Loading a URL from a local server

Most people reaching for a local server want a Root, which serves the same directory with no server to start and no port to pick. Reach for a server when you already have one: a dev server with hot reload, or an application that genuinely speaks HTTP.

from functools import partial
from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
from multiprocessing import Process
from pathlib import Path

from dry import Webview

ROOT = Path(__file__).parent / 'dist'
PORT = 8000


def serve() -> None:
    handler = partial(SimpleHTTPRequestHandler, directory=str(ROOT))
    ThreadingHTTPServer(('127.0.0.1', PORT), handler).serve_forever()


if __name__ == '__main__':
    server = Process(target=serve, daemon=True)
    server.start()

    wv = Webview(app_id='com.example.myapp', url=f'http://localhost:{PORT}')
    wv.run()

A daemon process goes down with its parent, so closing the window stops the server. The full file is examples/server.py.

A thread works too, since 0.4.0

run() releases the GIL before the event loop takes the main thread and never takes it back, so ordinary Python threads keep running for the whole life of the window — there is a regression test that opens a real window and counts a thread’s ticks inside it.

Before 0.4.0 that was not true: run() held the GIL, every Python thread in the process stopped, and a server started in a threading.Thread accepted no connection while the window was up. If you carried a multiprocessing.Process around to work past that, a threading.Thread is now enough:

from threading import Thread

Thread(target=serve, daemon=True).start()

A separate process still buys isolation — a crashing server does not take the window with it — which is why the shipped example uses one.

Serve plain HTTP, not a self-signed HTTPS

Plain http:// loads on macOS exactly as it does on Windows. App Transport Security does not stand between a Python process and its own local server: an interpreter run from a terminal has no app bundle and no Info.plist, so there is no policy to apply. This was measured, including against a real DNS hostname rather than only localhost and raw IPs.

HTTPS with a certificate the system does not trust is what fails. WKWebView abandons the navigation with no prompt and no visible error. Dry now notices — after five seconds without a page it diagnoses the address from Python and writes what it found to the dry.webview logger — but the window is still blank. Serve local development over plain HTTP on localhost.

See Errors and logging for how to see that diagnosis.