I'm trying to implement some push technology on an app of mine. I intend to use node.js for that but I don't think it is relevant for my question. What I will do is basically long-polling to the server, and as I understand the event driven way nodejs works, I don't have to care much about the server side of the stuff.
My only worry is on the client side: after how much time will the browser stop waiting for the answer ? It is a programming question because I need to release a response before this time is spent, so that the long-polling is reloaded.
Side question : when the browser stops waiting, what answer does it give to the request ?
I have done stuff like this before, and the answer to the question is quite simple: it depends on the browser, and how the user has configured it.
In FF there is a setting somewhere in about:config that controls this (I forget what the setting is, exactly). IE's default timeout is controlled in the registry, and is documented here. I never found the answer for Chrome or Opera - I don't think it's controllable. Opera seems to give up after no data has been received for around 20 seconds, but it also seems to vary somewhat - no idea why.
I concluded that the best thing to do here is to design your architecture so the page is reloaded periodically or if your using AJAX, periodically cancel the request and start a new one (I found that 1 minute works well). Also, keep pushing little bits of data to the browser every few seconds, as this will prevent Opera from giving up. You can simply push a javascript:void(0); event to keep the connection alive but not actually do anything at the client side.
To answer your side question: Nothing. The browser simply closes the TCP connection and no further data is exchanged. How the server handles this is no longer the concern of the browser.