Programmatically creating an ad-hoc network in Big Sur

Question

Before Mac OS Big Sur, one could create an ad-hoc network by calling the startIBSSModeWithSSID:security:channel:password:error: function of a CWInterface obtained from a CWWifiClient. It seems that after an update to Big Sur, the above function is deprecated and throws a kCWOperationNotPermittedErr (-3930) error every time.

I tried launching the application from root, and it still refused to create an ad-hoc network. Meanwhile, using the "Create Network" option in the WiFi dropdown menu works with an administrator password.

A previous answer on this site I have come across is outdated and the code does not work anymore. There is a post on the Apple Developer forums created 5 months ago but it remains unanswered, with the "solution" being to file a tech support incident.

This is the code I am using:

#import <Foundation/Foundation.h>
#import <CoreWLAN/CoreWLAN.h>
#import <SecurityFoundation/SFAuthorization.h>
#import <objc/message.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        bool success = 0;
        
        CWWiFiClient* wifiClient = [CWWiFiClient sharedWiFiClient];
        CWInterface* interface = [wifiClient interface];
        
        NSString* namestr = @"very_creative_ssid";
        NSData* name = [namestr dataUsingEncoding:NSUTF8StringEncoding];
        NSString* pass = @"very_cruel_framework"; // not used
        NSError* err = nil;
        
        success = [interface startIBSSModeWithSSID:name
                                               security:kCWIBSSModeSecurityNone
                                                channel:11
                                               password:nil
                                                  error:&err];
        
        if (!success) {
            NSLog(@"%@", err);
            return 1;
        }
        
        [NSRunLoop.currentRunLoop run];
    }
    return 0;
}

Is there a way to programmatically create an ad-hoc network in Big Sur without throwing an error?

Edit: Here is the console output (1 line):

2022-01-12 05:25:03.723 cwlantest[15305:448617] Error Domain=com.apple.coreWLAN.error Code=-3930 "(null)"

Answer 1

I'm going to put this as an answer, if anyone finds anything new or Apple adds this feature in the future, I'll be very happy to be wrong.

TLDR: Not anymore!

Since Apple removed the "Create network..." option from the wifi menubar, the only way to create an ad-hoc network is through Network Sharing. I followed https://www.makeuseof.com/how-to-create-a-secure-ad-hoc-network-in-macos/ under the How to Create a Secure Ad Hoc Network section to make a network:

sudo networksetup -createnetworkservice AdHoc lo0
sudo networksetup -setmanual AdHoc 192.168.1.88 255.255.255.255

And in System Preferences, share your network connection from AdHoc over WiFi.

With that on, I checked the CWInterface.interfaceMode() and it was in HostAP mode. Pure speculation, but I think IBSS was removed completely, it's marked as Deprecated in the developer documentation. -3930 is kCWOperationNotPermittedErr, so I'm not 100% sure that's accurate, but it's possible.

There are private interfaces to set HostAP mode in CoreWLAN:

https://github.com/onmyway133/Runtime-Headers/blob/master/macOS/10.13/CoreWLAN.framework/CWInterface.h https://medium.com/swlh/calling-ios-and-macos-hidden-api-in-style-1a924f244ad1 https://gist.github.com/wolever/4418079

After replacing objc_msgsend with NSInvocation in the last link since objc_msgsend seems to have been removed:

#import <CoreWLAN/CoreWLAN.h>
#import <objc/message.h>

int main(int argc, char* argv[]) {
  @autoreleasepool {
    int ch;
    NSString *ssid = nil, *password = nil;

    while((ch = getopt(argc, argv, "s:p:h")) != -1) {
      switch(ch) {
      case 's':
        ssid = [NSString stringWithUTF8String:optarg];
        break;
      case 'p':
        password = [NSString stringWithUTF8String:optarg];
        break;
      case '?':
      case 'h':
      default:
        printf("USAGE: %s [-s ssid] [-p password] [-h] command\n", argv[0]);
        printf("\nOPTIONS:\n");
        printf("   -s ssid     SSID\n");
        printf("   -p password WEP password\n");
        printf("   -h          Print help\n");
        printf("\nCOMMAND:\n");
        printf("   status      Print interface mode\n");
        printf("   start       Start Host AP mode\n");
        printf("   stop        Stop Host AP mode\n");
        return 0;
      }
    }

