code: @Override
      public void messageSent(final NextFilter nextFilter,
              final IoSession session, final WriteRequest writeRequest)
              throws Exception {
          if (writeRequest.getMessage() != null
                  && writeRequest.getMessage() instanceof ProxyHandshakeIoBuffer) {
              // Ignore buffers used in handshaking
              return;
          }
  
          nextFilter.messageSent(session, writeRequest);
      }
docs: Filter handshake related messages from reaching the messageSent callbacks of
  downstream filters.
  
  @param nextFilter the next filter in filter chain
  @param session the session object
  @param writeRequest the data written