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using System; using System.Collections.Generic; using System.IO; using System.Net; using System.Net.Sockets; using System.Text; namespace TestDnsResolver { class Program { static void Main(string[] args) { ***DnsResolver dnsResolver = ***DnsResolver.Instance(); string domain = "www.google.com"; string ip = dnsResolver.***Resolve(domain); Console.WriteLine(ip + " " + domain); Console.ReadKey(); } } public class ***DnsResolver { private static ***DnsResolver resolver = null; private static string DNS_SERVER = "8.8.8.8"; private Encoding coding = Encoding.UTF8; private bool debug = false; private bool cache = false; private int maxTryTimes = 2; private int waitTimes = 3; private Dictionary<string, string> dnsCache = new Dictionary<string, string>(); string[] blackList = { "74.125.127.102", "74.125.155.102", "74.125.39.102", "74.125.39.113", "209.85.229.138", "128.121.126.139", "159.106.121.75", "169.132.13.103", "192.67.198.6", "202.106.1.2", "202.181.7.85", "203.161.230.171", "203.98.7.65", "207.12.88.98", "208.56.31.43", "209.145.54.50", "209.220.30.174", "209.36.73.33", "211.94.66.147", "213.169.251.35", "216.221.188.182", "216.234.179.13", "243.185.187.39", "37.61.54.158", "4.36.66.178", "46.82.174.68", "59.24.3.173", "64.33.88.161", "64.33.99.47", "64.66.163.251", "65.104.202.252", "65.160.219.113", "66.45.252.237", "72.14.205.104", "72.14.205.99", "78.16.49.15", "8.7.198.45", "93.46.8.89"}; public static ***DnsResolver Instance() { if (resolver == null) { resolver = new ***DnsResolver(); } return resolver; } private ***DnsResolver() { } private bool IsBadReply(string ip) { for (int i = 0; i < blackList.Length; i++) { if (blackList[i].Equals(ip)) { return true; } } return false; } public string ***Resolve(string domain) { IPAddress[] address = Dns.GetHostAddresses(domain); string ip = address[0].ToString(); if (!IsBadReply(ip)) { return ip; } else if (cache && dnsCache.ContainsKey(domain)) { return dnsCache[domain]; } for (int i = 0; i < maxTryTimes; i++) { ip = Resolve(domain); if (IsBadReply(ip) || ip == null) { continue; } else { if (cache) { dnsCache.Add(domain, ip); } return ip; } } return string.Empty; } private void HexDump(byte[] bytes) { Console.WriteLine(BytesToHex(bytes)); } private string BytesToHex(byte[] bytes) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < bytes.Length; i++) { sb.AppendFormat("{0:X2}", bytes[i]); } string hex = sb.ToString(); return hex; } private string Resolve(string domain) { byte[] recvData = new byte[512]; byte[] data = BuildRequestData(domain); string result = null; if (debug) { Console.WriteLine(" =============== dns query request package dump: ================"); HexDump(data); } IPEndPoint iep = new IPEndPoint(IPAddress.Parse(DNS_SERVER), 53); Socket dataSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp); dataSocket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 6 * 1000); dataSocket.SendTo(data, iep); byte[] respData = new byte[512]; for (int i = 0; i < waitTimes; i++) { try { int intReceived = dataSocket.Receive(respData); byte[] dataReceive = new byte[intReceived]; Array.Copy(respData, dataReceive, intReceived); if (debug) { Console.WriteLine("============ dns query answer package dump"); HexDump(dataReceive); } string ip = DecodeDnsResponse(dataReceive, domain); if (IsBadReply(ip)) { continue; } else { result = ip; break; } } catch (SocketException ex) { throw ex; } } dataSocket.Close(); return result; } private byte[] BuildRequestData(string host) { // head + (host length +1) + eof sign + qtype + qclass int size = 12 + host.Length + 1 + 1 + 4; using (MemoryStream buff = new MemoryStream(size)) { byte[] tmp = null; Random random = new Random(); byte[] seq = new byte[2]; random.NextBytes(seq); buff.Write(seq, 0, seq.Length); byte[] header = new byte[] { 0x01, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }; buff.Write(header, 0, header.Length); string[] parts = host.Split('.'); for (int i = 0; i < parts.Length; i++) { buff.WriteByte((byte)parts[i].Length); byte[] partsByte = coding.GetBytes(parts[i]); buff.Write(partsByte, 0, partsByte.Length); } tmp = new byte[] { 0x00 }; buff.Write(tmp, 0, tmp.Length); tmp = new byte[] { 0x00, 0x01, 0x00, 0x01 }; buff.Write(tmp, 0, tmp.Length); return buff.ToArray(); } } private string DecodeDnsResponse(byte[] resp, string host) { using (MemoryStream stream = new MemoryStream(resp)) { using (BinaryReader buffer = new BinaryReader(stream)) { //parse the query answer count. int pos = 7; stream.Position = pos; ushort qncount = buffer.ReadUInt16(); //skip query answer field pos = 12 + 1 + host.Length + 1 + 4; stream.Position = pos; for (int i = 0; i < qncount; i++) { stream.Position = pos; byte pointFlg = buffer.ReadByte(); if ((pointFlg & 0xc0) == 0xc0) { pos += 3; } else { pos += 2 + host.Length + 1; } stream.Position = pos; ushort queryType = buffer.ReadUInt16(); if (debug) { Console.WriteLine("qncount:" + qncount + "pos:" + pos + "queryType:" + queryType); } pos += 8; stream.Position = pos; int dataLen = buffer.ReadByte(); pos += 1; //A record if (queryType == 0x0001) { if (debug) { Console.WriteLine("parse A record"); } string ip = string.Empty; for (int j = 0; j < dataLen; j++) { stream.Position = pos; int v = buffer.ReadByte(); v = v > 0 ? v : 0x0ff & v; ip += v + (j == dataLen - 1 ? "" : "."); pos += 1; } return ip; } else { pos += dataLen; } } return string.Empty; } } } } }
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