@deftypefun {int} {gnutls_pkcs7_add_attr} (gnutls_pkcs7_attrs_t * @var{list}, const char * @var{oid}, gnutls_datum_t * @var{data}, unsigned @var{flags})
@var{list}: A list of existing attributes or pointer to @code{NULL}  for the first one

@var{oid}: the OID of the attribute to be set

@var{data}: the raw (DER-encoded) data of the attribute to be set

@var{flags}: zero or @code{GNUTLS_PKCS7_ATTR_ENCODE_OCTET_STRING} 

This function will set a PKCS @code{7}  attribute in the provided list.
If this function fails, the previous list would be deallocated.

Note that any attributes set with this function must either be
DER or BER encoded, unless a special flag is present.

@strong{Returns:} On success, the new list head, otherwise @code{NULL} .

@strong{Since:} 3.4.2
@end deftypefun