[Python] How to display local HTML files in Flet's WebView in Android device?

I have problems with the WebView element in Android. I would like to display local HTML files with JavaScript and CSS.

My first attempt was to use directly local files: When I use file:// scheme, it seems not to work.

So I've created a local server with http.server and I call http://localhost:8000/file.html.

import flet as ft
import http.server
import socketserver
import threading
import sys
import ssl

SERVER = "localhost"
PORT = 8000
HTML_DIRECTORY = "assets/html"


class HookHandler(http.server.SimpleHTTPRequestHandler):
def __init__(self, *args, **kwargs):
super().__init__(*args, directory=HTML_DIRECTORY, **kwargs)

class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
pass

def start_server():
with ThreadedTCPServer((SERVER, PORT), HookHandler) as httpd:
httpd.serve_forever()


def main(page: ft.Page):
wv = ft.WebView(
f"http://{SERVER}:{PORT}/file.html",
expand=True
)
page.add(wv)

server_thread = threading.Thread(target=start_server)
server_thread.daemon = True
server_thread.start()
app = ft.app(main)


But when I access the files, there is a security error ERR_CLEARTEXT_NOT_PERMITTED. I find no way to disable this security in the WebView component.

So I've added SSL to my server, with self signed certificate for localhost and I call http://localhost:8000/file.html.

import flet as ft
import http.server
import socketserver
import threading
import sys
import ssl

SERVER = "localhost"
PORT = 8000
HTML_DIRECTORY = "assets/html"


class HookHandler(http.server.SimpleHTTPRequestHandler):
def __init__(self, *args, **kwargs):
super().__init__(*args, directory=HTML_DIRECTORY, **kwargs)

class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
pass

def get_ssl_context(certfile, keyfile):
context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
context.load_cert_chain(certfile, keyfile)
return context

def start_server():
with ThreadedTCPServer((SERVER, PORT), HookHandler) as httpd:
context = get_ssl_context("cert.pem", "key.pem")
httpd.socket = context.wrap_socket(httpd.socket, server_side=True)
print("Serving at port", PORT)
httpd.serve_forever()


def main(page: ft.Page):
wv = ft.WebView(
f"https://{SERVER}:{PORT}/file.html",
expand=True,
)
page.add(url_input, submit_btn, wv)


server_thread = threading.Thread(target=start_server)
server_thread.daemon = True
server_thread.start()
app = ft.app(main)



When I open my application, it's blank. If I open the same URL in my Android's Firefox browser, I see a security alert (because the certificate is self signed), but I can check "I'm OK, continue" and the HTML file is well rendered.

My question : How can I display local files with Flet's WebView?

After a lot of searching, I've found a workaround that does't satisfy me: modify the Androidmanifest.xml to add a android:usesCleartextTraffic="true" property. But this implies to decompile APK, modify the file by hand, compile a new APK, sign this APK. Is there a way to add custom elements / properties in this file automatically in the flet build apkcommand?

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