AWSAppSyncReachability.swift

/*
Copyright (c) 2014, Ashley Mills
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/

import SystemConfiguration
import Foundation

public enum AWSAppSyncReachabilityError: Error {
    case failedToCreateWithAddress(sockaddr, Int32)
    case failedToCreateWithHostname(String, Int32)
    case unableToSetCallback(Int32)
    case unableToSetDispatchQueue(Int32)
    case unableToGetFlags(Int32)
}

@available(*, unavailable, renamed: "Notification.Name.reachabilityChanged")
public let ReachabilityChangedNotification = NSNotification.Name("ReachabilityChangedNotification")

public extension Notification.Name {
    static let reachabilityChanged = Notification.Name("reachabilityChanged")
}

public class AWSAppSyncReachability {

    public typealias NetworkReachable = (AWSAppSyncReachability) -> Void
    public typealias NetworkUnreachable = (AWSAppSyncReachability) -> Void

    @available(*, unavailable, renamed: "Connection")
    public enum NetworkStatus: CustomStringConvertible {
        case notReachable, reachableViaWiFi, reachableViaWWAN
        public var description: String {
            switch self {
            case .reachableViaWWAN: return "Cellular"
            case .reachableViaWiFi: return "WiFi"
            case .notReachable: return "No Connection"
            }
        }
    }

    public enum Connection: CustomStringConvertible {
        @available(*, deprecated, renamed: "unavailable")
        case none
        case unavailable, wifi, cellular
        public var description: String {
            switch self {
            case .cellular: return "Cellular"
            case .wifi: return "WiFi"
            case .unavailable: return "No Connection"
            case .none: return "unavailable"
            }
        }
    }

    public var whenReachable: NetworkReachable?
    public var whenUnreachable: NetworkUnreachable?

    @available(*, deprecated, renamed: "allowsCellularConnection")
    public let reachableOnWWAN: Bool = true

    /// Set to `false` to force Reachability.connection to .none when on cellular connection (default value `true`)
    public var allowsCellularConnection: Bool

    // The notification center on which "reachability changed" events are being posted
    public var notificationCenter: NotificationCenter = NotificationCenter.default

    @available(*, deprecated, renamed: "connection.description")
    public var currentReachabilityString: String {
        return "\(connection)"
    }

    @available(*, unavailable, renamed: "connection")
    public var currentReachabilityStatus: Connection {
        return connection
    }

    public var connection: Connection {
        if flags == nil {
            try? setReachabilityFlags()
        }
        
        switch flags?.connection {
        case .unavailable?, nil: return .unavailable
        case .none?: return .unavailable
        case .cellular?: return allowsCellularConnection ? .cellular : .unavailable
        case .wifi?: return .wifi
        }
    }

    fileprivate var isRunningOnDevice: Bool = {
        #if targetEnvironment(simulator)
            return false
        #else
            return true
        #endif
    }()

    fileprivate(set) var notifierRunning = false
    fileprivate let reachabilityRef: SCNetworkReachability
    fileprivate let reachabilitySerialQueue: DispatchQueue
    fileprivate let notificationQueue: DispatchQueue?
    fileprivate(set) var flags: SCNetworkReachabilityFlags? {
        didSet {
            guard flags != oldValue else { return }
            notifyReachabilityChanged()
        }
    }

    required public init(reachabilityRef: SCNetworkReachability,
                         queueQoS: DispatchQoS = .default,
                         targetQueue: DispatchQueue? = nil,
                         notificationQueue: DispatchQueue? = .main) {
        self.allowsCellularConnection = true
        self.reachabilityRef = reachabilityRef
        self.reachabilitySerialQueue = DispatchQueue(label: "uk.co.ashleymills.reachability", qos: queueQoS, target: targetQueue)
        self.notificationQueue = notificationQueue
    }

    public convenience init(hostname: String,
                            queueQoS: DispatchQoS = .default,
                            targetQueue: DispatchQueue? = nil,
                            notificationQueue: DispatchQueue? = .main) throws {
        guard let ref = SCNetworkReachabilityCreateWithName(nil, hostname) else {
            throw AWSAppSyncReachabilityError.failedToCreateWithHostname(hostname, SCError())
        }
        self.init(reachabilityRef: ref, queueQoS: queueQoS, targetQueue: targetQueue, notificationQueue: notificationQueue)
    }

    public convenience init(queueQoS: DispatchQoS = .default,
                            targetQueue: DispatchQueue? = nil,
                            notificationQueue: DispatchQueue? = .main) throws {
        var zeroAddress = sockaddr()
        zeroAddress.sa_len = UInt8(MemoryLayout<sockaddr>.size)
        zeroAddress.sa_family = sa_family_t(AF_INET)

