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 the Mac I can probably use the SystemConfiguration framework as mentioned in the first answer, however the exact method of doing so is not immediately obvious.

For instance SCDynamicStoreCopyDHCPInfo returns some of the dynamic DHCP related data but not the DNS server addresses.

Whimsical

Answer 1

They are also available from /etc/resolv.conf

Conklin

Answer 2

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);
long servicesCount = CFArrayGetCount(services);
for (long i = 0; i < servicesCount; i++) {
    const SCNetworkServiceRef service = (const SCNetworkServiceRef)CFArrayGetValueAtIndex(services, i);
    CFStringRef interfaceServiceID = SCNetworkServiceGetServiceID(service);
    CFStringRef primaryservicepath = CFStringCreateWithFormat(NULL,NULL,CFSTR("State:/Network/Service/%@/DNS"),interfaceServiceID);
    SCDynamicStoreRef dynRef = SCDynamicStoreCreate(kCFAllocatorSystemDefault, CFSTR("DNSSETTING"), NULL, NULL);
    CFPropertyListRef propList = SCDynamicStoreCopyValue(dynRef,primaryservicepath);
    if (propList) {
        CFDictionaryRef dict = (CFDictionaryRef)propList;
        CFArrayRef addresses = (CFArrayRef)CFDictionaryGetValue(dict, CFSTR("ServerAddresses"));
        long addressesCount = CFArrayGetCount(addresses);
        for (long j = 0; j < addressesCount; j++) {
            CFStringRef address = (CFStringRef)CFArrayGetValueAtIndex(addresses, j);
            // Print address
            CFShow(address);
        }
        CFRelease(propList);
    }
    CFRelease(dynRef);
    CFRelease(primaryservicepath);
}
CFRelease(services);
CFRelease(prefsDNS);

Septilateral

Answer 3

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);

Travers

good code. minor improvement: don't forget to link with libresolv.dylib – Monogamous

alternative version, without peeking into res_state structure internals: https://mcmap.net/q/1021290/-get-dns-server-ip-from-iphone-settings – Impressionable

Answer 4

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.

Osanna

Ok, I've initially trying SCDynamicStoreCopyDHCPInfo and that gets me the current IP address and netmask + a few other things I don't understand, but not the DNS servers. Is there any chance you can be more specific? – Whimsical

Answer 5

You could read from /etc/resolv.conf.

Limonite