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//Dnslite.cs
//From: http://www.csharphelp.com/2005/12/dns-client-utility/
/**
csc /target:library /out:DnsLib.dll /keyfile:..\..\Duplicati\GUI\Duplicati.snk DnsLite.cs
*/
using System;
using System.Net;
using System.IO;
using System.Text;
using System.Net.Sockets;
using System.Collections;
namespace DnsLib
{
public class MXRecord
{
public int preference = -1;
public string exchange = null;
public override string ToString()
{
return "Preference : " + preference + " Exchange : " + exchange;
}
}
public class DnsLite
{
private byte[] data;
private int position, id, length;
private string name;
private ArrayList dnsServers;
private static int DNS_PORT = 53;
readonly Encoding ASCII = Encoding.ASCII;
public DnsLite()
{
id = DateTime.Now.Millisecond * 60;
dnsServers = new ArrayList();
}
public void setDnsServers(ArrayList dnsServers)
{
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 a new id
return ++id;
}
public ArrayList getMXRecords(string host, string serverAddress)
{
//opening the UDP socket at DNS server
//use UDPClient, if you are still with Beta1
UdpClient dnsClient = new UdpClient(serverAddress, DNS_PORT);
//preparing the DNS query packet.
makeQuery(getNewId(), host);
//send the data packet
dnsClient.Send(data, data.Length);
// 2017-01-09: Fix not sending null to UDPClient.Receive
IPEndPoint endpoint = new IPEndPoint(IPAddress.Loopback, DNS_PORT);
//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] = 1; data[3] = 0;
data[4] = 0; data[5] = 1;
data[6] = 0; data[7] = 0;
data[8] = 0; data[9] = 0;
data[10] = 0; data[11] = 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++] = 0; data[position++] = 0;
data[position++] = 15; data[position++] = 0;
data[position++] = 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;
}
}
}
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