The NSWorkspace class gathers together a large number of capabilities needed for workspace management.

The make_services tool examines all applications (anything with a.app,.debug, or.profile suffix) in the system, local, and user Apps directories, and caches information about the services each app provides (extracted from the Info-gnustep.plist file in each application).

In addition to the cache of services information, it builds a cache of information about all known applications (including information about file types they handle).

NSWorkspace reads the cache and uses it to determine which application to use to open a document and which icon to use to represent that document.

The NSWorkspace API has been extended to provide methods for finding/setting the preferred icon/application for a particular file type. NSWorkspace will use the 'best' icon/application available.

To determine the executable to launch, if there was an Info-gnustep.plist/Info.plist in the app wrapper and it had an NSExecutable field - it uses that name. Otherwise, it tries to use the name of the app - eg. foo.app/foo
The executable is launched by NSTask, which handles the addition of machine/os/library path components as necessary.

To determine the icon for a file, it uses the value from the cache of icons for the file extension, or use an 'unknown' icon.

To determine the icon for a folder, if the folder has a '.app', '.debug' or '.profile' extension - the Info-gnustep.plist file is examined for an 'NSIcon' value and NSWorkspace tries to use that. If there is no value specified - it tries 'foo.app/foo.png' or 'foo.app/foo.tiff' or 'foo.app/.dir.png' or 'foo.app/.dir.tiff'

If the folder was not an application wrapper, it just tries the.dir.png and.dir.tiff file.

If no icon was available, it uses a default folder icon or a special icon for the root directory.

The information about what file types an app can handle needs to be stored in Info-gnustep.plist in an array keyed on the name NSTypes, within which each value is a dictionary.

In the NSTypes fields, NSWorkspace uses NSIcon (the icon to use for the type) NSUnixExtensions (a list of file extensions corresponding to the type) and NSRole (what the app can do with documents of this type Editor, Viewer, or None). In the AppList cache, make_services generates a dictionary, keyed by file extension, whose values are the dictionaries containing the NSTypes dictionaries of each of the apps that handle the extension. The NSWorkspace class makes use of this cache at runtime.

If the Info-gnustep.plist of an application says that it can open files with a particular extension, then when NSWorkspace is asked to open such a file it will attempt to send an -application:openFile: message to the application (which must be handled by the applications delegate). If the application is not running, NSWorkspace will instead attempt to launch the application passing the filename to open after a '-GSFilePath' flag in the command line arguments. For a GNUstep application, the application will recognize this and invoke the -application:openFile: method passing it the file name.

This command line argument mechanism provides a way for non-gnustep applications to be used to open files simply by provideing a wrapper for them containing the appropriate Info-gnustep.plist.
For instance - you could set up xv.app to contain a shellscript 'xv' that would start the real xv binary passing it a file to open if the '-GSFilePath' argument was given. The Info-gnustep.plist file could look like this:

 
 {
   NSExecutable = "xv";
   NSIcon = "xv.png";
   NSTypes = (
     {
       NSIcon = "tiff.tiff";
       NSUnixExtensions = (tiff, tif);
     },
     {
       NSIcon = "xbm.tiff";
       NSUnixExtensions = (xbm);
     }
);
 }