We've developed a web application which is hosted on premises available for people in the shop floor via Wifi. However, the wifi signal is not reliable and it's not possible to use wired network or improve the signal.
I am looking for a solution to handle this issue. Is there a way to put the http requests into a local queue and process it asynchronously at the background? If so, how to do it? Or is there any other alternative approach?
Any thoughts are greatly appreciated.
I have the same problem in the company where I work, there are certain places where the WiFi can not reach, and the system needs to get information from the DB in order to show that info to the user and then upload some new info.
Part of this system is done with iPads, so to solve the problem I use LocalStorage to store a JSON object that contains the info the user need to work, I store the info that is going to be uploaded in another JSON object, and when there is a connection available the info is Uploaded.
Hope it helps
I would recommend to build the web app with angularjs or another javascript framework of your choice. Once the user has loaded the site you can perform asynchronous ajax/http requests to load the required data and the web app will never reload the entire page.
In case one http request fails you can implement that the web app should try one more time or whatever :)
Related
I am wondering about what the best way to keep users in sync with each other in a social network is. The concerned stack is an iOS app with a NodeJS backend. Let me give you an example:
Say X and Y are friends on a social network. Y's posts appear in X's feed, and as such, Y is cached somewhere on the X's phone. This morning, Y decided to change profile pictures however. Everything is well, the new picture is uploaded to the server, but how do we go about letting X know about the change of profile picture?
My possible solution: Create a route /<UID>/updates that contains a stack of "cookies" which lets the user know what and who changed since the last time they made a GET request to the route.
This seems elegant enough, but what worries me is what happens on the client side (am I supposed to make a GET request every 2 minutes during my app's uptime?). Are there any other solutions?
One solution is indeed to poll the server, but that's not very elegant. A better way is to make use of websockets:
WebSockets is an advanced technology that makes it possible to open an interactive communication session between the user's browser and a server. With this API, you can send messages to a server and receive event-driven responses without having to poll the server for a reply.
They are a 2-way connection between client and server, allowing the server to notify the client of any changes. This is the underlying technology used in the Meteor framework for example.
Take a look at this blogpost for an example of how to use websockets between an iOS client and a NodeJS backend. They make use of the open source SocketRocket iOS library.
I have a specific issue where I'm using WebRTC (voice and video).
I want to keep a connection/voice/video streams alive between webpages on a website. I thought I could use shared web workers to run in the background?
Any guidance would be great. I've looked at other posts but they're quite old and wondered if anyone had any, more, up-to-date information or ways I could tackle this issue?
UPDATE:
Shared Web Workers are the incorrect way of tackling this problem. Service Workers are the way forward for maintaining after the web page is terminated.
Keeping the webRTC connection alive between page loads seems like a rare use case. Normally, you start a call and remain on a single page. I guess it could make sense if you wanted to embed a customer support like webRTC widget on a site and have that widget follow a user through page navigations under a single domain.
I don't think saving/reusing the blob URL will allow you to reconnect on a page reload for security issues/hijacking potential.
There is the IceRestart constraint which might help. Apparently you can save the SDP info to local storage, reuse the negotiated SDP, then call an IceRestart to quickly reconnect.
As described in section 3, the nominated ICE candidate pair is
exchanged during an SDP offer/answer procedure, which is maintained
by the JavaScript. The JavaScript can save the SDP information on
the application server or in browser local storage. When a page
reload has happened, a new JavaScript will be reloaded, which will
create a new PeerConnection and retrieve the saved SDP information
including the previous nominated candidate pair. Then the JavaScript
can request the previous resource by sending a setLocalDescription(),
which includes the saved SDP information. Instead of restart an ICE
procedure without additional action hints, the new JavaScript SHALL
send an updateIce() which indicates that it has happended because of
a page reload. If the ICE agent then can allocate the previous
resource for the new JavaScript, it will use the previous nominated
candidate pair for the first connectivity check, and if it succeeds
the ICE agent will keep it marked as selected. The ICE agent can now
send media using this candidate pair, even if it is running in
Regular Nomination mode.
https://bugs.chromium.org/p/webrtc/issues/detail?id=979
https://datatracker.ietf.org/doc/html/draft-li-rtcweb-ice-page-reload-02
I am making an iOS app that will display images, videos, and textual information that I provide.
this information needs to be updated and refreshed as the user requests, time interval, and when the user opens the app. Not hardcoded and changed on app store updates.
How would i go about doing this?
Do I need to create an online web server that I pull the information from?
If so how would I go about creating a server?
Could anyone point me in the correct direction?
yeah you have to use web Services. that means you have to create one server & from that server you can send images,text as you required without making hardcoded. you just have to pull the value from web service.
images,text all this can be send through xml & you have to accept that xml & have to parse it
You can install an Apache server on your MacOS, read read this:
http://osxdaily.com/2012/09/02/start-apache-web-server-mac-os-x/
I ended up using parse which has excellent mobile support. And is free until you receive a certain amount of traction. I recommend it!
I'm just starting to learn about iOS development, and I figure the best way to get started is to build a simple (but non-trivial) app. My idea is this: have a web interface where a user can create a survey, and then access those surveys through the app and send responses back to the server. The web design part probably won't be terribly difficult -- I've done similar things with Django before. The part that will require learning/effort is the iPhone app.
