[GRPC] Handle the null span case

[sublime1809]

Describe the bug: ...

To Reproduce

1. Setup ElasticAPM in Django
2. Integrate with Google PubSub client
3. Try to publish message from your script
4. Stacktrace:

Exception in thread Thread-CommitBatchPublisher:
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.8/threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.8/site-packages/google/cloud/pubsub_v1/publisher/_batch/thread.py", line 274, in _commit
    response = self._client._gapic_publish(
  File "/usr/local/lib/python3.8/site-packages/google/cloud/pubsub_v1/publisher/client.py", line 272, in _gapic_publish
    return super().publish(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/google/pubsub_v1/services/publisher/client.py", line 781, in publish
    response = rpc(
  File "/usr/local/lib/python3.8/site-packages/google/api_core/gapic_v1/method.py", line 113, in __call__
    return wrapped_func(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/google/api_core/retry.py", line 349, in retry_wrapped_func
    return retry_target(
  File "/usr/local/lib/python3.8/site-packages/google/api_core/retry.py", line 191, in retry_target
    return target()
  File "/usr/local/lib/python3.8/site-packages/google/api_core/timeout.py", line 120, in func_with_timeout
    return func(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/google/api_core/grpc_helpers.py", line 72, in error_remapped_callable
    return callable_(*args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/grpc/_interceptor.py", line 247, in __call__
    response, ignored_call = self._with_call(request,
  File "/usr/local/lib/python3.8/site-packages/grpc/_interceptor.py", line 287, in _with_call
    call = self._interceptor.intercept_unary_unary(continuation,
  File "/usr/local/lib/python3.8/site-packages/elasticapm/contrib/grpc/client_interceptor.py", line 97, in intercept_unary_unary
    client_call_details = self.attach_traceparent(client_call_details, span)
  File "/usr/local/lib/python3.8/site-packages/elasticapm/contrib/grpc/client_interceptor.py", line 195, in attach_traceparent
    if not span.transaction:
AttributeError: 'NoneType' object has no attribute 'transaction'

Environment (please complete the following information)

• OS: Linux
• Python version: 3.8
• Framework and version [e.g. Django 2.1]: Django 3.8
• APM Server version: 7.15
• Agent version: 6.14.0

Additional context

Add any other context about the problem here.

• requirements.txt:

  Click to expand

  google-cloud-pubsub==2.13.11
  

Initial digging
Looks like the span is not being returned from the context manager, but the grpc code is not handling the None case.

• context manager
• grpc code

I can make a patch to handle the None case (and just return the client call details), but not sure if that is the right call here. Any guidance would be appreciated!

[beniwohli]

Hey @sublime1809, thanks for the detailed report. Your analysis was spot on, we needed to handle the case where the capture_span context manager doesn't return a span, but didn't. I opened a #1740 to address this (I missed your offer to contribute a patch, sorry about that).

We'll release this in a patch release in the coming days.

[ckoehn]

@beniwohli Any chance to get the patch release this week?