I have to program websites, but I rather don't like the static HTML nature. I prefer more of a client-server architecture.
Now I've figured, that with XMLhttp, you can basically dynamically update your page and send/request for information/action to/from a server. So this would basically cover the client area.
But to complete a client-server architecture, it is necessary for the server to send/request information, too, without being queried.
Is there any way, for example for a chat server, to send back a received message to all clients (the clients use a web browser) without that the clients have to query in a fixed interval? I want to implement that one can see while you type something in.
There are several different ways to accomplish this. Some of them are already answered here, but I wanted to include a few more as well as my thoughts on them.
1. Polling
Frequent requests are made to the server to check for new info. This is the worst way to do this, but probably the easiest. If your site will have a low number of users, it might be worth doing it this way.
This can be accomplished by using setInterval(myFunction, n) in javascript to send XMLHttpRequests to the server every n milliseconds. Then, on the server, you respond to this with your new info, when you have it, or some message that implies no new info.
2. Long Polling
When the page is loaded, it makes a request to the server for new info. The server holds the connection open until there is something to send back. This method reduces the amount of network traffic used, but increases the resources used on the server. You can use this for a small number of users, but it doesn't scale very well.
The easiest way to do this is to have the page that handles the AJAX request simply wait for new information to be available, then respond. This can tie up a lot connections on your server. So, use with care.
3. COMET
COMET is basically long polling, but the server is setup properly for it. It knows that these connections aren't "real" and it uses less resources to handle them. This is a great solution for this problem, but it requires that the server is explicitly setup for this purpose. There are COMET servers and COMET addins for other popular servers, but it will require some setup and sometimes some money.
Implementing this on .NET isn't the easiest thing in the world. You can pay for solutions, try to find someone else's code that does something similar, or try to write it yourself. I've not found any decent free solutions for this. If someone else has, please comment.
4. RIA
Another solution would be to include Flash, Silverlight, or Java Applet on your page. People often do this by using a 1x1 object so that they can use Flash or Silverlight to talk to the server. If you don't mind adding the dependency, this is a decent solution. If you already know Silverlight or Flash, it could be relatively simple to implement.
You can find tutorials on the internet for each of these options.
5. Web Sockets
If you are on the cutting edge, you can look into Web Sockets. It's only available in the latest builds of modern browsers. It was part of HTML5, but it might be its own spec now. Regardless, it means that older browsers won't be able to handle it. But, if you don't mind limiting yourself to the latest of browsers, you can use this amazing feature.
I believe that Chromium is the only browser that currently supports it. However, there is work being done to implement this in Firefox and WebKit.
I'll spare you the controversy and simply say that this does exactly what you want it to. The Abstract of the spec says it all.
This specification defines an API that enables Web pages to use the Web Sockets protocol for two-way communication with a remote host.
Special Mention
If you are interested in the world of Node JS, you can't go wrong with Socket IO. It will implement the best of whichever technology is available to the browser.
Conclusion
The best option is Socket.IO on Node JS. However, for an ASP.Net solution, go for COMET or Web Sockets, if you can. Otherwise, using Flash/Silverlight isn't terrible. Finally, polling and long polling should be last resorts. You could always support one of these, then fall back to another if there isn't support for it in the client's browser.
Yes, you can use COMET.
The client has to tell the server when the client-user begins typing. You've got a couple options here.
Frequent requests from the server for the latest activity. This would be taking place for each user involved in the chat. The same request could be used to send user-specific activity to the server as well: "Jonathan is typing..."
Long-polling. This essentially requests information from the server, and the server keeps the connection opened until it has something to send back. So your requests are minimized, but your connections stay opened longer.
Depending on your traffic, type of data being transmitted, server-environment, and many other factors, one of these options may shine more than the other.
You can use Silverlight for push notifications. Look at PollingDuplexHttpBinding. Since you are using ASP.Net MVC, adding Silverlight will be easy.
Look at this page for more information.
Based upon the REST architecture the html system is based upon, the servers role is to simply act as a resource for the client to pull from. I am generalizing but there are tools to implement this type of action on the client side, rather than on the server side.
