'How to use SCNetworkReachability in Swift

I'm trying to convert this code snippet to Swift. I'm struggling on getting off the ground due to some difficulties.

- (BOOL) connectedToNetwork
{
    // Create zero addy
    struct sockaddr_in zeroAddress;
    bzero(&zeroAddress, sizeof(zeroAddress));
    zeroAddress.sin_len = sizeof(zeroAddress);
    zeroAddress.sin_family = AF_INET;

    // Recover reachability flags
    SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL, (struct sockaddr *)&zeroAddress);
    SCNetworkReachabilityFlags flags;

    BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
    CFRelease(defaultRouteReachability);

    if (!didRetrieveFlags)
    {
        return NO;
    }

    BOOL isReachable = flags & kSCNetworkFlagsReachable;
    BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;

    return (isReachable && !needsConnection) ? YES : NO;
}

The first and the main issue I'm having is on how to define and work with C structs. In the first line (struct sockaddr_in zeroAddress;) of the above code, I think they're defining a instance called zeroAddress from the struct sockaddr_in(?), I assume. I tried declaring a var like this.

var zeroAddress = sockaddr_in()

But I get the error Missing argument for parameter 'sin_len' in call which is understandable because that struct takes a number of arguments. So I tried again.

var zeroAddress = sockaddr_in(sin_len: sizeof(zeroAddress), sin_family: AF_INET, sin_port: nil, sin_addr: nil, sin_zero: nil)

As expected I get some other error Variable used within its own initial value. I understand the cause of that error too. In C, they declare the instance first and then fill up the parameters. Its not possible in Swift as far as I know. So I'm truly lost at this point on what to do.

I read Apple's official document on interacting with C APIs in Swift but it has no examples in working with structs.

Can anyone please help me out here? I'd really appreciate it.

Thank you.

UPDATE: Thanks to Martin I was able to get past the initial problem. But still Swift ain't making it easier for me. I'm getting multiple new errors.

func connectedToNetwork() -> Bool {

    var zeroAddress = sockaddr_in(sin_len: 0, sin_family: 0, sin_port: 0, sin_addr: in_addr(s_addr: 0), sin_zero: (0, 0, 0, 0, 0, 0, 0, 0))
    zeroAddress.sin_len = UInt8(sizeofValue(zeroAddress))
    zeroAddress.sin_family = sa_family_t(AF_INET)

    var defaultRouteReachability: SCNetworkReachabilityRef = SCNetworkReachabilityCreateWithAddress(UnsafePointer<Void>, UnsafePointer<zeroAddress>) // 'zeroAddress' is not a type
    var flags = SCNetworkReachabilityFlags()

    let didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, UnsafeMutablePointer<flags>) // 'flags' is not a type
    defaultRouteReachability.dealloc(1) // 'SCNetworkReachabilityRef' does not have a member named 'dealloc'

    if didRetrieveFlags == false {
        return false
    }

    let isReachable: Bool = flags & kSCNetworkFlagsReachable // Cannot invoke '&' with an argument list of type '(@lvalue UInt32, Int)'
    let needsConnection: Bool = flags & kSCNetworkFlagsConnectionRequired // Cannot invoke '&' with an argument list of type '(@lvalue UInt32, Int)'

    return (isReachable && !needsConnection) ? true : false
}

EDIT 1: Okay I changed this line to this,

var defaultRouteReachability: SCNetworkReachabilityRef = SCNetworkReachabilityCreateWithAddress(UnsafePointer<Void>(), &zeroAddress)

The new error I'm getting at this line is 'UnsafePointer' is not convertible to 'CFAllocator'. How to you pass NULL in Swift?

Also I changed this line and the error is gone now.

let didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags)

EDIT 2: I passed nil in this line after seeing this question. But that answer contradicts with the answer here. It says there is no equivalent to NULL in Swift.

var defaultRouteReachability: SCNetworkReachabilityRef = SCNetworkReachabilityCreateWithAddress(nil, &zeroAddress)

Anyway I get a new error saying 'sockaddr_in' is not identical to 'sockaddr' at the above line.

