Default to self-assigned VirtualCdj device number.

CHANGELOG.md

@@ -8,6 +8,14 @@ This change log follows the conventions of
 
 - Nothing so far.
 
+## [0.1.7] - 2016-05-31
+
+### Added
+
+- Unless you assign an explicit `deviceNumber` to `VirtualCdj`, it will
+  watch the DJ Link network looking for an unused player number between
+  5 and 15 to assign itself when it starts up.
+
 ## [0.1.6] - 2016-05-27
 
 ### Fixed
@@ -121,7 +129,8 @@ This change log follows the conventions of
 - Intial early release of DeviceFinder.
 
 
-[unreleased]: https://github.com/brunchboy/beat-link/compare/v0.1.6...HEAD
+[unreleased]: https://github.com/brunchboy/beat-link/compare/v0.1.7...HEAD
+[0.1.7]: https://github.com/brunchboy/beat-link/compare/v0.1.6...v0.1.7
 [0.1.6]: https://github.com/brunchboy/beat-link/compare/v0.1.5...v0.1.6
 [0.1.5]: https://github.com/brunchboy/beat-link/compare/v0.1.4...v0.1.5
 [0.1.4]: https://github.com/brunchboy/beat-link/compare/v0.1.3...v0.1.4

pom.xml

@@ -4,7 +4,7 @@
 
     <groupId>org.deepsymmetry</groupId>
     <artifactId>beat-link</artifactId>
-    <version>0.1.6</version>
+    <version>0.1.7</version>
     <packaging>jar</packaging>
 
     <name>beat-link</name>

src/main/java/org/deepsymmetry/beatlink/DeviceFinder.java

@@ -33,6 +33,12 @@ public class DeviceFinder {
      */
     private static DatagramSocket socket;
 
+    /**
+     * Track when we started listening for announcement packets, to help judge how long the {@link VirtualCdj} needs
+     * to wait in order to avoid device number collisions.
+     */
+    private static long startTime;
+
     /**
      * Check whether we are presently listening for device announcements.
      *
@@ -42,6 +48,19 @@ public static synchronized boolean isActive() {
         return socket != null;
     }
 
+    /**
+     * Get the timestamp of when we started listening for device announcements.
+     *
+     * @return the system millisecond timestamp when {@link #start()} was called.
+     * @throws IllegalStateException if we are not listening for announcements.
+     */
+    public static synchronized long getStartTime() {
+        if (!isActive()) {
+            throw new IllegalStateException("DeviceFinder is not active");
+        }
+        return startTime;
+    }
+
     /**
      * Keep track of the announcements we have seen.
      */
@@ -92,6 +111,7 @@ public static synchronized void start() throws SocketException {
 
         if (!isActive()) {
             socket = new DatagramSocket(ANNOUNCEMENT_PORT);
+            startTime = System.currentTimeMillis();
 
             final byte[] buffer = new byte[512];
             final DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

src/main/java/org/deepsymmetry/beatlink/VirtualCdj.java

@@ -75,6 +75,9 @@ public static synchronized InetAddress getBroadcastAddress() {
 
     /**
      * Get the device number that is used when sending presence announcements on the network to pose as a virtual CDJ.
+     * This starts out being zero unless you explicitly assign another value, which means that the <code>VirtualCdj</code>
+     * should assign itself an unused device number between 5 and 15 by watching the network when you call
+     * {@link #start()}.
      *
      * @return the virtual player number
      */
@@ -84,6 +87,9 @@ public static synchronized byte getDeviceNumber() {
 
     /**
      * Set the device number to be used when sending presence announcements on the network to pose as a virtual CDJ.
+     * If this is set to zero before calling {@link #start()}, the <code>VirtualCdj</code> will watch the network to
+     * look for an unused device number between 5 and 15, and assign itself that number during startup. If you
+     * explicitly assign a non-zero value, it will use that device number instead.
      *
      * @param number the virtual player number
      */
@@ -129,7 +135,7 @@ public static synchronized void setAnnounceInterval(int interval) {
     private static byte[] announcementBytes = {
             0x51, 0x73, 0x70, 0x74,  0x31, 0x57, 0x6d, 0x4a,   0x4f, 0x4c, 0x06, 0x00,  0x62, 0x65, 0x61, 0x74,
             0x2d, 0x6c, 0x69, 0x6e,  0x6b, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
-            0x01, 0x02, 0x00, 0x36,  0x05, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
+            0x01, 0x02, 0x00, 0x36,  0x00, 0x00, 0x00, 0x00,   0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
             0x01, 0x00, 0x00, 0x00,  0x01, 0x00
     };
 
@@ -316,6 +322,41 @@ private static InterfaceAddress findMatchingAddress(DeviceAnnouncement aDevice,
         return null;
     }
 
+    /**
+     * The number of milliseconds for which the {@link DeviceFinder} needs to have been watching the network in order
+     * for us to be confident we can choose a device number that will not conflict.
+     */
+    private static final long SELF_ASSIGNMENT_WATCH_PERIOD = 2500;
+
+    /**
+     * Try to choose a device number, greater than 4, which we have not seen on the network. Start by making sure
+     * we have been watching long enough to have seen the other devices.
+     */
+    private static boolean selfAssignDeviceNumber() {
+        final long now = System.currentTimeMillis();
+        final long started = DeviceFinder.getStartTime();
+        if (now - started < SELF_ASSIGNMENT_WATCH_PERIOD) {
+            try {
+                Thread.sleep(SELF_ASSIGNMENT_WATCH_PERIOD - (now - started));  // Sleep until we hit the right time
+            } catch (InterruptedException e) {
+                logger.log(Level.WARNING, "Interrupted waiting to self-assign device number, giving up.");
+                return false;
+            }
+        }
+        Set<Integer> numbersUsed = new HashSet<Integer>();
+        for (DeviceAnnouncement device : DeviceFinder.currentDevices()) {
+            numbersUsed.add(device.getNumber());
+        }
+        for (int result = 5; result < 16; result++) {   // Try all player numbers less than Rekordbox uses
+            if (!numbersUsed.contains(result)) {  // We found one that is not used, so we can use it
+                setDeviceNumber((byte) result);
+                return true;
+            }
+        }
+        logger.log(Level.WARNING, "Found no unused device numbers between 5 and 15, giving up.");
+        return false;
+    }
+
     /**
      * Once we have seen some DJ Link devices on the network, we can proceed to create a virtual player on that
      * same network.
@@ -342,6 +383,12 @@ private static synchronized boolean createVirtualCdj() throws SocketException {
             return false;
         }
 
+        if (getDeviceNumber() == 0) {
+            if (!selfAssignDeviceNumber()) {
+                return false;
+            }
+        }
+
         // Copy the chosen interface's hardware and IP addresses into the announcement packet template
         System.arraycopy(matchedInterface.getHardwareAddress(), 0, announcementBytes, 38, 6);
         System.arraycopy(matchedAddress.getAddress().getAddress(), 0, announcementBytes, 44, 4);