fix: catch ClosedResourceError in error handler to prevent crash on client disconnect#2160
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…lient disconnect When a client disconnects during request processing, _handle_message receives the exception and tries to send a log message back to the client via send_log_message(). Since the write stream is already closed, this raises ClosedResourceError (or BrokenResourceError), which is unhandled and crashes the stateless session with an ExceptionGroup. Wrap the send_log_message() call in a try/except that catches both anyio.ClosedResourceError and anyio.BrokenResourceError, since failing to notify a disconnected client is expected and harmless. This is a different code path from PR modelcontextprotocol#1384, which fixed the message router loop. This fix covers the _handle_post_request → _handle_message → send_log_message error recovery path. Fixes modelcontextprotocol#2064
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Closing in favor of #2161 which covers the same scenario. |
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Summary
Fixes #2064
When a client disconnects during request processing,
_handle_messagereceives the exception and tries to send a log message back viasend_log_message(). Since the write stream is already closed, this raisesClosedResourceError, which is unhandled and crashes the stateless session with anExceptionGroup.Root Cause
In
lowlevel/server.py, theExceptionbranch of_handle_message(line ~418) callssession.send_log_message()unconditionally. When the error is a client disconnect, the write stream is already closed, so the chainsend_log_message → send_notification → _write_stream.send()raisesClosedResourceError.This is a different code path from PR #1384, which fixed
ClosedResourceErrorin the message router loop. This fix covers the_handle_post_request → _handle_message → send_log_messageerror recovery path.Fix
Wrap the
send_log_message()call in a try/except that catches bothanyio.ClosedResourceErrorandanyio.BrokenResourceError, logging a warning instead of crashing. Failing to notify a disconnected client is expected and harmless.Test Results
475 server tests pass (2 consecutive clean runs).