What are my offline and socket options for a modern web application?
So I have been thinking about building quite a complex application. The idea of building an html5 version has become quite an attractive possibility. I have a few questions about it first however.
My first concern is how reliable the offline application API's are at the moment. I have been looking into this standard: http://www.whatwg.org/specs/web-apps/current-work/multipage/offline.html and it looks pretty easy to implement and use, but I am wondering how easy it is to use? And assuming you set up the manifest etc, is the web application just accessed (offline) by going to the same url you originally downloaded the application from?
My other concern is the use of sockets. This offline application still needs to be able to communicate with local servers, I ideally wanted to avoid having to host a web-server, a socket connection however would be plausible. How well do websockets currently work when the browser is offline? Is it possible, to have a fully networked / interactive browser application running even without an active internet connection? (after the app is first downloaded)
Any insight would be great!
That's a lot of questions, you may want to consider breaking it up into more easily answerable portions more directly related to what, exactly, you're trying to achieve. In the meantime I'll try to provide a short answer to each of your questions:
My first concern is how reliable the offline application API's are at the moment.
Fairly reliable, they have been implemented for a number of versions across most major web browsers (except IE).
is the web application just accessed (offline) by going to the same url you originally downloaded the application from?
Yes. Once the offline app has been cached, the application is served from that cache. No network requests will be made unless you explicitly request URLs from the NETWORK or FALLBACK sections of the manifest or aren't covered by the manifest at all, apart from to check whether the manifest itself has changed.
This offline application still needs to be able to communicate with local servers, I ideally wanted to avoid having to host a web-server, a socket connection however would be plausible.
A Web Socket still requires a web server. The initial handshake for a Web Socket is over HTTP. A Web Socket is not the same thing as a socket in TCP/IP.
How well do websockets currently work when the browser is offline?
They won't work at all, when you've set a browser to offline mode it won't make any network requests at all. Note that a browser being set to offline is not the same thing as the offline in 'offline API'. The offline API is primarily concerned with whether or not the server hosting the application can be reached, not whether the the browser is currently connected to a network or whether that network is connected to the internet. If the server goes down then the app is just as 'offline' as if the network cable on the user's computer got unplugged. Have a read through this blog post, in particular the comments. My usual approach to detecting offline status is to set up a pair of files in the FALLBACK section such that you get one when online and the other when offline - request that file with AJAX and see what you get.
Is it possible, to have a fully networked / interactive browser application running even without an active internet connection?
Yes, but I don't think that means what you think it does. Separate instances of the app running on different browsers on different machines would not be able to communicate with each other without going via the web server. However, there's no requirement that the web server be 'on the internet', it will do just fine sitting on the local network.
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