Bug: return in finally can swallow exceptions

[iritkatriel]

At this location:

aws-sam-cli/samcli/local/apigw/local_apigw_service.py

Line 721 in 97e63dc

return auth_service_error

there is a return statement in a finally block, which would swallow any in-flight exception.

This means that if a BaseException (such as KeyboardInterrupt) is raised from the try body, or any exception is raised from an except: clause, it will not propagate on as expected.

See also https://docs.python.org/3/tutorial/errors.html#defining-clean-up-actions.

[lucashuy]

Thanks for opening this issue, this might be by design since this control block is within the Flask app, and an exception raised within this block will halt the entire sam local start-api command, which is supposed to be left open in the background.

The return only triggers if we catch a specific, known, Lambda execution error. The catch all should still be raised/re-raised normally since we aren't creating a Flask service exception in the catch all block.

Was there a specific exception or behaviour that you saw during sam local start-api that was swallowed, but shouldn't have?

[iritkatriel]

Was there a specific exception or behaviour that you saw during sam local start-api that was swallowed, but shouldn't have?

No, my comment is based on inspection of the code.

I see what you mean - perhaps it's worth adding a comment stating this is deliberate, in case someone else has my reaction.

[iritkatriel]

On second thought - you don't expect there to be an in-flight exception when the return executes, so perhaps just dedent the

            if auth_service_error:
                return auth_service_error

so that it's not in the finally?