Python agent errors on using capture exception in decorator function

[codeninja55]

Describe the bug: ...
When trying to capture an exception in a decorator function, APM produces the following error.

File "/opt/conda/lib/python3.7/site-packages/flask_restful/__init__.py", line 573, in dispatch_request
    resp = meth(*args, **kwargs)
  File "/usr/src/app/sim_api/middleware.py", line 343, in decorated_func
    apm.capture_exception()
  File "/opt/conda/lib/python3.7/site-packages/elasticapm/contrib/flask/__init__.py", line 214, in capture_exception
    return self.client.capture_exception(*args, **kwargs)
  File "/opt/conda/lib/python3.7/site-packages/elasticapm/base.py", line 224, in capture_exception
    return self.capture("Exception", exc_info=exc_info, handled=handled, **kwargs)
  File "/opt/conda/lib/python3.7/site-packages/elasticapm/base.py", line 194, in capture
    event_type, date=date, context=context, custom=custom, stack=stack, handled=handled, **kwargs
  File "/opt/conda/lib/python3.7/site-packages/elasticapm/base.py", line 377, in _build_msg_for_logging
    result = handler.capture(self, **kwargs)
  File "/opt/conda/lib/python3.7/site-packages/elasticapm/events.py", line 119, in capture
    exc_type = exc_type.__name__
AttributeError: 'NoneType' object has no attribute '__name__'

To Reproduce

Take this function:

def auth_restful(f)
    @wraps(f)
    def decorated_func(*args, **kwargs):
        resp = User.decode_auth_token(auth_token=auth_token)
       
        if not user.is_admin:
            response['message'] = 'Not authorized.'
           # Error occurs HERE
            apm.capture_exception()
            return response, 403
        return f(user, *args, **kwargs)
    return decorated_func

The Flask-RESTful library and code to do this is as follows:

class UserList(Resource):
    """Return all users (admin only)"""

    method_decorators = {'get': [auth_restful]}

    def get(self, _) -> Tuple[dict, int]:
        """Get all users only available to admins."""
        user_list = User.as_dict
        response = {'status': 'success', 'data': {'users': user_list}}
        return response, 200

Expected behavior: ...

Environment (please complete the following information)

• OS: [e.g. Linux]: Docker base continuumio/miniconda3:4.6.14
• Python version: 3.7.3
• Framework and version [e.g. Django 2.1]: Flask-RESTful
• APM Server version: 5.1.2
• Agent version: 5.1.2

Additional context

Add any other context about the problem here.

• requirements.txt:

  Click to expand

  Flask==1.0.2
  elastic-apm[flask]==5.1.2
  fluent-logger==0.9.3
  Flask-RESTful==0.3.7
  Flask-Testing==0.7.1
  

[beniwohli]

Hi @codeninja55

Thanks for opening the issue. While there is indeed a bug here, I think you'd want to use capture_message instead, something like apm.capture_message("Unauthorized access"). capture_exception requires an actual Python exception to be present.

The bug is that we should detect if capture_exception is used when no exception is present, and warn instead of exploding. The actual problem is here:

apm-agent-python/elasticapm/events.py

Lines 85 to 90 in d0f2a39

	if not exc_info or exc_info is True:
	new_exc_info = True
	exc_info = sys.exc_info()
	if not exc_info:
	raise ValueError("No exception found")

When no exception is present, sys.exc_info() returns (None, None, None), not None as the if not exc_info line seems to think.

[codeninja55]

Thanks for the response. I'll do as you suggest.

[basepi]

Better error handling in #600 ^

Thanks again for the report!