How should I implement bi-directional networking between an iPhone application and an Objective-C server-side application?

I'm looking for advice on the best way to implement some kind of bi-directional communication between a "server-side" application, written in Objective-C and running on a mac, and a client application running on an iPhone.

To cut a long story short, I'm adapting an existing library for use in a client-server environment. The library (which runs on the server) is basically a search engine which provides periodic results, and additionally can provide updates for any of those results at a later date. In an ideal world therefore I would be able to achieve the following with my hypothetical networking solution:

• Start queries on the server.
• Have the server "push" results to the client as they arrive.
• Have the server "push" updates to individual results to the client as they arrive.

If I was writing this client to run on another Mac, I might well look at using Distributed Objects to mask the fact that the server was actually running remotely, but DO is not available on an iPhone.

If I was writing a more generic client-server application I would probably look at using HTTP to provide some kind of RESTful interface to searches, but this solution does not lend itself well to asynchronous updates and additionally what I am proposing doe开发者_如何学运维s not fit well with the "stateless" tennet of REST: I would have to model my protocol so I "created" a search resource that I could subsequently query the state of and I would have to poll for updates to it.

One suggestion someone made was to make use of something like BLIP to provide me with a two-way pipe between the client and the server and implement my own "proxy" type objects for the server-side resources that knew how to fetch data from the server and additionally were addressable so that the server could push updates to them. Whilst BLIP provides the low-level messaging framework needed to communicate bi-directionally it still leaves me with a few questions:

• How will I manage the lifetime of the objects on the server? I can have a message type that "creates" a search object, but when should that object be destroyed?
• How well with this perform on an iPhone: if I have a persistent connection to the server will this drain the batteries too fast? This question is also pertinent in the HTTP world: most async updates are done using a COMET type hack which again requires a persistent connection.

So right now I'm still completely unsure what the best way to go is: I've done a lot of searching and reading but have not settled on any solution. I'm asking here on SO because I'm sure that there are many of you out there who have already solved this problem.

How have you gone about achieving real-time bidirectional networking between the iPhone and an Objective-C server-side app?