Calling function on remote server.

[John Andrews]

So I have a Scala/Lift application, using CometActors and REST. I'm trying to figure out if there's a secure methodology such that I can call a function on one server from another Scala/Lift application on a different server.

This is mostly to get around the Same Origin Policy, but I'm not particular on where this is done client/javascript side or server side. In essence I'm trying to make it so that when I click a button on a client to 'Play' the other open server/client is told to 'Play' as well.

There's a few things I've read about Ajax and XMLHttpRequest (as well as other things that use Flash/iFrame which isn't helpful for a Lift app) but most seem hacky/subverting security and I want to see if there's a nice Java/Scala/Lift solution.

Anyone have any ideas the best method to do this, and if it can be secureable?

[Diego Medina]

For this I would do the communication on the server side, using something like a message queue (RabbitMQ, etc)

Where you can pass information from server A in, let's say json, which will include enough info for server B to "start playing".

Something along the lines of what I wrote here: http://blog.fmpwizard.com/blog/distributed-comet-chat-lift but instead of using couchDB, just use a message queue.

Hope that helps.

Diego

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Diego Medina
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[Antonio Salazar Cardozo]

There are another couple of options:

 - Using CORS to allow a call from the page on server B to reach server A. Provided

   the right headers, this should be transparent to the AJAX code, I believe.

 - Using JSONP in your responses, though this means you won't be able to use the

   default Lift mechanism for AJAX requests, as you need to create them in a JSONP-

   compatible way. This can get nasty.

Thanks,

Antonio

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[John Andrews]

Yeah I saw JSONP - but I quickly saw that would mess with Ajax and Lift so that's out. I'll see if CORS is possible, but hopefully Diego's RabbitMQ is feasible as I think this is preferable to work server side so that Lift/Ajax isn't impacted.

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[Antonio Salazar Cardozo]

Cool, as long as you have a way forward :)

Thanks,

Antonio

[John Andrews]

I've been looking at examples for CORS, and none of them seem to actually outline how you would make a call on 1 server, and what the other server actually does. Most just go into specifics of 'you must do this for cross-origin and headers' without really specifying where any of that goes. Do you know of a good example that shows "Press Button on A, Function on B is called" - and details how CORS accomplishes this?

[Antonio Salazar Cardozo]

CORS is just a way of telling the browser that it's allowed to do a cross-domain request. Once

that is allowed, everything else looks exactly the same way a standard AJAX request would. It's

just that without CORS, you can only make such a request to the same domain that the page

is served from.

Thanks,

Antonio

[Diego Medina]

This page shows a good outline on the topic,
https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS

And to be more specific, if you control both, server A and server B, and the user is on server A and needs to send an ajax request to server B, on server B you need to setup the LiftRule to add the header:

Access-Control-Allow-Origin: http://serverA.com

Hope that helps.