Stacktrace w/ gRPC and generators

[jlintz]

Summary of problem

APM appears to be breaking on python grpc calls, coming from https://github.com/DataDog/dd-trace-py/blob/main/ddtrace/contrib/internal/grpc/client_interceptor.py#L128 when a generator is passed in

We believe a fix would be to initialize _span = None in the above code location as follows...

class _WrappedResponseCallFuture(wrapt.ObjectProxy):
    _span = None
    def __init__(self, wrapped, span):
        # everything else is the same

basic test case:

import wrapt
class _WrappedResponseCallFuture(wrapt.ObjectProxy):
	_span = None 
	def __init__(self, wrapped, span):
		super(_WrappedResponseCallFuture, self).__init__(wrapped)
		self._span = span
		
		
def gen(n):
	yield n
	yield n + 1
	

_WrappedResponseCallFuture(gen, 'foo')

Removing _span = None will break the above code.

Which version of dd-trace-py are you using?

2.9.2

Which version of pip are you using?

n/a

Which libraries and their versions are you using?

Python 3.10
grpcio 1.49.1

How can we reproduce your problem?

What is the result that you get?

~/dev-vscode/.base_universe/glibc-2.31-x86_64/ext/public/python/grpcio/1/49/1/dist/lib/python3.10/grpc/_interceptor.py in __next__(self)
    142 
    143     def __next__(self):
--> 144         raise self._exception
    145 
    146     def next(self):

~/dev-vscode/.base_universe/glibc-2.31-x86_64/ext/public/python/grpcio/1/49/1/dist/lib/python3.10/grpc/_interceptor.py in __call__(self, request, timeout, metadata, credentials, wait_for_ready, compression)
    333 
    334         try:
--> 335             return self._interceptor.intercept_unary_stream(
    336                 continuation, client_call_details, request)
    337         except Exception as exception:  # pylint:disable=broad-except

~/dev-vscode/.base_universe/glibc-2.31-x86_64/ext/public/python/ddtrace/2/9/2/dist/lib/python3.10/ddtrace/contrib/grpc/client_interceptor.py in intercept_unary_stream(self, continuation, client_call_details, request)
    253         )
    254         response_iterator = continuation(client_call_details, request)
--> 255         response_iterator = _WrappedResponseCallFuture(response_iterator, span)
    256         return response_iterator
    257 

~/dev-vscode/.base_universe/glibc-2.31-x86_64/ext/public/python/ddtrace/2/9/2/dist/lib/python3.10/ddtrace/contrib/grpc/client_interceptor.py in __init__(self, wrapped, span)
    128     def __init__(self, wrapped, span):
    129         super(_WrappedResponseCallFuture, self).__init__(wrapped)
--> 130         self._span = span
    131         # Registers callback on the _MultiThreadedRendezvous future to finish
    132         # span in case StopIteration is never raised but RPC is terminated

AttributeError: 'generator' object has no attribute '_span'

What is the result that you expected?

No stacktrace