You are better off writing/using a library that can request updates from the server periodically. You can encapsulate these types of requests in a javascript object that can fire events. This way your client side script can act like it's getting notified from the server. Review some common stuff with COMET you can probably find some tools to help you client side code.
HTML 5 has some tentative attempts at this type of functionality, but if you want your app to work on older browsers, your better off using more stable methods, like AJAX requested updates.
Related
I am writing a PHP backend, JS/Jquery front end application that will allow users to "communicate" in near real time. That is the hope at least, my question is what is my best course of action? Am I best to use WebSockets to send data between the server and client or would use AJAX and some sort of timer (x amount of seconds) be better. My worry with the AJAX way is that it may be taxing on the server to have 10+ clients all asking for data every 15-30 seconds. I need it to be near real-time and so 5 minutes is not really realistic.
An example of what I am trying to do would be if I had 5 users all on a page and user 1 updates their status, I would want users 2,3,4, and 5 to see the update as fast as possible without having to refresh.
I am mixed on what I think is best and I don't want to start doing it one way and find out it is insecure or terrible after getting halfway done. What is my best route with an application like this?
Here's a list of popular possible solutions:
Short polling (what you're referring to in AJAX
Long Polling (AJAX too, but not too many requests)
Websockets
WebRTC
So, for short polling as you've said it consumes lots of resources so let's remove that from the list.
as for long polling, its idea is that a request is send to server and the server doesn't respond unless a new event has happened (keeps the request) but its rarely used in modern development. so If you're going to work with other developers its kind of bad decision.
for WebRTC, browser compatibility is not that great and still a draft in W3C.
Thus, you're left out with WebSockets, and yes they consume ram but not CPU. ram is much cheaper (and it doesn't consume that much too).
As for security they can be considered equal (except for WebRTC which is better because it is actually P2P Communication)
Side note: don't overthink it :)
Here's some resources that can help you:
https://webrtc.org/
https://github.com/walkor/phpsocket.io //Socket library for PHP similar to Socket.io
https://socket.io
What are the realtime communication protocols available for the web? List of the protocols
https://codeburst.io/polling-vs-sse-vs-websocket-how-to-choose-the-right-one-1859e4e13bd9 great article for polling, websockets & covers SSE too
there is one way to make the RTC, RealTime App, Just Use the Socket.io "WebSocket " for signaling and before that take a full view of these webPages:
https://bloggeek.me/
https://www.html5rocks.com/en/tutorials/webrtc
https://w3c.github.io/webrtc-pc/#rtcsignalingstate-enum
https://www.w3.org/TR/mediacapture-streams/#legacy-interface-extensions
and i start to development this technology with this book enter link description here it will open your view of RTC usage and All Details.
I put together an AJAX chat a while back ASP.NET MVC and jQuery. The javascript would hit the server about every 7 seconds to check for new messages. Obviously this was horrible on performance as the chat grew and included more and more users. The site traffic grew exponentially with so many requests going on. A user could leave the computer on all day and not even be there and they would still be making hits every 7 seconds.
Is there a better way to do this? I have heard of something called "push" but I haven't really been able to wrap my head around it. I think I just need pointed in the right direction.
1.) What is the best way to develop an AJAX chat and have it be scalable?
2.) What is push and how would I just that with jQuery?
1.) What is the best way to develop an AJAX chat and have it be scalable?
I agree with #freakish about the complexity and potential lack of scaling of IIS.
However, there is a relatively new Microsoft option in the works called SignalR which could become a core part of ASP.NET. More details in this related SO Question:
AJAX Comet - Is there any solution Microsoft is working on or supports to allow it to be scalable?
2.) What is push and how would I just that with jQuery?
Partially answered elsewhere, but it's a long-held persistent connection between the server and the client which means the server can instantly 'push' data to the client when it has new data available.
jQuery does support making AJAX requests but the core library doesn't support expose ways of doing HTTP Long-Polling or HTTP Streaming. More information in this SO answer to 'Long Polling/HTTP Streaming General Questions'.
Server push is a technology that allows the server to push data back to the client without forcing client to make many requests (like every 7 seconds). It is not really a matter of javascript but rather good server scripting. The upcoming HTML5 will make it simple due to server-sent events and/or WebSockets. This will be a true TCP connection between different machines.
