private static Int16 toSetAppropriateEndianess(Int16 value)
{
return(Endianess.MachineArchIsLittleEndian ? Endianess.toBigEndian(value) : value);
}
public bool AskDNS(string domain, string email)
{
var transactionID = (Int16)(new Random().Next(maxValue: Int16.MaxValue));
var header = new DNSHeader
{
transactionID = transactionID,
flags = 0x0100, // Just a standard query
questionResourceCount = 1, // We have one question
answerResourceCount = 0,
authorityResourceCount = 0,
additionalResourceCount = 0
};
var question = new DNSQuestion(domain,
DNSQuestion.Types.MailExchangeRecord); // We want to know about mail server
var sizeDNSQuery = header.SizeOf() + question.SizeOf();
var arrDNSQuery = new byte[sizeDNSQuery];
IntPtr ptrHeader = Marshal.AllocHGlobal(header.SizeOf());
Marshal.StructureToPtr(header, ptrHeader, true);
Marshal.Copy(ptrHeader, arrDNSQuery, 0, header.SizeOf());
Marshal.FreeHGlobal(ptrHeader);
// Copy char data, no need to worry about endianess for char
question.name.CopyTo(arrDNSQuery, header.SizeOf());
var arrQuestionType = BitConverter.GetBytes(Endianess.toBigEndian(question.type));
var arrQuestionClassType = BitConverter.GetBytes(Endianess.toBigEndian(question.classType));
arrQuestionType.CopyTo(arrDNSQuery, header.SizeOf() + question.name.Length * sizeof(byte));
arrQuestionClassType.CopyTo(arrDNSQuery, header.SizeOf() + question.name.Length * sizeof(byte) + arrQuestionType.Length);
// Send datagram
_dNSClient.Send(arrDNSQuery, arrDNSQuery.Length * sizeof(byte));
// Get response
do
{
var result = _dNSClient.ReceiveAsync().Result;
// Make sure it is from correct domain
if (result.RemoteEndPoint.Address.Equals(_dNSServer))
{
// Make sure packet has valid size header
if (result.Buffer.Length > header.SizeOf())
{
// Convert to DNSHeader
ptrHeader = Marshal.AllocHGlobal(header.SizeOf());
Marshal.Copy(result.Buffer, 0, ptrHeader, header.SizeOf());
header = (DNSHeader)Marshal.PtrToStructure(ptrHeader, header.GetType());
Marshal.FreeHGlobal(ptrHeader);
// Check that this is the correct transaction packet response
if (header.transactionID == transactionID)
{
// Check that flags has no error and there is atleast one answer
if (((header.flags & 0xf) != 0) || header.answerResourceCount == 0)
{
return(false);
}
// List of mail servers and their preferences
List <Tuple <int, string> > listMailServerAndPrefs = new List <Tuple <int, string> >();
// Determine the start index of Answers structure
int indexStartOfAnswer = arrDNSQuery.Length;
for (int i = 0; i < header.answerResourceCount; ++i)
{
if ((result.Buffer[indexStartOfAnswer] & 0xC0) == 0)
{
throw new NotImplementedException("DNS answer name must be an offset");
}
// Convert from byte stream to answer structure
IntPtr ptrAnswer = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(DNSResource)));
Marshal.Copy(result.Buffer, indexStartOfAnswer, ptrAnswer, Marshal.SizeOf(typeof(DNSResource)));
var answer = (DNSResource)Marshal.PtrToStructure(ptrAnswer, typeof(DNSResource));
Marshal.FreeHGlobal(ptrAnswer);
// Increment index ahead
indexStartOfAnswer += answer.SizeOf();
if (indexStartOfAnswer > result.Buffer.Length)
{
break;
}
// Read preference no, smaller number is more preferred server
if (answer.dataLength < 2)
{
continue;
}
