stephenhillier / starlette_exporter

I noticed that setting the root_path via Uvicorn breaks all metrics having a path label when filter_unhandled_paths is enabled.

The FastAPI docs suggest that setting root_path via uvicorn is equivalent to the FastAPI attribute of the same name

This exporter however seems to make the assumption that it's set via FastAPI. I believe this is the problematic bit of code.

starlette_exporter/starlette_exporter/middleware.py

Line 375 in 0de22e7

if hasattr(app, "root_path"):

In my case, I simply switched to setting root_path via the FastAPI attribute.

I'd be happy to submit a fix, but I'm not sure what the best way to inspect the uvicorn settings parameters in this context. Any tips would be appreciated.

Thanks!

I don't know of a way to inspect uvicorn parameters from middleware, my guess is that it's not feasible.

I wonder if the only option is to add another optional config param root_path e.g.:

app.add_middleware(
  PrometheusMiddleware,
  app_name="hello_world",
  root_path="/api",

I don't know of a way to inspect uvicorn parameters from middleware, my guess is that it's not feasible.

I wonder if the only option is to add another optional config param root_path e.g.:
app.add_middleware(
  PrometheusMiddleware,
  app_name="hello_world",
  root_path="/api",

Yeah... I like that idea. Unfortunately I've noticed some weird differences (in FastAPI) between setting it via uvicorn and the FastAPI app.

~~This is probably caused by issue in Starlette, fixed only in 0.33.0: encode/starlette#2352~~

~~But FastAPI does not support this version yet: tiangolo/fastapi#10798~~

Well, I've tried starlette==0.34.0, but without any success. It looks starlette-exporter itself does not handle root_path properly. See #81

filter_unhandled_paths broken with root_path set via Uvicorn