wlan-ucentral-schema/system/probe_services.uc

let fail = {},
dhcp = {},
dns = { localhost: [ "127.0.0.1" ] };

function lookup_wan() {
	let i = ctx.call("network.interface.wan", "status");

	if (i["dns-server"])
		dns.wan = i["dns-server"];

	if (i["l3_device"])
		dhcp.wan = i["l3_device"];
}

function lookup_ip(iface) {
	let i = ctx.call("network.interface", "status", { interface: iface });

	if (i["ipv4-address"] && i["ipv4-address"][0])
		dns[iface] = [ i["ipv4-address"][0]["address"] ];

	if (i["l3_device"])
		dhcp[iface] = i["l3_device"];
}

function service_probe() {
	lookup_wan();

	let cursor = uci.cursor();

	cursor.load("dhcp");
	cursor.foreach("dhcp", "dhcp", function(d) {
		if (d.ignore != 1)
			lookup_ip(d.interface);
	});

	for (let iface, ips in dns) {
		let failed = true;

		for (let ip in ips) {
			let rc = system(['/usr/sbin/dnsprobe', '-s', ip]);

			if (rc == 0)
				failed = false;
		}

		if (!failed)
			continue;

		fail.dns = fail.dns || {};
		fail.dns[iface] = ips;
	}

	for (let iface, dev in dhcp) {
		let rc = system(['/usr/sbin/dhcpdiscover', '-i', dev, '-t', '5']);

		if (rc != 0) {
			fail.dhcp = fail.dhcp || {};
			fail.dhcp[iface] = dev;
		}
	}

	return fail;
}

let services = service_probe();

if (length(services))
	state.serviceprobe = services;