WIP: Enable instructors to grab a learner's session

[fghaas]

For a while now, we've wanted to provide instructors with a way to take over, or share, a learner's session. We might just be able to do so by simply adding the show_in_read_only_mode attribute to the XBlock.

show_in_read_only_mode is an attribute that is False by default, and means that when an instructor is masquerading (that is, using the LMS with "View this course as: Specific learner" option), the XBlock is replaced by the text "This type of component cannot be shown while viewing the course as a specific student" (in lms/djangoapps/courseware/masquerade.py):

def filter_displayed_blocks(block, unused_view, frag, unused_context):
    """
    A wrapper to only show XBlocks that set `show_in_read_only_mode` when masquerading as a specific user.

    We don't want to modify the state of the user we are masquerading as, so we can't show XBlocks
    that store information outside of the XBlock fields API.
    """
    if getattr(block, 'show_in_read_only_mode', False):
        return frag
    return Fragment(
        _(u'This type of component cannot be shown while viewing the course as a specific student.')
    )

Now the first thing we'd need to thus do is to set show_in_read_only_mode to True, so that the XBlock is rendered even when masquerading.

I think (or I hope) that by pointing the instructor's browser at the same Guacamole session as the learner, they'll both be able to interact with the learner's terminal. The devil may very much be in the details. For example, the learner's session might be cut off the moment the instructor connects to it.

Even if so, that may be something that is worth accepting, because the instructor could temporarily take over the learner's session, and when they're done, the learner could just refresh the page. Later on, we could figure out how to actually make the session shareable (if that's even possible).

In addition, making the attribute a read-only property on the XBlock is just a first stab — arguably, it would be smart to make this configurable for course authors.

[codecov]

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[arbrandes]

I've just tested it, and it's way cool! The instructor, when viewing the course as a student, gets to access the stack as one would expect. Staff debug info even gives the correct user info, including stack name.

However, as you feared, it is not possible to access the same session simultaneously. Or at least, not with xrdp, which is what I tested. The last to get in gets access transparently, the first gets a "whoops aborted" message.

Still, not bad. I still have to test suspend/resume behavior, which can't be done reliably on a devstack. guac-dev to the rescue. :)

[fghaas]

Just to mention it, Staff Debug has always given the correct username and stack name; that part has nothing to do what show_in_read_only_mode is set to.

I think what we really need here is exposing connection errors in a more user-friendly fashion. "Whoops! Aborted. See Logs" is pretty terrible UX, if we're being honest. So if we can make this something like "connection to stack lost, this may be due to network connectivity issues", that would be a step in the right direction. Better still if we can word it in a way that tells people to refresh the page except if they have just asked an instructor for help (for in that latter case, they'd probably get a connection but kick the instructor out).

By the way: screen sharing is something that is supported in Guac, if I read https://glyptodon.org/jira/browse/GUAC-844 correctly. So to me this looks like a "doable but perhaps complicated" kind of thing.

[fghaas]

Rebased on current master.

[fghaas]

Note, https://glyptodon.org/jira/browse/GUAC-844 is no longer available but https://issues.apache.org/jira/browse/GUACAMOLE-13 is, and it indicates that the modifications GUAC-844 was meant to track have been merged, and https://guacamole.apache.org/doc/gug/using-guacamole.html#sharing-the-connection now covers connection sharing for the Guacamole Tomcat application.