用C#来实现NslookUP的功能

using System; 
 using System.Collections; 
 using ; 
 using System.IO; 
 using System.Text; 
 using .Sockets; namespace Wuyin.Network.Components
 {    public class NsLookUp 
     { 
         private byte[] data; 
         private int position, id, length; 
         private string name; 
         private ArrayList dnsServers; 
         private static int DNS_PORT = 53;         Encoding ASCII = Encoding.ASCII; 
        public NsLookUp(ArrayList dnsServers) 
         { 
             id = DateTime.Now.Millisecond * 60; 
             this.dnsServers = dnsServers; 
         }         public ArrayList getMXRecords(string host) 
         { 
             ArrayList mxRecords = null; 
             for(int i=0; i < dnsServers.Count; i++) 
             { 
                 try 
                 { 
                     mxRecords = getMXRecords(host,(string)dnsServers[i]); 
                     break; 
                 } 
                 catch(IOException) 
                 { 
                     continue; 
                 } 
             } 
             return mxRecords; 
         }         private int getNewId() 
         { 
             return ++id; 
         }         public ArrayList getMXRecords(string host,string serverAddress) 
         { 
             UdpClient dnsClient = new UdpClient(serverAddress, DNS_PORT); 
             //preparing the DNS query packet. 
             makeQuery(getNewId(),host); 
             //send the data packet 
             dnsClient.Send(data,data.Length); 
             IPEndPoint endpoint = null; 
             //receive the data packet from DNS server 
             data = dnsClient.Receive(ref endpoint); 
             length = data.Length; 
             //un pack the byte array & makes an array of MXRecord objects. 
             return makeResponse(); 
         }         //for packing the information to the format accepted by server 
         public void makeQuery(int id,String name) 
         { 
             data = new byte[512]; 
             for(int i = 0; i < 512; ++i) 
             { 
                 data[i] = 0; 
             } 
             data[0]    = (byte) (id >> 8); 
             data[1] = (byte) (id & 0xFF ); 
             data[2] = (byte) 1; data[3] = (byte) 0; 
             data[4] = (byte) 0; data[5] = (byte) 1; 
             data[6] = (byte) 0; data[7] = (byte) 0; 
             data[8] = (byte) 0; data[9] = (byte) 0; 
             data[10] = (byte) 0; data[11] = (byte) 0; 
             string[] tokens = name.Split(new char[] {'.'}); 
             string label; 
             position = 12; 
             for(int j=0; j<tokens.Length; j++) 
             { 
                 label = tokens[j]; 
                 data[position++] = (byte) (label.Length & 0xFF); 
                 byte[] b = ASCII.GetBytes(label); 
                 for(int k=0; k < b.Length; k++) 
                 { 
                     data[position++] = b[k]; 
                 } 
             } 
             data[position++] = (byte) 0 ; data[position++] = (byte) 0; 
             data[position++] = (byte) 15; data[position++] = (byte) 0 ; 
             data[position++] = (byte) 1 ; 
         } 
         //for un packing the byte array 
         public ArrayList makeResponse() 
         { 
             ArrayList mxRecords = new ArrayList(); 
             MXRecord mxRecord; 
             //NOTE: we are ignoring the unnecessary fields. 
             //      and takes only the data required to build 
             //      MX records. 
             int qCount = ((data[4] & 0xFF) << 8) | (data[5] & 0xFF); 
             if (qCount < 0) 
             { 
                 throw new IOException("invalid question count"); 
             } 
             int aCount = ((data[6] & 0xFF) << 8) | (data[7] & 0xFF); 
             if (aCount < 0) 
             { 
                 throw new IOException("invalid answer count"); 
             } 
             position=12; 
             for( int i=0;i<qCount; ++i) 
             { 
                 name = ""; 
                 position = proc(position); 
                 position += 4; 
             } 
             for (int i = 0; i < aCount; ++i) 
             { 
                 name = ""; 
                 position = proc(position); 
                 position+=10; 
                 int pref = (data[position++] << 8) | (data[position++] & 0xFF); 
                 name=""; 
                 position = proc(position); 
                 mxRecord = new MXRecord(); 
                 mxRecord.preference = pref; 
                 mxRecord.exchange = name; 
                 mxRecords.Add(mxRecord); 
             } 
             return mxRecords;
         }        private int proc(int position) 
         { 
             int len = (data[position++] & 0xFF); 
             if(len == 0) 
             { 
                 return position; 
             } 
             int offset; 
             do 
             { 
                 if ((len & 0xC0) == 0xC0) 
                 { 
                     if (position >= length) 
                     { 
                         return -1; 
                     } 
                     offset = ((len & 0x3F) << 8) | (data[position++] & 0xFF); 
                     proc(offset); 
                     return position; 
                 } 
                 else 
                 { 
                     if ((position + len) > length) 
                     { 
                         return -1; 
                     } 
                     name += ASCII.GetString(data, position, len); 
                     position += len; 
                 } 
                 if (position > length) 
                 { 
                     return -1; 
                 } 
                 len = data[position++] & 0xFF; 
                 if (len != 0) 
                 { 
                     name += "."; 
                 } 
             }while (len != 0); 
             return position; 
         }    
     }     public class MXRecord : IComparable 
     { 
         public int preference = -1; 
         public string exchange = null; 
         public override string ToString() 
         { 
             return "Preference : " + preference + " Exchange : " + exchange; 
         } 
         int IComparable.CompareTo(object obj) 
         { 
             if (this.preference < ((MXRecord) obj).preference) 
                 return -1; 
             if (this.preference > ((MXRecord) obj).preference) 
                 return 1; 
             return 0; 
         } 
     } 
 }