We're investigating porting a fat-client .NET application to be an HTML5-based webapp, but a hangup is that we interface with a variety of usb/serial/shared devices (receipt printers, report printers, specialty archive printers, sigpads, scanners, webcams, etc).
Is there any feasible way to get an HTML5 site the ability to interface with local USB/serial peripherals, or with a local service (e.g., browse to www.site.com/app and have it interact with localhost:1234/api to request things like signatures and send stuff like print jobs)?
The other option I was thinking of is to have a local thin-client type setup, which requests UI elements from the remote server's API, but internally has logic to know what peripherals are doing and passes data via the API.
The least preferential item is to try to write some sort of browser plugin, which is is tied with using a java applet. Silverlight might work, but I haven't researched it too much.
Ideally we'd like to do this to make our app cross-platform, and we're not sure what the best practices are for our situation, or what is the path of least resistance, etc.
Try to embed a web browser into a standalone application and code the interaction in the backend:
Some alternatives:
CEF is cross platform https://code.google.com/p/chromiumembedded/
Old and tried SHDocVw ActiveX for embedding IE using COM on Windows http://msdn.microsoft.com/en-us/library/aa752040(v=vs.85).aspx
You could of course use a local service application to do the dirty work for you and you would have to communicate somehow: WebSockets, AJAX requests. There are ways around the security measures that are coded into modern browsers (cross domain requests and DNS trickery) but the major hurdle will be to get your customers to install a service. If you manage that, then the service could very well serve HTML pages directly and handle requests for peripherals.
Related
I can go to the webpage https://open.spotify.com and select songs that are then immediately played on my desktop spotify application. How does this work? I could imagine a scenario where the webpage sends a request to a server which then tells my desktop application to play, but the website and my application seem too in sync. Sure the web is fast, but the song time counters are perfectly in sync and there is no lag when I click play.
I guess they could do something clever with syncing the song time counter, but I'm wondering if they're dong something even more clever: not using a server at all.
So the real question: Is there a way to have direct communication between a webpage and an application running on the client?
The mechanism is described on How does the Spotify web browser button interact with the Spotify app?. When you install Spotify's desktop application, a process called SpotifyWebHelper runs in the background. This process acts as a local server and receives requests from open.spotify.com to interact with the current playback. As you see, there is a way to communicate a web site and a local application.
It's worth noting that there is an increase concern by browser vendors about this mechanism (see https://bugs.chromium.org/p/chromium/issues/detail?id=378566) and it will stop working at some point in the future. A more future-proof solution could be based on a proxy service that gets requests from the web page and updates your application, and viceversa. Web sockets are a good candidate for this. Although the proxy, acting as a state management service, introduces some delay, it also allows for some other use cases: eg you don't need to have the application installed on the same machine on which the web page is browsed, and one could for instance control a mobile client.
I created a scheduling software for beauty salons as a web application. The idea is that the business owner can schedule customer appointments with a hair stylist. I made it web based because eventually these beauty salons need to integrated into a larger cloud service. So far, I've only put in about 40 hours of coding.
One challenge i am encountering is that a lot of beauty salons may have poor internet connectivity. They may experience temporary outage that last several hours to several days. But during this time, they still want access to this web application .. at the very least for read only purposes.
I understand that html 5 in modern browsers support offline capabilities via things like localStorage and cache manifest. It appears to me that at the moment, I need to do a drastic rewrite of my existing application to make use of localStorage and cache manifest to allow the web application to work offline. The reason this is so is because my web application writes/saves a lot of information to urls like http://mywebsite.com/api/somefunction?queryparams=value1 via ajax calls. These ajax calls need to be replaced by function calls that write to localstorage.
So my questions are:
a) To enable my web application to work offline (at the very least, read only of the website should be offline), I should replace my ajax calls with calls to localStorage. Is this the best approach?
b) Would it have been better to create this application as a .NET desktop application? Especially if there are microsoft technologies that help with synchronizing stored client data with an external database at a later time?
