Implementation of access plug-ins

As explained in 4, access methods are implemented as dynamically loaded plug-ins. Even the file plug-in that accesses local files is implemented as a plug-in.

Dynamic loading of plug-ins happens during GnomeVFSURI parsing (see section 5.1): the URI is split into its #-separated subparts, the library looks up the access method names (such as file, http and so on), and tries to locate the corresponding plug-in library, by using both a system-wide and a user-wide configuration file called gnome-vfs.conf. If the library is located, it gets linked in dynamically; otherwise, a return code is returned, reporting that the URI is invalid.

Every access method module must provide an initialization function; the initialization function returns a simple vtable containing pointers to the implementations of the GNOME VFS operations for that access method. Pointers to these vtables are stored directly into the GnomeVFSURI object, ready for the first operation to be invoked on it.

At the time of writing, the following modules have been implemented:

• A bzip2 module, for files that are compressed with the bzip program.
• A gzip module, for files that are compressed with the gzip program.
• An ftp method for accessing remote sites through the Internet FTP protocol.
• An http method for accessing remote sites through the HTTP 1.1 protocol. This module also supports WebDAV.
• An extfs module, supporting Midnight Commander's generic archive file support based on simple shell scripts. This multipurpose module makes GNOME VFS able to deal with zip, zoo, rpm, deb, arj and other formats.
• A gconf protocol to access the new GNOME configuration database, called GConf.

Other modules, including a tar one, are being developed.

While this is not supported at the time of writing yet, there are also plans to support CORBA-based access method plug-ins, possibly using the Bonobo component model. [CORBA]

This will have important consequences:

• It will become possible to write plug-ins in any CORBA-aware language. For example, you could have plug-ins written in Perl, Python, or other scripting languages for which CORBA support exists. This will make it extremely simple for people to come up with their own special scripts for special directories or file systems.
• It will become possible to make GNOME VFS see file systems that are implemented in a different process. The external process might be running all the time, and would be contacted through CORBA. For example, you see the list of active print jobs in the print spooler as a normal GNOME VFS directory.