Network interface helper in Swift

NetInfo.swift

// authored by @nythepegasus
// with help from others

public struct NetInfo: Hashable {
    public let name: String
    public let host: String
    public let dest: String?
    public let mask: String
    
    public init(name: String, host: String, dest: String?, mask: String) {
        self.name = name
        self.host = host
        self.dest = dest
        self.mask = mask
    }
    
    private init?(_ addr: ifaddrs) {
        guard var hostaddr = addr.ifa_addr?.pointee,
              var destaddr = addr.ifa_dstaddr?.pointee,
              var maskaddr = addr.ifa_netmask?.pointee,
              let name = String(utf8String: addr.ifa_name),
              let host = NetInfo.sockname(&hostaddr),
              let mask = NetInfo.sockname(&maskaddr) else { return nil }
        self = .init(name: name, host: host, dest: NetInfo.sockname(&destaddr), mask: mask)
    }
    
    private static func sockname(_ sock: inout sockaddr) -> String? {
        var buf = [CChar](repeating: 0, count: Int(NI_MAXHOST))
        guard getnameinfo(&sock, socklen_t(sock.sa_len), &buf, socklen_t(buf.count), nil, socklen_t(0), NI_NUMERICHOST) == 0,
            let str = String(utf8String: buf) else {
            return nil
        }
        return str
    }
    
    public static func addrs(_ check: (ifaddrs) -> Bool = { _ in true }) -> Set<NetInfo> {
        var addresses = Set<NetInfo>()
        var head: UnsafeMutablePointer<ifaddrs>? = nil
        guard getifaddrs(&head) == 0, let first = head else { return addresses }
        defer { freeifaddrs(head) }
        var ifaddr: UnsafeMutablePointer<ifaddrs>? = first
        while let next = ifaddr {
            if let info = NetInfo(next.pointee),
               check(next.pointee) { addresses.insert(info) }
            ifaddr = next.pointee.ifa_next
        }
        return addresses
    }
    
    public static func v4addrs() -> Set<NetInfo> {
        addrs { ifaddr in
            (ifaddr.ifa_addr.pointee.sa_family == UInt8(AF_INET)) &&
            (Int32(ifaddr.ifa_flags) & (IFF_UP|IFF_RUNNING|IFF_LOOPBACK)) == (IFF_UP|IFF_RUNNING)
        }
    }
    
    public static func nextOpenV4() -> NetInfo? {
        v4addrs().first { $0.mask != "255.255.255.255" && $0.host != "10.7.0.0" }
    }
    
    public static func sideVPN() -> NetInfo? {
        addrs().first { $0.host == "10.7.0.0" }
    }
}