[Bug]: If hostname is localhost, the server fallback URL always defaults to localhost:3000, even when it is running on a different port

[amanape]

          If hostname is `localhost`, the server fallback URL to communicate with the backend is always `localhost:3000`. This is incorrect in your scenario since the server is now running on `localhost:3001`.

OpenHands/frontend/src/utils/get-valid-fallback-host.ts

Lines 12 to 20 in caa77cf

	export const getValidFallbackHost = () => {
	if (typeof window !== "undefined") {
	const { hostname, host } = window.location;
	if (hostname !== "localhost") return host;
	}
	// Fallback is localhost:3000 because that is the default port for the server
	return "localhost:3000";
	};

For now, you can run OpenHands locally (pull and run make build && make run). Feel free to set the environment variable to whichever URL you need here:

OpenHands/frontend/.env.sample

Line 1 in caa77cf

VITE_BACKEND_BASE_URL="localhost:3000" # Backend URL without protocol (e.g. localhost:3000)

Note that in this mode, the frontend is expected to be served on localhost:3001, another limitation but its because:

OpenHands/openhands/server/listen.py

Line 79 in caa77cf

allow_origins=['http://localhost:3001', 'http://127.0.0.1:3001'],

Originally posted by @amanape in #4344 (comment)