Bug#917126: Bug#874003: Nautilus does not launch applications

[Simon McVittie]

On Sat, 22 Dec 2018 at 20:06:26 -0800, Ross Vandegrift wrote:
> On Sat, Dec 22, 2018 at 11:41:20PM +0000, Simon McVittie wrote:
> > While researching this in codesearch.debian.net I found that e17
> > (Enlightenment) still sets the user-preferred file manager by setting
> > it as an x-scheme-handler/file handler. e17 maintainers, please
> > don't do this: the interoperable freedesktop.org pseudo-MIME-type
> > for a general-purpose file manager like Nautilus, Thunar, Dolphin
> > or (presumably) enlightenment_filemanager is inode/directory, and
> > enlightenment_filemanager's desktop file already announces it as an
> > inode/directory handler.
> 
> Untested patch attached.  I'm travelling the next week and may not have time to
> test/package until January.

I don't use enlightenment myself, but the patch looks like what I had
in mind.

> I don't know the fdo specs well, but this behavior of x-scheme-handler/file
> seems like a pretty bad misfeature to me.  Does it exist only for the gdm3
> use-case?

x-scheme-handler/file isn't really a feature at all, more a consequence
of a more general feature that *is* useful. It makes a lot more sense
to set a handler for all mailto URLs (for example associating Evolution
or Mutt with x-scheme-handler/mailto), or for all rtsp URLs (for example
associating a media player with x-scheme-handler/rtsp), or for all xmpp
URLs, or any other single-purpose URL scheme. x-scheme-handler/http for
general-purpose web browsers like Firefox and Chromium is perhaps a bit
more of a stretch (because there are lots of things you can do over HTTP
that aren't browsing the web interactively) but still makes some sense,
because if you have a http URL out-of-context and you are told to open it,
what else would you do with it other than open a web browser? But setting
a single handler for all of x-scheme-handler/file is only ever going
to block useful functionality, because it's a much broader match than
anything you'd want to do under normal circumstances.

gdm3 uses x-scheme-handler/file because it *wants* to block useful
functionality: the idea is to make sure there is no way to trick the
greeter session into opening a normal application. This is exploiting a
side-effect of a consequence of the x-scheme-handler design, more than
something that was designed in.

Whenever a design provides a very general mechanism, there will be
things you can do with that mechanism that don't really make sense. For
instance, POSIX scripts start with #! and the path to an interpreter,
so if you wanted to, you could write a #!/bin/rm script that deletes
itself, or a #!/bin/cat script that is a quine; either would be pointless,
but both are just as valid as a #!/bin/sh script.

    smcv