Check internet connection with Swift 4.x

The code below swift reference from source: stackoverflow

Create Reachability.swift file:

    import Foundation
    import SystemConfiguration

    class Reachability {
        var hostname: String?
        var isRunning = false
        var isReachableOnWWAN: Bool
        var reachability: SCNetworkReachability?
        var reachabilityFlags = SCNetworkReachabilityFlags()
        let reachabilitySerialQueue = DispatchQueue(label: "ReachabilityQueue")
        init?(hostname: String) throws {
            guard let reachability = SCNetworkReachabilityCreateWithName(nil, hostname) else {
                throw Network.Error.failedToCreateWith(hostname)
            }
            self.reachability = reachability
            self.hostname = hostname
            isReachableOnWWAN = true
            try start()
        }
        init() throws {
            var zeroAddress = sockaddr_in()
            zeroAddress.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
            zeroAddress.sin_family = sa_family_t(AF_INET)
            guard let reachability = withUnsafePointer(to: &zeroAddress, {
                $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                    SCNetworkReachabilityCreateWithAddress(nil, $0)
                }
            }) else {
                throw Network.Error.failedToInitializeWith(zeroAddress)
            }
            
            self.reachability = reachability
            isReachableOnWWAN = true
            
            try start()
        }
        
        var status: Network.Status {
            return  !isConnectedToNetwork ? .unreachable :
                    isReachableViaWiFi    ? .wifi :
                    isRunningOnDevice     ? .wwan : .unreachable
        }
        
        var isRunningOnDevice: Bool = {
            #if targetEnvironment(simulator)
                return false
            #else
                return true
            #endif
        }()
        deinit { stop() }
    }

//***

    extension Reachability {
        
        func start() throws {
            guard let reachability = reachability, !isRunning else { return }
            var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
            context.info = Unmanaged<Reachability>.passUnretained(self).toOpaque()
            guard SCNetworkReachabilitySetCallback(reachability, callout, &context) else { stop()
                throw Network.Error.failedToSetCallout
            }
            guard SCNetworkReachabilitySetDispatchQueue(reachability, reachabilitySerialQueue) else { stop()
                throw Network.Error.failedToSetDispatchQueue
            }
            reachabilitySerialQueue.async { self.flagsChanged() }
            isRunning = true
        }
        
        func stop() {
            defer { isRunning = false }
            guard let reachability = reachability else { return }
            SCNetworkReachabilitySetCallback(reachability, nil, nil)
            SCNetworkReachabilitySetDispatchQueue(reachability, nil)
            self.reachability = nil
        }
        
        var isConnectedToNetwork: Bool {
            return isReachable &&
                   !isConnectionRequiredAndTransientConnection &&
                   !(isRunningOnDevice && isWWAN && !isReachableOnWWAN)
        }
        
        var isReachableViaWiFi: Bool {
            return isReachable && isRunningOnDevice && !isWWAN
        }

        /// Flags that indicate the reachability of a network node name or address, including whether a connection is required, and whether some user intervention might be required when establishing a connection.
        var flags: SCNetworkReachabilityFlags? {
            guard let reachability = reachability else { return nil }
            var flags = SCNetworkReachabilityFlags()
            return withUnsafeMutablePointer(to: &flags) {
                SCNetworkReachabilityGetFlags(reachability, UnsafeMutablePointer($0))
                } ? flags : nil
        }
        
        /// compares the current flags with the previous flags and if changed posts a flagsChanged notification
        func flagsChanged() {
            guard let flags = flags, flags != reachabilityFlags else { return }
            reachabilityFlags = flags
            NotificationCenter.default.post(name: .flagsChanged, object: self)
        }
        
        /// The specified node name or address can be reached via a transient connection, such as PPP.
        var transientConnection: Bool { return flags?.contains(.transientConnection) == true }
        
        /// The specified node name or address can be reached using the current network configuration.
        var isReachable: Bool { return flags?.contains(.reachable) == true }
        