        guard let ref = SCNetworkReachabilityCreateWithAddress(nil, &zeroAddress) else {
            throw AWSAppSyncReachabilityError.failedToCreateWithAddress(zeroAddress, SCError())
        }

        self.init(reachabilityRef: ref, queueQoS: queueQoS, targetQueue: targetQueue, notificationQueue: notificationQueue)
    }

    deinit {
        stopNotifier()
    }
}

public extension AWSAppSyncReachability {

    // MARK: - *** Notifier methods ***
    func startNotifier() throws {
        guard !notifierRunning else { return }

        let callback: SCNetworkReachabilityCallBack = { (reachability, flags, info) in
            guard let info = info else { return }

            // `weakifiedReachability` is guaranteed to exist by virtue of our
            // retain/release callbacks which we provided to the `SCNetworkReachabilityContext`.
            let weakifiedReachability = Unmanaged<AWSAppSyncReachabilityWeakifier>.fromOpaque(info).takeUnretainedValue()

            // The weak `reachability` _may_ no longer exist if the `Reachability`
            // object has since been deallocated but a callback was already in flight.
            weakifiedReachability.reachability?.flags = flags
        }

        let weakifiedReachability = AWSAppSyncReachabilityWeakifier(reachability: self)
        let opaqueWeakifiedReachability = Unmanaged<AWSAppSyncReachabilityWeakifier>.passUnretained(weakifiedReachability).toOpaque()

        var context = SCNetworkReachabilityContext(
            version: 0,
            info: UnsafeMutableRawPointer(opaqueWeakifiedReachability),
            retain: { (info: UnsafeRawPointer) -> UnsafeRawPointer in
                let unmanagedWeakifiedReachability = Unmanaged<AWSAppSyncReachabilityWeakifier>.fromOpaque(info)
                _ = unmanagedWeakifiedReachability.retain()
                return UnsafeRawPointer(unmanagedWeakifiedReachability.toOpaque())
            },
            release: { (info: UnsafeRawPointer) -> Void in
                let unmanagedWeakifiedReachability = Unmanaged<AWSAppSyncReachabilityWeakifier>.fromOpaque(info)
                unmanagedWeakifiedReachability.release()
            },
            copyDescription: { (info: UnsafeRawPointer) -> Unmanaged<CFString> in
                let unmanagedWeakifiedReachability = Unmanaged<AWSAppSyncReachabilityWeakifier>.fromOpaque(info)
                let weakifiedReachability = unmanagedWeakifiedReachability.takeUnretainedValue()
                let description = weakifiedReachability.reachability?.description ?? "nil"
                return Unmanaged.passRetained(description as CFString)
            }
        )

        if !SCNetworkReachabilitySetCallback(reachabilityRef, callback, &context) {
            stopNotifier()
            throw AWSAppSyncReachabilityError.unableToSetCallback(SCError())
        }

        if !SCNetworkReachabilitySetDispatchQueue(reachabilityRef, reachabilitySerialQueue) {
            stopNotifier()
            throw AWSAppSyncReachabilityError.unableToSetDispatchQueue(SCError())
        }

        // Perform an initial check
        try setReachabilityFlags()

        notifierRunning = true
    }

    func stopNotifier() {
        defer { notifierRunning = false }

        SCNetworkReachabilitySetCallback(reachabilityRef, nil, nil)
        SCNetworkReachabilitySetDispatchQueue(reachabilityRef, nil)
    }

    // MARK: - *** Connection test methods ***
    @available(*, deprecated, message: "Please use `connection != .none`")
    var isReachable: Bool {
        return connection != .unavailable
    }

    @available(*, deprecated, message: "Please use `connection == .cellular`")
    var isReachableViaWWAN: Bool {
        // Check we're not on the simulator, we're REACHABLE and check we're on WWAN
        return connection == .cellular
    }

   @available(*, deprecated, message: "Please use `connection == .wifi`")
    var isReachableViaWiFi: Bool {
        return connection == .wifi
    }

    var description: String {
        return flags?.description ?? "unavailable flags"
    }
}

fileprivate extension AWSAppSyncReachability {

    func setReachabilityFlags() throws {
        try reachabilitySerialQueue.sync { [unowned self] in
            var flags = SCNetworkReachabilityFlags()
            if !SCNetworkReachabilityGetFlags(self.reachabilityRef, &flags) {
                self.stopNotifier()
                throw AWSAppSyncReachabilityError.unableToGetFlags(SCError())
            }
            
            self.flags = flags
        }
    }
    
    func notifyReachabilityChanged() {
        let notify = { [weak self] in
            guard let self = self else { return }
            if self.connection != .unavailable {
                self.whenReachable?(self)
            } else {
                self.whenUnreachable?(self)
            }
            self.notificationCenter.post(name: .reachabilityChanged, object: self)
        }

