ios如何解析dns

   var addresses: [String]?

   var hints = addrinfo()

   hints.ai_family = AF_UNSPEC

   hints.ai_socktype = SOCK_STREAM

   hints.ai_flags = AI_CANONNAME

   var result: UnsafeMutablePointer<addrinfo>?

   let status = getaddrinfo(hostname, nil, &hints, &result)

   if status == 0 {

       var ptr = result

       while ptr != nil {

           if let addr = ptr?.pointee.ai_addr {

               var hostname = [CChar](repeating: 0, count: Int(NI_MAXHOST))

               if getnameinfo(addr, socklen_t(addr.pointee.sa_len), &hostname, socklen_t(hostname.count), nil, 0, NI_NUMERICHOST) == 0 {

                   addresses?.append(String(cString: hostname))

               }

           }

           ptr = ptr?.pointee.ai_next

       }

       freeaddrinfo(result)

   }

   return addresses

   print("IP addresses for \(hostname): \(addresses)")

   print("Failed to resolve DNS for \(hostname)")

   let config = URLSessionConfiguration.default

   config.dnsSettings = [kCFNetworkProxiesSupplementalMatchDomains: [hostname],

                         kCFNetworkProxiesSupplementalMatchOrders: [0],

                         kCFNetworkProxiesDNSServer: ["8.8.8.8", "8.8.4.4"]]

   let session = URLSession(configuration: config)

   let task = session.dataTask(with: URL(string: "https://\(hostname)")!) { (data, response, error) in

       if let error = error {

           print("Failed to resolve DNS for \(hostname): \(error.localizedDescription)")

       } else {

           if let response = response as? HTTPURLResponse {

               print("IP addresses for \(hostname): \(response.allHeaderFields["X-Resolved-IP"] ?? "")")

           }

       }

   }

   task.resume()