[Zope] Sending an alarm message to all logged-in users

[Sean Hastings]

It is possible to have the clients browser poll the server for a message
every N seconds.

Your standard page template can include a small frame that calls a page
containing an HTML reload directive. The reload would call a function for
maintaining "logged in" state, and returning a page with messages, and
another reload in N seconds command. Your concept of "Logged In" then
becomes any user that still has your page open on their web browser - a user
is no longer "logged in" when the server has not recorded such a request in
the last N+1 seconds. The function could also check for any new server
status or alarm messages and include them in the returned page, display
status messages discreetly in the small frame, and alarm messages as a
JavaScript popup window activated from an onLoad command on the returned
page.

One annoying side effect would be that some browsers play a CLICK noise
whenever reloading a page, and this would happen every N seconds - although
it might serve as a reminder to users that they have left themselves "logged
in" to your system. :-)

--Sean


> -----Original Message-----
> From: zope-bounces at zope.org [mailto:zope-bounces at zope.org]On Behalf Of
> Dennis Allison
> Sent: Monday, October 18, 2004 12:20 AM
> To: Jens Vagelpohl
> Cc: Zope List Mailing
> Subject: Re: [Zope] Sending an alarm message to all logged-in users
>
>
> We have a fairly complex multi-frame presentation.  As I indicated,
> I could do it by doing a test, but that's costly in our particular
> situation.  I'm looking for something a bit lower overhead.
>
> On Sun, 17 Oct 2004, Jens Vagelpohl wrote:
>
> > On Oct 17, 2004, at 18:14, Tino Wildenhain wrote:
> >
> > > Hi,
> > >
> > > Am So, den 17.10.2004 schrieb Dennis Allison um 17:52:
> > >> Occasionally I have wished for a mechanism that would allow me to
> > >> write
> > >> all logged-in users.  Of course, this could be acomplished with an
> > >> explicit test, but making the test costs a lot of overhead.   Is
> > >> there a
> > >> better way?
> > >
> > > HTTP is stateless. There is no such thing like "logged in".
> > > Calls are only send from client to server, never the
> > > other way round. Thus, you cannot "send" something to all
> > > users.
> >
> > One way to fake this out (as Tino already says, the concept of "logged
> > in user" is kind of meaningless) would be to have a slot in your main
> > template that would display something if...
> >
> > - the current visitor has sent valid login information for the request
> > (meaning the user for the duration of the request is not "Anonymous
> > User")
> >
> > - you fill some variable, maybe a property at the site root, or change
> > a script that returns something, with your message.
> >
> > Those things can be tested for easily.
> >
> > jens
> >
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