(Delphi DLL) Retrieve Metadata from Gzip Data in Memory (BinData)

This example demonstrates how to use the GetGzipInfoBd method to retrieve metadata from Gzip data stored in memory within a BinData object.

The Gzip data is first loaded into the BinData instance. The GetGzipInfoBd method then extracts any available metadata from the Gzip header, including the embedded filename, comment, and optional extra data.

The metadata is returned in a JsonObject. Because these fields are optional, the example checks for the existence of each JSON member using HasMember before retrieving its value.

Note: This example requires Chilkat v11.5.0 or greater.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Gzip, BinData, JsonObject;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
gzip: HCkGzip;
bd: HCkBinData;
json: HCkJsonObject;
filename: PWideChar;
comment: PWideChar;
extraData: PWideChar;

begin
success := False;

// This example demonstrates how to retrieve metadata from Gzip data
// stored in a BinData object.

gzip := CkGzip_Create();
bd := CkBinData_Create();
json := CkJsonObject_Create();

// Load a Gzip file into BinData:
success := CkBinData_LoadFile(bd,'example.txt.gz');
if (success = False) then
  begin
    Memo1.Lines.Add(CkBinData__lastErrorText(bd));
    Exit;
  end;

// Get the metadata information from the in-memory Gzip data:
success := CkGzip_GetGzipInfoBd(gzip,bd,json);
if (success = False) then
  begin
    Memo1.Lines.Add(CkGzip__lastErrorText(gzip));
    Exit;
  end;

// Output the JSON containing metadata:
Memo1.Lines.Add('Gzip metadata JSON:');
Memo1.Lines.Add(CkJsonObject__emit(json));

// Access individual fields only if they exist:

if (CkJsonObject_HasMember(json,'filename') = True) then
  begin
    filename := CkJsonObject__stringOf(json,'filename');
    Memo1.Lines.Add('Filename: ' + filename);
  end;

if (CkJsonObject_HasMember(json,'comment') = True) then
  begin
    comment := CkJsonObject__stringOf(json,'comment');
    Memo1.Lines.Add('Comment: ' + comment);
  end;

if (CkJsonObject_HasMember(json,'extraData') = True) then
  begin
    extraData := CkJsonObject__stringOf(json,'extraData');
    Memo1.Lines.Add('ExtraData (Base64): ' + extraData);
  end;

CkGzip_Dispose(gzip);
CkBinData_Dispose(bd);
CkJsonObject_Dispose(json);

end;