问题
In almost every long polling examples I see, there is something like a timeout of 30 seconds client-side. What is the precise reason for this?
回答1:
Some routers, proxies or whatever device there is in the middle might decide to drop TCP/IP connections being idle for extensive period of time. Also refreshing connection once in a while makes sure you'll discover server failure quicker.
来源：https://stackoverflow.com/questions/14903223/why-setting-a-client-side-timeout-when-using-long-polling