I've made a chat that I can connect with Telnet to. My chat is currently implemented as a Twisted TCP Server. How do I transform it into a chat for the browser?
I suppose I should use a comet server (e.g. Orbited) to be able to serve static HTML and dynamic content simultaneously. Is such a comet server necessary for a fast and reliable chat?
Comet is the best option without using anything special (like Flash, see below). It's a proven technology and is used by many big sites, like Gmail's chat and Facebook's chat.
The only other option you have is polling, but that can sometimes get a bit intense on the server. You basically have to weigh server load against speed - if you poll often, you get a very responsive client, but you put a lot of load on your server. Poll too little and you keep the load light but clients can only receive messages every n seconds so it can seem slow.
If you decide to poll, you could always create a "back off" system. For example, the page checks every 2 seconds to see if there are any chat messages sent. It does this 5 times and if there is nothing, it increases the delay to 3 seconds. It does this 5 times and after nothing it goes to 4 seconds..etc. When a chat message is sent it goes back down to the shortest delay.
Another option to consider that is even better is using a Flex or Flash client. This way, you can just use TCP sockets which only send data if there is any. But that's only if you really want a Flash app on your site.
Yeah it is! Check www.meebo.com ! They use comet as their basic platform!
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I'm attempting to make a mail client that is HTML5/JS only where users would have to define their mail server and credentials.
I've surfed google leading to dead ends and figured that this is the next best place (or superuser.com).
I was thinking of using HTML5 WebSocket if I could to make the connection to the server but I don't know enough of smtp, imap, or pop3's architecture to understand how javascript could pass the args and perform what I want it to do.
PHP cannot be involved in this project otherwise I wouldn't be asking the question.
Any help in locating this would be fantastic.
Nothing is impossible. Except this.
In standard HTML or JavaScript, you can't make raw-socket connections, which is what you'd need to speak any of the protocols you've listed. The WebSocket API doesn't help you, because the server must also speak WebSockets, and mail servers don't. This is actually all a good thing, though. Imagine if you visited a random website and it telnetted to your home router, setting it on fire and burning down your house. That's what websites would be able to do if they could initiate plain TCP socket connections.
You have a few options I can think of, neither of which involves building a webpage. (And to be clear, you didn't say your project had to be a webpage; you merely said HTML/JS, so these are indeed legitimate options.)
First is something like node-webkit. As the readme says, "You can write native apps in HTML and Javascript with node-webkit." You'll still have to distribute it as a native app, because that's what it is.
Second is a Chrome app, specifically using the chrome.socket API. But have fun writing a TLS layer over those sockets, which you'll find is a requirement for almost any mail server these days. If you succeed in doing that, you'll be able to distribute your mail client in the Chrome Web Store, where I assure you an email client will be quite popular.
Third, write a webserver that operates locally, so your users will visit something like http://localhost:9999/mail in their browser. This will be a real pain to distribute, but you can use almost any technology you want.
I'm sure there's a fourth valid option, and someone else can chime in on that one.
Best of luck.
I have been searching to see if it is possible to include a script that will push a low bandwidth version of a web site for those who have dial up. There are two sites (one with lots of JS, images, code, etc.) and a site that is limited. I would like those who have dial up to view that page instead of the slow loading page.
Is there a script for this?
Thanks.
You could send the client a tiny ajax script that calls back the server. The process can be timed and you can make your decision based on the result time. However some time will be lost in the process, but the time saved for the slow browser could be significant.
As far as I know, at the current moment, late 2011 the max-connections-per-server limit remains 6. Please correct me if I am wrong. This is bad that we cannot fix this easily as in Firefox. As far as I know this value is hardcoded.
One of the solutions is to download the Chromium's sources and rebuild them. Is there a more easy solution?
Is there any tricky way to hack this without creating a dozen of mirror-domains?
