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middleware causes exceptions to not be raised/handled silently (back again) #2625

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fraser-langton opened this issue Jun 19, 2024 · 6 comments · May be fixed by #2696
Open

middleware causes exceptions to not be raised/handled silently (back again) #2625

fraser-langton opened this issue Jun 19, 2024 · 6 comments · May be fixed by #2696

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@fraser-langton
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fraser-langton commented Jun 19, 2024

Regression of #1976 #1977 #1609 #1940

This time I have noticed that changing MyExc(Exception) to MyExc(BaseException) means the error does get sent to stdout (if that helps) I tried to have a dig but I am not too sure where that catch exception is that is catching the Exception (and silently passing) and not the BaseException

starlette==0.37.2
fastapi==0.111.0

import uvicorn
from fastapi import FastAPI
from starlette.middleware.base import BaseHTTPMiddleware

app = FastAPI()


class MyExc(Exception):  # change to BaseException and then both exceptions are sent to stdout
    ...


@app.get("/info")
def info():
    # raises Exception as expected, the traceback is seen in console
    raise MyExc


private_api = FastAPI()


@private_api.get("/info")
def info():
    # exception is handled silently, no traceback is seen in console
    raise MyExc


app.mount("/private", private_api)


class Middleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        return await call_next(request)


app.add_middleware(Middleware)  # when this is removed, the exceptions are raised for all routes

if __name__ == "__main__":
    uvicorn.run(app, port=8000)

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@daniilmastrangeli
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I have the same issue

@fraser-langton
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fraser-langton commented Jun 27, 2024

@daniilmastrangeli a fix I have found for now is to add_exception_handler which catches the exception and if re-raised will display the trace to stdout as expected

import uvicorn
from fastapi import FastAPI, Request
from starlette.middleware.base import BaseHTTPMiddleware

app = FastAPI()


class MyExc(Exception):  
    ...


@app.get("/info")
def info():
    raise MyExc


private_api = FastAPI()


@private_api.get("/info")
def info():
    raise MyExc


app.mount("/private", private_api)


class Middleware(BaseHTTPMiddleware):
    async def dispatch(self, request, call_next):
        return await call_next(request)


def re_raise_exception(_: Request, exc: Exception):
    raise exc from exc


app.add_middleware(Middleware) 
app.add_exception_handler(Exception, re_raise_exception)  # raises the exception in the handler which results in getting handled by a different context

if __name__ == "__main__":
    uvicorn.run(app, port=8000)

@daniilmastrangeli
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@fraser-langton ty, it's worked

@b4stien
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b4stien commented Aug 6, 2024

The root cause is here: #2194 (comment).

For more references, see also: fastapi/fastapi#8577 (comment)

@Kludex
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Kludex commented Sep 21, 2024

This regression happened on 0.29.0.

@Kludex
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Kludex commented Sep 21, 2024

I've started some work on #2696.

@Kludex Kludex linked a pull request Sep 21, 2024 that will close this issue
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4 participants