Pascal (Lazarus/Delphi)

Prefetch a DKIM Public Key from DNS

Demonstrates the Chilkat Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and caches it for a specific selector and domain. The arguments are the selector and the domain. The TXT lookup is made at selector._domainkey.domain.

Background: DkimVerify already fetches the key from DNS on demand, so prefetching is about when the lookup happens: doing it up front lets you separate a potentially slow network step from the verification itself, warm the cache before a batch of messages from the same domain, or confirm the key is publishable before relying on it. After a successful prefetch, verification of a matching signature uses the cached key with no further DNS traffic.

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Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Dkim;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  dkim: TDkim;

begin
  success := False;

  //  Demonstrates the Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and
  //  caches it for a specific selector and domain.  The 1st argument is the selector and the 2nd is
  //  the domain.

  dkim := TDkim.Create;

  //  Retrieve the public key from the DNS TXT record at selector._domainkey.domain and cache it.
  //  A later DkimVerify for the same selector and domain then uses the cached key.
  success := dkim.PrefetchPublicKey('myselector','example.com');
  if (success = False) then
    begin
      WriteLn(dkim.LastErrorText);
      Exit;
    end;
  WriteLn('Public key prefetched from DNS and cached.');


  dkim.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.