code: public void returnOutputContext(OutputContext ctx) {
          List<ByteBuffer> remaining = ctx.releaseRemaining();
          if (pending == null) {
              pending = remaining;
          } else {
              List<ByteBuffer> tmp = pending;
              pending = remaining;
              pending.addAll(tmp);
          }
      }
docs: Re-transfer ownership of a given output buffer to the connection
  
  @param ctx An OutputContext previously returned by {@link #borrowOutputContext()}