My opinion:
a) I wouldn't say you should replace your Ajax calls. Rather, you want your code to notice when it is offline and store stuff in localStorage then. You wouldn't always store in localStorage as your clients are going to be online sometimes.
b) That's kind of a loaded question I think. :) So... my thinking is this: Building a web site makes sense as it would let your clients at the salon access their data both from computers in the store and other devices as well. So for example - if the salon's internet access is down, the employees could perhaps use your website via their mobile phones too. Having the data be web bound gives them more ways to get to it.
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.
How can I get the MAC address (or something unique for each pc -at least standard user knowledge level-) from client side with js,flash,java or etc. using a crossbrowser method?
You probably know when we are coding a poll we should use cookies to prevent multiple voting.
I couldn't find a crossbrowser javascript method (without MS IEs activex). Javascript, java applet or flash files will be welcome.
Thank you
Caglar
There are no standard Javascript APIs for getting a mac address.
It is possible to get this information using a Java applet, but it would need to be signed and have a policy file in order to access hardware info, and it wouldn't really be transparent to the user. See Getting MAC address on a web page using a Java applet
If you just need to track a client, the most reliable thing you can do is use a combination of APIs available to Javascript to create a persistent cookie. It's possible to create a very resilient cookie using a combination of standard HTTP cookies, session storage APIs, caching tricks, and plugins. Evercookie is a great example: http://samy.pl/evercookie/
You can't do that with JavaScript. Otherwise any one can lure you to visit their website will be able to peek your MAC address, and that would be a security issue. You can only do it through plug-ins. And the browser will have to prompt user to explicitly allow that plugin first.
Is it possible to build an application inside in browser? An application means:
1 Where there is connection (online mode) between the browser and an remote application server:
the application runs in typical web-based mode
the application stores necessary data in offline storage, to be used in offline mode (2)
the application sync/push data (captured during offline mode) back to the server when it is resumed from offline mode back to online mode
2 Where there is no connection (offline mode) between the browser and an remote application server:
the application will still run (javascript?)
the application will present data (which is stored offline) to user
the application can accept input from user (and store/append in offline storage)
Is this possible? If the answer is a yes, is there any (Ruby/Python/PHP) framework being built?
Thanks
Yes, that is possible.
You need to write the application in Javascript, and detect somehow whether the browser is in offline mode (simplest is to poll a server once in a while). (Edit: see comments for a better way to detect offline mode)
Make sure that your application consists of only static HTML, Js and CSS files (or set the caching policy manually in your script so that your browser will remember them in offline mode). Updates to the page are done through JS DOM manipulation, not through the server (a framework such as ExtJS http://www.extjs.com will help you here)
For storage, use a module such as PersistJS ( http://github.com/jeremydurham/persist-js ), which uses the local storage of the browser to keep track of data. When connection is restored, synchronize with the server.
You need to pre-cache images and other assets used, otherwse they will be unavailable in offline mode if you didn't use them before.
Again: the bulk of your app needs to be in javascript, a PHP/Ruby/Python framework will help you little if the server is unreachable. The server is probably kept as simple as possible, a REST-like AJAX API to store and load data.
The "Let's Take This Offline" chapter in Mark Pilgrim's (online) book Dive Into HTML5 is a very nice overview of writing offline web apps with HTML5 technologies.
Note: Since Mark Pilgrim's original Dive Into HTML5 link seems to be down.
Copies can now be found here among other places.
Jake Archibald wrote "The offline cookbook". A modern (9 December 2014) and nice approach with ServiceWorker:
http://jakearchibald.com/2014/offline-cookbook/
The answer in 2018 is to leverage the service worker, and to build a Progressive Web App:
https://developers.google.com/web/progressive-web-apps/
i was looking for this also, i found out abt HTML5 Offline Web Apps. havent tried it tho
Users of typical online Web applications are only able to use the applications while they have a connection to the Internet. When they go offline, they can no longer check their e-mail, browse their calendar appointments, or prepare presentations with their online tools. Meanwhile, native applications provide those features: e-mail clients cache folders locally, calendars store their events locally, presentation packages store their data files locally.
Have a look at Google Gears, http://code.google.com/apis/gears/. Although they have been phased out in favour of HTML5. However, it seems that what is being pushed as HTML5 is Google Gears.