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Archive for the ‘1771’ Category

IE cache for Ajax requests

Posted by javier ramirez on January 14, 2010

A few days ago I ran into an issue that is now obvious but took me a while to figure out. I was programming a chat client and everything was working fine in Firefox and Chrome, but when I tested it on IE (6 and 8) things were not looking so good.

This chat is following the polling pattern, issuing an Ajax call every three seconds to check for any updates and receiving a JSON array with the pending messages, if any. Using prototype.js the code to call the javascript function every three seconds is this

new PeriodicalExecuter(Aspchat.chatRemotePoll, 3);

On IE the chat was initialized properly, the first call to the remote server was working fine, but the periodical poller was not issuing any further calls. At first I thought the problem was on PeriodicalExecuter, but after a bit of debugging I could see “Aspchat.chatRemotePoll” was being called, but the Ajax call inside was apparently ignored.

To make things more interesting, I could see some other Ajax requests were working fine (for example, the one to send messages or to update the user list).

Comparing the requests that were successfully sent with the ones that were ignored, I could see the difference. In the working requests I was using POST (the default when using prototype) but in the ignored calls I was using GET.

Once I saw this, it was easy to diagnose what the problem was. IE was caching the GET requests, even when using AJAX. To be honest, this time I will not even blame IE, since I understand a GET request is subject to cache. In this case, I would even say I prefer the IE behaviour over that of Firefox and Chrome.

There are basically three things you can do to prevent this kind of behaviour:

  • The easy way out would be to convert my GET request to a POST one. Alas, I didn’t want to do it because in this case I was being RESTful and I was using the same URL for two different actions. When calling “/aspchat/messages” via GET I’m asking for new messages, but when calling via POST I’m sending a new message to the channel.
  • Set HTTP headers to control client cache
  • Make the request unique by adding a timestamp (or similar) to the URL

The solution I like the best is the one with HTTP headers, so I just went to my poller action (which by the way is managed via a Rails metal middleware) and added the Cache-Control: no-cache header. Just to be really sure, I also added the timestamp for extra security.

The prototype for the Ajax call with the timestamp looks like this

new Ajax.Request('/aspchat/messages', {
           parameters: {timestamp:new Date().getTime()}, //we need this to avoid IE caching of the AJAX get
           method: 'get',
           onSuccess: function(transport){
               Aspchat.displayChatMessages(eval(transport.responseText));  //pass the JSON array to displayChatMessages

As an extra ball, you can see how I’m using the onSuccess callback to interpret the JSON I’m receiving from the server.

Now you cannot say you didn’t know your AJAX requests could be cached. Let’s be careful out there.

Posted in 1771, development, internet, javier ramirez, ruby on rails | Tagged: , , , , , | 15 Comments »

Ruby on Rails on unofficial Chrome OS

Posted by javier ramirez on September 29, 2009

update: I thought this Chrome OS distribution was THE google distro. I was wrong. It’s just someone who used SUSE Studio to make a customized version of Open SUSE around the Chromium theme. With the site being on a google site and the code on a google code repository, I thought this was it, but no.. this distro is totally unrelated to google.

Chrome OS is by now just a bit more than a curiosity. In the meanwhile, you can go and download a non-official distribution mimicking what it could be, but be warned, all you are going to get is an Open Suse distribution with Chromium installed and a blue theme with a cute logo. Hopefully the real ChromeOS will be much lighter and more user-friendly.

Starting the virtual appliance from VirtualBox is easy. You create a new virtual media with the virtual media manager and then a virtual machine using this new media. That should be it. If you leave the default options (64MB) you’ll end up with a really slow boot. I set the base memory to 512K and things are much better.

What will you find in this distribution apart from Chromium? Zip, Zero, Null.. or if you are into ruby, nil.

Truth is, this distribution is a bit too rough around the edges (when it comes to internationalization, even if it ask you for the keyboard settings, it will just ignore them), but being a SUSE, you can install whatever you want. The only thing you’ll need is the root password. Since I’m such a hacker it took me almost no time to realize the root password was “root” (my other options being “sergei”, “larry” and “640Koughttobeenough”.