        // notify on the configured `notificationQueue`, or the caller's (i.e. `reachabilitySerialQueue`)
        notificationQueue?.async(execute: notify) ?? notify()
    }
}

extension SCNetworkReachabilityFlags {

    typealias Connection = AWSAppSyncReachability.Connection

    var connection: Connection {
        guard isReachableFlagSet else { return .unavailable }

        // If we're reachable, but not on an iOS device (i.e. simulator), we must be on WiFi
        #if targetEnvironment(simulator)
        return .wifi
        #else
        var connection = Connection.unavailable

        if !isConnectionRequiredFlagSet {
            connection = .wifi
        }

        if isConnectionOnTrafficOrDemandFlagSet {
            if !isInterventionRequiredFlagSet {
                connection = .wifi
            }
        }

        if isOnWWANFlagSet {
            connection = .cellular
        }

        return connection
        #endif
    }

    var isOnWWANFlagSet: Bool {
        #if os(iOS)
        return contains(.isWWAN)
        #else
        return false
        #endif
    }
    var isReachableFlagSet: Bool {
        return contains(.reachable)
    }
    var isConnectionRequiredFlagSet: Bool {
        return contains(.connectionRequired)
    }
    var isInterventionRequiredFlagSet: Bool {
        return contains(.interventionRequired)
    }
    var isConnectionOnTrafficFlagSet: Bool {
        return contains(.connectionOnTraffic)
    }
    var isConnectionOnDemandFlagSet: Bool {
        return contains(.connectionOnDemand)
    }
    var isConnectionOnTrafficOrDemandFlagSet: Bool {
        return !intersection([.connectionOnTraffic, .connectionOnDemand]).isEmpty
    }
    var isTransientConnectionFlagSet: Bool {
        return contains(.transientConnection)
    }
    var isLocalAddressFlagSet: Bool {
        return contains(.isLocalAddress)
    }
    var isDirectFlagSet: Bool {
        return contains(.isDirect)
    }
    var isConnectionRequiredAndTransientFlagSet: Bool {
        return intersection([.connectionRequired, .transientConnection]) == [.connectionRequired, .transientConnection]
    }

    var description: String {
        let W = isOnWWANFlagSet ? "W" : "-"
        let R = isReachableFlagSet ? "R" : "-"
        let c = isConnectionRequiredFlagSet ? "c" : "-"
        let t = isTransientConnectionFlagSet ? "t" : "-"
        let i = isInterventionRequiredFlagSet ? "i" : "-"
        let C = isConnectionOnTrafficFlagSet ? "C" : "-"
        let D = isConnectionOnDemandFlagSet ? "D" : "-"
        let l = isLocalAddressFlagSet ? "l" : "-"
        let d = isDirectFlagSet ? "d" : "-"

        return "\(W)\(R) \(c)\(t)\(i)\(C)\(D)\(l)\(d)"
    }
}

/**
 `ReachabilityWeakifier` weakly wraps the `Reachability` class
 in order to break retain cycles when interacting with CoreFoundation.

 CoreFoundation callbacks expect a pair of retain/release whenever an
 opaque `info` parameter is provided. These callbacks exist to guard
 against memory management race conditions when invoking the callbacks.

 #### Race Condition

 If we passed `SCNetworkReachabilitySetCallback` a direct reference to our
 `Reachability` class without also providing corresponding retain/release
 callbacks, then a race condition can lead to crashes when:
 - `Reachability` is deallocated on thread X
 - A `SCNetworkReachability` callback(s) is already in flight on thread Y

 #### Retain Cycle

 If we pass `Reachability` to CoreFoundtion while also providing retain/
 release callbacks, we would create a retain cycle once CoreFoundation
 retains our `Reachability` class. This fixes the crashes and his how
 CoreFoundation expects the API to be used, but doesn't play nicely with
 Swift/ARC. This cycle would only be broken after manually calling
 `stopNotifier()` — `deinit` would never be called.

 #### ReachabilityWeakifier

 By providing both retain/release callbacks and wrapping `Reachability` in
 a weak wrapper, we:
 - interact correctly with CoreFoundation, thereby avoiding a crash.
 See "Memory Management Programming Guide for Core Foundation".
 - don't alter the public API of `Reachability.swift` in any way
 - still allow for automatic stopping of the notifier on `deinit`.
 */
private class AWSAppSyncReachabilityWeakifier {
    weak var reachability: AWSAppSyncReachability?
    init(reachability: AWSAppSyncReachability) {
        self.reachability = reachability
    }
}