zeroconf

[yst-one]

Add the zeroconf package to implement mDNS functionality
https://pypi.org/project/zeroconf/

[ndonkoHenri]

zeroconf 0.150.0 is now supported on Android and iOS: https://pypi.flet.dev/zeroconf

zeroconf gives your Flet app mDNS service discovery and advertising (the protocol behind AirPlay/Chromecast/HomeAssistant device discovery) — find services on the local Wi-Fi, and/or announce your app so others can find it. Fully offline: it talks only to the local network, no internet needed.

Installation

Just add zeroconf to your dependencies. On Android you'll also want pyjnius (see why below):

[project]
dependencies = ["flet", "zeroconf"]

[tool.flet.android]
dependencies = ["pyjnius"]

[tool.flet.android.permission]
"android.permission.CHANGE_WIFI_MULTICAST_STATE" = true
"android.permission.ACCESS_NETWORK_STATE" = true

[tool.flet.ios.info]
NSLocalNetworkUsageDescription = "Finds and announces services on your local network."
NSBonjourServices = ["_demo._tcp"]   # list every service type you browse

(android.permission.INTERNET is a Flet default. Both Android permissions are install-time, no runtime prompt.)

Minimal example

Registers a service and browses for that type, so it always discovers at least itself and the list is never empty:

import os, socket
import flet as ft

def main(page: ft.Page):
    page.title = "mDNS demo"
    found = ft.ListView(expand=True)
    page.add(ft.Text("Discovered _demo._tcp services:", weight=ft.FontWeight.BOLD), found)

    if page.platform == ft.PagePlatform.ANDROID:
        # Wi-Fi chipsets drop incoming multicast unless the app holds a MulticastLock —
        # without this, zeroconf can send but hears (almost) nothing. Keep the lock
        # referenced for the app's lifetime; release it when you stop discovery.
        from jnius import autoclass
        Context = autoclass("android.content.Context")
        activity = autoclass(os.getenv("MAIN_ACTIVITY_HOST_CLASS_NAME")).mActivity
        wifi = activity.getApplicationContext().getSystemService(Context.WIFI_SERVICE)
        page.data = lock = wifi.createMulticastLock("zeroconf")
        lock.acquire()

    from zeroconf import ServiceBrowser, ServiceInfo, ServiceStateChange, Zeroconf

    def on_change(zeroconf, service_type, name, state_change, **kwargs):
        if state_change is ServiceStateChange.Added:
            found.controls.append(ft.Text(name))
            page.update()

    zc = Zeroconf()
    zc.register_service(ServiceInfo(
        "_demo._tcp.local.", "my-flet-app._demo._tcp.local.",
        addresses=[socket.inet_aton("127.0.0.1")], port=8080,
    ))
    ServiceBrowser(zc, "_demo._tcp.local.", handlers=[on_change])

ft.run(main)

To be discoverable by other devices, advertise your device's real LAN address instead of 127.0.0.1 (e.g. open a UDP socket to 8.8.8.8 and read getsockname()[0]). There's also a fully async API (zeroconf.asyncio.AsyncZeroconf) if you prefer it inside Flet's async apps.

Android notes

• The MulticastLock + CHANGE_WIFI_MULTICAST_STATE combo above is not optional for discovery: skipping it doesn't raise — packets just never arrive on most devices, and "discovery finds nothing" is the only symptom.
• Emulators don't pass real LAN multicast (self-discovery as in the example works; discovering other machines needs a physical phone on real Wi-Fi).
• Long-running background discovery isn't dependable — some devices tighten multicast filtering when the screen is off even with the lock held. Foreground use is the supported scenario. The lock also has a battery cost; release it when you stop browsing.

iOS notes

• Works out of the box on the simulator (which is also why simulator success proves nothing about devices — the simulator doesn't enforce iOS network privacy).
• On physical devices, iOS 14+ requires Apple's restricted com.apple.developer.networking.multicast entitlement for the raw multicast sockets python-zeroconf uses (requested from Apple per developer account); without it, sends fail with OSError: [Errno 65] No route to host. On top of that, the entitlement must be added to the app's signing — flet build currently has no way to add iOS entitlements, so you'd need a forked build template or post-build Xcode edits, plus the capability on your provisioning profile. The Info.plist keys above (settable via [tool.flet.ios.info]) cover the user-consent prompt, but they do not replace the entitlement.
• Practical recommendation: treat zeroconf as the Android + desktop + iOS-simulator solution. For discovery on iOS devices, use the OS Bonjour APIs instead (e.g. NSNetServiceBrowser via pyobjus, or a Flutter plugin) — those need only the two Info.plist keys and no special entitlement.