IE cache for Ajax requests

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.

Eclipse buttons not working on Ubuntu Karmic Koala

Lately I was experiencing a strange behavior when working with Eclipse/RadRails. Some of the buttons didn’t work anymore. I could click on them, but they’d just appear as selected, without performing any actions. I had to use the enter key to actually click on the button.

Since I had run an update some days ago, I was blaming some new version of one of the installed plugins.. but I was wrong.

Today I read this post where it explains how to fix it. It’s a conflict between Eclipse and the latest versions of GTK+. By setting the GDK_NATIVE_WINDOWS variable to use native windows, everything is back to normal.

And they lived happily ever after (or until the next major release anyway)

Pasting code into vi

Every time I try to paste a big chunk of code into vi, it gets all messed up because of the autoindent. Each line gets indented taking the previous one as a reference, so when I try to paste something like..


global $wp_query;
parse_str($args, $r);
if (!isset($r['current'])) $r['current'] = -1;
if (!isset($r['show_all_parents'])) $r['show_all_parents'] = 0;
if (!isset($r['show_root'])) $r['show_root'] = 0;
if (!isset($r['list_tag'])) $r['show_root'] = 1;


..what I really get is..


global $wp_query;
  parse_str($args, $r);
    if (!isset($r['current'])) $r['current'] = -1;
      if (!isset($r['show_all_parents'])) $r['show_all_parents'] = 0;
        if (!isset($r['show_root'])) $r['show_root'] = 0;
          if (!isset($r['list_tag'])) $r['show_root'] = 1;


..and that’s no good. Fortunately the solution is really simple. Just enter command mode and write

:set paste

Now you can paste in all its glory. When you are done, you can get back to normal with

:set nopaste

So now you don’t have any excuses left to write original code. Get out there and copy the whole internet before I format it!!!

Ruby on Rails on unofficial Chrome OS

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

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

Multiple rubygems versions, GEM_HOME and GEM_PATH

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.

Video of my talk “Jruby On Rails” at the Sun Open Communities Forum

I just knew the video of my talk about JRuby on Rails at the Sun Open communities Forum is already online. Funny how a google alert let me know this video has been published even before the official web page of the event was updated.

The talk is in Spanish and the slides I used are available at slideshare.

If you are a Java developer interested in JRuby and you are going to be in Madrid in September, stay tuned because it’s very likely I will be speaking again about JRuby in SIMO

it’s not the framework, it’s you

I’m getting tired already of the hype about Ruby on Rails and how it is better than any other framework past, present or future.

Sure Rails is a cute piece of software, and Ruby is a gorgeous language (supposing you are into programming languages, that is), but if you take a critical look at Rails, you could just say it’s another MVC framework.. Big deal.. And with some coupling issues between the layers too, which are fortunately being targeted on Rails 3.

Moreover, if you take a look at some of its components they could frankly be better. ActiveRecord, for example, is a wrapper ORM, which is implicitly tying you to the physical database layer, with one class per table, as opposed to a mapper ORM such as DataMapper or Hibernate. And the principle of least surprise is kind of a joke when it comes to some of the ActionView helpers and the parameters you have to pass along.

Still, as we like to say around here “Ruby on Rails mola infinito”, and it’s right now my favourite framework for non trivial web applications.

So.. what makes this framework so special? Is it only the absence of configuration and the sensible defaults? Would we sell ourselves for a couple of parlor tricks like those? Surely not.. specially with so many frameworks providing already sensible defaults. Come on, even in Java you can kind of forget about writing so much XML code if you make proper use of annotations and the like. No, it has to be something else.

Ruby on Rails has something that transcends the framework itself. It has you. The Mighty Developer. The Early Adopter. The Status Quo Challenger. The so-called Community —whatever that means.

Bottom line is, when I get together with people working with Rails, they are always in search of the holy grail of web development —or the nearest tavern, whatever comes first.. you have to love that kind of pragmatism. We like to break our assumptions, to learn new things and forget about the ones we already know.

We embrace Rails *today* but we are willing to embrace any other tool as long as we like it better. Do you remember the months before the Merb-Rails love affair? Half the Rails developers I know were already making eyes at Merb without the slightest hint of shame.

And by challenging the system, we are obliged to keep learning… and to find new ways to build the web. And instead of trying to make a carbon copy of what we did before, we like to start anew, because that’s where the fun is.

Sure you can argue this attitude is not the exclusive property of the Rails community. And I would second you on that based on theory.. but in practice, I have seen other some other communities lack this need of challenging. Maybe it’s because they have maturity models and certifications and black belts and whatnot…. And maybe having so many constraints is killing creativity; but fact is in some environments trying to take a step forward is seen as something odd, not desirable.

Rails will pass —or not— but as long as we keep alive the spirit of embracing change, we are entitled to be on the fun side of web development.

So, if you ask me, that’s the secret ingredient of Rails. Sure the language and the framework are cool, but the real power of Ruby on Rails is you.. and me.

update: please read the comments, since I was a bit ambiguous in the post and some points needed further explanation :)

it’s the end of the e-world as we know it

Five years

I’ve been working for companies that didn’t last for so long. I’ve never been working in a company for so long come to think of it ;). I had best friends that didn’t last for so long either and I’ve seen plenty of marriages finishing much earlier than that.

Living on the world we live, it’s hard to remember exactly how it was five years ago. I’d say I was still using a landline for internet access. And I was sharing the 54K connection using a proxy.. how uncool is that? ;)

A bit over five years ago, gmail was launched.. More than five years later, gmail is finally removing the “beta” tag.

http://googleblog.blogspot.com/2009/07/google-apps-is-out-of-beta-yes-really.html

And I feel fine

sudo: rake: command not found

I hate it when it happens, don’t you?

And it’s not only rake, but some other utilities too.

Bottom line is, in Ubuntu sudo is by default set to use a secure path. You can change the secure path if you are compiling from source, but we are talking Ubuntu here, the windows for the rest of us, so you get what your package says you get and that’s fine.

There are a couple of good solutions (other than switching to gentoo or slackware ;) )

If you want to use always the same PATH as you are using in your environment, you can just set an alias to sudo and make it set the PATH every time you are invoking it.

alias sudo=”sudo env PATH=$PATH”

It’s safe enough, but notice every time you are using sudo, you will be setting the environment to that of the calling user. Do your maths and reckon whether you are comfortable with that or not.

The option I chose is a bit pickier, making a link to the rake executable from /usr/local/bin, which is one of the secure paths.

sudo ln -s `which rake` /usr/local/bin/

Either way, your problem is solved. Now go save the world! You’re welcome ;)

My slides for “Jruby on Rails: Ruby on Rails sobre la JVM”

It was interesting to be at the Sun Open Communities Forum and meet people I used to work with (or even teach to) as back in time as in 1996.

It was also interesting to have the opportunity to introduce Ruby and Ruby on Rails to Java developers and show them how they could use it from the familiar JVM.

As usual, I uploaded to slideshare the slides I used in my presentation.

The layout might be a bit enterprisey for my standards, but I was representing my company, so I used the company template. Anyway, the presentation is under Creative Commons, so feel free to use it in any way you can imagine, as long as you respect the “non commercial attribution share alike” license.