Add previous server to ServerConnectedEvent

api/src/main/java/com/velocitypowered/api/event/player/ServerConnectedEvent.java

@@ -3,6 +3,8 @@ package com.velocitypowered.api.event.player;
 import com.google.common.base.Preconditions;
 import com.velocitypowered.api.proxy.Player;
 import com.velocitypowered.api.proxy.server.RegisteredServer;
+import java.util.Optional;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * This event is fired once the player has successfully connected to the target server and the
@@ -12,10 +14,13 @@ public final class ServerConnectedEvent {
 
   private final Player player;
   private final RegisteredServer server;
+  private final @Nullable RegisteredServer previousServer;
 
-  public ServerConnectedEvent(Player player, RegisteredServer server) {
+  public ServerConnectedEvent(Player player, RegisteredServer server,
+      @Nullable RegisteredServer previousServer) {
     this.player = Preconditions.checkNotNull(player, "player");
     this.server = Preconditions.checkNotNull(server, "server");
+    this.previousServer = previousServer;
   }
 
   public Player getPlayer() {
@@ -26,6 +31,10 @@ public final class ServerConnectedEvent {
     return server;
   }
 
+  public Optional<RegisteredServer> getPreviousServer() {
+    return Optional.ofNullable(previousServer);
+  }
+
   @Override
   public String toString() {
     return "ServerConnectedEvent{"

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/TransitionSessionHandler.java

@@ -80,7 +80,8 @@ public class TransitionSessionHandler implements MinecraftSessionHandler {
     // The goods are in hand! We got JoinGame. Let's transition completely to the new state.
     smc.setAutoReading(false);
     server.getEventManager()
-        .fire(new ServerConnectedEvent(serverConn.getPlayer(), serverConn.getServer()))
+        .fire(new ServerConnectedEvent(serverConn.getPlayer(), serverConn.getServer(),
+            existingConnection != null ? existingConnection.getServer() : null))
         .whenCompleteAsync((x, error) -> {
           // Strap on the ClientPlaySessionHandler if required.
           ClientPlaySessionHandler playHandler;