But if you intend to make a webpage compatible with older browsers, then the most common technique is the long polling. The client sends request to the server and the server does not respond to it until it has new data. If it does then the response is made and the client immediatly after receiving data calls the server with new request. In practice however this requires the server to be well-written (for example it has to maintain thousands of idle requests at the same time) and can become a rather big challenge for developers.
I hope this helps. :) Good luck!
The technique you should use is the real-time persistent long running connections over a web page using WebSockets. You can use this library.
Node.js is becoming quite popular to build something like this and supports socket connections so you could push the data out only when there is a new message. But that would be learning something completely new.
Another nice potential would be to use MVC's OutputCacheAttribute and use the SQL dependency option so your AJAX page could be cached and would only be a new request when a new chat message appears. Also you would want your controller to be an Asynchronous controller to help reduce the load on IIS.
Enjoy, optimization is always fun and very time consuming!
The common way, I think, is making a periodic "ping" to the server, but I don't like how it looks too much like
"Is there anything new? - No"
"Is there anything new? - No"
"Is there anything new? - No"
"Is there anything new? - No"
"Is there anyt..."
I've seen another approach where client ask for news and server "retains" the request (with a sleep loop, for example) until there is anything new. That's cool, but I'd really like to hear about another options.
Unfortunately there isn't really any cross browser mechanism for pushing data from the server to the browser. For example, back in 1995 Netscape released a server push technology that uses a special content type -- multipart/x-mixed-replace but from what I understand IE doesn't support it. WebSockets are a new one but support is just coming out now.
So you're forced to use the tools at hand, which means the client needs to ask the server if there's any new data -- polling. Polling comes in 2 varieties: polling on an interval, and long polling. When you poll on an interval you simply make a request to the server every n seconds asking for data. This is fairly chatty (pardon the pun) if there is no new data to return. This is what people think of when you say "polling."
The other option, long polling, is similar in that the client makes a request to the server to see if there's new data. But in this case the server doesn't send a response until it has something to say. In this case the client is left hanging for a response for an undetermined amount of time. When the client eventually gets its response it parses the response and immediately makes another request which will stay hanging until there's data.
Both of these polling approaches consume a lot of HTTP overhead, but if you want to use XHRs this is about the only way to do it.
A word of warning about long polling: When working with long polling it's important to ensure that all of your XHRs are running asynchronously otherwise you'll see the browser's UI thread lock up.
If you're not interested in using AJAX then you can always use the tried and testing IFRAME-that-never-finishes-loading. In this case you have an IFRAME with the chat log and another IFRAME that contains your message area. In this case the server simply never closes the connection for the IFRAME that contains the chat log. Instead, it just keeps pushing chat messages into the body.
WebSockets can be helpful if you're okay if some browsers aren't able to use it.
If you want to it in JavaScript, there is no alternative to polling in intervals.
What you need is ajax push or reverse ajax.
There are lots of ajax based frameworks who support push. In Java for example nextapp echo2, or you can give a shot to ape project as well.
Options
Long-Polling: keep the request open until data arrives. Receive data and close connection. Open a new connection to receive data again. For this to scale you need to have non-blocking IO)for all communication). This approach is the simplest to implement. You could even use blocking I/O if your server does not have a lot of concurrency.
HTTP-Streaming: Do not close the connection when receiving data. For this to work cross-browser you have to do some "hacking" to make it work in all browsers.
XMPP over BOSH For this you use your XMPP server and sprinkle it with some BOSH(XMPP over HTTP). Prosody for example is an easy XMPP server which supports BOSH. Next you could write the client-side with the excellent strophe.js library.
Websockets: I guess this will be the future, but right now the browser support is not sufficient to really use it for all browsers.
Server-Sent Events: Also pretty cool html5 feature. This protocol is in my opinion simpler then websockets. This also is not widely supported by all the majar browsers yet.
Flash: You could also communicate via flash if you like. The browser has to have flash plugin installed, but that will be the case most of the times.
What is the best way?
