Improve robot disovery in noisy Wi-Fi

UDP is lossy, so send multiple broadcast packets until
we receive a response from the robot.

lib/discovery.js

@@ -4,17 +4,33 @@ const dgram = require('dgram');
 
 function discovery (cb, full) {
   const server = dgram.createSocket('udp4');
+  let robotFound = false;
+  let broadcastInterval;
+
+  function sendBroadcast() {
+    const message = new Buffer('irobotmcs');
+    server.setBroadcast(true);
+
+    for (let i = 0; i < 3; i++) {
+      server.send(message, 0, message.length, 5678, '255.255.255.255');
+    }
+  }
 
   server.on('error', (err) => {
     server.close();
     cb(err);
   });
 
   server.on('message', (msg) => {
+    if (robotFound) {
+      return;
+    }
     try {
       let parsedMsg = JSON.parse(msg);
       if (parsedMsg.hostname && parsedMsg.ip && parsedMsg.hostname.split('-')[0] === 'Roomba') {
         server.close();
+        robotFound = true;
+        clearInterval(broadcastInterval);
         console.log('Robot found! with blid/username: ' + parsedMsg.hostname.split('-')[1]);
         console.log(parsedMsg);
         cb(null, full ? parsedMsg : parsedMsg.ip);
@@ -27,9 +43,7 @@ function discovery (cb, full) {
   });
 
   server.bind(5678, function () {
-    const message = new Buffer('irobotmcs');
-    server.setBroadcast(true);
-    server.send(message, 0, message.length, 5678, '255.255.255.255');
+    broadcastInterval = setInterval(() => sendBroadcast(), 5000);
   });
 }