public static List <string> LookUp(string domain, DNSKind kind, string dnsServer = "8.8.8.8")
{
var entries = new List <DNSEntry>();
string qtype;
switch (kind)
{
case DNSKind.A: qtype = "1"; break;
case DNSKind.MX: qtype = "15"; break;
default: throw new Exception("Invalid DNS type");
}
UdpClient udpc = new UdpClient(dnsServer, 53);
// send request to dns server
var list = new List <byte>();
list.AddRange(new byte[] { 88, 89, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0 });
string[] tmp = domain.Split('.');
foreach (string s in tmp)
{
list.Add(Convert.ToByte(s.Length));
char[] chars = s.ToCharArray();
foreach (char c in chars)
{
list.Add(Convert.ToByte(Convert.ToInt32(c)));
}
}
list.AddRange(new byte[] { 0, 0, Convert.ToByte(qtype), 0, 1 });
byte[] req = new byte[list.Count];
for (int i = 0; i < list.Count; i++)
{
req[i] = list[i];
}
udpc.Send(req, req.Length);
// obtain and process response
IPEndPoint ep = null;
byte[] recv = udpc.Receive(ref ep);
udpc.Close();
int[] resp;
resp = new int[recv.Length];
for (int i = 0; i < resp.Length; i++)
{
resp[i] = Convert.ToInt32(recv[i]);
}
int status = resp[3];
if (status != 128)
{
throw new Exception($"dns failure, error code: {status}");
}
int answers = resp[7];
if (answers == 0)
{
throw new Exception("dsn failure, no results");
}
int pos = domain.Length + 18;
switch (qtype)
{
// MX record
case "15":
{
while (answers > 0)
{
int preference = resp[pos + 13];
pos += 14; //offset
string host = GetMXRecord(resp, pos, out pos);
entries.Add(new DNSEntry(preference, host));
answers--;
}
break;
}
// A record
case "1":
{
while (answers > 0)
{
pos += 11; // offset
string str = GetARecord(resp, ref pos);
entries.Add(new DNSEntry(0, str));
answers--;
}
break;
}
default:
{
throw new Exception($"dsn failure, unsupported dns type {qtype}");
}
}
return(entries.OrderBy(x => x.preference).Select(x => x.host).ToList());
}
public static List <string> LookUp(string domain, DNSKind kind, string dnsServer = "8.8.8.8")
{
var entries = new List <DNSEntry>();
string qtype;
switch (kind)
{
case DNSKind.A: qtype = "1"; break;
case DNSKind.MX: qtype = "15"; break;
default: throw new Exception("Invalid DNS type");
}
UdpClient udpc = new UdpClient(dnsServer, 53);
// SEND REQUEST--------------------
List <byte> list = new List <byte>();
list.AddRange(new byte[] { 88, 89, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0 });
string[] tmp = domain.Split('.');
foreach (string s in tmp)
{
list.Add(Convert.ToByte(s.Length));
char[] chars = s.ToCharArray();
foreach (char c in chars)
{
list.Add(Convert.ToByte(Convert.ToInt32(c)));
}
}
list.AddRange(new byte[] { 0, 0, Convert.ToByte(qtype), 0, 1 });
byte[] req = new byte[list.Count];
for (int i = 0; i < list.Count; i++)
{
req[i] = list[i];
}
udpc.Send(req, req.Length);
// RECEIVE RESPONSE--------------
IPEndPoint ep = null;
byte[] recv = udpc.Receive(ref ep);
udpc.Close();
int[] resp;
resp = new int[recv.Length];
for (int i = 0; i < resp.Length; i++)
{
resp[i] = Convert.ToInt32(recv[i]);
}
int status = resp[3];
if (status != 128)
{
throw new Exception(string.Format("{0}", status));
}
int answers = resp[7];
if (answers == 0)
{
throw new Exception("No results");
}
int pos = domain.Length + 18;
if (qtype == "15") // MX record
{
while (answers > 0)
{
int preference = resp[pos + 13];
pos += 14; //offset
string host = GetMXRecord(resp, pos, out pos);
entries.Add(new DNSEntry(preference, host));
answers--;
}
}
else if (qtype == "1") // A record
{
while (answers > 0)
{
pos += 11; //offset
string str = GetARecord(resp, ref pos);
entries.Add(new DNSEntry(0, str));
answers--;
}
}
return(entries.OrderBy(x => x.preference).Select(x => x.host).ToList());
}
