Function peek

3rd/asio-1.24.0/include/asio/buffered_stream.hpp:268–271

  /// Throws an exception on failure.
  template <typename MutableBufferSequence>
  std::size_t peek(const MutableBufferSequence& buffers)
  {
    return stream_impl_.peek(buffers);
  }

  /// Peek at the incoming data on the stream. Returns the number of bytes read,
  /// or 0 if an error occurred.