[iPhone] Objective-C : How to fetch the router address?

Question

Hey there!

I tried to fetch the router address this way.

- (NSString *) routerIp {

  NSString *address = @"error";
  struct ifaddrs *interfaces = NULL;
  struct ifaddrs *temp_addr = NULL;
  int success = 0;

  // retrieve the current interfaces - returns 0 on success
  success = getifaddrs(&interfaces);
  if (success == 0)
  {
    // Loop through linked list of interfaces
    temp_addr = interfaces;
    while(temp_addr != NULL)
    {
      if(temp_addr->ifa_addr->sa_family == AF_INET)
      {
        // Check if interface is en0 which is the wifi connection on the iPhone
        if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"])
        {
          // Get NSString from C String //ifa_addr
          address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_dstaddr)->sin_addr)];
        }
      }

      temp_addr = temp_addr->ifa_next;
    }
  }

  // Free memory
  freeifaddrs(interfaces);

  return address;
}

The router address always looks like xxx.xxx.255.255 but it is supposed to look like xxx.xxx.0.1 or something this way...

Is there anything to do to get the valid address?

Thanks for your help!

Answer 1

xxx.xxx.255.255 is the subnet mask. You need the gateway address.

See table 3-10, there is an entry for router in thsi pdf: http://developer.apple.com/Mac/library/documentation/Networking/Conceptual/SystemConfigFrameworks/SystemConfigFrameworks.pdf

The HTML version is here: http://developer.apple.com/Mac/library/documentation/Networking/Conceptual/SystemConfigFrameworks/SC_Overview/SC_Overview.html

Answer 2

Here is some code I wrote to find the routes for the machine. I copied the system calls from the code for netstat. Note that I was strongly recommended against doing this, as these system calls are not a supported API and may change at any time. They recommended I just parse the output of netstat.

CustomRoute.c:

#import "CustomRoute.h"
@implementation CustomRoute

+ (NSMutableArray*) getRoutes
{
    NSMutableArray* routeArray = [NSMutableArray array];
    CustomRoute* route = nil;

    size_t needed;
    int mib[6];
    char *buf, *next, *lim;
    register struct rt_msghdr2 *rtm;

    mib[0] = CTL_NET;
    mib[1] = PF_ROUTE;
    mib[2] = 0;
    mib[3] = 0;
    mib[4] = NET_RT_DUMP2;
    mib[5] = 0;

    if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0) {
        err(1, "sysctl: net.route.0.0.dump estimate");
    }

    if ((buf = malloc(needed)) == 0) {
        err(2, "malloc(%lu)", (unsigned long)needed);
    }
    if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0) {
        err(1, "sysctl: net.route.0.0.dump");
    }

    lim  = buf + needed;

    for (next = buf; next < lim; next += rtm->rtm_msglen) {
        rtm = (struct rt_msghdr2 *)next;
        route = [self getRoute:rtm];
        if(route != nil)
        {
            [routeArray addObject:route];
        }
    }
    free(buf);
    printf("Total routes: %u\n",    [routeArray count]);
    return routeArray;
}


+ (CustomRoute*) getRoute:(struct rt_msghdr2 *)rtm
{
    //sockaddrs are after the message header
    struct sockaddr* dst_sa = (struct sockaddr *)(rtm + 1);

    CustomRoute* route = nil;

    if(rtm->rtm_addrs & RTA_DST)
    {
        switch(dst_sa->sa_family)
        {
            case AF_INET:
                if(dst_sa->sa_family == AF_INET && !((rtm->rtm_flags & RTF_WASCLONED) && (rtm->rtm_parentflags & RTF_PRCLONING)))
                {
                    route = [[CustomRoute alloc] initWithRtm:rtm];
                }
            break;

        }
    }

    return route;
}

-(void) setAddr:(struct sockaddr*)sa index:(int)rtax_index
{
    if(rtax_index >= 0 && rtax_index < RTAX_MAX)
    {
        memcpy(&(m_addrs[rtax_index]), sa, sizeof(struct sockaddr));
    }

