Fixed duplicate sending of resource packs responses to backend server (#1249)

Also fixes the sending of SUCCESSFUL responses to the backend server that will apply a resource pack in case Velocity has already applied one or more resource packs to the player

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientConfigSessionHandler.java

@@ -95,9 +95,6 @@ public class ClientConfigSessionHandler implements MinecraftSessionHandler {
 
   @Override
   public boolean handle(ResourcePackResponsePacket packet) {
-    if (player.getConnectionInFlight() != null) {
-      player.getConnectionInFlight().ensureConnected().write(packet);
-    }
     return player.resourcePackHandler().onResourcePackResponse(
         new ResourcePackResponseBundle(packet.getId(),
             packet.getHash(),

proxy/src/main/java/com/velocitypowered/proxy/connection/player/resourcepack/ModernResourcePackHandler.java

@@ -146,10 +146,20 @@ public final class ModernResourcePackHandler extends ResourcePackHandler {
       }
       // The resource pack has been applied correctly.
       case SUCCESSFUL -> {
+        pendingResourcePacks.remove(uuid);
         if (queued != null) {
           appliedResourcePacks.put(uuid, queued);
+        } else {
+          // When transitioning to another server that has a resource pack to apply,
+          // if one or more resource packs have already been applied from Velocity,
+          // the player sends more than 1 SUCCESSFUL response to the backend server,
+          // which results in the server receiving more resource pack responses
+          // than the server has sent requests to the player
+          final ResourcePackInfo appliedPack = appliedResourcePacks.get(uuid);
+          if (appliedPack != null) {
+            return handleResponseResult(appliedPack, bundle);
+          }
         }
-        pendingResourcePacks.remove(uuid);
       }
       // An error occurred while trying to download the resource pack to the client,
       // so the resource pack cannot be applied.

proxy/src/main/java/com/velocitypowered/proxy/connection/player/resourcepack/ResourcePackHandler.java

@@ -20,6 +20,7 @@ package com.velocitypowered.proxy.connection.player.resourcepack;
 import com.velocitypowered.api.network.ProtocolVersion;
 import com.velocitypowered.api.proxy.player.ResourcePackInfo;
 import com.velocitypowered.proxy.VelocityServer;
+import com.velocitypowered.proxy.connection.backend.VelocityServerConnection;
 import com.velocitypowered.proxy.connection.client.ConnectedPlayer;
 import com.velocitypowered.proxy.connection.player.VelocityResourcePackInfo;
 import com.velocitypowered.proxy.protocol.packet.ResourcePackRequestPacket;
@@ -147,12 +148,15 @@ public abstract sealed class ResourcePackHandler
           final @Nullable ResourcePackInfo queued,
           final @NotNull ResourcePackResponseBundle bundle
   ) {
+    // If Velocity, through a plugin, has sent a resource pack to the client,
+    // there is no need to report the status of the response to the server
+    // since it has no information that a resource pack has been sent
     final boolean handled = queued != null
-            && queued.getOriginalOrigin() != ResourcePackInfo.Origin.DOWNSTREAM_SERVER;
+            && queued.getOriginalOrigin() == ResourcePackInfo.Origin.PLUGIN_ON_PROXY;
     if (!handled) {
-      if (player.getConnectionInFlight() != null
-              && player.getConnectionInFlight().getConnection() != null) {
-        player.getConnectionInFlight().getConnection().write(new ResourcePackResponsePacket(
+      final VelocityServerConnection connectionInFlight = player.getConnectionInFlight();
+      if (connectionInFlight != null && connectionInFlight.getConnection() != null) {
+        connectionInFlight.getConnection().write(new ResourcePackResponsePacket(
                 bundle.uuid(), bundle.hash(), bundle.status()));
       }
     }