Why I'm asking the question: My task is to create a html-javascript slideshow that will run inside a fullscreened browser, and a huge monitor is hanging on the wall. The javascript is really complicated, it preloads photos and makes a lot of ajax calls to my web services. If WIFI connection is slow, if 6 photos are loading, the AJAX calls fail, the application runs bad. I want a fast solution based, on http or browser or ubuntu tweak something else, because rebuilding the javascript app will take days.
Offtopic: do you know any other things that can be tweaked in my concrete situation?
IE is even worse with 2 connection per domain limit. But I wouldn't rely on fixing client browsers. Even if you have control over them, browsers like chrome will auto update and a future release might behave differently than you expect. I'd focus on solving the problem within your system design.
Your choices are to:
Load the images in sequence so that only 1 or 2 XHR calls are active at a time (use the success event from the previous image to check if there are more images to download and start the next request).
Use sub-domains like serverA.myphotoserver.com and serverB.myphotoserver.com. Each sub domain will have its own pool for connection limits. This means you could have 2 requests going to 5 different sub-domains if you wanted to. The downfall is that the photos will be cached according to these sub-domains. BTW, these don't need to be "mirror" domains, you can just make additional DNS pointers to the exact same website/server. This means you don't have the headache of administrating many servers, just one server with many DNS records.
I don't know that you can do it in Chrome outside of Windows -- some Googling shows that Chrome (and therefore possibly Chromium) might respond well to a certain registry hack.
However, if you're just looking for a simple solution without modifying your code base, have you considered Firefox? In the about:config you can search for "network.http.max" and there are a few values in there that are definitely worth looking at.
Also, for a device that will not be moving (i.e. it is mounted in a fixed location) you should consider not using Wi-Fi (even a Home-Plug would be a step up as far as latency / stability / dropped connections go).
BTW, HTTP 1/1 specification (RFC2616) suggests no more than 2 connections per server.
Clients that use persistent connections SHOULD limit the number of simultaneous connections that they maintain to a given server. A single-user client SHOULD NOT maintain more than 2 connections with any server or proxy. A proxy SHOULD use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines are intended to improve HTTP response times and avoid congestion.
There doesn't appear to be an external way to hack the behaviour of the executables.
You could modify the Chrome(ium) executables as this information is obviously compiled in. That approach brings a lot of problems with support and automatic upgrades so you probably want to avoid doing that. You also need to understand how to make the changes to the binaries which is not something most people can pick up in a few days.
If you compile your own browser you are creating a support issue for yourself as you are stuck with a specific revision. If you want to get new features and bug fixes you will have to recompile. All of this involves tracking Chrome development for bugs and build breakages - not something that a web developer should have to do.
I'd follow #BenSwayne's advice for now, but it might be worth thinking about doing some of the work outside of the client (the web browser) and putting it in a background process running on the same or different machines. This process can handle many more connections and you are just responsible for getting the data back from it. Since it is local(ish) you'll get results back quickly even with minimal connections.
Client has a dating site and would like to have a popup (either a nice javascript overlay or a new browser window popup. we're flexible.) displayed to users when another user is visiting their page.
I'm familiar with push technology and Comet but it's quite challenging to implement this and may place serious strain on a server with over 100,000 unique visitors per day.
I'm wondering if there is a way of faking this, perhaps by not being accurate to the second. I can't really think of any way.
This is a classic LAMP environment.
Anyone?
EDIT: what about this: placing an iframe on the page that refreshes every few seconds and at each page load it checks in the db if a visitor has been logged on this profile page. if so, it shows a message. the message would be visible but the background of the iframe would blend in with the background of the site and be invisible. if the message fades in and out, it would look like a JS box "popping up".
The only way to "fake" comet is via polling of some sort, which is always a possibility. An iframe, xhr, or jsonp request are all possibilities for performing said polling.
You might be better off purchasing a pre-built comet server (I'll recommend, of course, the one I helped build, WebSync for IIS/ASP.NET). If you're worried about the load, you could check out our On-Demand version where we'll host it for you.
