public DnsDatagram Resolve(DnsDatagram request)
{
int bytesRecv;
byte[] responseBuffer = null;
int nextServerIndex = 0;
int retries = _retries;
byte[] requestBuffer;
IDnsCache dnsCache = null;
//serialize request
using (MemoryStream mS = new MemoryStream(32))
{
if (_tcp)
{
mS.Position = 2;
}
//write dns datagram
request.WriteTo(mS);
requestBuffer = mS.ToArray();
if (_tcp)
{
byte[] length = BitConverter.GetBytes(Convert.ToUInt16(requestBuffer.Length - 2));
requestBuffer[0] = length[1];
requestBuffer[1] = length[0];
}
}
//init server selection parameters
if (_servers.Length > 1)
{
retries = retries * _servers.Length; //retries on per server basis
byte[] select = new byte[1];
_rnd.GetBytes(select);
nextServerIndex = select[0] % _servers.Length;
}
int retry = 0;
while (retry < retries)
{
//select server
NameServerAddress server;
if (_servers.Length > 1)
{
server = _servers[nextServerIndex];
nextServerIndex = (nextServerIndex + 1) % _servers.Length;
}
else
{
server = _servers[0];
}
if (server.EndPoint == null)
{
if (dnsCache == null)
{
dnsCache = new SimpleDnsCache();
}
server.ResolveAddress(dnsCache, _proxy, _preferIPv6, _tcp, _retries);
if (server.EndPoint == null)
{
retry++;
continue;
}
}
//query server
Socket _socket = null;
SocksUdpAssociateRequestHandler proxyRequestHandler = null;
try
{
retry++;
DateTime sentAt = DateTime.UtcNow;
bool dnsTcp;
if (_proxy == null)
{
if (_tcp)
{
_socket = new Socket(server.EndPoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
_socket.NoDelay = true;
_socket.SendTimeout = _sendTimeout;
_socket.ReceiveTimeout = _recvTimeout;
IAsyncResult result = _socket.BeginConnect(server.EndPoint, null, null);
if (!result.AsyncWaitHandle.WaitOne(_connectionTimeout))
{
throw new SocketException((int)SocketError.TimedOut);
}
if (!_socket.Connected)
{
throw new SocketException((int)SocketError.ConnectionRefused);
}
}
else
{
_socket = new Socket(server.EndPoint.AddressFamily, SocketType.Dgram, ProtocolType.Udp);
_socket.SendTimeout = _sendTimeout;
_socket.ReceiveTimeout = _recvTimeout;
}
dnsTcp = _tcp;
}
else
{
switch (_proxy.Type)
{
case NetProxyType.Http:
_socket = _proxy.HttpProxy.Connect(server.EndPoint, _connectionTimeout);
_socket.NoDelay = true;
_socket.SendTimeout = _sendTimeout;
_socket.ReceiveTimeout = _recvTimeout;
dnsTcp = true;
break;
case NetProxyType.Socks5:
if (!_tcp)
{
try
{
proxyRequestHandler = _proxy.SocksProxy.UdpAssociate(_connectionTimeout);
proxyRequestHandler.ReceiveTimeout = _recvTimeout;
dnsTcp = false;
break;
}
catch (SocksClientException)
{ }
}
using (SocksConnectRequestHandler requestHandler = _proxy.SocksProxy.Connect(server.EndPoint, _connectionTimeout))
{
_socket = requestHandler.GetSocket();
_socket.NoDelay = true;
_socket.SendTimeout = _sendTimeout;
_socket.ReceiveTimeout = _recvTimeout;
dnsTcp = true;
}
break;
default:
throw new NotSupportedException("Proxy type not supported by DnsClient.");
}
}
if (dnsTcp)
{
_socket.Send(requestBuffer);
if ((responseBuffer == null) || (responseBuffer.Length == 512))
{
responseBuffer = new byte[64 * 1024];
}
bytesRecv = _socket.Receive(responseBuffer, 0, 2, SocketFlags.None);
if (bytesRecv < 1)
{
throw new SocketException((int)SocketError.ConnectionReset);
}
Array.Reverse(responseBuffer, 0, 2);
ushort length = BitConverter.ToUInt16(responseBuffer, 0);
int offset = 0;
while (offset < length)
{
bytesRecv = _socket.Receive(responseBuffer, offset, length, SocketFlags.None);
if (bytesRecv < 1)
{
throw new SocketException((int)SocketError.ConnectionReset);
}
offset += bytesRecv;
}
bytesRecv = length;
}
else
{
if (responseBuffer == null)
{
responseBuffer = new byte[512];
}
if (proxyRequestHandler == null)
{
_socket.SendTo(requestBuffer, server.EndPoint);
EndPoint remoteEP;
if (server.EndPoint.AddressFamily == AddressFamily.InterNetworkV6)
{
remoteEP = new IPEndPoint(IPAddress.IPv6Any, 0);
}
else
{
remoteEP = new IPEndPoint(IPAddress.Any, 0);
}
bytesRecv = _socket.ReceiveFrom(responseBuffer, ref remoteEP);
}
else
{
proxyRequestHandler.SendTo(requestBuffer, 0, requestBuffer.Length, new SocksEndPoint(server.EndPoint));
bytesRecv = proxyRequestHandler.ReceiveFrom(responseBuffer, 0, responseBuffer.Length, out SocksEndPoint socksRemoteEP);
}
}
//parse response
using (MemoryStream mS = new MemoryStream(responseBuffer, 0, bytesRecv, false))
{
double rtt = (DateTime.UtcNow - sentAt).TotalMilliseconds;
DnsDatagram response = new DnsDatagram(mS, server, (_tcp ? ProtocolType.Tcp : ProtocolType.Udp), rtt);
if (response.Header.Identifier == request.Header.Identifier)
{
return(response);
}
}
}
catch (SocketException)
{ }
finally
{
if (_socket != null)
{
_socket.Dispose();
}
if (proxyRequestHandler != null)
{
proxyRequestHandler.Dispose();
}
}
}
throw new DnsClientException("DnsClient failed to resolve the request: no response from name servers.");
}