}

-(NSString*) getDestination
{
    return [self getAddrStringByIndex:RTAX_DST];
}

-(NSString*) getNetmask
{
    return [self getAddrStringByIndex:RTAX_NETMASK];
}

-(NSString*) getGateway
{
    return [self getAddrStringByIndex:RTAX_GATEWAY];
}

-(NSString*) getDetails
{
    NSMutableString* result = [[NSMutableString alloc] init];
    [result appendFormat: [NSString stringWithFormat: @"message type: 0x%06x\n", m_rtm.rtm_type]];
    [result appendFormat: [NSString stringWithFormat: @"flags: 0x%06x\n", m_rtm.rtm_flags]];
    [result appendFormat: [NSString stringWithFormat: @"addrs: 0x%06x\n", m_rtm.rtm_addrs]];


    return result;
}


-initWithRtm: (struct rt_msghdr2*) rtm
{
    int i;
    struct sockaddr* sa = (struct sockaddr*)(rtm + 1);


    //copy over the route message
    memcpy(&(m_rtm), rtm, sizeof(struct rt_msghdr2));
    for(i = 0; i < RTAX_MAX; i++)
    {
        [self setAddr:&(sa[i]) index:i];
    }
    return self;
}

- init
{
    memset(m_addrs, 0, sizeof(m_addrs));
    return self;
}

@end


@implementation CustomRoute (Private)

-(NSString*) getAddrStringByIndex: (int)rtax_index
{
    NSString * routeString = nil;
    struct sockaddr* sa = &(m_addrs[rtax_index]);
    int flagVal = 1 << rtax_index;

    if(!(m_rtm.rtm_addrs & flagVal))
    {
        return @"none";
    }


    if(rtax_index >= 0 && rtax_index < RTAX_MAX)
    {
        switch(sa->sa_family)
        {
            case AF_INET:
            {
                struct sockaddr_in* si = (struct sockaddr_in *)sa;
                if(si->sin_addr.s_addr == INADDR_ANY)
                    routeString = @"default";
                else
                    routeString = [NSString stringWithCString:(char *)inet_ntoa(si->sin_addr) encoding:NSASCIIStringEncoding];
            }
            break;

            case AF_LINK:
                {
                    struct sockaddr_dl* sdl = (struct sockaddr_dl*)sa;
                    if(sdl->sdl_nlen + sdl->sdl_alen + sdl->sdl_slen == 0)
                    {
                        routeString = [NSString stringWithFormat: @"link #%d", sdl->sdl_index];
                    }
                    else
                        routeString = [NSString stringWithCString:link_ntoa(sdl) encoding:NSASCIIStringEncoding];
                }
            break;

            default:
                {
                    char a[3 * sa->sa_len];
                    char *cp;
                    char *sep = "";
                    int i;

                    if(sa->sa_len == 0)
                    {
                        routeString = @"empty";
                    }
                    else
                    {
                        a[0] = (char)NULL;
                        for(i = 0, cp = a; i < sa->sa_len; i++)
                        {
                            cp += sprintf(cp, "%s%02x", sep, (unsigned char)sa->sa_data[i]);
                            sep = ":";
                        }
                        routeString = [NSString stringWithCString:a encoding:NSASCIIStringEncoding];
                    }
                }
        }
    }
    return routeString;
}

@end

CustomRoute.h:

#import <Cocoa/Cocoa.h>
#import <net/route.h>
#import <sys/socket.h>
#import <netinet/in.h>
#import <net/if_dl.h>
#import <sys/sysctl.h>

@interface CustomRoute : NSObject {
    struct sockaddr     m_addrs[RTAX_MAX];
    struct rt_msghdr2   m_rtm;
    int                 m_len;      /* length of the sockaddr array */
}

+ (NSMutableArray*) getRoutes;
+ (CustomRoute*) getRoute:(struct rt_msghdr2 *)rtm;

- (void) setAddr:(struct sockaddr*)sa index:(int)rtax_index;

- (NSString*) getDestination;
- (NSString*) getNetmask;
- (NSString*) getGateway;
- initWithRtm: (struct rt_msghdr2*) rtm;


@end