route resolution fails when titiler is mounted as a subapp

[geospatial-jeff]

request.url_for fails to find the correct route when titiler is mounted as a sub application (https://github.com/developmentseed/titiler/blob/nonTMSReader/titiler/endpoints/factory.py#L1013):

from fastapi import FastAPI
from titiler.endpoints.stac import STACTiler

app = FastAPI()

titiler_app = FastAPI()
titiler_app.include_router(STACTiler().router)

app.mount("/titiler", titiler_app)

This is because request.url_for uses the router of the request's current scope which in this case is app and not titiler_app. Because sub applications are independent of the parent app, the titiler routes are not actually registered on app, so starlette can't find the route and raises starlette.routing.NoMatchFound.

A solution that works is replacing calls to request.url_for with self.router.url_path_for which has the same signature (its called under the hood by request.url_for) but only searches the specific router, ensuring that route resolution will always work no matter how the app is mounted.

[vincentsarago]

oh that's nice, maybe we don't need the prefix then?

[geospatial-jeff]

Yeah I think the prefix could be removed with this

[vincentsarago]

I tried the self.router.url_path_for it nice but sadly it returns an absolute path. You can prefix this with the request.base_url but then it's missing prefix (if you mount the router with one, like we do for COG or STAC).

👇 this is working (basically searching for prefix in the request's path) but I'm not sure it's the best approach.

base_url = str(request.base_url)
prefix = request["path"].replace(f"/{tms.identifier}", "").replace("/tilejson.json", "")
if prefix:
    base_url = base_url + prefix.lstrip("/")

relative_tiles_url = self.router.url_path_for("tile", **kwargs)
tiles_url = relative_tiles_url.make_absolute_url(base_url=base_url)