capabilities : Java Glossary

The capabilities scheme has been replaced by a totally different scheme controlled by a policy file in Java 1.2+. Capabilities are called permissions in 1.3+.

Overview

To get out of the Java sandbox using Netscape 4.79, you must digitally sign your Applet and you have to use the netscape.security. PrivilegeManager class. When you its enablePrivilege method for the first time, a dialog box will automatically be prompted to ask the user to grant this privilege. If the user grants it, the privilege will be enabled during the lifetime of the method. This means that you have to ask for this privilege again if you want to use it in another method. In this case, of course, if the user previously granted the privilege, the dialog box won’t be prompted again.

If the user denies the privilege, or if you misspell it, you will trigger a netscape.security. ForbiddenTargetException. If you attempt a restricted action without getting permission first, you will trigger a netscape.security. AppletSecurityException.

The Code

Gotchas

You must put the Netscape 4.79 security classes on your classpath when you compile. They live in:

\program files\netscape\communicator\program\java\classes\java40.jar

Netscape 7.1 does not use this scheme. It uses the Sun policy file based scheme instead.

According to RJHM van den Bergh <rvdb@nedernet.nl>, on Windows, there are some bugs in the Netscape capabilities. For example, you may have to ask for UniversalConnect when you really wanted UniversalFileAccess. I discovered that FullInstall is not recognised. However, by peeking inside \Program Files\netscape\communicator\program\java\classes\java40.jar at the target.class and AppletSecurity.class with a hex viewer, you can guess what those twits at Netscape really called their targets. For example FullInstall is actually called SoftwareInstall. UniversalClassLoaderAccess for letting you use a ClassLoader is both undocumented and it does not work.

When you run System.loadLibrary in static init code, you must disarm the Netscape security manager with:

PrivilegeManager.enablePrivilege( "UniversalLinkAccess" );

in the static init code, even though the code that is indirectly calling that static init code may have already disarmed it.

System.loadLibrary fails for some reason if the DLL (Dynamic Link Library) was not present at the time Netscape fired up. The System. .loadLibrary can’t seem to see a DLL installed dynamically. This makes no sense since the DLL is not loaded until System. .loadLibrary is called. Even more baffling is why System. load would show the same behaviour. Mark Leone tells me you must not have your app in a jar for System. load to work.

Targets & Capablities

The Netscape documentation on capabilities is abominable. So I created this table by looking for human-readable strings in the binary file Target.class. I then tested all the strings to see which ones really worked in PrivilegeManager.. enablePrivilege and what the grant dialog said it was for. This list might not be complete. However, it is more accurate than Netscape’s.