Lazarus Pascal

Add Custom Extra Data to a Gzip File

This example demonstrates how to use the SetExtraData method to include custom binary data in the Gzip header using a hex-encoded string.

The hex string represents the raw bytes to embed in the Gzip metadata. When a compression method is called, this data is included in the Gzip header.

The example also shows how to retrieve the metadata using GetGzipInfo to verify that the extra data was successfully embedded. The retrieved value is returned as a Base64-encoded string.

Lazarus Pascal

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.JsonObject,
  Chilkat.Gzip;

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

procedure RunDemo;
var
  success: Boolean;
  gzip: TGzip;
  json: TJsonObject;
  inputFile: string;
  outputFile: string;

begin
  success := False;

  //  This example demonstrates how to include custom extra data
  //  in the Gzip header when compressing.

  //  The extra data is provided as a hex-encoded string.

  gzip := TGzip.Create;
  json := TJsonObject.Create;

  //  Set extra data using a hex string.
  //  This example represents 4 bytes: 00 01 02 03
  success := gzip.SetExtraData('00010203','hex');
  if (success = False) then
    begin
      WriteLn(gzip.LastErrorText);
      Exit;
    end;

  //  Compress a file so the extra data is embedded in the Gzip header:
  inputFile := 'example.txt';
  outputFile := 'example.txt.gz';

  success := gzip.CompressFile(inputFile,outputFile);
  if (success = False) then
    begin
      WriteLn(gzip.LastErrorText);
      Exit;
    end;

  WriteLn('Gzip file created with extra data.');

  //  (Optional) Retrieve the metadata to verify:
  success := gzip.GetGzipInfo(outputFile,json);
  if (success = False) then
    begin
      WriteLn(gzip.LastErrorText);
      Exit;
    end;

  WriteLn('Metadata JSON:');
  WriteLn(json.Emit());


  gzip.Free;
  json.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.