    NSString *command = nil;
    if(argv[optind]) {
      command = [NSString stringWithUTF8String:argv[optind]];
    }

    CWInterface *iface = [[CWWiFiClient sharedWiFiClient] interface];

    if(!command || [command isEqualToString:@"status"]) {
      NSString *mode = nil;
      switch(iface.interfaceMode) {
      case kCWInterfaceModeStation:
        mode = @"Station";
        break;
      case kCWInterfaceModeIBSS:
        mode = @"IBSS";
        break;
      case kCWInterfaceModeHostAP:
        mode = @"HostAP";
        break;
      case kCWInterfaceModeNone:
      default:
        mode = @"None";
      }
      printf("%s\n", [mode UTF8String]);
    } else if([command isEqualToString:@"stop"]) {
      // Stop Host AP mode
      if(getuid() != 0) {
        printf("this may need root (trying anyway)...\n");
      }
        SEL selector = @selector(stopHostAPMode);
        NSMethodSignature *signature = [iface methodSignatureForSelector: selector];
        NSInvocation *invocation =
        [NSInvocation invocationWithMethodSignature:signature];
        invocation.target = iface;
        invocation.selector = selector;
        
        [invocation invoke];
        printf("Done?");
        
      //objc_msgSend(iface, @selector(stopHostAPMode));
        
    } else if([command isEqualToString:@"start"]) {
      if(!ssid) {
        printf("error: an ssid must be specified\n");
        return 1;
      }

      // known security types:
      //   2: no securiry
      //   16: wep
      // Note: values [-127..127] have been tried, and all but these return errors.
      unsigned long long securityType = 2;
      if(password) {
        if([password length] < 10) {
          printf("error: password too short (must be >= 10 characters)\n");
          return 1;
        }
        securityType = 16;
      }

      NSSet *chans = [iface supportedWLANChannels];
      //printf("chan count: %lu\n", [chans count]);

      NSEnumerator *enumerator = [chans objectEnumerator];
      CWChannel *channel;
      while ((channel = [enumerator nextObject])) {
        //printf("channel: %lu\n", [channel channelNumber]);
        if ([channel channelNumber] == 11)
          break;
      }
        
        printf("Found Channel: %d\n", channel.channelNumber);

        // Start Host AP mode
        NSError *error = nil;
        NSError **errorptr = &error;
        
        SEL selector = @selector(startHostAPModeWithSSID:securityType:channel:password:error:);
        NSMethodSignature *signature = [iface methodSignatureForSelector: selector];
        NSInvocation *invocation =
        [NSInvocation invocationWithMethodSignature:signature];
        invocation.target = iface;
        invocation.selector = selector;
            NSString * ssidstr = @"Test";
            NSString * pass = @"barbarbarr";
        NSData * ssidArg = [ssidstr dataUsingEncoding:NSUTF8StringEncoding];
        [invocation setArgument: &ssidArg atIndex:2];
        [invocation setArgument: &securityType atIndex:3];
        [invocation setArgument: &channel atIndex:4];
        [invocation setArgument: &pass atIndex:5];
        [invocation setArgument: &errorptr atIndex:6];
        
        [invocation invoke];
        BOOL success;
        [invocation getReturnValue:&success];
        
        if (!success) {
            printf("startHostAPModeWithSSID error: %s\n", [(*errorptr).localizedDescription UTF8String]);
            return 1;
        } else {
            printf("Success?\n");
            return 0;
        }
    }

    return 0;
  }
}

./hostap stop does successfully kick me out of hostap mode started from network sharing, but ./hostap start fails with -3903 kCWNotSupportedErr. Also, using startHostAPMode: without other settings does succeed, but the wifi menu shows WiFi: Internet Sharing, so I think this is a private api meant specifically for network sharing and will likely need other configuration to get working. You could potentially continue down that road, but it didn't look very promising. The best bet is to just use network sharing or potentially look into scripting System Preferences with AppleScript if you really want a scripted approach.