Avoid a memory copy in creating modern-style forwarding data

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

@@ -117,32 +117,28 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
 
   private static ByteBuf createForwardingData(byte[] hmacSecret, String address,
       GameProfile profile) {
-    ByteBuf dataToForward = Unpooled.buffer();
-    ByteBuf finalData = Unpooled.buffer();
+    ByteBuf forwarded = Unpooled.buffer(2048);
     try {
-      ProtocolUtils.writeVarInt(dataToForward, VelocityConstants.FORWARDING_VERSION);
-      ProtocolUtils.writeString(dataToForward, address);
-      ProtocolUtils.writeUuid(dataToForward, profile.getId());
-      ProtocolUtils.writeString(dataToForward, profile.getName());
-      ProtocolUtils.writeProperties(dataToForward, profile.getProperties());
+      ProtocolUtils.writeVarInt(forwarded, VelocityConstants.FORWARDING_VERSION);
+      ProtocolUtils.writeString(forwarded, address);
+      ProtocolUtils.writeUuid(forwarded, profile.getId());
+      ProtocolUtils.writeString(forwarded, profile.getName());
+      ProtocolUtils.writeProperties(forwarded, profile.getProperties());
 
       SecretKey key = new SecretKeySpec(hmacSecret, "HmacSHA256");
       Mac mac = Mac.getInstance("HmacSHA256");
       mac.init(key);
-      mac.update(dataToForward.array(), dataToForward.arrayOffset(), dataToForward.readableBytes());
+      mac.update(forwarded.array(), forwarded.arrayOffset(), forwarded.readableBytes());
       byte[] sig = mac.doFinal();
-      finalData.writeBytes(sig);
-      finalData.writeBytes(dataToForward);
-      return finalData;
+
+      return Unpooled.wrappedBuffer(Unpooled.wrappedBuffer(sig), forwarded);
     } catch (InvalidKeyException e) {
-      finalData.release();
+      forwarded.release();
       throw new RuntimeException("Unable to authenticate data", e);
     } catch (NoSuchAlgorithmException e) {
       // Should never happen
-      finalData.release();
+      forwarded.release();
       throw new AssertionError(e);
-    } finally {
-      dataToForward.release();
     }
   }
 }