The root_path is missing from the redirects from an url with trailing slash to the same url without it

[Mattiam2]

Issue opened also in the FastAPI discussions here.

Example Code

from fastapi import FastAPI

app = FastAPI(root_path="/wms")


@app.get("/hello")
async def root():
    return {"message": "Hello World"}

The program runs in gunicorn (using the uvicorn worker class) behind a nginx proxy which strips away the root_path (as described in Behind a proxy).

Before fastapi 0.109 (and before starlette 0.35.0) an URL with a trailing slash (ex. https://127.0.0.1/wms/hello/) would be redirected to the corresponding URL without the trailing slash (ex. https://127.0.0.1/wms/hello) as expected.

From fastapi 0.109 (and from starlette 0.35.0) the redirect no more includes the root_path, so from https://127.0.0.1/wms/hello/ the application redirects to https://127.0.0.1/hello which results in a 404 Not Found error.

Here the headers of the redirect request:

I think the issue came from this change which strips away the root_path from the path in the URL constructor which seems to me off, even considering the ASGI specs.