333 lines
12 KiB
C#
333 lines
12 KiB
C#
using System;
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using System.Collections.Generic;
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using System.IO;
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using System.Net;
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using System.Net.Sockets;
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using System.Text;
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using System.Threading.Tasks;
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namespace EonaCat.DnsTester.Helpers
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{
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class DnsHelper
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{
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public static event EventHandler<string> OnLog;
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private static readonly Random random = new Random();
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public static async Task<DnsResponse> SendDnsQueryPacket(string dnsId, string server, int port, byte[] queryBytes)
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{
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var stopwatch = System.Diagnostics.Stopwatch.StartNew();
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var endPoint = new IPEndPoint(IPAddress.Parse(server), port);
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using (var client = new UdpClient(endPoint.AddressFamily))
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{
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client.DontFragment = true;
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client.EnableBroadcast = false;
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client.Client.SendTimeout = DnsSendTimeout;
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client.Client.ReceiveTimeout = DnsReceiveTimeout;
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byte[] responseBytes;
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if (FakeResponse)
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{
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responseBytes = GetExampleResponse();
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}
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else
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{
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await client.SendAsync(queryBytes, queryBytes.Length, endPoint);
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var responseResult = await client.ReceiveAsync();
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responseBytes = responseResult.Buffer;
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}
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var response = ParseDnsResponsePacket(dnsId, stopwatch.ElapsedTicks, server, responseBytes);
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return response;
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}
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}
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// For testing purposes
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public static bool FakeResponse { get; set; }
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public static int DnsSendTimeout { get; set; } = 5;
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public static int DnsReceiveTimeout { get; set; } = 5;
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public static byte[] CreateDnsQueryPacket(string domainName, DnsRecordType recordType)
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{
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var id = (ushort)random.Next(0, 65536);
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var flags = (ushort)0x0100; // recursion desired
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var qdcount = (ushort)1;
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var ancount = (ushort)0;
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var nscount = (ushort)0;
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var arcount = (ushort)0;
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using (var stream = new MemoryStream())
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using (var writer = new BinaryWriter(stream))
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{
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writer.Write(id);
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writer.Write(flags);
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writer.Write(qdcount);
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writer.Write(ancount);
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writer.Write(nscount);
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writer.Write(arcount);
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var labels = domainName.Split('.');
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foreach (var label in labels)
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{
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writer.Write((byte)label.Length);
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writer.Write(Encoding.ASCII.GetBytes(label));
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}
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writer.Write((byte)0); // Null terminator
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writer.Write((ushort)recordType);
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writer.Write((ushort)1); // Record class: IN (Internet)
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return stream.ToArray();
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}
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}
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public static byte[] GetExampleResponse()
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{
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// Example response bytes for the A record of google.com
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return new byte[]
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{
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0x9d, 0xa9, // Query ID
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0x81, 0x80, // Flags
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0x00, 0x01, // Questions: 1
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0x00, 0x01, // Answer RRs: 1
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0x00, 0x00, // Authority RRs: 0
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0x00, 0x00, // Additional RRs: 0
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0x06, 0x67, 0x6f, 0x6f, 0x67, 0x6c, 0x65, // Query: google
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0x03, 0x63, 0x6f, 0x6d, // Query: com
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0x00,
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0x00, 0x01, // Record type: A
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0x00, 0x01, // Record class: IN
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0xc0, 0x0c, // Name pointer to google.com
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0x00, 0x01, // Record type: A
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0x00, 0x01, // Record class: IN
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0x00, 0x00, 0x00, 0x3d, // TTL: 61 seconds
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0x00, 0x04, // Data length: 4 bytes
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0xac, 0xd9, 0x03, 0x3d // Data: 172.217.3.61
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};
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}
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private static DnsResponse ParseDnsResponsePacket(string dnsId, long startTime, string server, byte[] responseBytes)
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{
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if (responseBytes.Length < 12)
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{
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throw new Exception("Invalid DNS response");
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}
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var offset = 0;
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var id = (ushort)((responseBytes[offset++] << 8) | responseBytes[offset++]);
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var flags = (ushort)((responseBytes[offset++] << 8) | responseBytes[offset++]);
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var isResponse = (flags & 0x8000) != 0;
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var qdcount = (ushort)((responseBytes[offset++] << 8) | responseBytes[offset++]);
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if (!isResponse)
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{
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throw new Exception("Invalid DNS response");
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}
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var nscount = (ushort)((responseBytes[offset++] << 8) | responseBytes[offset++]);
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var arcount = (ushort)((responseBytes[offset++] << 8) | responseBytes[offset++]);
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var questions = new List<DnsQuestion>();
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for (int i = 0; i < qdcount; i++)
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{
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var question = ParseDnsQuestionRecord(responseBytes, ref offset);
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if (question != null)
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{
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questions.Add(question);
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}
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}
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var answers = new List<ResourceRecord>();
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for (int i = 0; i < qdcount; i++)
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{
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try
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{
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var answer = ParseDnsAnswerRecord(responseBytes, ref offset);
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if (answer != null)
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{
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answers.Add(answer);
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}
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}
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catch (Exception exception)
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{
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OnLog?.Invoke(null, $"Answer exception: {exception.Message}");
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}
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}
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// Parse the DNS authority records
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var authorities = new List<ResourceRecord>();
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for (int i = 0; i < nscount; i++)
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{
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try
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{
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var authority = ParseDnsAnswerRecord(responseBytes, ref offset);
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if (authority != null)
