How to use idDnsServer

[aydın]

I don't know how to use idDnsServer, one sample code is enough.

Thanks you in advance for your help.

[KodeZwerg]

I just tried it once many many years ago and i gave up trying to play with it.
I decided to write my own class for that purpose where "TIdUDPServer" was the "Father"-Class from what my class derived.
Maybe i do find its source somewhere...

[aydın]

I created an idUdpServer, assigned 0.0.0.0 as ip, 53 as port.

When I searched www.jixoi.com, I got the answer "b~
 
      wwwjixoicom 

".

How should I read this data and respond back?

[KodeZwerg]

My source is broken, i do not have my full source anymore but some things of how i did survived:

class Header:

Code: Pascal  [Select][+][-]

1. type
2.   TSimpleDNSServer = class(TIdUDPServer)
3.   protected
4.     procedure DoUDPRead(AData: TIdBytes; ABinding: TIdSocketHandle); override; // called on receive data
5.   private
6.     function ReadPackage(Data: TBytes): TDNSPackage; // read packet
7.     procedure HandlePackage(var DNSPackage: TDNSPackage; Binding: TIdSocketHandle); // handle packet
8.     procedure SendDNSPackage(DNSPackage: TDNSPackage; Binding: TIdSocketHandle); // answer
9.   end;

packet header

Code: Pascal  [Select][+][-]

1. type
2.   TDNSHeader = record
3.     ID: Word; // 16bitu Identifier
4.     QR: Boolean; // 1bit False=Query True=Response
5.     OPCODE: Array[0..3] of Boolean; // 4bit 0=Query 1=IQuery 2=Status 3-15 Reserved
6.     AA: Boolean; // 1bit True in Response - Authoritative Answer
7.     TC: Boolean; // 1bit TrunCation
8.     RD: Boolean; // 1bit Recursion Desired
9.     RA: Boolean; // 1bit Recursion Available
10.     Z: Array[0..2] of Boolean; // 3bit Reserved --> 0
11.     RCODE: Array[0..3] of Boolean; // 4bit - Response Code
12.     QDCOUNT: Word; // 16bitu Number of Entries in Question Section
13.     ANCOUNT: Word; // 16bitu Number of RRs in Answer Section
14.     NSCOUNT: Word; // 16bitu Number of Nameserver RRs in the Authority Records Section
15.     ARCOUNT: Word; // 16bitu Number of RRs in Additional Records Section
16.   end;

request header

Code: Pascal  [Select][+][-]

1. type
2.   TDNSQuestion = record
3.    QNAME: String; // Query-Name
4.    NamePointer: Integer; // Compression (etwas komplizierter, erkläre ich später)
5.    QTYPE: Word; // 16bitu Type of Query
6.    QCLASS: Word; // 16bitu Class of Query
7.   end;

content header

Code: Pascal  [Select][+][-]

1. type
2.   TResorceRecord = record
3.     NAME: TBytes; // a domain name to which this resource record pertains.
4.     RTYPE: Word; // 16bitu Meaning of Data in RDATA
5.     RCLASS: Word; // 16bitu Class of Data in RDATA
6.     TTL: LongWord; // 32bitu Cache-Time
7.     RDLENGTH: Word; // 16bitu Number of Octets in RDATA
8.     RDATA: TBytes; // data storage
9.   end;

putting things together

Code: Pascal  [Select][+][-]

1. type
2.   TDNSPackage = record
3.     Header : TDNSHeader;
4.     Question : Array of TDNSQuestion;
5.     Answer : Array of TResorceRecord;
6.   end;

class methods

Code: Pascal  [Select][+][-]

1. procedure TSimpleDNSServer.DoUDPRead(AData: TIdBytes; ABinding: TIdSocketHandle);
2. var
3.   DNSPackage: TDNSPackage;
4. begin
5.   DNSPackage := ReadPackage(AData);
6.   HandlePackage(DNSPackage, ABinding);
7.   SendDNSPackage(DNSPackage, Binding);
8.   FreePackage(DNSPackage);
9. end;

class methods

Code: Pascal  [Select][+][-]

