Destroying liftSession from within a comet request gives NullPointerException

[Matt Feury]

Greetings,

I'm attempting to force logout on a user. My flow is as such:

1. Comets get sent a BootUser message

2. The comet handler for this message calls UserSessions.logout and returns a reload command

However, in my logout method I'm attempting to destroy the liftSession (S.session) by calling destroySession. This seems to consistently result in a NullPointerException (at LiftSession.scala:711). 

Is there some issue with getting the request/session while in a comet? How can this session properly be destroyed?

thanks,

Matt

(I am on 2.3-M1)

[Diego Medina]

You are getting a NPE because a comet actor can be on several browser
windows belonging to different users/ sessions. How about using a
regular snippet to destroy the session and after that send a message
to your comet actor to refresh or update the page?

You can use something like this to send your comet a message from a snippet

for (sess <- S.session) sess.sendCometActorMessage(
"CometClassNameHere", Full("messageAsString"), cometNameIThink
)

Regards.

Diego

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[Peter Brant]

Actually comet actors are associated with a single session (and hence
a single user). They might be sending updates to several tabs or
windows though. On the other hand, they are independent of any given
request. I suspect it's the lack of an underlying request instance
that's causing the NPE (i.e. at some point
HttpServletRequest#getSession() is being called on a null
HttpServletRequest). We might be able to handle this more gracefully,
but I agree with Diego that your approach sounds more complicated than
it needs to be.

Pete

[Antonio Salazar Cardozo]

Yeah it's not actually possible to run it in a snippet, I'm afraid. What we're trying to do is put a user suspension/ban into effect. The state is saved to the database and then the user is `kicked'. The suspension/ban is executed by another user (a moderator), travels to an actor, and then the actor sends a message to the various comets telling them they've been kicked. The comet then logs its session out, which destroys the liftSession.

That's where we're getting the nullpointer. A new approach is forming in my mind at the moment, but it would still be awesome if this one could work for simplicity's sake.

Thanks,

Antonio

[Peter Brant]

I wonder if there are any issues with holding onto the HttpSession
object in the actor. I know the HttpServletRequest instance can only
be used during request processing, but I don't know if any similar
rules exist for HttpSession.

Pete

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[Diego Medina]

Sent from my cell
Diego

On Aug 11, 2011 3:55 PM, "Antonio Salazar Cardozo" <savedf...@gmail.com> wrote:
>
> Yeah it's not actually possible to run it in a snippet, I'm afraid.

I haven't tried this yet but from your comet you can do a SetHtml (id, S.RunTemplate (name here))

And in that template you can have your snippet do the logout

I can expand later tonight when I have more time

Diego

What we're trying to do is put a user suspension/ban into effect. The state is saved to the database and then the user is `kicked'. The suspension/ban is executed by another user (a moderator), travels to an actor, and then the actor sends a message to the various comets telling them they've been kicked. The comet then logs its session out, which destroys the liftSession.
>
> That's where we're getting the nullpointer. A new approach is forming in my mind at the moment, but it would still be awesome if this one could work for simplicity's sake.
> Thanks,
> Antonio
>

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[David Pollak]

On Wed, Aug 10, 2011 at 12:31 PM, Matt Feury <matt...@gmail.com> wrote:

Greetings,

I'm attempting to force logout on a user. My flow is as such:

1. Comets get sent a BootUser message

2. The comet handler for this message calls UserSessions.logout and returns a reload command

However, in my logout method I'm attempting to destroy the liftSession (S.session) by calling destroySession. This seems to consistently result in a NullPointerException (at LiftSession.scala:711). 

The issue is that the Req instance that is used in CometActors is a mock Req instance that is not associated with a session.  It's a bug that Lift throws an NPE... please open a ticket at http://ticket.liftweb.net (you must be a watcher of the LiftWeb space on Assembla to open tickets.)
 

Is there some issue with getting the request/session while in a comet? How can this session properly be destroyed?

I'd suggest doing a partialUpdate(RedirectTo("/user_mgt/logout")) in your CometActor.  That will redirect all tabs that have the CometActor open to the logout page.  The logout page will destroy the session.

Does that help?
 

thanks,

Matt

(I am on 2.3-M1)

Please upgrade to Lift 2.3 or 2.4-M3.
 

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[Tim Williams]

I think this also causes an issue when unit testing with logged in users.

e.g. taking the assembla example and adding below line after the login call also results in a NPE from the destroySessions method.

User.logUserOut()

http://www.assembla.com/spaces/liftweb/wiki/Unit_Testing_Snippets_With_A_Logged_In_User

I'm trying to test whether User object is correctly tracking how many users are logged in, not sure if there is a different logout method I should be using.