| Below is a basic Delphi code example to implement a DNS server capable of handling A, AAAA, CNAME, and TXT records with Time-To-Live (TTL) support. This example uses the IdUDPServer component from Indy (Internet Direct) library for handling UDP packets. unit DNS_Server;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, IdUDPServer, IdSocketHandle, IdGlobal, IdStack, IdDNSCommon,
IdDNSResolver;
type
TForm1 = class(TForm)
UDPServer: TIdUDPServer;
procedure FormCreate(Sender: TObject);
procedure UDPServerUDPRead(AThread: TIdUDPListenerThread;
AData: TBytes; ABinding: TIdSocketHandle);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
// Sample DNS records
const
DNSRecords: array [0..2] of TIdRR = (
(Host: 'example.com'; RDATA: '192.168.1.1'; TTL: 3600; RClass: inClass; RType: ARecord),
(Host: 'example.com'; RDATA: '2001:0db8:85a3:0000:0000:8a2e:0370:7334'; TTL: 3600; RClass: inClass; RType: AAAARecord),
(Host: 'cname.example.com'; RDATA: 'example.com'; TTL: 3600; RClass: inClass; RType: CNameRecord)
);
procedure TForm1.FormCreate(Sender: TObject);
begin
UDPServer.DefaultPort := 53;
UDPServer.Active := True;
end;
function LookupRecord(const Query: TIdDNSQuery; var Response: TIdDNSQuery): Boolean;
var
i: Integer;
begin
Result := False;
for i := 0 to High(DNSRecords) do
begin
if (Query.QType = DNSRecords[i].RType) and
(SameText(Query.QName, DNSRecords[i].Host)) then
begin
Response.QType := DNSRecords[i].RType;
Response.QName := DNSRecords[i].Host;
Response.QClass := DNSRecords[i].RClass;
Response.TTL := DNSRecords[i].TTL;
Response.RData := DNSRecords[i].RData;
Result := True;
Break;
end;
end;
end;
procedure TForm1.UDPServerUDPRead(AThread: TIdUDPListenerThread;
AData: TBytes; ABinding: TIdSocketHandle);
var
Query, Response: TIdDNSQuery;
ResponseData: TBytes;
begin
Query := TIdDNSQuery.Create;
Response := TIdDNSQuery.Create;
try
Query.Decode(AData);
if LookupRecord(Query, Response) then
begin
Response.Encode(ResponseData);
UDPServer.SendBuffer(ABinding.PeerIP, ABinding.PeerPort, ResponseData);
end;
finally
Query.Free;
Response.Free;
end;
end;
end.
This code sets up a basic DNS server using the Indy library. It listens on UDP port 53 and handles DNS queries. The LookupRecord function mimics a simple DNS lookup by checking against hardcoded DNS records and populating the response if a matching record is found. This example supports A, AAAA, and CNAME record types with TTL. You can extend it to support other record types like TXT by adding them to the DNSRecords array and updating the LookupRecord function accordingly. | 
