Send 'pfls' event when changing track, seeking and pausing + minor refactoring (#325)

Author: devgianlu

player/src/main/java/xyz/gianlu/librespot/player/Player.java

@@ -988,6 +988,10 @@ private void sendVolume(int value) {
             metadataPipe.safeSend(MetadataPipe.TYPE_SSNC, MetadataPipe.CODE_PVOL, volData);
         }
 
+        private void sendPipeFlush() {
+            metadataPipe.safeSend(MetadataPipe.TYPE_CORE, MetadataPipe.CODE_PFLS);
+        }
+
         void playbackEnded() {
             for (EventsListener l : new ArrayList<>(listeners))
                 executorService.execute(l::onPlaybackEnded);
@@ -997,12 +1001,15 @@ void playbackPaused() {
             long trackTime = state.getPosition();
             for (EventsListener l : new ArrayList<>(listeners))
                 executorService.execute(() -> l.onPlaybackPaused(trackTime));
+
+            if (metadataPipe.enabled()) executorService.execute(this::sendPipeFlush);
         }
 
         void playbackResumed() {
             long trackTime = state.getPosition();
             for (EventsListener l : new ArrayList<>(listeners))
                 executorService.execute(() -> l.onPlaybackResumed(trackTime));
+
             if (metadataPipe.enabled()) {
                 executorService.execute(() -> {
                     sendTrackInfo();
@@ -1027,13 +1034,20 @@ void trackChanged() {
             TrackOrEpisode metadata = currentMetadata();
             for (EventsListener l : new ArrayList<>(listeners))
                 executorService.execute(() -> l.onTrackChanged(id, metadata));
+
+            if (metadataPipe.enabled()) executorService.execute(this::sendPipeFlush);
         }
 
         void seeked(int pos) {
             for (EventsListener l : new ArrayList<>(listeners))
                 executorService.execute(() -> l.onTrackSeeked(pos));
 
-            if (metadataPipe.enabled()) executorService.execute(this::sendProgress);
+            if (metadataPipe.enabled()) {
+                executorService.execute(() -> {
+                    sendPipeFlush();
+                    sendProgress();
+                });
+            }
         }
 
         void volumeChanged(@Range(from = 0, to = Player.VOLUME_MAX) int value) {

player/src/main/java/xyz/gianlu/librespot/player/metadata/MetadataPipe.java

@@ -26,6 +26,7 @@ public final class MetadataPipe {
     public static final String CODE_PVOL = "70766f6c";
     public static final String CODE_PRGR = "70726772";
     public static final String CODE_PICT = "50494354";
+    public static final String CODE_PFLS = "70666C73";
     private static final Logger LOGGER = LogManager.getLogger(MetadataPipe.class);
     private final File file;
     private FileOutputStream out;
@@ -34,15 +35,12 @@ public MetadataPipe(@NotNull PlayerConfiguration conf) {
         file = conf.metadataPipe;
     }
 
-    public void safeSend(@NotNull String type, @NotNull String code, @Nullable String payload) {
-        if (!enabled())
-            return;
+    public void safeSend(@NotNull String type, @NotNull String code) {
+        safeSend(type, code, (String) null);
+    }
 
-        try {
-            send(type, code, payload == null ? null : payload.getBytes(StandardCharsets.UTF_8));
-        } catch (IOException ex) {
-            LOGGER.error("Failed sending metadata through pipe!", ex);
-        }
+    public void safeSend(@NotNull String type, @NotNull String code, @Nullable String payload) {
+        safeSend(type, code, payload == null ? null : payload.getBytes(StandardCharsets.UTF_8));
     }
 
     public void safeSend(@NotNull String type, @NotNull String code, @Nullable byte[] payload) {
@@ -60,7 +58,7 @@ private synchronized void send(@NotNull String type, @NotNull String code, @Null
         if (file == null) return;
         if (out == null) out = new FileOutputStream(file);
 
-        if (payload != null) {
+        if (payload != null && payload.length > 0) {
             out.write(String.format("<item><type>%s</type><code>%s</code><length>%d</length>\n<data encoding=\"base64\">%s</data></item>\n", type, code,
                     payload.length, new String(Base64.getEncoder().encode(payload), StandardCharsets.UTF_8)).getBytes(StandardCharsets.UTF_8));
         } else {