获取 X509 数字证书里面的使用者信息 (openssl)

#define ENTRY_COUNT  7

struct entry {
int key;
char *name;
};
static const struct entry nids[ENTRY_COUNT] = {
{NID_countryName, "countryName"},
{NID_stateOrProvinceName, "stateOrProvinceName"},
{NID_localityName, "localityName"},
{NID_organizationName, "organiationName"},
{NID_organizationalUnitName, "organizationalUnitName"},
{NID_commonName, "commonName"},
{NID_pkcs9_emailAddress, "emailAddress"},
};

static int  x509_get_subject(X509 *x)
{
X509_NAME *xn = NULL;
ASN1_STRING *d = NULL;

int j = 0;
int pos = -1;
unsigned i = 0;
xn = X509_get_subject_name(x);
j = X509_NAME_entry_count(xn);

for (i = 0; i < ENTRY_COUNT; i++) {
pos = -1;
for (;;) {
pos = X509_NAME_get_index_by_NID(xn, nids[i].key, pos);
if (pos >=0 && pos <= j) {   // pos != -1
d = X509_NAME_ENTRY_get_data(X509_NAME_get_entry(xn, pos));
printf("%s = %s [%d]\n", nids[i].name, d->data, d->length);
}
}
}
return 0;
}