Method copy

3rd/asio-1.24.0/include/asio/impl/buffered_write_stream.hpp:471–482

template <typename Stream>
template <typename ConstBufferSequence>
std::size_t buffered_write_stream<Stream>::copy(
    const ConstBufferSequence& buffers)
{
  using asio::buffer_size;
  std::size_t orig_size = storage_.size();
  std::size_t space_avail = storage_.capacity() - orig_size;
  std::size_t bytes_avail = buffer_size(buffers);
  std::size_t length = bytes_avail < space_avail ? bytes_avail : space_avail;
  storage_.resize(orig_size + length);
  return asio::buffer_copy(
      storage_.data() + orig_size, buffers, length);
}

} // namespace asio