Regardless, WebSync (or whatever other pre-packaged product you might check out) would scale to a hundred thousand users a day without much of a problem, and would potentially be more efficient than polling, since it would only hit your database when new users arrived, rather than every couple seconds; that said, if you keep the "check for new users" query simple enough, and a few seconds of delay is OK, the polling idea would be the "simpler" solution.
Check out http://en.wikipedia.org/wiki/Web_Sockets if you want to do real push. This isn't widely supported in browsers yet, but there are plenty of JavaScript and Flash libraries that provide it already.
Or a cheaper way is to record in your DB each page view.
Then when any user makes a web request, check in the DB if anybody has visited their page since their last web request.
If so, pop up your dialog.
This second way wouldn't popup anything if the user just left their browser sitting there, but if they were actively interacting with the site, it would achieve your goals very easily.
I would start with this second simpler solution, which is very easy to implement. If your client wants it more interactive, you can provide solutions and tradeoffs/costs for various options.
Gather statistics as to how many visitors that user's website gets per day, and then subdivide that, so that it's a percentage chance that the user will be told there is a user on his site (even if there actually isn't), based within the timeframe he's at the part where he can receive the popup. I think this is the closest you are going to get without having some sort of notification being sent.
You could do this to minimize server usage if you wanted push:
When a user visits a website, check and see if the person who would be getting the notification is online and capable of being notified, and if so, THEN do all the push stuff, otherwise forget it.
Let's say I have two applications which have to work together to a certain extent.
A web application (PHP, Ruby on Rails, ...)
A desktop application (Java, C++, ...)
The desktop application has to be notified from the web application and the delay between sending and receiving the notification must be short. (< 10 seconds)
What are possible ways to do this? I can think of polling in a 10 second interval, but that would produce much traffic if many desktop applications have to be notified. On a LAN I'd use an UDP broadcast, but unfortunately that's not possible here...
I appreciate any ideas you could give me.
I think the "best practice" here will depend on the number of desktop clients you expect to serve. If there's just one desktop to be notified, then polling may well be a fine approach -- yes, polling is much more overhead than an event-based notification, but it'll certainly be the easiest solution to implement.
If the overhead of polling is truly unacceptable, then I see two basic alternatives:
Keep a persistent connection open between the desktop and web-server (could be a "comet"-style web request, or a raw socket connection)
Expose a service from within the desktop app, and register the address of the service with the web-server. This way, the web-server can call out to the desktop as needed.
Be warned, though -- both alternatives are chock full of gotchas. A few highlights:
Keeping a connection open can be tricky, since you want your web-servers to be hot-swappable
Calling out to an external service (eg, your desktop) from a web-server is dangerous, because this request could hang. You'd want move this notification onto a separate thread to avoid tying up the webserver.
To mitigate some of the concerns, you might decouple the unreliable desktop from the web-server by introducing an intermediary notification server -- the web-server could post an update somewhere, and the desktop could poll/connect/register there to be notified. To avoid reinventing the wheel here, this could involve some sort of MessageQueue system... This, of course, adds the complexity of needing to maintain the new intermediary.
Again, all of these approaches are probably quite complex, so I'd say polling is probably the best bet.
I can see two ways:
Your desktop application polls the web app
Your web app notifies the desktop application
Your web app could publish an RSS feed, but your desktop app will still have to poll the feed every 10 s.
The traffic need not be huge: if you use an HTTP HEAD request, you'll get a small packet with the date of the last modification (conveniently named Last-Modified).
I don't know exactly what to do to achieve your task but I can suggest to create a windows service at the desktop application PC.
This service checks the web application every interval of time for new changes and if changes occurred it can run the desktop application with notification that there is a change in the web application and in the web application when any change occurrs you can response with acknowledgment
I hope that this may be useful I didn't try it exactly but I am suggesting using like this idea.
A layer of syndication would help to scale out the system.
The desktop app can register itself with a "publisher" service (running on one of several/many machines) This publisher service receives the "notice" from your web app that something has changed, and immediately starts notifying all of its registered subscribers.
The number of publishers you need will increase with the number of users.
Edit: Forgot to mention that the desktop app will need to listen on a socket.