asn_build_string
uchar_t *asn_build_string(uchar_t *, size_t *, uchar_t, uchar_t *, size_t);
p = asn_build_string(p, &bufsz, id, pdu->community, pdu->community_len);
p = asn_build_string(p, bufsz_p, id, (uchar_t *)val, val_len);