1. function TSimpleDNSServer.ReadPackage(Data: TBytes): TDNSPackage;
2. var
3.   Buffer16bit: TBytes;
4.   Position: Integer;
5.   Flags, Flags2: Array[0..7] of Boolean; // byte to bit
6.   i: Integer;
7. begin
8.   SetLength(Buffer16bit, 2);
9.   Result.Header.ID := BytesToWord(ReadFromBytes(Data, 0, 2));
10.   Flags := ByteToBits(Data[2]);
11.   Flags2 := ByteToBits(Data[3]);
12.   with Result.Header do
13.   begin
14.     QR := Flags[0];
15.     OPCODE[0] := Flags[1];
16.     OPCODE[1] := Flags[2];
17.     OPCODE[2] := Flags[3];
18.     OPCODE[3] := Flags[4];
19.     AA := Flags[5];
20.     TC := Flags[6];
21.     RD := Flags[7];
22.     RA := Flags2[0];
23.     Z[0] := Flags2[1];
24.     Z[1] := Flags2[2];
25.     Z[2] := Flags2[3];
26.     RCODE[0] := Flags2[4];
27.     RCODE[1] := Flags2[5];
28.     RCODE[2] := Flags2[6];
29.     RCODE[3] := Flags2[7];
30.   end;
31.   Result.Header.QDCOUNT := BytesToWord(ReadFromBytes(Data, 4, 2));
32.   Result.Header.ANCOUNT := BytesToWord(ReadFromBytes(Data, 6, 2));
33.   Result.Header.NSCOUNT := BytesToWord(ReadFromBytes(Data, 8, 2));
34.   Result.Header.ARCOUNT := BytesToWord(ReadFromBytes(Data, 10, 2));
35.   SetLength(Result.Question, Result.Header.QDCOUNT);
36.   Position := 12;
37.   for i := 0 to Result.Header.QDCOUNT-1 do
38.   begin
39.     Result.Question[i].QNAME := GetStringInBytes(Data, Position);
40.     Result.Question[i].NamePointer := Position;
41.     Position := Position + Length(Result.Question[i].QNAME);
42.     Result.Question[i].QTYPE := BytesToWord(ReadFromBytes(Data, Position, 2));
43.     Inc(Position, 2);
44.     Result.Question[i].QCLASS := BytesToWord(ReadFromBytes(Data, Position, 2));
45.     Inc(Position, 2);
46.   end;
47.   SetLength(Buffer16bit, 0);
48. end;

class methods

Code: Pascal  [Select][+][-]

1. procedure TSimpleDNSServer.HandlePackage(var DNSPackage: TDNSPackage; Binding: TIdSocketHandle);
2. var
3.   i: Integer;
4.   CompressionBytes: TBytes;
5.   Compression1: Array[0..7] of Boolean;
6.   IPAddress: Array[0..3] of Byte;
7. begin
8.   if DNSPackage.Header.QR then
9.     Exit;
10.   with DNSPackage do
11.   begin
12.     with Header do
13.     begin
14.       QR := True;
15.       AA := False;
16.       RA := True;
17.       RCODE := 0;
18.       ANCOUNT := DNSPackage.Header.QDCOUNT;
19.     end;
20.   end;
21.   SetLength(DNSPackage.Answer, DNSPackage.Header.ANCOUNT);
22.   for i := 0 to DNSPackage.Header.QDCOUNT-1 do
23.   begin
24.     if (DNSPackage.Question[i].QTYPE = 1) and (DNSPackage.Question[i].QCLASS = 1) then
25.     begin
26.       with DNSPackage.Answer[i] do
27.       begin
28.         IPAddress := DNSPackage.Question[i].QNAME;
29.         CompressionBytes := WordToBytes(DNSPackage.Question[i].NamePointer);
30.         Compression1 := ByteToBits(CompressionBytes[0]);
31.         Compression1[0] := True;
32.         Compression1[1] := True;
33.         CompressionBytes[0] := BitsToByte(Compression1);
34.         SetLength(NAME, 2);
35.         NAME[0] := CompressionBytes[0];
36.         NAME[1] := CompressionBytes[1];
37.         RTYPE := 1;
38.         RCLASS := 1;
39.         TTL := 300;
40.         RDLENGTH := 4;
41.         SetLength(RDATA, 4);
42.         RDATA[0] := IPAddress[0];
43.         RDATA[1] := IPAddress[1];
44.         RDATA[2] := IPAddress[2];
45.         RDATA[3] := IPAddress[3];
46.       end;
47.     end;
48.   end;
49. end;

class methods

Code: Pascal  [Select][+][-]

