NWPathMonitor.swift

       let monitor = NWPathMonitor()
        
        /* closure called when path changes */
        let pathUpdateHandler = {(path:NWPath) in
            let availableInterfaces = path.availableInterfaces

            if !availableInterfaces.isEmpty {
                //e.g. [ipsec4, en0, pdp_ip0]
                let list = availableInterfaces.map { $0.debugDescription }.joined(separator: "\n")
            }
            
            var status = "undetermined"
            switch path.status {
            case .requiresConnection:
                status =  "requires connection"
            case .satisfied:
                status = "satisfied"
            case .unsatisfied:
                status = "unsatisfied"
            }
        }
        
        /* set the closure */
        monitor.pathUpdateHandler = pathUpdateHandler

        /* create the queue */
        let queue = DispatchQueue.init(label: "monitor queue", qos: .userInitiated)

        /* start monitoring for changes */
        monitor.start(queue: queue)
    }