DNS.cs

using System;
using UnityEngine;
using System.Net;

namespace X
{
    public class DnsEx 
    {
		public static IPAddress GetIPAddress(string host)
		{
			var hostEntry = Dns.GetHostEntry(host);
			foreach (var ip in hostEntry.AddressList)
			{
				if (ip.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork)
					return ip;
			}
			return null;
		}
		
		public static IPAddress GetIPAddressByHttpDns(string host)
		{
			var webclient = new System.Net.WebClient();
			var ip = webclient.DownloadString("http://119.29.29.29/d?dn=" + host);
			
			try
			{
				return IPAddress.Parse(ip);
			}
			catch(Exception e)
			{
				Debug.LogWarning(string.Format("GetIPAddressByHttpDns failed.host:[{0}] ip:[{1}]", host, ip));
				throw e;
			}
		}

		public class IPAddressAsyn
		{
			IPAddress IPAddress;
			Exception Exception;
			WebRequest WebRequest;
			WebResponse WebResponse;
			System.IO.Stream Stream;
			byte[] Buffer = new byte[128];
			int BufferOffset = 0;

			public IPAddressAsyn(string url, int millisecondsTimeout)
			{
				WebRequest = WebRequest.Create(url);
				WebRequest.Timeout = millisecondsTimeout;
				WebRequest.BeginGetResponse(GetResponseCallback, null);

			}

			void GetResponseCallback(IAsyncResult asyncResult)
			{
				try
				{
					WebResponse = WebRequest.EndGetResponse(asyncResult);
					Stream = WebResponse.GetResponseStream();

					BufferOffset = 0;
					Stream.BeginRead(Buffer, BufferOffset, Buffer.Length, ReadCallback, null);
				}
				catch(System.Exception e)
				{
					Exception = e;
				}
			}

			void ReadCallback(IAsyncResult asyncResult)
			{
				try
				{
					var size = Stream.EndRead(asyncResult);
					if (size <= 0)
					{
						var ip = System.Text.Encoding.ASCII.GetString(Buffer);
						IPAddress = IPAddress.Parse(ip);
						return;
					}

					BufferOffset += size;
					Stream.BeginRead(Buffer, BufferOffset, Buffer.Length - BufferOffset, ReadCallback, null);
				}
				catch(System.Exception e)
				{
					Exception = e;
				}
			}

			public IPAddress GetIPAddress()
			{
				if (Exception != null)
					throw Exception;
				return IPAddress;
			}
		}

		public static IPAddressAsyn GetIPAddressAsynByHttpDns(string host, int millisecondsTimeout)
		{
			var ret = new IPAddressAsyn("http://119.29.29.29/d?dn=" + host, millisecondsTimeout);
			return ret;
		}
    }
}