Finding DNS server settings programmatically on Mac OS X

StackOverflow https://stackoverflow.com/questions/260518

  •  06-07-2019
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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.

Was it helpful?

Solution

They are also available from /etc/resolv.conf

OTHER TIPS

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.

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.

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);

You could read from /etc/resolv.conf.

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