        /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. If this flag is set, the kSCNetworkReachabilityFlagsConnectionOnTraffic flag, kSCNetworkReachabilityFlagsConnectionOnDemand flag, or kSCNetworkReachabilityFlagsIsWWAN flag is also typically set to indicate the type of connection required. If the user must manually make the connection, the kSCNetworkReachabilityFlagsInterventionRequired flag is also set.
        var connectionRequired: Bool { return flags?.contains(.connectionRequired) == true }
        
        /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. Any traffic directed to the specified name or address will initiate the connection.
        var connectionOnTraffic: Bool { return flags?.contains(.connectionOnTraffic) == true }
        
        /// The specified node name or address can be reached using the current network configuration, but a connection must first be established.
        var interventionRequired: Bool { return flags?.contains(.interventionRequired) == true }
        
        /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. The connection will be established "On Demand" by the CFSocketStream programming interface (see CFStream Socket Additions for information on this). Other functions will not establish the connection.
        var connectionOnDemand: Bool { return flags?.contains(.connectionOnDemand) == true }
        
        /// The specified node name or address is one that is associated with a network interface on the current system.
        var isLocalAddress: Bool { return flags?.contains(.isLocalAddress) == true }
        
        /// Network traffic to the specified node name or address will not go through a gateway, but is routed directly to one of the interfaces in the system.
        var isDirect: Bool { return flags?.contains(.isDirect) == true }
        
        /// The specified node name or address can be reached via a cellular connection, such as EDGE or GPRS.
        var isWWAN: Bool { return flags?.contains(.isWWAN) == true }
        
        /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. If this flag is set
        /// The specified node name or address can be reached via a transient connection, such as PPP.
        var isConnectionRequiredAndTransientConnection: Bool {
            return (flags?.intersection([.connectionRequired, .transientConnection]) == [.connectionRequired, .transientConnection]) == true
        }
    }

//***

    func callout(reachability: SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutableRawPointer?) {
        guard let info = info else { return }
        DispatchQueue.main.async {
            Unmanaged<Reachability>
                .fromOpaque(info)
                .takeUnretainedValue()
                .flagsChanged()
        }
    }

//***

    extension Notification.Name {
        static let flagsChanged = Notification.Name("FlagsChanged")
    }

//***

    struct Network {
        static var reachability: Reachability!
        enum Status: String {
            case unreachable, wwan, wifi
          
        }
        enum Error: Swift.Error {
            case failedToSetCallout
            case failedToSetDispatchQueue
            case failedToCreateWith(String)
            case failedToInitializeWith(sockaddr_in)
        }
    }

Usage: Initialize it in your AppDelegate.swift didFinishLaunchingWithOptions method and handle any errors that might occur:

import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        do {
            try Network.reachability = Reachability(hostname: "www.google.com")
        }
        catch {
            switch error as? Network.Error {
            case let .failedToCreateWith(hostname)?:
                print("Network error:\nFailed to create reachability object With host named:", hostname)
            case let .failedToInitializeWith(address)?:
                print("Network error:\nFailed to initialize reachability object With address:", address)
            case .failedToSetCallout?:
                print("Network error:\nFailed to set callout")
            case .failedToSetDispatchQueue?:
                print("Network error:\nFailed to set DispatchQueue")
            case .none:
                print(error)
            }
        }
        return true
    }
}

View controller sample:

import UIKit
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default
            .addObserver(self,
                         selector: #selector(statusManager),
                         name: .flagsChanged,
                         object: nil)
        updateUserInterface()
    }
    func updateUserInterface() {
        switch Network.reachability.status {
        case .unreachable:
            view.backgroundColor = .red
        case .wwan:
            view.backgroundColor = .yellow
        case .wifi:
            view.backgroundColor = .green
        }
        print("Reachability Summary")
        print("Status:", Network.reachability.status)
        print("HostName:", Network.reachability.hostname ?? "nil")
        print("Reachable:", Network.reachability.isReachable)
        print("Wifi:", Network.reachability.isReachableViaWiFi)
    }
    @objc func statusManager(_ notification: Notification) {
        updateUserInterface()
    }
}