https://burgers.io/better-user-agent

UserAgent.swift

//
//  UserAgent.swift
//

import Foundation

class UserAgent {
    static func getUserAgent() -> String {
        let bundleDict = NSBundle.mainBundle().infoDictionary!
        let appName = bundleDict["CFBundleName"] as! String
        let appVersion = bundleDict["CFBundleShortVersionString"] as! String
        let appDescriptor = appName + "/" + appVersion

        let currentDevice = UIDevice.currentDevice()
        let osDescriptor = "iOS/" + currentDevice.systemVersion

        let hardwareString = self.getHardwareString()

        return appDescriptor + " " + osDescriptor + " (" + hardwareString + ")"
    }

    static func getHardwareString() -> String {
        var name: [Int32] = [CTL_HW, HW_MACHINE]
        var size: Int = 2
        sysctl(&name, 2, nil, &size, &name, 0)
        var hw_machine = [CChar](count: Int(size), repeatedValue: 0)
        sysctl(&name, 2, &hw_machine, &size, &name, 0)

        let hardware: String = String.fromCString(hw_machine)!
        return hardware
    }
}

Works for Swift 5:

class UserAgent {
    static func getUserAgent() -> String {
        let bundleDict = Bundle.main.infoDictionary!
        let appName = bundleDict["CFBundleName"] as! String
        let appVersion = bundleDict["CFBundleShortVersionString"] as! String
        let appDescriptor = appName + "/" + appVersion

        let currentDevice = UIDevice.current
        let osDescriptor = "iOS/" + currentDevice.systemVersion

        let hardwareString = self.getHardwareString()

        return appDescriptor + " " + osDescriptor + " (" + hardwareString + ")"
    }

    static func getHardwareString() -> String {
        var name: [Int32] = [CTL_HW, HW_MACHINE]
        var localname: [Int32] = [CTL_HW, HW_MACHINE]
        var size: Int = 2
        localname = name
        sysctl(&name, 2, nil, &size, &localname, 0)
        var hw_machine = [CChar](repeating: 0, count: Int(size)) //[CChar](count: Int(size), repeatedValue: 0)
        sysctl(&name, 2, &hw_machine, &size, &localname, 0)

        let hardware: String = String(cString: hw_machine)
        return hardware
    }
}