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{
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authorities.Add(authority);
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}
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}
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catch (Exception exception)
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{
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OnLog?.Invoke(null, $"Authority answer exception: {exception.Message}");
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}
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}
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// Parse the DNS additional records
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var additionals = new List<ResourceRecord>();
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for (int i = 0; i < arcount; i++)
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{
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try
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{
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var additional = ParseDnsAnswerRecord(responseBytes, ref offset);
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if (additional != null)
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{
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additionals.Add(additional);
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}
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}
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catch (Exception exception)
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{
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OnLog?.Invoke(null, $"Additional answer exception: {exception.Message}");
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}
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}
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return new DnsResponse
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{
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Id = id,
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StartTime = startTime,
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Resolver = server,
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Flags = flags,
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Class = (DnsRecordClass)((flags >> 3) & 0x0f),
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DnsId = dnsId,
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Questions = questions,
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Answers = answers,
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Authorities = authorities,
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Additionals = additionals,
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};
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}
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private static DnsQuestion ParseDnsQuestionRecord(byte[] queryBytes, ref int offset)
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{
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var name = DnsNameParser.ParseName(queryBytes, ref offset);
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if (name == null)
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{
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return null;
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}
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var type = (DnsRecordType)((queryBytes[offset++] << 8) | queryBytes[offset++]);
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var qclass = (DnsRecordClass)((queryBytes[offset++] << 8) | queryBytes[offset++]);
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return new DnsQuestion
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{
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Name = name,
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Type = type,
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Class = qclass,
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};
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}
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private static ResourceRecord ParseDnsAnswerRecord(byte[] responseBytes, ref int offset)
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{
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var name = DnsNameParser.ExtractDomainName(responseBytes, ref offset);
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if (name == null)
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{
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return null;
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}
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var type = (DnsRecordType)((responseBytes[offset++] << 8) + responseBytes[offset++]);
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var klass = (DnsRecordClass)((responseBytes[offset++] << 8) + responseBytes[offset++]);
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var ttl = (responseBytes[offset++] << 24) + (responseBytes[offset++] << 16) + (responseBytes[offset++] << 8) + responseBytes[offset++];
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var dataLength = (responseBytes[offset++] << 8) + responseBytes[offset++];
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string dataAsString = null;
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switch (type)
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{
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case DnsRecordType.A:
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if (dataLength != 4)
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{
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return null;
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}
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dataAsString = new IPAddress(responseBytes, offset).ToString();
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offset += dataLength;
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break;
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case DnsRecordType.CNAME:
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case DnsRecordType.NS:
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dataAsString = DnsNameParser.ExtractDomainName(responseBytes, ref offset);
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break;
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case DnsRecordType.MX:
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var preference = (responseBytes[offset++] << 8) + responseBytes[offset++];
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var exchange = DnsNameParser.ExtractDomainName(responseBytes, ref offset);
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dataAsString = $"{preference} {exchange}";
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break;
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case DnsRecordType.TXT:
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dataAsString = Encoding.ASCII.GetString(responseBytes, offset, dataLength);
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offset += dataLength;
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break;
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default:
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offset += dataLength;
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break;
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}
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return new ResourceRecord
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{
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Name = name,
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Type = type,
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Class = klass,
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Ttl = TimeSpan.FromSeconds(ttl),
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Data = dataAsString,
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DataLength = (ushort)dataLength,
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};
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}
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}
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public class DnsQuestion
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{
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public string Name { get; set; }
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public DnsRecordType Type { get; set; }
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public DnsRecordClass Class { get; set; }
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}
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public class ResourceRecord
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{
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public string Name { get; set; }
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public DnsRecordType Type { get; set; }
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public string Data { get; set; }
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public DnsRecordClass Class { get; set; }
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public TimeSpan Ttl { get; set; }
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public ushort DataLength { get; set; }
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}
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public class DnsResponse
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{
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public ushort Id { get; set; }
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public ushort Flags { get; set; }
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public DnsRecordClass Class { get; set; }
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public List<ResourceRecord> Answers { get; set; }
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public long StartTime { get; set; }
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public string Resolver { get; set; }
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public string DnsId { get; set; }
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public List<DnsQuestion> Questions { get; set; }
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public List<ResourceRecord> Authorities { get; set; }
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public List<ResourceRecord> Additionals { get; set; }
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}
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public enum DnsRecordType : ushort
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{
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A = 1,
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NS = 2,
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CNAME = 6,
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MX = 15,
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TXT = 16,
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AAAA = 28,
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}
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public enum DnsRecordClass : ushort
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{
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Internet = 1,
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CS = 2,
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CH = 3,
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HS = 4,
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None = 254,
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ANY = 255
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}
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}
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