I've got enough Objective-C that the data structures (model) won't be hard to code, and the UI (view, controller) part shouldn't be bad either. I predict that the interface between web and phone will be difficult, though. In particular, how will I be able to access the database on the server from the phone? I'd like to have a single DB that both web and phone apps use.
What I'd really like to have is a general, broad-strokes description of what I'll need to do to get this all up and running. Am I right in believing that the networking will be the hardest part? Are there any other possible snags? Any advice, or pointers to good resources on the subject, would be greatly appreciated.
Networking will probably not be the hardest part here, you're just guessing because that aspect is unfamiliar to you. For example, you can use NSURLConnection to take care of pretty much all the details of server connection. You can use NSJSONSerialization to convert your data to and from a format that is suitable for sending over the wire.
Basically what you might do is:
Mobile app sends a HTTP GET request to the server for survey info.
Server responds with a JSON description of the survey.
User fills out survey.
When done, the app sends the responses back in JSON format as a HTTP POST to the server.
Server stores the results in the database.
One of the key points here is that the app on the phone does not try to access the database directly. All requests go through your Django web app.
I am to build a web application which will accept different events from external sources and present them quickly to the user for further actions. I want to use Ruby on Rails for the web application. This project is a internal development project. I would prefer simple and easy to use solutions for rapid development over high reliable and complex systems.
What it should do
The user has the web application opened in his browser. Now an phone call comes is. The phone call is registered by a PBX monitoring daemon. In this case via the Asterisk Manager Interface. The daemon sends the available information (remote extension, local extension, call direction, channel status, start time, end time) somehow to the web application. Next the user receives a notified about the phone call event. The user now can work with this. For example by entering a summary or by matching the call to a customer profile.
The duration from the first event on the PBX (e.g. the creation of a new channel) to the popup notification in the browser should be short. Given a fast network I would like to be within two seconds. The single pieces of information about an event are created asynchronously. The local extension may be supplied separate from the remote extension. The user can enter a summary before the call has ended. The end time, new status etc. will show up on the interface as soon as one party has hung up.
The PBX monitor is just one data source. There will be more monitors like email or a request via a web form. The monitoring daemons will not necessarily run on the same host as the database or web server. I do not image the application will serve thousands of logged in users or concurrent requests soon. But from the design 200 users with maybe about the same number of events per minute should not be a scalability issue.
How should I do?
I am interested to know how you would design such an application. What technologies would you suggest? How do the daemons communicate their information? When and by whom is the data about an event stored into the main database? How does the user get notified? Should the browser receive a complete dataset on behalf of a daemon or just a short note that new data is available? Which JS library to use and how to create the necessary code on the server side?
On my research I came across a lot of possibilities: Message brokers, queue services, some rails background task solutions, HTTP Push services, XMPP and so on. Some products I am going to look into: ActiveMQ, Starling and Workling, Juggernaut and Bosh.
Maybe I am aiming too hight? If there is a simpler or easier way, like just using the XML or JSON interface of Rails, I would like to read this even more.
I hope the text is not too long :)
Thanks.
If you want to skip Java and Flash, perhaps it makes sense to use a technology in the Comet family to do the push from the server to the browser?
http://en.wikipedia.org/wiki/Comet_%28programming%29
For the sake of simplicity, for notifications from daemons to the Web browser, I'd leave Rails in the middle, create a RESTful interface to that Rails application, and have all of the daemons report to it. Then in your daemons you can do something as simple as use curl or libcurl to post the notifications. The Rails app would then be responsible for collecting the incoming notifications from the various sources and reporting them to the browser, either via JavaScript using a Comet solution or via some kind of fatter client implemented using Flash or Java.
You could approach this a number of ways but my only comment would be: Push, don't pull. For low latency it's not only quicker it's more efficient, as your server now doesn't have to handle n*clients once a second polling the db/queue. ActiveMQ is OK, but Starling will probably serve you better if you're not looking for insane levels of persistence.
You'll almost certainly end up using Flash on the client side (Juggernaut uses it last time I checked) or Java. This may be an issue for your clients (if they don't have Flash/Java installed) but for most people it's not an issue; still, a fallback mechanism onto a pull notification system might be prudent to implement.
Perhaps http://goldfishserver.com might be of some use to you. It provides a simple API to allow push notifications to your web pages. In short, when your data updates, send it (some payload data) to the Goldfish servers and your client browsers will be notified, with the same data.
Disclaimer: I am a developer working on goldfish.
The problem
There is an event - either external (or perhaps internally within your app).
Users should be notified.
One solution
I am myself facing this problem. I haven't solved it yet, but this is how I intend to do it. It may help you too:
(A) The app must learn about the event (via an exposed end point)
Expose an end point by which you app can be notified about external events.
When the end point is hit (and after authentication then users need to be notified).
(B) Notification
You can notify the user directly by changing the DOM on the current web page they are on.
You can notify users by using the Push API (but you need to make sure your browsers can target that).
All of these notification features should be able to be handled via Action Cable: (i) either by updating the DOM to notify you when a phone call comes in, or (ii) via a push notification that pops up in your browser.
Summary: use Action Cable.
(Also: why use an external service like Pusher, when you have ActionCable at your disposal? Some people say scalability, and infrastructure management. But I do not know enough to comment on these issues. )