Does not automatically record FastAPI arguments of subapplications

[freddyaboulton]

Description

What I see

If I define a post request in a FastAPI subapplication, it will not be recorded in the platform.

from fastapi import FastAPI
import secrets
import logfire
from pydantic import BaseModel
from typing import Any

class PredictBody(BaseModel):
    session_hash: str
    data: list[Any]

app = FastAPI()
subapp = FastAPI()

@subapp.post("/predict")
async def predict(body: PredictBody):
    return {"id": secrets.token_hex(16)}

app.mount("/api", subapp)

logfire.configure(pydantic_plugin=logfire.PydanticPlugin(record="all"))
logfire.instrument_fastapi(app)

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, port=7860)

No FastAPI arguments are recorded in the POST trace

If I don't use a subapplication, the FastAPI arguments are recorded

from fastapi import FastAPI
import secrets
import logfire
from pydantic import BaseModel
from typing import Any

class PredictBody(BaseModel):
    session_hash: str
    data: list[Any]

app = FastAPI()

@app.post("/predict")
async def predict(body: PredictBody):
    return {"id": secrets.token_hex(16)}

logfire.configure(pydantic_plugin=logfire.PydanticPlugin(record="all"))
logfire.instrument_fastapi(app)

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, port=7860)

What I would like to see

I would like the FastAPI arguments to be automatically recorded for my subapplications.

Python, Logfire & OS Versions, related packages (not required)

logfire="0.32.0"
platform="macOS-13.3.1-arm64-arm-64bit"
python="3.10.13 (main, Sep 11 2023, 08:16:02) [Clang 14.0.6 ]"
[related_packages]
requests="2.31.0"
pydantic="2.7.1"
fastapi="0.111.0"
protobuf="4.25.3"
rich="13.7.1"
tomli="2.0.1"
opentelemetry-api="1.24.0"
opentelemetry-exporter-otlp-proto-common="1.24.0"
opentelemetry-exporter-otlp-proto-http="1.24.0"
opentelemetry-instrumentation="0.45b0"
opentelemetry-instrumentation-asgi="0.45b0"
opentelemetry-instrumentation-fastapi="0.45b0"
opentelemetry-proto="1.24.0"
opentelemetry-sdk="1.24.0"
opentelemetry-semantic-conventions="0.45b0"
opentelemetry-util-http="0.45b0"

[sneakyPad]

Thanks for the well organized issue. I've gone through it and found that the problem is that the sub app is not registered within logfire. When you write the following:

logfire.instrument_fastapi(app)
logfire.instrument_fastapi(subapp)

The arguments will be logged along with the request. I think it's not ideal because it's a duplication in the code and the UI also shows it as a nested duplication (?), but a first step to mitigate your problem.

I'd like to take this and work on a solution. Can someone assign this to me?