int silc_stream_write(SilcStream stream, const unsigned char *data,
                          SilcUInt32 data_len);

    Writes `data_len' bytes of data to the stream indicated by `stream' from
    data buffer indicated by `data'.  Returns the amount of data written,
    zero (0) if end of stream occurred, -1 if data could not be written
    at this moment, or -2 if error occurred.  If -1 is returned the
    notifier callback will later be called with SILC_STREAM_CAN_WRITE
    status when stream is again ready for writing.