How To Manually Modify and Rebuild CAB Files

When using the Visual Basic 5.0 Application Setup Wizard to create an Internet Component Download Setup for your ActiveX control or ActiveX document, you may need to modify the CAB file created by the Setup Wizard.

This article describes how to modify the CAB files that the Visual Basic Setup Wizard creates and specifically shows how to extract the files from a CAB file and how to rebuild the CAB file.

For distributing ActiveX components, you may choose to build an Internet Component Download Setup using the Visual Basic 5 Application Setup Wizard.

The wizard creates two key files: an HTM file (Hypertext Markup Language File, also known as HTML file) and a CAB file (Cabinet file, a compressed file). The HTM file contains the information necessary to extract and install the information stored in the CAB file. The CAB file contains the actual components of your OCX, EXE, or DLL.

When you open the HTM file with Internet Explorer (IE), IE executes the <OBJECT> tag within the HTML code. In its simplest terms, an <OBJECT> tag tells Internet Explorer how to install your ActiveX component onto the client machine.

The following is an example of an <OBJECT> tag;

In the <OBJECT> tag above, Internet Explorer uses the ID and CLSID to see if the specified control is already installed on the client computer. If it is not already installed or if it out of date, IE uses the CODEBASE argument to locate the ActiveX.CAB file to install the ActiveX control or document.

The Contents of a .CAB File

A CAB file contains compressed files that are crucial for installing your ActiveX components. The Setup Wizard places an uncompressed copy of each file it placed into your cabinet file into a directory named "Support," which can be found in the same location as the CAB and HTM files.

In all cases, the Setup Wizard will place at least three files in the Support folder: a .DDF file, an ActiveX component file (.EXE, .DLL or .OCX file), and an .INF file.

• .DDF: The DDF file is known as a Diamond Directive File, a text file that may be opened in Notepad or any text editor. The DDF contains specific information required to compress your files into a cabinet file; the DDF file itself is not placed into the CAB file. NOTE: This file should not be modified unless absolutely necessary.
• Component File (.EXE, .DLL or .OCX): The type of ActiveX component you create determines the file extension of the file included here. All ActiveX controls have a .OCX extension. Other ActiveX components either .EXEs or .DLLs. This file is your ActiveX component being installed.
• .INF: This is the Information file that contains information about what other files your ActiveX component depends on (dependency files), where to get copies of those files, and how to install those files.

Extracting the Contents of a CAB File

In order to extract what is in a cabinet file, you must use the Extract utility. Extract.Exe can be found in your Windows folder or on your Windows 95, Windows 98, Windows NT, or Windows 2000 installation CD-ROM.

Extract.Exe is a command-line utility; therefore it is used from an MS-DOS command prompt. To extract the files within a cabinet file, be sure the Extract.Exe utility is in the MS-DOS Path or copy the Extract utility to the same folder as the cabinet file.

From the MS-DOS command prompt, you can run the following command to extract all of the files in a CAB file into the current directory: where "ActiveX.CAB" is the name of your cabinet file.

For more information on using the Extract.Exe utility, you may type the following command at an MS-DOS command prompt: For even more information on Extract.Exe, please see the ActiveX SDK documentation as referred to in the REFERENCES section of this article.

Rebuilding a CAB File

Once you've extracted the files within a CAB, you can make modifications and then proceed to rebuild the CAB file manually.

To rebuild a CAB file, you must use the MakeCab.Exe utility that ships with Visual Basic. The MakeCab utility is installed by default in the following directory: It may also be found on your Visual Basic 5.0 installation CD-ROM in the following directory: To rebuild the cabinet file, place any modified files and the original .DDF file into a single folder. Also, make sure the MakeCab.Exe utility is in the MS-DOS path or copy it to the same folder as the .DDF.

From a command prompt, type the following command: where "ActiveX.DDF" is the name of your .DDF file.

For more information on the MakeCab utility ,you may use the "/?" switch or see the ActiveX SDK documentation as referred to in the REFERENCES section of this article.

Notes on Rebuilding Cabinet Files

Usually, it should not be necessary to modify the files within a cabinet file. However, situations may arise where you need to do so. When modifying cabinet files, please use the following guidelines to avoid problems:

1. Never add or remove files from a CAB file. The only files that should be in a CAB file are those added by the Application Setup Wizard. If you need to add or remove files from the cabinet file, re-run the Application Setup Wizard. Otherwise, you will need to modify the .DDF file.
2. If you modify the INF file, be sure that your changes are syntactically correct and do not contain errors. For more information about modifying INF files, see the ActiveX SDK in the REFERENCES section of this article. Problems with the INF file may result in undesired behavior when the component attempts to download.
3. You should not modify the ActiveX component (.OCX, .EXE or .DLL) in any way. If you feel you need to modify the ActiveX component, rebuild the cabinet file using the Application Setup Wizard.

For more information about how to use the Extract.exe and the MakeCab.exe files and how to modify .ddf or .inf files, see the ActiveX Software Development Kit (SDK) documentation.