Transfer orphaned players when possible

src/main/kotlin/dev/arbjerg/lavalink/client/LavalinkClient.kt

@@ -125,6 +125,32 @@ class LavalinkClient(val userId: Long) : Closeable, Disposable {
      */
     fun getLinkIfCached(guildId: Long): Link? = linkMap[guildId]
 
+    /**
+     * Finds all players on unavailable nodes and transfers them to [node].
+     */
+    internal fun transferOrphansTo(node: LavalinkNode) {
+        // This *should* never happen, but just in case...
+        if (!node.available) {
+            return
+        }
+
+        val orphans = findOrphanedPlayers()
+
+        orphans.mapNotNull { linkMap[it.guildId] }
+            .forEach { link ->
+                link.transferNode(node)
+            }
+    }
+
+    /**
+     * Finds all players that are on unavailable nodes.
+     */
+    private fun findOrphanedPlayers(): List<LavalinkPlayer> {
+        val unavailableNodes = nodes.filter { !it.available }
+
+        return unavailableNodes.flatMap { it.playerCache.values }
+    }
+
     internal fun onNodeDisconnected(node: LavalinkNode) {
         // Don't do anything if we are shutting down.
         if (!clientOpen) {
@@ -138,9 +164,21 @@ class LavalinkClient(val userId: Long) : Closeable, Disposable {
             return
         }
 
+        // If we have no nodes available, don't attempt to load-balance.
+        if (nodes.all { !it.available }) {
+            linkMap.filter { (_, link) -> link.node == node }
+                .forEach { (_, link) ->
+                    link.state = LinkState.DISCONNECTED
+                }
+            return
+        }
+
         linkMap.forEach { (_, link) ->
-            if (link.node == node)  {
-                link.transferNode(loadBalancer.selectNode(region = null))
+            if (link.node == node) {
+                val voiceRegion = link.cachedPlayer?.voiceRegion
+
+                link.state = LinkState.CONNECTING
+                link.transferNode(loadBalancer.selectNode(region = voiceRegion))
             }
         }
     }

src/main/kotlin/dev/arbjerg/lavalink/client/LavalinkNode.kt

@@ -134,6 +134,7 @@ class LavalinkNode(
 
         return rest.getPlayer(guildId)
             .map { it.toLavalinkPlayer(this) }
+            // TODO: check for 404 status code, if not 404, don't create
             .onErrorResume { createOrUpdatePlayer(guildId) }
             .doOnSuccess {
                 // Update the player internally upon retrieving it.
@@ -399,6 +400,10 @@ class LavalinkNode(
      */
     fun getCachedPlayer(guildId: Long): LavalinkPlayer? = playerCache[guildId]
 
+    internal fun transferOrphansToSelf() {
+        lavalink.transferOrphansTo(this)
+    }
+
     override fun equals(other: Any?): Boolean {
         if (this === other) return true
         if (javaClass != other?.javaClass) return false

src/main/kotlin/dev/arbjerg/lavalink/client/LavalinkPlayer.kt

@@ -1,5 +1,6 @@
 package dev.arbjerg.lavalink.client
 
+import dev.arbjerg.lavalink.client.loadbalancing.VoiceRegion
 import dev.arbjerg.lavalink.client.protocol.Track
 import dev.arbjerg.lavalink.client.protocol.toCustom
 import dev.arbjerg.lavalink.protocol.v4.*
@@ -44,6 +45,15 @@ class LavalinkPlayer(private val node: LavalinkNode, protocolPlayer: Player) : I
             }
         }
 
+    val voiceRegion: VoiceRegion?
+        get() {
+            if (voiceState.endpoint.isBlank()) {
+                return null
+            }
+
+            return VoiceRegion.fromEndpoint(voiceState.endpoint)
+        }
+
     override fun setTrack(track: Track?) = PlayerUpdateBuilder(node, guildId)
         .setTrack(track)
 

src/main/kotlin/dev/arbjerg/lavalink/client/Link.kt

@@ -1,6 +1,7 @@
 package dev.arbjerg.lavalink.client
 
 import dev.arbjerg.lavalink.protocol.v4.VoiceState
+import java.time.Duration
 import java.util.function.Consumer
 
 /**
@@ -67,6 +68,8 @@ class Link(
             node.removeCachedPlayer(guildId)
             newNode.createOrUpdatePlayer(guildId)
                 .applyBuilder(player.stateToBuilder())
+                // Delay by 500ms to hopefully prevent a race-condition from triggering
+                .delayElement(Duration.ofMillis(500))
                 .subscribe()
         }
 

src/main/kotlin/dev/arbjerg/lavalink/internal/LavalinkSocket.kt

@@ -60,6 +60,9 @@ class LavalinkSocket(private val node: LavalinkNode) : WebSocketListener(), Clos
                         .setNoReplace(false)
                         .subscribe()
                 }
+
+                // Move players from older, unavailable nodes to ourselves.
+                node.transferOrphansToSelf()
             }
 
             Message.Op.Stats -> {
@@ -126,19 +129,13 @@ class LavalinkSocket(private val node: LavalinkNode) : WebSocketListener(), Clos
     }
 
     override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) {
-        node.lavalink.onNodeDisconnected(node)
-
         when(t) {
             is EOFException -> {
                 logger.debug("Got disconnected from ${node.name}, trying to reconnect", t)
-                node.available = false
-                open = false
             }
 
             is SocketTimeoutException -> {
                 logger.debug("Got disconnected from ${node.name} (timeout), trying to reconnect", t)
-                node.available = false
-                open = false
             }
 
             is ConnectException -> {
@@ -153,14 +150,17 @@ class LavalinkSocket(private val node: LavalinkNode) : WebSocketListener(), Clos
                 }
 
                 logger.warnOrTrace("Socket error on ${node.name}, reconnecting in ${reconnectInterval / 1000} seconds", t)
-                node.available = false
-                open = false
             }
 
             else -> {
                 logger.error("Unknown error on ${node.name}", t)
             }
         }
+
+        node.available = false
+        open = false
+
+        node.lavalink.onNodeDisconnected(node)
     }
 
     override fun onClosing(webSocket: WebSocket, code: Int, reason: String) {

testbot/src/main/java/me/duncte123/testbot/Main.java

@@ -38,12 +38,12 @@ public static void main(String[] args) throws InterruptedException {
 
     private static void registerLavalinkNodes(LavalinkClient client) {
         List.of(
-            /*client.addNode(
+            client.addNode(
                 "Testnode",
                 URI.create("ws://localhost:2333"),
                 "youshallnotpass",
                 RegionGroup.EUROPE
-            )*/
+            ),
 
             client.addNode(
                 "Pi-local",