Solution 1:^[1]

Swift 3, IPv4, IPv6

Based on the Martin R's answer:

import SystemConfiguration

func isConnectedToNetwork() -> Bool {
    guard let flags = getFlags() else { return false }
    let isReachable = flags.contains(.reachable)
    let needsConnection = flags.contains(.connectionRequired)
    return (isReachable && !needsConnection)
}

func getFlags() -> SCNetworkReachabilityFlags? {
    guard let reachability = ipv4Reachability() ?? ipv6Reachability() else {
        return nil
    }
    var flags = SCNetworkReachabilityFlags()
    if !SCNetworkReachabilityGetFlags(reachability, &flags) {
        return nil
    }
    return flags
}

func ipv6Reachability() -> SCNetworkReachability? {
    var zeroAddress = sockaddr_in6()
    zeroAddress.sin6_len = UInt8(MemoryLayout<sockaddr_in>.size)
    zeroAddress.sin6_family = sa_family_t(AF_INET6)

    return withUnsafePointer(to: &zeroAddress, {
        $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
            SCNetworkReachabilityCreateWithAddress(nil, $0)
        }
    })
}

func ipv4Reachability() -> SCNetworkReachability? {
    var zeroAddress = sockaddr_in()
    zeroAddress.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
    zeroAddress.sin_family = sa_family_t(AF_INET)

    return withUnsafePointer(to: &zeroAddress, {
        $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
            SCNetworkReachabilityCreateWithAddress(nil, $0)
        }
    })
}

Solution 2:^[2]

Swift 5, Using NWPathMonitor

import Network

func configureNetworkMonitor(){
        let monitor = NWPathMonitor()
        
        monitor.pathUpdateHandler = { path in
            
            if path.status != .satisfied {
                print("not connected")
            }
            else if path.usesInterfaceType(.cellular) {
                print("Cellular")
            }
            else if path.usesInterfaceType(.wifi) {
                print("WIFI")
            }
            else if path.usesInterfaceType(.wiredEthernet) {
                print("Ethernet")
            }
            else if path.usesInterfaceType(.other){
                print("Other")
            }else if path.usesInterfaceType(.loopback){
                print("Loop Back")
            }
        }
        
        monitor.start(queue: DispatchQueue.global(qos: .background))
    }

Solution 3:^[3]

This has nothing to do with Swift, but the best solution is to NOT use Reachability to determine whether the network is online. Just make your connection and handle errors if it fails. Making a connection can at times fire up the dormant offline radios.

The one valid use of Reachability is to use it to notify you when a network transitions from offline to online. At that point you should retry failed connections.

Solution 4:^[4]

The best solution is to use ReachabilitySwift class, written in Swift 2, and uses SCNetworkReachabilityRef.

Simple and easy:

let reachability = Reachability.reachabilityForInternetConnection()

reachability?.whenReachable = { reachability in
    // keep in mind this is called on a background thread
    // and if you are updating the UI it needs to happen
    // on the main thread, like this:
    dispatch_async(dispatch_get_main_queue()) {
        if reachability.isReachableViaWiFi() {
            print("Reachable via WiFi")
        } else {
            print("Reachable via Cellular")
        }
    }
}
reachability?.whenUnreachable = { reachability in
    // keep in mind this is called on a background thread
    // and if you are updating the UI it needs to happen
    // on the main thread, like this:
    dispatch_async(dispatch_get_main_queue()) {
        print("Not reachable")
    }
}

reachability?.startNotifier()

Working like a charm.

