static inline
    unsigned char *silc_buffer_put_head(SilcBuffer sb,
                                          const unsigned char *data,
                                          SilcUInt32 len);

    Puts data at the head of the buffer. Returns pointer to the copied
    data area. Returns NULL on error.

    ---------------------------------
    | head  | data       | tail     |
    ---------------------------------
    ^
    Puts data to the head section.

    silc_buffer_put_head(sb, data, data_len);