static void Main(string[] args)
{
// Start P2P thread
Thread p2pListener = new Thread(new ThreadStart(P2P.Run));
p2pListener.Start();
// Open UDP socket
UdpClient listener = new UdpClient(listenPort);
IPEndPoint groupEP;
// Receive a packet
try
{
byte[] recv_buf;
while (true)
{
// Set listen address
groupEP = new IPEndPoint(IPAddress.Any, listenPort);
// Receive data, client will be placed in groupEP
recv_buf = listener.Receive(ref groupEP);
// Parse DNS data
MemoryStream ms = new MemoryStream(recv_buf);
BinaryReader br = new BinaryReader(ms);
DNS_header header = new DNS_header();
header.Read(br);
if (header.QDcount != 1)
{
Console.WriteLine("Cannot parse DNS request where QDcount != 1");
continue;
}
DNS_question question = new DNS_question();
question.Read(br);
// Get the answer to the query
byte[] ans_ip = new byte[4];
DNScache.resolve(question.name, ref ans_ip);
// Send a response
MemoryStream ms_out = new MemoryStream();
BinaryWriter bw = new BinaryWriter(ms_out);
// Modify DNS header
header.qr = true;
header.rcode = 0;
header.ANcount = 1;
// Write DNS header
header.Write(bw);
// Write question
question.Write(bw);
// Generate answer
DNS_answer answer = new DNS_answer();
answer.name = question.name;
answer.atype = 1;
answer.aclass = 1;
answer.ttl = 60;
answer.rdlen = 4;
answer.rdata = ans_ip;
// Write answer
answer.Write(bw);
// Send the packet
byte[] buf_out = ms_out.ToArray();
listener.Send(buf_out, buf_out.Length, groupEP);
}
} catch (Exception e)
{
Console.WriteLine(e.ToString());
Console.ReadLine();
}
p2pListener.Interrupt();
}
public static bool resolve(string name, ref byte[] result)
{
// If the cache contains the result, return it
lock (_lock_cache)
{
if (_cache.ContainsKey(name))
{
cache_entry ce = _cache[name];
if (ce.expiry < DateTime.Now)
{
_cache.Remove(name);
}
else
{
if (ce.success)
{
Array.Copy(ce.address, result, 4);
}
#if DEBUG
Console.WriteLine("Resolved through local cache!");
#endif
log.Info("cache");
return(ce.success);
}
}
}
// Query P2P before delegating to real DNS server
if (P2P.resolve(name, ref result))
{
#if DEBUG
Console.WriteLine("Resolved through P2P!");
#endif
log.Info("p2p");
return(true);
}
// Otherwise, we must query a real DNS server
// TODO: Change from hardcoded DNS server to configurable server
DNS_header req = new DNS_header();
req.ID = 1337;
req.qr = false;
req.opcode = 0;
req.tc = false;
req.rd = true;
req.QDcount = 1;
req.ANcount = 0;
req.NScount = 0;
req.ARcount = 0;
DNS_question req_q = new DNS_question();
req_q.name = name;
req_q.qclass = 1;
req_q.qtype = 1;
// Set up the packet
MemoryStream ms = new MemoryStream();
BinaryWriter bw = new BinaryWriter(ms);
req.Write(bw);
req_q.Write(bw);
// Send the packet
byte[] req_buf = ms.ToArray();
UdpClient client = new UdpClient();
client.Connect(IPAddress.Parse("8.8.8.8"), 53);
client.Send(req_buf, req_buf.Length);
// Receive a packet
IPEndPoint ipep = new IPEndPoint(IPAddress.Parse("8.8.8.8"), 53);
client.Client.ReceiveTimeout = 1000;
byte[] res_buf;
try
{
res_buf = client.Receive(ref ipep);
} catch (SocketException ex)
{
return(false);
}
MemoryStream res_ms = new MemoryStream(res_buf);
BinaryReader res_br = new BinaryReader(res_ms);
DNS_header res_h = new DNS_header();
res_h.Read(res_br);
if (!res_h.qr)
{
Console.WriteLine("Received packet was a query!");
return(false);
}
if (res_h.rcode != 0)
{
lock (_lock_cache)
{
cache_entry ce = new cache_entry();
ce.success = false;
ce.expiry = DateTime.Now.AddMinutes(15);
_cache.Add(name, ce);
}
return(false);
}
DNS_question[] res_qs = new DNS_question[res_h.QDcount];
DNS_answer[] res_as = new DNS_answer[res_h.ANcount];
#if DEBUG
Console.WriteLine("Questions: {0}\nAnswers: {1}", res_h.QDcount, res_h.ANcount);
#endif
for (int i = 0; i < res_h.QDcount; i++)
{
res_qs[i] = new DNS_question();
res_qs[i].Read(res_br);
#if DEBUG
Console.WriteLine("Question {0}: {1}\n", i, res_qs[i].name);
#endif
}
byte[] address = new byte[4];
uint ttl = 0;
bool answer = false;
for (int i = 0; i < res_h.ANcount; i++)
{
res_as[i] = new DNS_answer();
res_as[i].Read(res_br);
#if DEBUG
Console.WriteLine("Answer {0}: {1}\n", i, res_as[i].name);
#endif
if (res_as[i].atype == 1)
{
#if DEBUG
Console.WriteLine("{0}.{1}.{2}.{3} TTL: {4}", res_as[i].rdata[0], res_as[i].rdata[1], res_as[i].rdata[2], res_as[i].rdata[3], res_as[i].ttl);
#endif
for (int j = 0; j < 4; j++)
{
address[j] = res_as[i].rdata[j];
ttl = res_as[i].ttl;
answer = true;
}
}
}
if (answer)
{
lock (_lock_cache)
{
cache_entry ce = new cache_entry();
ce.success = true;
ce.address = address;
ce.expiry = DateTime.Now.AddSeconds(ttl);
_cache.Add(name, ce);
}
for (int i = 0; i < 4; i++)
{
result[i] = address[i];
}
#if DEBUG
Console.WriteLine("Resolved through DNS!");
#endif
log.Info("dns");
return(true);
}
return(false);
}
