Add support for retrieving the Player's client brand

api/src/main/java/com/velocitypowered/api/proxy/Player.java

@@ -275,4 +275,11 @@ public interface Player extends CommandSource, Identified, InboundConnection,
    */
   @Override
   boolean sendPluginMessage(ChannelIdentifier identifier, byte[] data);
+
+  /**
+   * Gets the player's client brand.
+   *
+   * @return the player's client brand
+   */
+  Optional<String> getClientBrand();
 }

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

@@ -230,6 +230,7 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
         player.getKnownChannels().removeAll(PluginMessageUtil.getChannels(packet));
         backendConn.write(packet.retain());
       } else if (PluginMessageUtil.isMcBrand(packet)) {
+        player.setClientBrand(PluginMessageUtil.readBrandMessage(packet.content()));
         backendConn.write(PluginMessageUtil
             .rewriteMinecraftBrand(packet, server.getVersion(), player.getProtocolVersion()));
       } else if (BungeeCordMessageResponder.isBungeeCordMessage(packet)) {

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

@@ -142,6 +142,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
   private final Queue<ResourcePackInfo> outstandingResourcePacks = new ArrayDeque<>();
   private @Nullable ResourcePackInfo pendingResourcePack;
   private @Nullable ResourcePackInfo appliedResourcePack;
+  private @Nullable String clientBrand;
 
   ConnectedPlayer(VelocityServer server, GameProfile profile, MinecraftConnection connection,
       @Nullable InetSocketAddress virtualHost, boolean onlineMode) {
@@ -871,6 +872,15 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
     return true;
   }
 
+  @Override
+  public Optional<String> getClientBrand() {
+    return Optional.ofNullable(clientBrand);
+  }
+
+  void setClientBrand(String clientBrand) {
+    this.clientBrand = clientBrand;
+  }
+
   @Override
   public void spoofChatInput(String input) {
     Preconditions.checkArgument(input.length() <= Chat.MAX_SERVERBOUND_MESSAGE_LENGTH,

proxy/src/main/java/com/velocitypowered/proxy/protocol/util/PluginMessageUtil.java

@@ -160,11 +160,15 @@ public final class PluginMessageUtil {
     return new PluginMessage(message.getChannel(), rewrittenBuf);
   }
 
-  private static String readBrandMessage(ByteBuf content) {
-    // Some clients (mostly poorly-implemented bots) do not send validly-formed brand messages.
-    // In order to accommodate their broken behavior, we'll first try to read in the 1.8 format, and
-    // if that fails, treat it as a 1.7-format message (which has no prefixed length). (The message
-    // Velocity sends will be in the correct format depending on the protocol.)
+  /**
+   * Some clients (mostly poorly-implemented bots) do not send validly-formed brand messages.
+   * In order to accommodate their broken behavior, we'll first try to read in the 1.8 format, and
+   * if that fails, treat it as a 1.7-format message (which has no prefixed length). (The message
+   * Velocity sends will be in the correct format depending on the protocol.)
+   * @param content the brand packet
+   * @return the client brand
+   */
+  public static String readBrandMessage(ByteBuf content) {
     try {
       return ProtocolUtils.readString(content.slice());
     } catch (Exception e) {