ZipArchive: Self-Extracting Archives

Self-Extracting Archives

Applies To: All But Multi-Segment Archives

Introduction
Creating a Self-Extracting Archive

Introduction

A self-extracting archive contains an executable stub added at the beginning, which handles the archive extraction.
The ZipArchive Library automatically detects self-extracting archives.

Creating a Self-Extracting Archive

First you need to create a self-extracting executable stub. The following sample code shows an example of it.

Sample Code

//Windows code
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE, LPSTR,    int)
{
    CZipArchive zip;
    // get the path of the executable
    TCHAR szBuff[_MAX_PATH];
    if (!::GetModuleFileName(hInstance, szBuff, _MAX_PATH))
        return -1;
    CZipString szDest;
    // ...
    // add some code here to get additional information from the user
    // such as the destination directory or a password, if needed
    zip.Open(szBuff, CZipArchive::zipOpenReadOnly); 
    // zipOpenReadOnly mode is necessary for self extract archives
    for (ZIP_INDEX_TYPE i = 0; i < zip.GetCount(); i++)
        zip.ExtractFile(i, szDest);
    zip.Close();
    return 0;
}

Appending Archive to Self-Extracting Stub

To create a self-extracting archive, create a new archive using the CZipArchive::zipCreateAppend mode and pass the path of your self-extracting stub to the
CZipArchive::Open(LPCTSTR) method. Then, you can for example add some files to it. This will create a self-extracting archive that is compatible with popular archivers.

Sample Code

CZipArchive zip;
zip.Open(_T("C:\\Temp\\my-sf-stub.exe"), CZipArchive::zipCreateAppend);
// now add some files
zip.AddNewFiles(_T("d:\\My Documents"), _T("*.doc"));
zip.Close();
// now your file z:\Temp\my-sf-stub.exe is a self-extracting archive.

You can later open the archive for modifications. In case you need it, the offset of the first file in the archive tells you the size of the self-extracting stub:

Sample Code

CZipArchive zip;
zip.Open(_T("C:\\Temp\\my-sf-stub.exe"));
ZIP_SIZE_TYPE stubSize = zip.GetFileInfo(0)->m_uOffset;
//...
zip.Close();

Converting Existing Archive to Self-Extracting Archive

To convert an existing archive into a self-extracting archive, use one of the following methods:

CZipArchive::ShiftData() - to make space at the beginning of the archive for a self-extracting stub. You can then copy your stub into this free space.
CZipArchive::PrependData(CZipAbstractFile&, LPCTSTR) - to copy your self-extracting stub contained in a file (it can be a memory file) to the beginning of the archive. This method can also change the extension of the archive (in this case the archive is closed). This method performs necessary shifting of the data.
CZipArchive::PrependData(LPCTSTR, LPCTSTR) - behaves similarly to the above method, but reads a self-extracting stub from a disk file.

All these method create self-extracting archives compatible with popular archivers.

Sample Code

CZipArchive zip;
zip.Open(_T("C:\\Temp\\test.zip"));
zip.PrependData(_T("C:\\Temp\\my-sf-stub.exe"));
// renaming is performed (lpszExt is not NULL) 
// so the archive will be closed after prepending
// now we have z:\temp\test.exe file that can be executed

Callbacks Called

While shifting data, the CZipActionCallback::cbMoveData callback is called. To read more about using callback objects, see Progress Notifications: Using Callback Objects.

Additional Considerations

For the data shifting and prepending methods to work, the following conditions must be satisfied:

The archive must be opened.
No file must be opened for compression or extraction.
The archive must not be a segmented archive.
There must be no bytes before the archive (the CZipArchive::GetBytesBeforeZip() method should return 0).

Binary Prepending

You can prepend a self-extracting stub to an existing archive without shifting data, e.g. using the following DOS command: copy /b Stub.exe + Archive.zip SelfExtract.exe

The ZipArchive Library will correctly operate on such archives, but they may be not compatible with other software.
You can request the size of the executable stub with the
CZipArchive::GetBytesBeforeZip() method.
This method will not work for archives in the Zip64 format (for the information about the Zip64 format, see Zip64 Format: Crossing the Limits of File Sizes and Number of Files and Segments).

Article ID: 0610242241