Claude Code