I have a question which I can't seem to answer after searching for an answer on google.
I have a website hosted on a web host, but I want to introduce some real-time functionality on it, like a real-time notification system, or maybe a chat system.
As I understand the short-polling and long-polling methods of simulating a live feature are kinda obsolete. Today with the modern HTML5, we can use Websockets as I understand, or APE(Ajax Push Engine).
The thing is that I don't understand, how do I use websocket or APE on the webhost if they require a server to which they connect in order to work ?
How can I run that server along with my website on the same host ? Or maybe I am missing something ?
Can you give me some information on this problem, that I can read?
Thank you.
WebSocket is just another protocol. It works on port 80, so luckly you don't need a new server.
You just need to implement an abstraction level on your backend (but maybe it can do itself) that gets the HTTP request and looks if there are the upgrade headers.
If the answer is yes, go to websocket code, if not use standard HTTP.
Of course I am aware of Ajax, but the problem with Ajax is that the browser should poll the server frequently to find whether there is new data. This increases server load.
Is there any better method (even using Ajax) other than polling the server frequently?
Yes, what you're looking for is COMET http://en.wikipedia.org/wiki/Comet_(programming). Other good Google terms to search for are AJAX-push and reverse-ajax.
Yes, it's called Reverse Ajax or Comet. Comet is basically an umbrella term for different ways of opening long-lived HTTP requests in order to push data in real-time to a web browser. I'd recommend StreamHub Push Server, they have some cool demos and it's much easier to get started with than any of the other servers. Check out the Getting Started with Comet and StreamHub Tutorial for a quick intro. You can use the Community Edition which is available to download for free but is limited to 20 concurrent users. The commercial version is well worth it for the support alone plus you get SSL and Desktop .NET & Java client adapters. Help is available via the Google Group, there's a good bunch of tutorials on the net and there's a GWT Comet adapter too.
Nowadays you should use WebSockets.
This is 2011 standard that allows to initiate connections with HTTP and then upgrade them to two-directional client-server message-based communication.
You can easily initiate the connection from javascript:
var ws = new WebSocket("ws://your.domain.com/somePathIfYouNeed?args=any");
ws.onmessage = function (evt)
{
var message = evt.data;
//decode message (with JSON or something) and do the needed
};
The sever-side handling depend on your tenchnology stack.
Look into Comet (a spoof on the fact that Ajax is a cleaning agent and so is Comet) which is basically "reverse Ajax." Be aware that this requires a long-lived server connection for each user to receive notifications so be aware of the performance implications when writing your app.
http://en.wikipedia.org/wiki/Comet_(programming)
Comet is definitely what you want. Depending on your language/framework requirements, there are different server libraries available. For example, WebSync is an IIS-integrated comet server for ASP.NET/C#/IIS developers, and there are a bunch of other standalone servers as well if you need tighter integration with other languages.
I would strongly suggest to invest some time on Comet, but I dont know an actual implementation or library you could use.
For an sort of "callcenter control panel" of a web app that involved updating agent and call-queue status for a live Callcenter we developed an in-house solution that works, but is far away from a library you could use.
What we did was to implement a small service on the server that talks to the phone-system, waits for new events and maintains a photograph of the situation. This service provides a small webserver.
Our web-clients connects over HTTP to this webserver and ask for the last photo (coded in XML), displays it and then goes again, asking for the new photo. The webserver at this point can:
Return the new photo, if there is one
Block the client for some seconds (30 in our setup) waiting for some event to ocurr and change the photograph. If no event was generated at that point, it returns the same photo, only to allow the connection to stay alive and not timeout the client.
This way, when clients polls, it get a response in 0 to 30 seconds max. If a new event was already generated it gets it immediately), otherwise it blocks until new event is generated.
It's basically polling, but it somewhat smart polling to not overheat the webserver. If Comet is not your answer, I'm sure this could be implemented using the same idea but using more extensively AJAX or coding in JSON for better results. This was designed pre-AJAX era, so there are lots of room for improvement.
If someone can provide a actual lightweight implementation of this, great!
An interesting alternative to Comet is to use sockets in Flash.
Yet another, standard, way is SSE (Server-Sent Events, also known as EventSource, after the JavaScript object).
Comet was actually coined by Alex Russell from Dojo Toolkit ( http://www.dojotoolkit.org ). Here is a link to more infomration http://cometdproject.dojotoolkit.org/
There are other methods. Not sure if they are "better" in your situation. You could have a Java applet that connects to the server on page load and waits for stuff to be sent by the server. It would be a quite a bit slower on start-up, but would allow the browser to receive data from the server on an infrequent basis, without polling.
You can use a Flash/Flex application on the client with BlazeDS or LiveCycle on the server side. Data can be pushed to the client using an RTMP connection. Be aware that RTMP uses a non standard port. But you can easily fall back to polling if the port is blocked.
It's possible to achive what you're aiming at through the use of persistent http connections.
Check out the Comet article over at wikipedia, that's a good place to start.
