Get DNS server IP from iphone settings

问题

I try to find a way how to get my DNS server ip which appear under settings->wi-fi->details->DNS. I don't know if apple allow to get this info programmatically.

回答1:

I used this on OS X and worked for me, (link to ibresolv.dylib as well)

#include <arpa/inet.h>
#include <ifaddrs.h>
#include <resolv.h>
#include <dns.h>

- (NSString *) getDNSAddressesStr 
{
    NSMutableString *addressStr = [[NSMutableString alloc]initWithString:@"DNS Addresses \n"];

    res_state res = malloc(sizeof(struct __res_state));

    int result = res_ninit(res);

    if ( result == 0 )
    {    
        for ( int i = 0; i < res->nscount; i++ )
        {
            NSString *s = [NSString stringWithUTF8String :  inet_ntoa(res->nsaddr_list[i].sin_addr)];
            [addressStr appendFormat:@"%@\n",s];
            NSLog(@"%@",s);
        }
    }
    else 
        [addressStr appendString:@" res_init result != 0"];

    return addressStr;
    }
}

回答2:

This is (IMHO) a better Swift3+ variant, which is an extract of my Swift wrapper for libresolv as used by dig for iOS, and correctly handles IPV6 name servers:

open class Resolver {

    fileprivate var state = __res_9_state()

    public init() {
        res_9_ninit(&state)
    }

    deinit() {
        res_9_ndestroy(&state)
    }

    public final func getservers() -> [res_9_sockaddr_union] {

        let maxServers = 10
        var servers = [res_9_sockaddr_union](repeating: res_9_sockaddr_union(), count: maxServers)
        let found = Int(res_9_getservers(&state, &servers, Int32(maxServers)))

        // filter is to remove the erroneous empty entry when there's no real servers
       return Array(servers[0 ..< found]).filter() { $0.sin.sin_len > 0 }
    }
}

Converting a res_9_sockaddr_union to its string value can be done with this:

extension Resolver {
    public static func getnameinfo(_ s: res_9_sockaddr_union) -> String {
        var s = s
        var hostBuffer = [CChar](repeating: 0, count: Int(NI_MAXHOST))

        len sinlen = socklen_t(s.sin.sin_len)
        let _ = withUnsafePointer(to: &s) {
            $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                Darwin.getnameinfo($0, sinlen,
                                   &hostBuffer, socklen_t(hostBuffer.count),
                                   nil, 0,
                                   NI_NUMERICHOST)
            }
        }

        return String(cString: hostBuffer)
    }
}

which all combined can get a String[] containing the list of servers like this:

let servers = Resolver().getservers().map(Resolver.getnameinfo)

回答3:

ObjC version with IPV6 support if Swift is not in your project:

#include <resolv.h>
#include <netdb.h>

@implementation DNSResolver {
    res_state _state;
}

- (instancetype)init {
    self = [super init];
    if (self) {
        _state = malloc(sizeof(struct __res_state));
        if (EXIT_SUCCESS != res_ninit(_state)) {
            free(_state);
            return nil;
        }
    }
    return self;
}

- (void)dealloc {
    res_ndestroy(_state);
    free(_state);
}

#pragma mark - Public

- (NSString *)getDNSAddressesCSV
{
    NSMutableArray *addresses = [NSMutableArray new];

    union res_sockaddr_union servers[NI_MAXSERV];

    int serversFound = res_9_getservers(_state, servers, NI_MAXSERV);

    char hostBuffer[NI_MAXHOST];
    for (int i = 0; i < serversFound; i ++) {
        union res_sockaddr_union s = servers[i];
        if (s.sin.sin_len > 0) {
            if (EXIT_SUCCESS == getnameinfo((struct sockaddr *)&s.sin,  // Pointer to your struct sockaddr
                                            (socklen_t)s.sin.sin_len,   // Size of this struct
                                            (char *)&hostBuffer,        // Pointer to hostname string
                                            sizeof(hostBuffer),         // Size of this string
                                            nil,                        // Pointer to service name string
                                            0,                          // Size of this string
                                            NI_NUMERICHOST)) {          // Flags given
                [addresses addObject:[NSString stringWithUTF8String:hostBuffer]];
            }
        }
    }

    return [addresses componentsJoinedByString:@","];
}


@end

回答4:

I think a free() is missing:

free(res);

ps for xCode 7 add "libresolv.tbd" to "link with Binary Library"

回答5:

This is Swift3 variant of the accepted answer:

func dnsServers() -> [in_addr_t] {
    var result = __res_9_state()
    guard res_9_ninit(&result) == 0 else { return [] }
    let sockets = result.nsaddr_list // note: nsaddr_list is a tuple, not an array
    let addresses = [sockets.0.sin_addr.s_addr, sockets.1.sin_addr.s_addr, sockets.2.sin_addr.s_addr]
    let filtered = addresses.filter { $0 != nil }
    return filtered
}

As usual, link libresolv.9.tbd and add #import <resolv.h> to bridging header

来源：https://stackoverflow.com/questions/31256024/get-dns-server-ip-from-iphone-settings