fix: notify session when SSE stream closes without event ID#1940
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kxbnb wants to merge 1 commit intomodelcontextprotocol:mainfrom
Open
fix: notify session when SSE stream closes without event ID#1940kxbnb wants to merge 1 commit intomodelcontextprotocol:mainfrom
kxbnb wants to merge 1 commit intomodelcontextprotocol:mainfrom
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Fixes modelcontextprotocol#1811 When an SSE stream closes without having received any events with IDs, the client would silently return without notifying the session layer. This left `call_tool()` hanging indefinitely since the session never received a response or error. Now when the stream closes without a `last_event_id` (meaning we can't reconnect), we send a JSONRPCError with CONNECTION_CLOSED code back to the session so the request properly fails instead of hanging. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
Fixes #1811
When an SSE stream closes without having received any events with IDs, the client silently returns without notifying the session layer. This leaves
call_tool()hanging indefinitely.Changes
elsebranch in_handle_sse_responseto handle the case wherelast_event_id is NoneJSONRPCErrorwithCONNECTION_CLOSEDcode back to the sessioncall_tool()properly raisesMcpErrorinstead of hangingRoot Cause
The issue occurs when:
_handle_sse_responsefunction exits silently (nolast_event_idto reconnect with)Validation
uv run pyrightpasses with 0 errorsCloses #1811