1. procedure TSimpleDNSServer.SendDNSPackage(DNSPackage: TDNSPackage; Binding: TIdSocketHandle);
2. var
3.   Bytes: TBytes;
4.   Flags, Flags2: Array[0..7] of Boolean;
5.   i: Integer;
6.   Position: Integer;
7. begin
8.   SetLength(Bytes, SizeOfPackage(DNSPackage));
9.   WriteToBytes(Bytes, WordToBytes(DNSPackage.Header.ID), 0);
10.   with DNSPackage.Header do
11.   begin
12.     Flags[0] := QR;
13.     Flags[1] := OPCODE[0];
14.     Flags[2] := OPCODE[1];
15.     Flags[3] := OPCODE[2];
16.     Flags[4] := OPCODE[3];
17.     Flags[5] := AA;
18.     Flags[6] := TC;
19.     Flags[7] := RD;
20.     Flags2[0] := RA;
21.     Flags2[1] := Z[0];
22.     Flags2[2] := Z[1];
23.     Flags2[3] := Z[2];
24.     Flags2[4] := RCODE[0];
25.     Flags2[5] := RCODE[1];
26.     Flags2[6] := RCODE[2];
27.     Flags2[7] := RCODE[3];
28.   end;
29.   Bytes[2] := BitsToByte(Flags);
30.   Bytes[3] := BitsToByte(Flags2);
31.   WriteToBytes(Bytes, WordToBytes(DNSPackage.Header.QDCOUNT), 4);
32.   WriteToBytes(Bytes, WordToBytes(DNSPackage.Header.ANCOUNT), 6);
33.   WriteToBytes(Bytes, WordToBytes(DNSPackage.Header.NSCOUNT), 8);
34.   WriteToBytes(Bytes, WordToBytes(DNSPackage.Header.ARCOUNT), 10);
35.   Position := 12;
36.   for i := 0 to DNSPackage.Header.QDCOUNT-1 do
37.   begin
38.     WriteToBytes(Bytes, ToBytes(DNSPackage.Question[i].QNAME), Position);
39.     Inc(Position, Length(DNSPackage.Question[i].QNAME));
40.     WriteToBytes(Bytes, WordToBytes(DNSPackage.Question[i].QTYPE), Position);
41.     Inc(Position, 2);
42.     WriteToBytes(Bytes, WordToBytes(DNSPackage.Question[i].QCLASS), Position);
43.     Inc(Position, 2);
44.   end;
45.   for i := 0 to DNSPackage.Header.ANCOUNT-1 do
46.   begin
47.     Bytes[Position] := DNSPackage.Answer[i].NAME[0];
48.     inc(Position);
49.     Bytes[Position] := DNSPackage.Answer[i].NAME[1];
50.     inc(Position);
51.     WriteToBytes(Bytes, WordToBytes(DNSPackage.Answer[i].RTYPE), Position);
52.     Inc(Position, 2);
53.     WriteToBytes(Bytes, WordToBytes(DNSPackage.Answer[i].RCLASS), Position);
54.     Inc(Position, 2);
55.     WriteToBytes(Bytes, LongWordToBytes(DNSPackage.Answer[i].TTL), Position);
56.     Inc(Position, 4);
57.     WriteToBytes(Bytes, WordToBytes(DNSPackage.Answer[i].RDLENGTH), Position);
58.     Inc(Position, 2);
59.     WriteToBytes(Bytes, DNSPackage.Answer[i].RDATA, Position);
60.     Inc(Position, DNSPackage.Answer[i].RDLENGTH);
61.   end;
62.   Binding.SendTo(Binding.PeerIP, Binding.PeerPort, Bytes);
63. end;

I hope it helps, more i can not find anymore.

[aydın]

Thanks KodeZwerg for the reply.

[Remy Lebeau]

I don't know how to use idDnsServer, one sample code is enough.

Unfortunately, I'm not aware of any examples for TIdDNSServer.

What exactly are you trying to accomplish?

[aydın]

I want to set up my own DNS server in my local network.

[loaded]

Instead of creating your own dns;
There are linux-based dns servers customized just for this job.
Or there may be such a setting on the modem you are using.
I think using them can solve your problem faster.

[Warfley]

I guess you probably want to create your own Recursive DNS server, and not an authoratative one. Generally all you need to do for that is parse incoming requests, go through each request individually and cascade down the line of authoratative DNS servers, once you get your record, you can more or less simply paste the result into your response.

DNS protocol specification: https://datatracker.ietf.org/doc/html/rfc1035
For the record and request formats you could checkout my DNS client implementation from AsyncNet: https://github.com/Warfley/AsyncNet/blob/master/src/dns/asyncnet.dns.resrecords.pas and https://github.com/Warfley/AsyncNet/blob/master/src/dns/asyncnet.dns.pas

It's not really hard but a bit tedious