Class _FrontendRoute

fastapi/routing.py:2007–2059

class _FrontendRoute(BaseRoute):
    def __init__(
        self,
        path: str,
        *,
        directory: str | os.PathLike[str],
        fallback: Literal["auto", "index.html", "404.html"] | None = "auto",
        check_dir: bool = True,
    ) -> None:
        if fallback not in {"auto", "index.html", "404.html", None}:
            raise AssertionError(
                "fallback must be 'auto', 'index.html', '404.html', or None"
            )
        self.path = _normalize_frontend_path(path)
        self.methods = {"GET", "HEAD"}
        self.app = _FrontendStaticFiles(
            directory=directory, fallback=fallback, check_dir=check_dir
        )

    def matches(self, scope: Scope) -> tuple[Match, Scope]:
        return self.matches_with_path(scope, self.path)

    def matches_with_path(self, scope: Scope, path: str) -> tuple[Match, Scope]:
        if scope["type"] != "http":
            return Match.NONE, {}
        frontend_path = self._get_frontend_path(path, get_route_path(scope))
        if frontend_path is None:
            return Match.NONE, {}
        child_scope = {
            _FASTAPI_SCOPE_KEY: {
                _FASTAPI_FRONTEND_PATH_KEY: frontend_path,
                _FASTAPI_FRONTEND_SPECIFICITY_KEY: _frontend_path_specificity(path),
            }
        }
        if scope["method"] not in self.methods:
            return Match.PARTIAL, child_scope
        return Match.FULL, child_scope

    def _get_frontend_path(self, path: str, route_path: str) -> str | None:
        if path == "/":
            return route_path.lstrip("/")
        if route_path == path:
            return ""
        prefix = path + "/"
        if route_path.startswith(prefix):
            return route_path[len(prefix) :]
        return None

    async def handle(self, scope: Scope, receive: Receive, send: Send) -> None:
        await self.app(scope, receive, send)

    def url_path_for(self, name: str, /, **path_params: Any) -> URLPath:
        raise NoMatchFound(name, path_params)


class _FrontendRouteGroup(BaseRoute):