Handle asyncio.CancelledError in ToolNode #6764
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Fixes langchain-ai#6726 When a tool execution raises asyncio.CancelledError and handle_tool_errors=True, the ToolNode now creates an error ToolMessage instead of letting the error propagate. This prevents INVALID_CHAT_HISTORY errors when tools are cancelled. Root cause: asyncio.CancelledError inherits from BaseException, not Exception, so it wasn't caught by the existing exception handler. Changes: - Add explicit asyncio.CancelledError handler in _execute_tool_async before the general Exception handler - When handle_tool_errors=True, convert CancelledError to error ToolMessage with appropriate error content - When handle_tool_errors=False, re-raise CancelledError - Add comprehensive tests for both error handling scenarios
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PR Review SummaryStatus: ✅ READY TO MERGEWell-handled edge case! This PR correctly catches which inherits from rather than , allowing proper error handling in ToolNode. Key Strengths:
Technical Details:Problem: inherits from , not , so it bypassed the existing exception handler and propagated unhandled Solution:
Test Coverage:
This is a clean fix for a subtle Python exception hierarchy issue. Proper error handling for async tool cancellation. Ready for merge! |
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Summary
Fixes #6726 - ToolNode now properly handles asyncio.CancelledError when handle_tool_errors=True.
Problem
When a tool execution is cancelled via
asyncio.CancelledError, theToolNodedoes not create an errorToolMessageeven whenhandle_tool_errors=True. This leaves the message history in an invalid state where anAIMessagehastool_callswithout correspondingToolMessages, causing INVALID_CHAT_HISTORY errors on subsequent LLM calls.Root cause:
asyncio.CancelledErrorinherits fromBaseException, notException, so it bypasses the existing exception handler which only catchesExceptionand its subclasses.Solution
Added an explicit handler for
asyncio.CancelledErrorin_execute_tool_async()that:CancelledErrorbefore the generalExceptionhandlerhandle_tool_errors=True, converts it to an errorToolMessagewith "Tool execution was cancelled" messagehandle_tool_errors=False, re-raises theCancelledError(preserving existing behavior)Test Plan
Added two comprehensive tests:
test_tool_node_handles_cancelled_error: Verifies that when a tool raises CancelledError and handle_tool_errors=True, it returns an error ToolMessage instead of propagating the errortest_tool_node_raises_cancelled_error_when_not_handled: Verifies that when handle_tool_errors=False, CancelledError is still raisedChanges
libs/prebuilt/langgraph/prebuilt/tool_node.py: Added CancelledError handlerlibs/prebuilt/tests/test_tool_node.py: Added regression tests