Enjoy

Solution 5:^[5]

updated juanjo's answer to create singleton instance

import Foundation
import SystemConfiguration

final class Reachability {

    private init () {}
    class var shared: Reachability {
        struct Static {
            static let instance: Reachability = Reachability()
        }
        return Static.instance
    }

    func isConnectedToNetwork() -> Bool {
        guard let flags = getFlags() else { return false }
        let isReachable = flags.contains(.reachable)
        let needsConnection = flags.contains(.connectionRequired)
        return (isReachable && !needsConnection)
    }

    private func getFlags() -> SCNetworkReachabilityFlags? {
        guard let reachability = ipv4Reachability() ?? ipv6Reachability() else {
            return nil
        }
        var flags = SCNetworkReachabilityFlags()
        if !SCNetworkReachabilityGetFlags(reachability, &flags) {
            return nil
        }
        return flags
    }

    private func ipv6Reachability() -> SCNetworkReachability? {
        var zeroAddress = sockaddr_in6()
        zeroAddress.sin6_len = UInt8(MemoryLayout<sockaddr_in>.size)
        zeroAddress.sin6_family = sa_family_t(AF_INET6)

        return withUnsafePointer(to: &zeroAddress, {
            $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                SCNetworkReachabilityCreateWithAddress(nil, $0)
            }
        })
    }
    private func ipv4Reachability() -> SCNetworkReachability? {
        var zeroAddress = sockaddr_in()
        zeroAddress.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
        zeroAddress.sin_family = sa_family_t(AF_INET)

        return withUnsafePointer(to: &zeroAddress, {
            $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                SCNetworkReachabilityCreateWithAddress(nil, $0)
            }
        })
    }
}

Usage

if Reachability.shared.isConnectedToNetwork(){

}

Solution 6:^[6]

This is in Swift 4.0

I am using this framework https://github.com/ashleymills/Reachability.swift
And Install Pod ..
In AppDelegate

var window: UIWindow?
var reachability = InternetReachability()!
var reachabilityViewController : UIViewController? = nil

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.

    reachabilityChecking()
    return true
}

extension AppDelegate {

func reachabilityChecking() {    
    reachability.whenReachable = { reachability in
        DispatchQueue.main.async {
            print("Internet is OK!")
            if reachability.connection != .none && self.reachabilityViewController != nil {

            }
        }
    }
    reachability.whenUnreachable = { _ in
        DispatchQueue.main.async {
            print("Internet connection FAILED!")
            let storyboard = UIStoryboard(name: "Reachability", bundle: Bundle.main)
            self.reachabilityViewController = storyboard.instantiateViewController(withIdentifier: "ReachabilityViewController")
            let rootVC = self.window?.rootViewController
            rootVC?.present(self.reachabilityViewController!, animated: true, completion: nil)
        }
    }
    do {
        try reachability.startNotifier()
    } catch {
        print("Could not start notifier")
    }
}
}

The reachabilityViewController screen will appear if internet is not there

Solution 7:^[7]

A SwiftUI take on Mithra Sigam's solution above:

import SwiftUI
import Network

class NetworkReachabilityManager: ObservableObject {
    @Published var networkPathStatus: NWPath.Status
    @Published var availableInterfaces: [NWInterface]
    
    let monitor = NWPathMonitor()
    
    init() {
        monitor.start(queue: DispatchQueue.global(qos: .background))
        
        let currentPath = monitor.currentPath
        
        networkPathStatus = currentPath.status
        availableInterfaces = currentPath.availableInterfaces
        
        monitor.pathUpdateHandler = { [self] networkPath in
            DispatchQueue.main.async {
                networkPathStatus = networkPath.status
                availableInterfaces = networkPath.availableInterfaces
            }
        }
    }
    
    deinit {
        monitor.cancel()
    }
}

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1
Solution 2
Solution 3	EricS
Solution 4
Solution 5	anoop4real
Solution 6
Solution 7	Peter Kreinz

'How to use SCNetworkReachability in Swift

Solution 1:[1]

Solution 2:[2]

Solution 3:[3]

Solution 4:[4]

Solution 5:[5]

Solution 6:[6]

Solution 7:[7]