Pull vs. Push MVC Architecture

I intended to write this post couple of months ago, when I worked on a pull based MVC framework for some site. Most web-developers are acquainted with the MVC architecture and almost all the major web-frameworks uses this concept, including Ruby on Rails, CakePHP, Django, Symfony and others. So what is MVC and what’s the difference between pull and push?
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Equality-at and Relation-at LaTeX Macros.

These are two useful LaTeX macros for creating equality-at and (the more general) relation-at signs. These macros depend on the mathtools package. As with all other macros you should add them to you preamble in order to use.

The general macro is the \relat. It takes two arguments, the relation and an expression where the relation takes place (the “at”). The equality-at macro, \eqat is a specific case of \relat. I’ve created it because it is commonly used and only requires passing the “at” argument.
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A Greasemonkey Fix to the Top Menu in Sheilta (Open University)

Following comments in Fixing the Home Link in the Telem System (Open U) I’ve decided to fix the top bar links in the Sheilta system too.

The links in the top bar are javascript links that open in a new window when clicked. My Greasemonkey script turns them into regular links that you can open in a new tab.

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Notes About Using amsmath split Environment In Hebrew Documents

Recently I’ve worked on a Hebrew document in LaTeX and wanted to use the split environment to typeset some multiline formula. The document which compiled just fine till that point, failed to compile with the following error:

Package amsmath Error: \begin{split} won't work here.

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Hidden Spam Links in WordPress

About a week ago, I’ve decided to look at the HTML source of my blog. I was in total shock to find a spam link hidden there. This is how it looked:

<!-- ocadia theme credits, downloaded from wpthemesfree.com -->
<u id="ocadia" style="display: none">Buy some <a href="http://detoxbuddy.com/categories/191.html">marijuana drug testing</a> products</u>

Ocadia is the name of theme I’m using, so I guessed the hidden link came from there. I was partially right. The code indeed resided in the index.php file of the theme, but as I later found out, the theme had nothing to do with that. I removed link and the comment immediately, and went to see if the it was distributed this way from Beccary (the author of the theme.
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Vim Syntax Highlighting For Google Gadgets

I started developing Google Gadgets for LabPixies, so one of the first thing I looked for was syntax highlighting. Vim recognized the gadgets’ code as XML file (which is correct), but I wanted also HTML syntax highlighting for the HTML part. So after searching a bit for some existing solution, I found one, but I didn’t like as it required me to wrap the HTML code with a specific comment. As I don’t like this kind of solution, I’ve decided to create my own syntax highlighting file for Vim.
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Scanning Documents Written in Blue Ink – biscan

After writing the post on converting PNMs to DjVu I’ve ran into some trouble scanning documents written in blue ink. The problem: XSane didn’t allow me to set the threshold for converting the scanned image to line-art (B&W). So, I tried scanning the document in grayscale and in color and convert it afterwards to bitonal using imagemagick. This ended up with two results. When I used the -monochrome command line switch, the conversion looked good, but it used halftones (dithering), when I tried to convert it to DjVu it resulted in a document size twice as large as normal B&W would. The other thing that I tried is using the -threshold switch. The DjVu compressed document size was much better now, but the document was awful looking, either it was too dark, or some of the text disappeared. After giving it some thought I knew I can find a better solution.
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Convert PNMs to DjVu

I’ve decided to scan some notebooks. After researching a bit, I’ve decided to use DjVu (instead of PDF which I normally use). I’ve chose to use DjVu because it offered great quality with very good compression rate (~26KB per page) in lineart (black and white).

While XSane can natively save a multipage project into PDF it can’t do so for DjVu. So, the solution is to use the PNMs generated by XSane and convert them using the command line tools offered by DjVuLibre to bundle them together to a DjVu file. As you can guess doing this manually is pretty hard work. To make this task easier I’ve written a small bash script to automate the process.
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Trailing Whitespace Causes a Session to be Destroyed in CakePHP

While working on a new project using CakePHP, I’ve came across a weird problem. In one of the controllers the the session always came out as invalid, as 

$this->Session->valid()

always returned false. I tried debugging this weird stuff, and it looked like all the session variables are unset. Using 

$this->Session->error()

to get the last error returned “Config doesn’t exist”. After further debugging “Config” turned out to be an internal array that is saved by CakePHP to the session and holds various internal data (some of it is used for validation like user-agent hash). I kept printing more and more debugging data as well as looking at CakePHP’s trac system.

I found an interesting bug (ticket #4217) and it looked very promising, as it almost fully described my problem. Unfortunately, the solution offered didn’t seem to work for me. But it inspired me to try and start the session manually using session_start() instead of using Cake’s startup and activate methods of the Session Component.

I found out that the session_id() returned empty string. Luckily calling session_start() directly from the controller, gave me a lead. The session seemed to work well but a nasty error about headers already been sent showed up.

I little more investigation lead up that I had a trailing newline after my closing PHP tag in that controller file. Deleting this trailing whitespace completely solved the problem. No need anymore to manually start the session. It’s pretty annoying that such a small thing like trailing new line can cause such seemingly unrelated problems in CakePHP’s session handling.

Maybe CakePHP should add a little debug notice when the session doesn’t start because header were already sent. This can be done by modifying the else statement in the __startSession() method in cake/lib/session.php (line 557 in version 1.2.0.6311). I wonder what the reason they had not to inform the developer when such event happens, as I don’t see why someone will deliberately try to start the session after sending the headers, I think it only happens by mistake (at least most of the time).