Int16 preferenceMailExchangeServer = BitConverter.ToInt16(result.Buffer, indexStartOfAnswer);
if (Endianess.MachineArchIsLittleEndian)
{
preferenceMailExchangeServer = Endianess.toLittleEndian(preferenceMailExchangeServer);
}
indexStartOfAnswer += Marshal.SizeOf(preferenceMailExchangeServer);
// Read server name
int sizeServerName = answer.dataLength - Marshal.SizeOf(preferenceMailExchangeServer);
if (sizeServerName < 2)
{
continue;
}
if (indexStartOfAnswer + sizeServerName > result.Buffer.Length)
{
break;
}
string serverName = string.Empty;
int j = indexStartOfAnswer;
while (j < indexStartOfAnswer + sizeServerName - 1)
{
if ((result.Buffer[j] & 0xC0) != 0)
{
// It's an offset
var offset = BitConverter.ToInt16(result.Buffer, j);
if (Endianess.MachineArchIsLittleEndian)
{
offset = Endianess.toLittleEndian(offset);
}
offset &= 0x3F; // Remove two most significant bits
j += Marshal.SizeOf(offset);
// Transverse position from offset until null
do
{
serverName += Encoding.ASCII.GetString(result.Buffer, offset + 1, result.Buffer[offset]) + '.';
offset += (Int16)(result.Buffer[offset] + 1);
} while (result.Buffer[offset] != 0);
}
else
{
// It's just size
serverName += System.Text.Encoding.ASCII.GetString(result.Buffer, j + 1, result.Buffer[j]) + '.';
j += result.Buffer[j] + 1;
}
}
indexStartOfAnswer += answer.dataLength - Marshal.SizeOf(preferenceMailExchangeServer);
if (string.IsNullOrEmpty(serverName) && serverName.Length > 2)
{
continue;
}
serverName = serverName.Substring(0, serverName.Length - 1); // Remove terminating dot
listMailServerAndPrefs.Add(new Tuple <int, string>((int)preferenceMailExchangeServer, serverName));
}
// Sort by preference
listMailServerAndPrefs = listMailServerAndPrefs.OrderBy(x => x.Item1).ToList();
// Connect with SMTP
_sMTPClient = new TcpClient();
_sMTPClient.ConnectAsync(listMailServerAndPrefs.First().Item2, _sMTPPort).Wait();
if (!_sMTPClient.Connected)
{
throw new WebException("SMTP server refused connection");
}
var arrSMTPResponse = new byte[256];
var sizeSMTPResponse = _sMTPClient.Client.Receive(arrSMTPResponse);
var connectResponse = Encoding.ASCII.GetString(arrSMTPResponse);
if (!connectResponse.StartsWith("220"))
{
throw new WebException("SMTP server refused to connect");
}
_sMTPClient.Client.Send(Encoding.ASCII.GetBytes("HELO " + HelloServer + "\r\n"));
sizeSMTPResponse = _sMTPClient.Client.Receive(arrSMTPResponse);
var heloResponse = Encoding.ASCII.GetString(arrSMTPResponse);
if (!heloResponse.StartsWith("250"))
{
throw new WebException("SMTP server refused to handshake");
}
_sMTPClient.Client.Send(Encoding.ASCII.GetBytes("MAIL FROM:<" + QueryEmail + ">\r\n"));
sizeSMTPResponse = _sMTPClient.Client.Receive(arrSMTPResponse);
var mailfromResponse = Encoding.ASCII.GetString(arrSMTPResponse);
if (!mailfromResponse.StartsWith("250"))
{
throw new WebException("SMTP server refused to accept mail from");
}
_sMTPClient.Client.Send(Encoding.ASCII.GetBytes("RCPT TO:<" + email + ">\r\n"));
sizeSMTPResponse = _sMTPClient.Client.Receive(arrSMTPResponse);
var rcpttoResponse = Encoding.ASCII.GetString(arrSMTPResponse);
_sMTPClient.Client.Send(Encoding.ASCII.GetBytes("QUIT")); // Bye
_sMTPClient.Close();
if (!rcpttoResponse.StartsWith("250"))
{
return(false);
}
break;
}
}
}
} while (true);
return(true);
}