Once you have root access, you can use Yast for installing anything you might need. Just for fun I installed ruby, rubygems and sqlite3 via Yast, and then rails using gem. I had to run a gem update –system so I could use rails 2.3.4 and I generated a scaffold to see if everything was fine. Well, it was :)

ruby on rails running on google chrome os

ruby on rails running on google chrome os

Well, even if it was utterly useless, at least I found a cool way of making customized SUSE distros in an easy way ;)

Posted in 1771, development, javier ramirez, ruby, ruby on rails | Tagged: , , , , , , , | 3 Comments »

Multiple rubygems versions, GEM_HOME and GEM_PATH

Posted by javier ramirez on September 28, 2009

Installing rubygems is failrly easy and it’s great to have a package manager so you can forget about manually installing and upgrading the components you use. After installing a gem, you can require it from any ruby script and use it hassle-free. Well, given your ruby interpreter can find it.

When you install rubygems, a lot of default configuration is done behind the scenes. If you must see to believe, you can run

gem environment

do you believe me now?

Unless you are on windows, you have probably experienced already that gems can get installed in different locations. If using a superuser account, the global configuration will be used, but with a regular account gems install under your home directory.

If you are not careful about how you install your gems, or if you are using rake gems:install from regular accounts, you might end up installing the same version of a gem twice. That’s not only WET (not DRY, bear with me here) but it eats up your poor HD.

Things can get a lot worse than that. Suppose you are working with both JRuby and Ruby MRI. When you use rubygems from JRuby, it will try to use a different gem location by default. So, depending on how you are installing gems, you could have up to three different copies of exactly the same version.

And if you are on ubuntu and you upgrade from an old version of rubygems to the latest one —you will have to if you install Rails 2.3.4; if you are having problems you can read right here how to update it— you might be surprised that your gems are being installed *again*. The reason is under older versions the default location was “/var/lib/gems” and the latest one defaults to “/usr/lib/ruby/gems”.

Well, four different copies of ActiveRecord 2.3.4 are three and a half more copies than I wanted, mind you.

So.. how can we stop this gem install frenzy? Easy. Don’t use the defaults. Each of your installations is using default values, but they can be easily overridden with command line parameters or much more conveniently with environment variables.

Remember the title of this post? Can you see anything there that would make a good candidate for environment variables? That’s right, all the rubygems versions honor the GEM_HOME and GEM_PATH variables, so if they are set they will be used.

Depending on your OS, you can set these variables in different places. I’m on ubuntu and a bit lazy, so I chose the easiest, which is by adding this to my .bashrc file.

export GEM_HOME=/var/lib/gems/1.8
export GEM_PATH=/var/lib/gems/1.8

And now, no matter what I’m using: Ruby MRI, JRuby, or the latest rubygems, my already installed gems will be used, and the new ones will be put in the same place.

Saving the world is a hard job, but someone has to do it.

Posted in 1771, development, jruby, ruby, ruby, ruby on rails, ruby on rails | Tagged: , , , , , , | 6 Comments »

Speaking at EuRuKo 2009

Posted by javier ramirez on April 23, 2009

It’s only two weeks for EuRuKo 2009, the most important Ruby conference in Europe.

As you probably know, EuRuKo is a grassroots itinerant conference, entirely organized by -and for- Ruby developers. This year, the conference will be held in Barcelona, and I have the honor of being a -tiny- part of the organization as a member of the Spanish Ruby Users Group, the local group preparing the event.

It’s also pretty cool that ASPgems is one of the sponsors. I cannot help but feel a tang of pride (awww, the diva in me ;) ) when I see the commitment and support of the company when it comes to community events.

The list of scheduled talks looks promising. Starting with Matz’s keynote there will be sessions about things like cross-platform mobile development, voice-enabled applications, interacting with MIDI instruments from Ruby, Image processing and other non-typical uses of Ruby. They have the sweet scent of EPIC WIN all over.

Did you take a look at the list of talks? Any familiar names? Well.. yours truly’s talk proposal was accepted and I’ll be speaking about game development using Ruby and Gosu. How cool is that?

I’ve been speaking at other technical events before, and I have a good deal of experience in training, but this will be the first time I do this in English. I’m sure it’s going to be an enriching personal experience.

I’m looking forward to seeing you all there.

Posted in 1771, EuRuKo, javier ramirez, madrid, ruby, ruby, ruby on rails | Tagged: , , , , , , | Leave a Comment »