docs: public void addBuffer(ReadableBuffer buffer) {
      if (!(buffer instanceof CompositeReadableBuffer)) {
        buffers.add(buffer);
        readableBytes += buffer.readableBytes();
        return;
      }
  
      CompositeReadableBuffer compositeBuffer = (CompositeReadableBuffer) buffer;
      while (!compositeBuffer.buffers.isEmpty()) {
        ReadableBuffer subBuffer = compositeBuffer.buffers.remove();
        buffers.add(subBuffer);
      }
      readableBytes += compositeBuffer.readableBytes;
      compositeBuffer.readableBytes = 0;
      compositeBuffer.close();
    }