Question

I have ZipForge for Delphi XE2 & Delphi XE2.

I try to test any invalid zip archives (e.g. not fully downloaded) like in their demo:

procedure TfmMain.bnStartClick(Sender: TObject);
begin
  with Archiver do
  begin
    FileName := 'c:\2.zip';
    OpenArchive;
    try
      TestFiles('*.*');
    except
      MessageDlg('Errors occurred in the archive file', mtError, [mbOk], 0);
    end;
    CloseArchive;
  end;
end;

But my exception doesn’t fire; ZipForge’s dialog fires instead of mine.

I tried Abbrevia Component but it even can’t recognize if an archive is invalid…

Please help me to make my exception working (not ZipForge’s one) or suggest me a better component for zip files with a test feature. Thanks!

Answer 1

Be aware that you can modify ZIP files, e.g. by truncating them somewhat, the ZIP file will still be valid. With my test file, I removed the final 5000 bytes and it was reported as valid. I extracted it successfully using my ZIP program. Of course the extracted contents were incorrect and not the original contents. Perhaps this is what was happening for you. Maybe your attempts to corrupt your ZIP file were not in fact making it into an invalid ZIP file.

Delphi XE2 comes with a built in ZIP component that worked well in my simple test and successfully detected an invalid file, once I had truncated the file enough to make it truly corrupt.

I used the IsValid method to check validity. Here is my very simple test program.

program ZipTest;

{$APPTYPE CONSOLE}

uses
  System.SysUtils, System.Zip;

procedure Main;
const
  ZipArchive = 'C:\desktop\test.zip';
var
  ZipFile: TZipFile;
  FileName: string;
begin
  ZipFile := TZipFile.Create;
  try
    if ZipFile.IsValid(ZipArchive) then begin
      ZipFile.Open(ZipArchive, zmRead);
      for FileName in ZipFile.FileNames do begin
        Writeln(FileName);
      end;
    end else begin
      Writeln(ZipArchive + ' not valid');
    end;
  finally
    ZipFile.Free;
  end;
end;

begin
  try
    Main;
    Readln;
  except
    on E: Exception do begin
      Writeln(E.ClassName, ': ', E.Message);
    end;
  end;
end.