fix: register a sender once when replaceTrack is given its current track

webrtc/src/main/java/dev/onvoid/webrtc/client/LocalTrackImpl.java

@@ -19,7 +19,9 @@
 import static java.util.Objects.requireNonNull;
 
 import java.util.ArrayList;
+import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 
 import dev.onvoid.webrtc.media.MediaStreamTrack;
@@ -54,7 +56,8 @@ abstract class LocalTrackImpl implements LocalTrack {
 
 	// Guarded by this.
 
-	private final List<SenderImpl> senders = new ArrayList<>();
+	/** A sender registers once, however often it is given this track. */
+	private final Set<SenderImpl> senders = new LinkedHashSet<>();
 
 	private final List<Runnable> endedHandlers = new ArrayList<>();
 
@@ -177,6 +180,10 @@ synchronized void unregister(SenderImpl sender) {
 		senders.remove(sender);
 	}
 
+	synchronized List<SenderImpl> registeredSenders() {
+		return new ArrayList<>(senders);
+	}
+
 	/**
 	 * @return true while the native track may be used, which callers check
 	 * under this object's lock.

webrtc/src/main/java/dev/onvoid/webrtc/client/SenderImpl.java

@@ -113,6 +113,10 @@ public CompletableFuture<Void> replaceTrack(LocalTrack replacement) {
 			if (next != null && !next.register(this)) {
 				throw new IllegalStateException("The track " + next.id() + " is closed");
 			}
+			if (next == track) {
+				// Already sent, and registered only once.
+				return;
+			}
 
 			try {
 				sender.replaceTrack(next == null ? null : next.nativeTrack());
@@ -127,7 +131,7 @@ public CompletableFuture<Void> replaceTrack(LocalTrack replacement) {
 			LocalTrackImpl previous = track;
 			track = next;
 
-			if (previous != null && previous != next) {
+			if (previous != null) {
 				previous.unregister(this);
 			}
 		});

webrtc/src/test/java/dev/onvoid/webrtc/client/MediaTests.java

@@ -219,6 +219,25 @@ void closedTrackLeavesEveryPeer() throws Exception {
 		assertEquals(other, one.track());
 	}
 
+	@Test
+	void sameTrackRegisteredOnce() throws Exception {
+		Peer[] peers = pair();
+		LocalTrackImpl voice = (LocalTrackImpl) rtc.media().customAudio("voice");
+		Sender sender = peers[0].addTrack(voice);
+
+		for (int i = 0; i < 3; i++) {
+			await(sender.replaceTrack(voice));
+		}
+
+		assertEquals(voice, sender.track());
+		assertEquals(Collections.singletonList(sender), voice.registeredSenders());
+
+		await(sender.remove());
+
+		// A removed sender, and its peer, are not kept by the track.
+		assertTrue(voice.registeredSenders().isEmpty());
+	}
+
 	@Test
 	void senderConfigured() throws Exception {
 		Peer[] peers = pair();