UDP broadcast using GCDAsyncUdpSocket through all available Network Interfaces

Question

I am using GCDAsyncUdpSocket for broadcasting UDP packets for searching my NAS devices.

Below is the code snippet for sending and receiving UDP packets

NSString *broadCastAddress = @"255.255.255.255";
NSInteger udpPort =  8097;

GCDAsyncUdpSocket  *gcdAsyncUdpSocket = [[GCDAsyncUdpSocket alloc]  initWithDelegate:selfdelegateQueue:dispatch_get_main_queue()];
[gcdAsyncUdpSocket bindToPort:udpPort error:&error];
[gcdAsyncUdpSocket setPreferIPv4];

NSData *data = @“Hi there”; // Sample data
[gcdAsyncUdpSocket  enableBroadcast:YES error:&error];
[gcdAsyncUdpSocket  beginReceiving:&error];

[gcdAsyncUdpSocket  sendData:data toHost:broadCastAddress port:udpPort withTimeout:-1 tag:1];

The above code can send packets through only single Network interface i.e either Wifi or Ethernet or Thunderbolt, the thing is i want to broadcast through all of the available Network Interfaces. (Ethernet, WiFi, Thunderbolt etc.).

Is there any way i can broadcast via all the available Network Interfaces (Ethernet, WiFi, Thunderbolt etc.) at the same time and using the same port.

Any help is appreciated, thanks in advance.

Answer 1

Phew!! I figured out a solution after lot of googling and trial & error methods. Here goes the solution.

1. First enumerate all the available Network interfaces using the below function.

   - (NSMutableArray *) enumerateAndGetDetailsOfAllNetworkInterfaces
   {
        NSMutableArray *interfaceArray = [[NSMutableArray alloc] init];
        struct ifaddrs *ifap, *ifa;
        struct sockaddr_in *sa;
        char *addr;
   
        getifaddrs (&ifap);
   
         for (ifa = ifap; ifa; ifa = ifa->ifa_next)
         {
          if (ifa->ifa_addr->sa_family==AF_INET)
           {
            QNInterfaceModel *interfaceModel = [[QNInterfaceModel alloc] init];
   
            sa = (struct sockaddr_in *) ifa->ifa_addr;
            addr = inet_ntoa(sa->sin_addr);
            printf("Interface: %s\tAddress: %s\n", ifa->ifa_name, addr);
   
            interfaceModel.interfaceName = [NSString stringWithCString:ifa->ifa_name encoding:NSUTF8StringEncoding];
            interfaceModel.interfaceIPAddress = [NSString stringWithCString:addr encoding:NSUTF8StringEncoding];
   
            [interfaceArray addObject:interfaceModel];
       }
   }
   
     freeifaddrs(ifap);
     return interfaceArray;
   }
   

I have created InterfaceModel which stores the Interface Name and its Address.

Step 2: Create a Socket for each Interface

    NSMutableArray *interfaceArray = [self enumerateAndGetDetailsOfAllNetworkInterfaces];

    for(QNInterfaceModel *interfaceModel in interfaceArray)
    {
       NSError *error;

       NSInteger udpPort =  8097;

       GCDAsyncUdpSocket *gcdAsyncUdpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self
                                                                         delegateQueue:dispatch_get_main_queue()];
       [gcdAsyncUdpSocket bindToPort:udpPort interface:interfaceModel.interfaceName error:&error];

       gcdAsyncUdpSocket.delegate = self;

       if(error == nil)
       {
         [_socketArray addObject:gcdAsyncUdpSocket];
       }
    }

Step 3: Store all the created sockets in a array and broadcast through each of them as follows, but before broadcasting, we need to create a listener socket to receive the response packets.

     NSError *error;

     NSString *broadCastString = @"255.255.255.255";

     NSInteger udpPort =  8097;
     GCDAsyncUdpSocket *listenerGCDAsyncUdpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self
                                                                  delegateQueue:dispatch_get_main_queue()];
    [listenerGCDAsyncUdpSocket bindToPort:udpPort error:&error];
    [listenerGCDAsyncUdpSocket setPreferIPv4];
    [listenerGCDAsyncUdpSocket  enableBroadcast:YES error:&error];
    [listenerGCDAsyncUdpSocket  beginReceiving:&error];


   // Send Packets through all the available Interfaces
   for(NSInteger i =0 ; i<_socketArray.count ;i++)
   {
    GCDAsyncUdpSocket *gcdAsyncUdpSocket = [_socketArray objectAtIndex:i];
    gcdAsyncUdpSocket.delegate = self;

    if(error)
    {
       // Error connecting
    }
    else
    {
        [gcdAsyncUdpSocket setPreferIPv4];

        NSData *data = @"Hi There";

        if (![gcdAsyncUdpSocket enableBroadcast:YES error:&error]) {

            QNDLog(@"Error enableBroadcast:%@",error);
            return;
        }

        [gcdAsyncUdpSocket  beginReceiving:&error];

        [gcdAsyncUdpSocket  sendData:data toHost:broadCastString port:udpPort withTimeout:-1 tag:i];
    }
}