FastAPI/Starlette: Unexpected argument app

Describe the bug: …

Hi, I cannot seem to add ElasticAPM as middleware for the following versions:

starlette==0.13.2 fastapi==0.52.0 elastic-apm==5.5.2

The error is:

Process SpawnProcess-1:
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/process.py", line 315, in _bootstrap
    self.run()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/xxx/.../venv/lib/python3.8/site-packages/uvicorn/subprocess.py", line 61, in subprocess_started
    target(sockets=sockets)
  File "/Users/xxx/.../venv/lib/python3.8/site-packages/uvicorn/main.py", line 382, in run
    loop.run_until_complete(self.serve(sockets=sockets))
  File "uvloop/loop.pyx", line 1456, in uvloop.loop.Loop.run_until_complete
  File "/Users/xxx/.../venv/lib/python3.8/site-packages/uvicorn/main.py", line 389, in serve
    config.load()
  File "/Users/xxx/.../venv/lib/python3.8/site-packages/uvicorn/config.py", line 288, in load
    self.loaded_app = import_from_string(self.app)
  File "/Users/xxx/.../venv/lib/python3.8/site-packages/uvicorn/importer.py", line 20, in import_from_string
    module = importlib.import_module(module_str)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 783, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "./app.py", line 20, in <module>
    app.add_middleware(ElasticAPM, client=elasticapm)
  File "/Users/xxx/.../venv/lib/python3.8/site-packages/starlette/applications.py", line 117, in add_middleware
    self.middleware_stack = self.build_middleware_stack()
  File "/Users/xxx/.../venv/lib/python3.8/site-packages/starlette/applications.py", line 81, in build_middleware_stack
    app = cls(app=app, **options)
TypeError: __init__() got an unexpected keyword argument 'app'

If you deep dive into the code for starlette you will notice that at some point it does the following as clearly stated by the applications.py code in starlette:

app = cls(app=app, **options)

however in ElasticApm we have:

def __init__(self, application, client):
    self.application = application
    self.client = client

so in the init it would be required to call application -> app

To Reproduce

Install python 3.8 and versions as mentioned above. Then:

app = FastAPI()
elasticapm = make_apm_client(config={
    'SERVICE_NAME': 'foo',
    'SECRET_TOKEN': ''
})
app.add_middleware(ElasticAPM, client=elasticapm)

Environment (please complete the following information)

• OS: MAC OS Catalina 10.15.3

• Python version: Python 3.8

• Framework and version [e.g. Django 2.1]: Starlette/FastAPI

  starlette==0.13.2 fastapi==0.52.0 elastic-apm==5.5.2

• APM Server version: apm-server-7.6.1

• Agent version:

[arocketman]

Hi, sure I can do a PR. Thanks for the quick response.

[basepi]

No problem! I’m glad it was easy!