RuntimeErrors are masked

[stepf]

Hey! Thanks for putting so much work into this project. My team and I recently tried it for our newest backend. Unfortunately we observed that raise RuntimeError(e) gets masked by the instrumentator.

Example stacktrace with masked error:

ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/uvicorn/protocols/http/httptools_impl.py", line 390, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/fastapi/applications.py", line 180, in __call__
    await super().__call__(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/applications.py", line 111, in __call__
    await self.middleware_stack(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/middleware/errors.py", line 181, in __call__
    raise exc from None
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/middleware/errors.py", line 159, in __call__
    await self.app(scope, receive, _send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/middleware/cors.py", line 78, in __call__
    await self.app(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/middleware/base.py", line 25, in __call__
    response = await self.dispatch_func(request, self.call_next)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/prometheus_fastapi_instrumentator/instrumentation.py", line 129, in dispatch_middleware
    instrumentation(info)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/prometheus_fastapi_instrumentator/metrics.py", line 462, in instrumentation
    int(info.response.headers.get("Content-Length", 0))
AttributeError: 'NoneType' object has no attribute 'headers'

Example stacktrace with desired error:

ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/uvicorn/protocols/http/httptools_impl.py", line 390, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/fastapi/applications.py", line 180, in __call__
    await super().__call__(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/applications.py", line 111, in __call__
    await self.middleware_stack(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/middleware/errors.py", line 181, in __call__
    raise exc from None
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/middleware/errors.py", line 159, in __call__
    await self.app(scope, receive, _send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/middleware/cors.py", line 78, in __call__
    await self.app(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/exceptions.py", line 82, in __call__
    raise exc from None
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/exceptions.py", line 71, in __call__
    await self.app(scope, receive, sender)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/routing.py", line 566, in __call__
    await route.handle(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/routing.py", line 227, in handle
    await self.app(scope, receive, send)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/starlette/routing.py", line 41, in app
    response = await func(request)
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/fastapi/routing.py", line 196, in app
    raw_response = await run_endpoint_function(
  File "[PATH TO VIRTUALENV]/lib/python3.8/site-packages/fastapi/routing.py", line 147, in run_endpoint_function
    return await dependant.call(**values)
  File "app/main.py", line 52, in runtimerror
    raise RuntimeError("example message")
RuntimeError: example message

[trallnag]

Hello @stepf, thanks for raising this issue and sorry for replying quite late. I managed to disable notifications for my own repository 😮. The issue is now fixed with the 5.2.1 release.

The problem was within the metrics module that contains all functions that performs the actual instrumentation based on the Info object that contains the request, response and so on. The response object can be None and the request / response size related code did not check for that.

[stepf]

Thanks for taking care of this 👍