Add API to allow plugins to request players switch to a texture pack. Adds BUKKIT-2579

The setTexturePack method causes the player's client to
download and switch to a texture pack specified by a URL.

Note: Players can disable server textures on their client, in which
case this API would not affect them.

src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java

@@ -47,6 +47,7 @@ import org.bukkit.inventory.InventoryView.Property;
 import org.bukkit.map.MapView;
 import org.bukkit.metadata.MetadataValue;
 import org.bukkit.plugin.Plugin;
+import org.bukkit.plugin.messaging.Messenger;
 import org.bukkit.plugin.messaging.StandardMessenger;
 
 @DelegateDeserialization(CraftOfflinePlayer.class)
@@ -782,6 +783,15 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
         }
     }
 
+    public void setTexturePack(String url) {
+        Validate.notNull(url, "Texture pack URL cannot be null");
+
+        byte[] message = (url + "\0" + "16").getBytes();
+        Validate.isTrue(message.length <= Messenger.MAX_MESSAGE_SIZE, "Texture pack URL is too long");
+
+        getHandle().playerConnection.sendPacket(new Packet250CustomPayload("MC|TPack", message));
+    }
+
     public void addChannel(String channel) {
         if (channels.add(channel)) {
             server.getPluginManager().callEvent(new PlayerRegisterChannelEvent(this, channel));