{5} Setfive - Talking to the World - Page 56 of 66 - Ramblings on code, startups, and everything in between

For a client we’ve been working with recently it came to our attention that they needed more frontend servers to keep up with the traffic for their surveys. They use LimeSurvey which is powerful open source survey platform. We set the client up in the cloud to scale as necessary with a load balancer in front. This is when we noticed the problem that LimeSurvey doesn’t work well when a user is bouncing between different frontend servers. LimeSurvey keeps all the user’s session attributes on the local server and not in the database. After googling around for a while, we found other people also had this problem before, and no one had really solved it. We figured we would.

We didn’t feel like doing a ton of extra work to reinvent the wheel in terms of storing the session in the database. We snagged most of the code straight from the Symfony “storage” module which handles it’s session management if you want to store the user sessions in a database. After a quick few modifications, we got it up:

This requires you create a table in your MySQL database called session. Here is a dump of the create statement for the table:

CREATE TABLE IF NOT EXISTS `session` (
  `id` int(11) NOT NULL auto_increment,
  `sess_id` varchar(255) NOT NULL,
  `sess_data` text NOT NULL,
  `sess_time` datetime NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=1;

Basically this uses PHP’s session_set_handler function to manipulate how the PHP retrieves, updates, and stores the user’s session. The final touches were to include this class where the user sessions are started in LimeSurvey. We found them in the index.php and sessioncontrol.php files. Include our file from above just before the session_start(); in the code in those two files. In admin/scripts/fckeditor.265/editor/filemanager/connectors/php/upload.php include the file before the first include. Lastly we need to update a couple locations where it does session_regenerate_id and replace it with $sfSessionHandler->regenerate(). You can find these edits in the following three files: admin/usercontrol.php on line 128, admin/login_check.php line 65, and index.php at lines 207 and 215. You should be up and running now, let us know if you have any problems.

Recently we found ourselves having a really weird problem on a project: Every time a page was loaded it seemed a bunch of different Javascript functions were being called multiple times and making many widgets on the page break and we couldn’t figure it out. Some of the functions were our own code, some part of the package we were using. After a while we narrowed it down to that all the functions in the

$(document).ready(...);

we’re being called twice. We had never seen this. After about an hour of removing javascript files and just headbanging, and many thanks to Ashish, we found the root cause. We had written in a quick hack for a late proof of concept to string replace on the entire HTML of a page a specific string. We did it this way:

$('body').html($('body').html().replace(/{REPLACETEXT}/i, "More important text"));

Basically we used a regex to parse the entire HTML tree and then replace it with the updated text. Unknowingly this caused the document ready event to be triggered again(though now it makes sense), causing many widgets to get extra HTML.

Let this save you some headbanging.

So earlier today I was working on a Facebook App and wanted to use “partials” in a similar fashion as Symfony’s partials. At this point, I realized I had no idea how Symfony placed variables into the current execution scope when you do things like

include_partial("somePartial", array("foo" => $foo, "bar" => $bar));

A bit of digging led me to the extract() function in PHP.

From the documentation, “extract — Import variables into the current symbol table from an array”.

Pretty neat.

Every now and then, I’ll end up having to scrape HTML pages for some content. I know, I know, there’s like a bazillion different ways to do this, but I *really* like doing it in PHP so I can jack right into Symfony. Usually, I just get down and dirty with the PHP DOM and use XPath to select nodes within the document. The problem with this is that the XPath sucks and the PHP implementation sucks…alot.

But hold on, we know a selector engine that doesn’t suck! The jQuery selector engine, called Sizzle is probably one of the best CSS/DOM selector engines to use. Turns out there is a PHP port! Enter phpQuery

At its root, phpQuery is a port of the jQuery selector syntax to PHP. Additionally, phpQuery includes dozens of the jQuery traversal methods like next(), prev(), find(), and so on. It also implements the CSS3 filters like :first, :last, :eq, ect.

Anyway, if you’re tired of suffering through the PHP XPath implementation and dig jQuery then you should definitely give phpQuery a whirl.

Happy holidays everyone! Hope everyone had an awesome Christmas and is getting excited for a fun New Years Eve and then a great 2010.

Anyway, since the sun never sets on the Setfive empire I was actually doing some coding earlier when I ran across an interesting little problem. What I was looking to do was “match” a string input against a set of acceptable strings. The caveat was that the inputs might have spelling mistakes or typos. For example, an input might be “onnlinee ad” matching against [“online ad”, “video”, “news”, “online”] with the goal of matching “online ad”.

Unfortunately, you can’t simply iterate over the two strings matching letters because a single wrong letter will cause you to miss all of the rest. Remembering back to some old engineering courses I found my way over to the Hamming distance article on Wikipedia. From there, I made my way over to the Levenshtein distance article which proved extremely useful.

So, at this point I figured I wanted to minimize the Levenshtein distance and that would be my matching string. Fortunately enough, PHP has a built in function to calculate Levenshtein distances! levenshtein() The Levenshtein distance works pretty well for what I was looking to do. In addition, PHP has another built in function – similar_text() for comparing two strings. similar_text will return the number of matching characters in the two input strings.

Anyway, the only thing to be aware of is that both these functions have really bad running times. similar_text clocks in at O(n^3) where n is the length of the longest string and levenshtein runs at O(m*n) where m and n are the lengths of the input strings.

Well that’s it for now. Happy string comparing.

javascript – $(document).ready getting called twice? Here’s why.

PHP: Adding variables in the current scope

Cool kid stuff: Sizzle for PHP!?

Happy Holidays!