csharp C＃DNS转发器

Posted 2021-05-12

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ARSoft.Tools;
using ARSoft;
using ARSoft.Tools.Net.Dns;
using DNSForwarderARSoft;
using ARSoft.Tools.Net;
using System.Net;
using System.Net.Sockets; 

namespace DNSForwarderARSoft
{
    class Program
    {
        static void Main(string[] args)
        {

            using (DnsServer server = new DnsServer(IPAddress.Any, 10, 10))
            {
                //server.
                server.QueryReceived += OnQueryReceived;
                
                server.Start();

                Console.WriteLine("Press any key to stop server");
                Console.ReadLine();
            }
        }

        static async Task OnQueryReceived(object sender, QueryReceivedEventArgs e)
        {
            DnsMessage message = e.Query as DnsMessage;
            

            if (message == null)
                return;

            DnsMessage response = message.CreateResponseInstance();
            

            if ((message.Questions.Count == 1))
            {
                // send query to upstream server
                DnsQuestion question = message.Questions[0];
                //DnsMessage upstreamResponse = await DnsClient.Default.ResolveAsync(question.Name, question.RecordType, question.RecordClass);

                IPAddress address = IPAddress.Parse("DNS Primary Forwarder");

                DnsClient dnsClient = new DnsClient(address, 10);
                DnsMessage upstreamResponse = await dnsClient.ResolveAsync(question.Name, question.RecordType, question.RecordClass);
               
                // if got an answer, copy it to the message sent to the client
                if (question != null)
                {

                    foreach (DnsRecordBase record in (upstreamResponse.AnswerRecords))
                    {
                        //response.AnswerRecords.Add(record);
                        Console.WriteLine("AnswerRecords: " + record.ToString());

                        string dnsRecord = record.ToString();
                        string[] splitDNSRecord = dnsRecord.Split(' ');

                        if ((dnsRecord.ToUpper().Contains("RCH")) || dnsRecord.ToUpper().Contains("NLR") || dnsRecord.ToUpper().Contains("S-"))
                        {
                            Console.WriteLine("------------------ Client Request ------------------");
                            foreach (string splitRecord in splitDNSRecord)
                            {
                                if (CheckIPValid(splitRecord))
                                {
                                    Console.WriteLine("valid IP: " + splitRecord);

                                    if (CheckTCPConnection(splitRecord) == true)
                                    {
                                        Console.WriteLine("Connection true: " + splitRecord);
                                        response.AnswerRecords.Add(record);
                                    }
                                }
                                else
                                {

                                }
                            }
                        }
                        else
                        {
                            //Console.WriteLine("------------------ Server Request------------------");
                            response.AnswerRecords.Add(record);
                        }
              
                    }

                    response.ReturnCode = ReturnCode.NoError;

                    // set the response
                    e.Response = response;
                }
            }
        }

        public static bool CheckIPValid(string strIP)
        {
            //  Split string by ".", check that array length is 3
            char chrFullStop = '.';
            string[] arrOctets = strIP.Split(chrFullStop);
            if (arrOctets.Length != 4)
            {
                return false;
            }
            //  Check each substring checking that the int value is less than 255 and that is char[] length is !> 2
            Int16 MAXVALUE = 255;
            Int32 temp; // Parse returns Int32
            foreach (String strOctet in arrOctets)
            {
                if (strOctet.Length > 3)
                {
                    return false;
                }

                temp = int.Parse(strOctet);
                if (temp > MAXVALUE)
                {
                    return false;
                }
            }
            return true;
        }

        public static bool CheckTCPConnection(string IP)
        {
            bool open;

            using (TcpClient tcpclient = new TcpClient())
            {
                
                    var result = tcpclient.BeginConnect(IP, 135, null, null);
                    result.AsyncWaitHandle.WaitOne(TimeSpan.FromSeconds(1));
                    if(tcpclient.Connected)
                    {
                        Console.WriteLine("Port open on ip: " + IP);
                        open = true;
                    }
                    else
                    {
                        Console.WriteLine("Port closed on ip: " + IP);
                        open = false;
                    }
            }
            return open; 
        }
    }
}