Fix the subscription to work with pyzmq

app/src/main/java/com/example/carcontroller/SLAM/ZmqSlamUpdater.java

@@ -7,6 +7,8 @@ import org.zeromq.SocketType;
 import org.zeromq.ZContext;
 import org.zeromq.ZMQ;
 
+import java.util.Arrays;
+
 /**
  * Connects to Pi and retrieves updates of the SLAM map,
  * notifying listeners of changes to the map when they arrive.
@@ -18,6 +20,7 @@ public class ZmqSlamUpdater extends SlamUpdater {
     private String host;
     private String port;
     private boolean running = false;
+    private static final byte[] SLAM_SUBSCRIPTION = "slam_map".getBytes();
 
     public ZmqSlamUpdater(String host, String port) {
         super();
@@ -39,11 +42,14 @@ public class ZmqSlamUpdater extends SlamUpdater {
         // Receive map from zmq and update appropriately.
         try (ZMQ.Socket socket = context.createSocket(SocketType.SUB)) {
             socket.connect("tcp://" + host + ":" + port);
-            socket.subscribe("slam_map");
+            socket.subscribe(SLAM_SUBSCRIPTION);
             while (running) {
                 byte[] map = socket.recv();
+                // Don't want to do the event when we just receive the header.
+                if (!Arrays.equals(map, SLAM_SUBSCRIPTION)) {
                     fireMapChanged(SlamScan.parseFrom(map));
                 }
+            }
         } catch (InvalidProtocolBufferException e) {
             System.out.println("Invalid map found");
             running = false;