Simplified buffer allocation for SubAck encoding part

netty_parser/src/main/java/org/dna/mqtt/moquette/parser/netty/SubAckEncoder.java

@@ -17,24 +17,18 @@ class SubAckEncoder extends DemuxEncoder<SubAckMessage> {
             throw new IllegalArgumentException("Found a suback message with empty topics");
         }
 
-        ByteBuf variableHeaderBuff = chc.alloc().buffer(4);
-        ByteBuf buff = null;
+        int variableHeaderSize = 2 + message.types().size();
+        ByteBuf buff = chc.alloc().buffer(6 + variableHeaderSize);
         try {
-            variableHeaderBuff.writeShort(message.getMessageID());
-            for (AbstractMessage.QOSType c : message.types()) {
-                variableHeaderBuff.writeByte(c.ordinal());
-            }
-
-            int variableHeaderSize = variableHeaderBuff.readableBytes();
-            buff = chc.alloc().buffer(2 + variableHeaderSize);
-
             buff.writeByte(AbstractMessage.SUBACK << 4 );
             buff.writeBytes(Utils.encodeRemainingLength(variableHeaderSize));
-            buff.writeBytes(variableHeaderBuff);
+            buff.writeShort(message.getMessageID());
+            for (AbstractMessage.QOSType c : message.types()) {
+                buff.writeByte(c.ordinal());
+            }
 
             out.writeBytes(buff);
         } finally {
-            variableHeaderBuff.release();
             buff.release();
         }
     }