You're not providing much info but if you're looking at building some kind of event-driven site (a'la digg spy) or something along the lines of that you'll probably be looking at implementing a hidden IFRAME that connects to a url where the connection never closes and then you'll push script-tags from the server to the client in order to perform the updates.
Might be worth checking out Meteor Server which is a web server designed for COMET. Nice demo and it also is used by twitterfall.
Once a connection is opened to the server it can be kept open and the server can Push content a long while ago I did with using multipart/x-mixed-replace but this didn't work in IE.
I think you can do clever stuff with polling that makes it work more like push by not sending content unchanged headers but leaving the connection open but I've never done this.
You could try out our Comet Component - though it's extremely experimental...!
please check this library https://github.com/SignalR/SignalR to know how to push data to clients dynamically as it becomes available
You can also look into Java Pushlets if you are using jsp pages.
Might want to look at ReverseHTTP also.
I have been working with node.js for a while, now when I'm looking deeper into it, for a chat aplication instead of sending message as client - server - client, there must be some possible ways for direct client to client message sending?
Browsers tend to communicate with servers via HTTP. Some implement other protocols, like websockets & SPDY, but again, these are mostly client-server protocols.
Some plug-ins (like Flash & Java) can open ports and communicate client-client. (AFAIK, haven't actually used them.)
Chrome is the only browser I'm aware of that can (soon) open TCP and UDP sockets from Javascript and do direct client-client communication. At the moment normal web apps can't do this, your app needs to be run as a "Chrome Packaged App", with a special manifest file.
Here are the docs, a blog post describing the feature and a browserify module that can behave like the net node.js module in the browser.
EDIT: This should probably not be tagged as [node.js] since you're trying to run in browsers (not in your node vm), this is a Javascript / Browser question.
This is maybe out of date question, but take a look on PeerJS.
It requires server only as a connection manager (broker). But all communication is done between clients directly.
This does not have anything with server. If you need something like that and if clients are flash you can use RTMFP . For JS i google this library which is js bridge for RTMFP, I dont know how it works. At the end you can write you own library to chat beetween clients but this is much harder(IP addresses are behind NAT, etc...)
I think answer for your question is here
PS Also exist open-source in-browser server which written using JS, but I didn't google it quickly. If you find it, please notify me.
If you just don't want to write your own server you can use:
https://httprelay.io
Use AJAX calls to communicate between peers.
I have an external application that is automating some tasks on a website. My goal is to implement a system which allows for the program and Chrome to synchronize cookies. While it is possible to query Chrome's cookie DB to read cookies, it is not possible to update the DB since Chrome maintains an I/O lock on the file, thus preventing easy synchronization.
The next logical step to me was to attempt to create an extension which will update cookies as necessary (through Chrome's cookie API). However, after about two days of research I have been unable to find an effective means to communicating cookie data between the browser and my application (which is written in Python.)
Sockets are out because it's for desktop based applications only. Websockets are out because as far as I can see it's impossible to setup a Websocket server using the HTML5 API (which is what I need since the browser needs to be the server and the program would be a connecting client). I'm really not sure what I am left with at this point. Is there something really obvious that I'm missing here? Any help is appreciated, cheers.
This feels like a very weird way to do whatever you're trying to do. Why are you doing this again?
Anyway, the most obvious solution is this:
You obviously have to secure communication between the app/plugin and the server. Again, this feels like a very weird way of doing stuff. But the solution will work. In this case both the app and the plugin are WS clients and your server is the arbiter.
Introduction: I want to develop the chat client that user can chat on the browser and I use the protocol call xmpp. Because of HTML5 web socket not yet available I try flash xmlsocket instead.
Problem: I cannot connect to the server via browser. I'm not sure why, but I think that it is the problem of the server configuration.
Question: Which is the best jabber server suitable for this job?
Most probably this is a permission issue. Either that or you've just configured the wrong host/port to connect to. Flash is not allowed to connect to other hosts than the one it was gotten from itself. You have to explicitely allow flash connections on the receiving side of the request (so on the chat server that you are connecting to). Google for crossdomain.xml to get more info.
ejabberd sounds like a suitable option for you. ejabberd is xmpp server written in erlang and is used quite widely. Many of the well known web based im services like www.meebo.com etc are known to be running on ejabberd. It allows you to install other transports which would let you enable talking to users of other protocol like yahoo, msn, icq etc.
You can also have a look at the xiff action script library by ignite realtime. It is an xmpp client library in action script. If you use this library you would just need to implement the ui components.
Hum... flash is ok, but you'd be better of using something like BOSH, which is basically an HTTP layer over XMPP.
Ejabberd would be a good server, as it supports BOSH, I don't know about OpenFire or Tigase (but I'd say they do). Other servers should be looked at carefully because they don't seem to have a "dynamic" community.
You will need a lot of Javascript, and for that, I can recommend StropheJS, which is probably the very best library out there today.
We have created a MUC (Multi-user chat room) client called Aristochat that works in the browser recently at Superfeedr. You can find the code on Github and an example here.