In my opinion long-polling is the easiest/best way to implement event-based messaging over HTTP. it definitely is not the fastest alternative, but every major browser supports it and the easiest to implement.
I think Websockets will be the best technology(future), but is not widely adopted in the browsers yet.
All though all the above technologies are pretty good. They all have there pros and cons.
If this is done with JavaScript, there really isn't any other way than pinging the server. You're only option is to heavily optimize the request, to avoid uselessly asking the "question".
I just learned about the AJAX Push Engine but it runs on Linux/Apache which is not an option for me.
http://www.ape-project.org/
Currently with AJAX to keep a page current I have to poll the server frequently which is not great for a high traffic site. The option to push data to the client only when necessary is a great option, but natively JavaScript does not support sockets, AFAIK. One trick I read about, but the site is now gone, is to use a Flash module to handle socket communications and relay message to JavaScript.
The trouble with researching this approach is that "JavaScript push" as keywords come up with the push function for arrays instead of the context I want.
How could establish a persistent connection with the server to do push communications in the browser? Do I need Flash/ActionScript or is there another option that would work with all of the currently active browsers? (IE6/7/8, FF3, Safari, Chrome)
When it comes to the server I also need to work out the complications due to Origin policy as well as port security. I appreciate anything you can point out that will explain the available options.
What you want is COMET, or I would also look up long polling.
I asked a similar question.
The Direct Web Remoting (DWR) library supports Reverse Ajax, which sounds like what you are looking for. It supports Comet (along with Polling and PiggyBack). More info on their website: http://directwebremoting.org/dwr/index.html
This is interesting stuff, but I did not read anything about scalability issues on these Wiki pages. What does a web server do if you have 10,000 open long-polling connections?
Also, for those not familiar with the underlying concepts, it is important to understand that pushing data from the server to the client in an ad-hoc fashion is impossible and will always be. Even if the HTTP protocol supported this, the network would not, particularly if there is a NAT firewall involved.
So any solutions that claim to offer server push communication must rely on connections that are initiated by the client, kept open, and will eventually time out. I have concerns about this because it must have negative consequences for server scalability and performance.
The thing you are looking for is websocket https://en.wikipedia.org/wiki/WebSocket
I'm trying to figure out if there's a way I can somehow notify a web browser of an event from a web server.
I know Ajax lets you asynchronously make a request to update a section of a page. I guess I could have a timer periodically ask for updates. But, I'd prefer to avoid a polling scheme, if possible. Is there a better way to go and still remain with a browser-based solution?
Check out "comet" techniques, where you basically hold a connection open to a server which pushes data back at you.
Well, you could try to set the "ignore-user-abort"-flag on, and make sure that the script doesn't terminates (while condition) sleep()). After you have echo'ed the information you need to transfer, flush() the text to the browser.
But i would't recommend this solution. Instead: Go with ajax, and use a polling scheme. Most up-to-date framework support it out of the box.
Comet is the thing you are looking for. There are some js libraries and http servers that make it easier to use. It's based on the idea of keeping connections open with a certain request and streaming back to the browser when the server has something to stream. You should be aware of he fact that browsers usually can have a very limited number of connections open to one domain (typicaly one I think). If you like to try this out take a look at:
dojo cometd
js io
orbited
apache tomcat advanced io
If you are into erlang check this:
http://yoan.dosimple.ch/blog/2008/05/15/
I guess I could have a timer periodically ask for updates. But, I'd prefer to avoid a polling scheme, if possible.
Tough luck: that's what you gotta do. The web is built on a request/response model: 1 request from the browser, 1 response from the server, and always in that order.
That said, you don't have to (and probably shouldn't) build that polling scheme yourself. You can probably find an existing implementation that abstracts away the details and make it look like the server is notifying the client.
You can use partial rendering. I would check out this article for more information.
Here is another article on the topic.
There is Server-Sent Events from the WHATWG Web Applications 1.0 specification that was added to Opera 9. Mozilla/Firefox seem to be working on it.
In the past I found nice article about streaming data in HTML:
http://ajaxpatterns.org/HTTP_Streaming
Can be usefull :)
Also check out juggernaut for RubyOnRails here