fix(streamable_http): handle ClientDisconnect during POST at WARNING level#4
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wiggzz merged 2 commits intodbt-labs/patched-1.27.0from May 5, 2026
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…level Catch ClientDisconnect in _handle_post_request so client disconnections (network timeout, cancel, LB drop) log at WARNING instead of ERROR and do not attempt to send a response to the closed socket. This fixes pattern 1 (67% of all prod ERRORs in ai-codegen-api): when the client disconnects mid-POST, the current except-Exception handler synthesizes a 500 response to a closed socket and logs ERROR-level noise to Datadog. Changes: - Catch ClientDisconnect before the generic except-Exception handler - Log at WARNING (honest level: we aborted but it wasn't our fault) - Notify the session writer so inner session tasks unblock cleanly - Suppress errors from writer.send() since the writer may already be closed - Skip sending a response (the socket is gone) Upstream context: - modelcontextprotocol#1647 (POST-only scope, right approach) - modelcontextprotocol#1947 (writer-notification semantics, skip-response) - modelcontextprotocol#1648 (tracking issue, still open, no PRs merged) This patch takes the spirit of modelcontextprotocol#1647 (POST-only scope) + the semantics of modelcontextprotocol#1947 (notify writer, skip response) in a tight ~10-line change. Github-Issue:modelcontextprotocol#1648
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Problem
When a client disconnects mid-POST (network timeout, cancel, LB drop), the MCP SDK's
_handle_post_requestcatchesClientDisconnectin its genericexcept Exceptionhandler, which:Solution
Catch
ClientDisconnectbefore the genericexcept Exceptionhandler in_handle_post_request:ClientDisconnect()so inner session tasks unblock cleanly (stateful sessions)_handle_post_requestTests
4 new unit tests in
tests/server/streamable_http/test_client_disconnect_post.py:test_client_disconnect_logs_warning_not_error— verifies WARNING, not ERRORtest_client_disconnect_does_not_send_response— verifies no ASGI sends to closed sockettest_client_disconnect_notifies_writer— verifies writer receives ClientDisconnecttest_client_disconnect_writer_suppresses_errors— verifies broken writer doesn't crash usAll existing streamable_http tests pass (pre-existing flaky test
test_stateless_get_returns_405excluded).Upstream context
This patch combines the approach of two open upstream PRs (neither merged):
This is a tight ~10-line change taking the spirit of modelcontextprotocol#1647 + semantics of modelcontextprotocol#1947. Tracking issue: modelcontextprotocol/python-sdk#1648.
Follow-up
After this lands in the fork and is verified in prod via ai-codegen-api bump:
ClientDisconnectHandlerMiddlewarein ai-codegen-api (no longer load-bearing for POST path)