#define SILC_STR_ADVANCE ...

    Advance the buffer to the end of the data after the formatting is
    done.  In normal operation when the formatted data is written the
    buffer is located at the start of the data.  With SILC_STR_ADVANCE
    the buffer will be located at the end of the data.  This makes it
    easy to add new data immediately after the previously added data.
    The SILC_STR_ADVANCE may also be used in unformatting.

    do {
      len = read(fd, buf, sizeof(buf));
      if (len > 0)
        // Add read data to the buffer
        silc_buffer_format(buffer,
                           SILC_STR_ADVANCE,
                           SILC_STR_DATA(buf, len),
                           SILC_STR_END);
    } while (len > 0);

    // Move to beginning of buffer
    silc_buffer_start(buffer);