Finding DNS server settings programmatically on Mac OS X

Question

I have some cross platform DNS client code that I use for doing end to end SMTP and on windows I can find the current DNS server ip addresses by looking in the registry. On

Answer 1

I know it's been a long time since you needed this, but there is nothing worse than a old unsolved answer. You can't access them from "/etc/resolv.conf" because of permission issues. After much searching, and a little luck I discovered you can get it via res_ninit() function.

// Get native iOS System Resolvers
res_ninit(&_res);
res_state res = &_res;

for (int i = 0; i < res->nscount; i++) {
  sa_family_t family = res->nsaddr_list[i].sin_family;
  int port = ntohs(res->nsaddr_list[i].sin_port);
  if (family == AF_INET) { // IPV4 address
    char str[INET_ADDRSTRLEN]; // String representation of address
    inet_ntop(AF_INET, & (res->nsaddr_list[i].sin_addr.s_addr), str, INET_ADDRSTRLEN);
  } else if (family == AF_INET6) { // IPV6 address
    char str[INET6_ADDRSTRLEN]; // String representation of address
    inet_ntop(AF_INET6, &(res->nsaddr_list [i].sin_addr.s_addr), str, INET6_ADDRSTRLEN);
  }
}
res_ndestroy(res);

Answer 2

You can use the SystemConfiguration framework. It's in C.

Update: apparently the rest of the web is harder to use than I thought. Search for the key "State:/Network/Service/ServiceID/DNS" where ServiceID is the ID of the service.

Answer 3

You could read from /etc/resolv.conf.

Answer 4

They are also available from /etc/resolv.conf

Answer 5

I know its very late to answer this question but may be helpful for the others.

This Code will help out for this task ..

SCPreferencesRef _prefsDNS = SCPreferencesCreate(NULL, CFSTR("DNSSETTING"), NULL);

CFArrayRef services = SCNetworkServiceCopyAll(_prefsDNS);

if (services) {
long count = CFArrayGetCount(services);
for (int i = 0; i < count; i++) {
service = CFArrayGetValueAtIndex(services, i);
interface = SCNetworkServiceGetInterface(service);
NSString *interfaceServiceID = (__bridge NSString*)SCNetworkServiceGetServiceID(service);
CFStringRef primaryservicepath = CFStringCreateWithFormat(NULL,NULL,CFSTR("State:/Network/Service/%@/DNS"),interfaceServiceID);
        //    NSLog(@"%@",primaryservicepath);


SCDynamicStoreRef dynRef=SCDynamicStoreCreate(kCFAllocatorSystemDefault, CFSTR("DNSSETTING"), NULL, NULL);
                // NSLog(@"%@",dynRef);
CFDictionaryRef dnskey = SCDynamicStoreCopyValue(dynRef,primaryservicepath);

           //     NSLog(@"%@",dnskey);
//dnskey will give you the DNS server address.