Add gio backend

[Michael Terry]

It would be nice if duplicity had a gio backend. That way it could accept any gio-supported schema and wouldn't have to worry about a lot of common server types. Or at least, gio-capable apps (like deja-dup) could pass them along.

In theory this means you could abandon the temperamental ssh and ftp backends (and webdav), but from my experience with your userbase, they would not want gio (and thus glib) to be used by default.

Since gio has its own set of schemas, it makes sense to trigger the gio backend not with a schema, but with a command line switch like --gio. Then the gio backend would be forced on, regardless of schema. The URL would then be passed on to the backend.

I'm partway through this work. Let me know if you see any major problems with the idea before I finish it! :)

[Michael Terry (mterry)]

Oh yeah, and gio probably requires the use of dbus, so it may not be very suitable for the general use case of running in a cron job. But it's still valuable for me and other use cases.

[Michael Terry (mterry)]

OK, here's the patch. Ignore my 'not suitable for cron' statement. I added code to start a session dbus if one isn't available, so everything works out.

This backend requires the use of the glib and gio python modules as well as the use of dbus. But it's not loaded by default. Only if the --gio argument is passed on the command line.

I've added tests for it and man and --help entries.

[Michael Terry (mterry)]

Whoops, here's an ever-so-slightly better one that doesn't use the wrong exception class in a couple 'except' statements.

[Kenneth Loafman (kenneth-loafman)]

Do we have any documentation on what GIO schema's look like?

[Michael Terry (mterry)]

Uh, no, actually. Couldn't find any easy stuff. The URIs all look the same:

schema://username@server/path

But I'm not sure of the list of schemas. Not all backends have the same features. Like they have an http:// schema, but you can't write to it. They have some goofy ones too, like gphoto2:// for talking to cameras. I couldn't find a concise list of schemas and what they supported...