Accessing the iOS WiFi IP address within a Unity app

At the moment, Manifold requires that a client supplies an appropriate IP address (although I might change this in the future). Mostly it is pretty easy to do but the .NET way of doing things (using Dns.GetHostEntry()) didn’t seem to pick up the WiFi IP address on an iPad. After wasting a lot of time, I decided to go back to basics and create a native plugin.

The basis of the code comes from here – it just needed the right wrapping to get it to work with Unity. I will be the first to admit that I know nothing about native iOS coding but, following the Bonjour example here, the code below  seemed to work just fine when placed in the Assets/Plugins/iOS directory of the project.

IPAddress.h:

#import <Foundation/Foundation.h>

@interface IPAddressDelegate : NSObject

- (NSString *)getAddress;
@end

IPAddress.m:

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

#import "IPAddress.h"
@implementation IPAddressDelegate

- (id)init
{
    self = [super init];
    return self;
}

- (NSString *)getAddress {
    NSString *address = @"error";
    struct ifaddrs *interfaces = NULL;
    struct ifaddrs *temp_addr = NULL;
    int success = 0;
    success = getifaddrs(&interfaces);
    if (success == 0) {
        temp_addr = interfaces;
        while(temp_addr != NULL) {
            if(temp_addr->ifa_addr->sa_family == AF_INET) {
                if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"]) {
                    address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];
                }
            }
            temp_addr = temp_addr->ifa_next;
        }
    }
    // Free memory
    freeifaddrs(interfaces);
    return address;
}
@end

static IPAddressDelegate* delegateObject = nil;

char* MakeStringCopy (const char* string)
{
    if (string == NULL)
        return NULL;
    
    char* res = (char*)malloc(strlen(string) + 1);
    strcpy(res, string);
    return res;
}

const char * getLocalWifiIpAddress()
{
    if (delegateObject == nil)
        delegateObject = [[IPAddressDelegate alloc] init];
    
    return MakeStringCopy([[delegateObject getAddress] UTF8String]);
}

To use the plugin is pretty straightforward. Just add this declaration to a C# class:

	[DllImport ("__Internal")]
	private static extern string getLocalWifiIpAddress();

Then call getLocalWiFiIpAddress() to get the dotted address string.

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