Oct 14

The simplest Observer design pattern example

A few days ago I got involved in a chat about the usage of Object-oriented design patterns. I brought up the problematic of their usage when not needed, that ends up in adapting the code to the pattern and altering it, risking to increase its complexity. I mentioned an example of usage of the Observer design pattern, that I’ve seen used even where one object A (Subject) just needed to keep an array of reference of objects B (Observers), but B didn’t actually need to refer back to A.

From wikipedia: The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

In this post, I’ll expose a case where the usage of that pattern is very simple to understand: a Newsletter system, with senders (Subject) and subscribers (Observers).

In this example, we have two users, John and Mike who both subscribe to the NewsletterSender (Subject). When the email is sent, both are notified by NewsletterSender::notifySubscribers() that iterates the users and call their update() passing its reference. Via this reference, the users will then be able to call the getter to read the email. So, John and Mike will both receive the reference to the NewsletterSender, John will print out the email text, but Mike only decides to say that there is an email (different implementation).

See the comment near each method with the classes and method names of the corresponding PHP interfaces SplObserver and SplSubject

Aug 14

How to modify columns in a DB with a script

One of my client recently needed to implement an application-level encryption for some existing applications.

Unfortunately, the design pattern used for the database layer obliged me to write an independent script to browse the database and encrypt the data for each user using a user-specific two-way encryption key.

So, I ended up writing a simple utility class that applies a user-defined function (modifies) to the defined columns and records (via a filter query) of each database table.

It can be used for any relational database server supported by PDO (MySQL, SQL Server, MySQL, Oracle). I’ve only used it with MySQL but it should work smoothly with all the others.

Db modifier https://github.com/elvisciotti/DbModifier

An example of usage is in the README, hope it’s clear enough.

You can basically use this to mass editing Db records with a function that is NOT easily implementable with a simple MySQL Query, e.g. encrypt the data with a custom PHP function.

Mar 14

File Upload from HTML form: client and server validation for maximum size

File uploading normally requires client validation (mainly as a UI improvement) and server validation (in case the client validation is bypassed/hacked).

The code

<input type="hidden" name="MAX_FILE_SIZE" 

only imposes a soft limit (in bytes) on the server side, therefore not a good practice since it can be altered by the user. The solution I adopted is composed by a server side validation AND a client validation (in JavaScript, mainly for a better user experience since it can be easily hacked as all the other JS solutions)

Client validation (JavaScript)

The idea is accessing the files JS property of the input field and read the file size on the ‘change’ event (when a file is selected from the user). If the selected files exceeds the max size, I simply display a clear user warning and disable the submit button. I’ve created a generic script that automatically listens to the change event for any file upload element, and reads the max upload size in bytes from the MAX_FILE_SIZE HTML input hidden element in the same form.

Server side validation (PHP)

Just set the desidered value for ‘upload_max_filesize’ and ‘post_max_size’ PHP settings (php.ini). Alternatively, if you need application specific settings and you use apache as webserver, add the following lines into the .htaccess in your webroot

php_value upload_max_filesize 25M
php_value post_max_size 25M

Mar 14

How to reload CSS without reloading the full page

Just drag this link Reload CSS into the browser bookmarks bar.

Source code on Github at this  link

Feb 14

Doctrine 2 + zf2 working with both SQL server and MySQL

The web application I’m working on (PHP 5.3, zf2, Doctrine2, on MySQL/Apache) has recently raised interest from the clients and it now needs to be installed on their premises, often a Windows server( arghhh!). That meant we had to make the application compatible with both MySQL and SQL-Server.
Here I summarize the changes and the solutions we adopted.
Continue reading →

Nov 13

Chrome, Firefox, IE browser plugin to reload CSS without reloading the page

When developing and adjusting the CSS, a methodology is using firebug to directly edit the styles and then re-apply the change on the real file with the editor.
In other cases, it’s more practical to change the CSS directly, but reloading the full page is a bit time consuming.

Here is a trick to reload only the CSS. There are browser extensions for it, but at the time of writing, none of existing ones works as expected, at least on chrome.
So, I simply solved by creating a browser tool-bar link that reloads the CSS without reloading the full page, with one-line of JavaScript.

From your browser toolbar: right click and select the option to add a new URL (“Add Page” on Chrome)
name: “Reload CSS”
url: the following script

Or just drag this into the toolbar Reload CSS

Nov 13

Recent code

I haven’t posted for a while. The main reason is that almost any technical solution is solved on stackoverflow, and when I find one, I tend to reply in there, in order to contribute to the community. Besides, I’m now actively developing a project (administrative software), that we started developing from the ground at LexisNexis, excellently backed by clear requirements and SCRUM. As a result, most of my efforts and time go into that project, constantly refactoring and improving the design.

You can find some of my recent snippets of code are on github:

  • cache wrapper utility with phpunit test (exhumed from an old post)
  • JQuery plugin to make inputbox with spinner buttons (click and hold with different increase/decrease rate)
  • other small JS scrips here and here

Nov 13

Chrome command line options for windowed HTML applications

An example of combination of chrome command line arguments to launch an HTML page…

  • windowed, that means in “app mode” (no toolbars, –app=”<url>” argument),
  • with no web security checks (= allowed DOM manipulation of frame loaded on a different domain, --disable-web-security), that allows Javascript to modify the content of forms loaded in other frames from external URLs, for full-flegded interactions.
  • with a custom user-agent (–user-agent). I personally use it for a website that – with a mobile User-Agent – displays much less annoying banners and a layout that better fits its small frame;
  • with independent user session settings (–user-data-dir=”C:/path-to-temp-files”). That’s necessary to avoid chrome sharing settings with your current chrome user session, and mandatory to enable ad-hoc settings like the web security

Aug 13

How to modify PDF files, inserting text and image / signature

This post is not related to PHP nor software development, it’s just a a simple tip about speeding up a small everyday task I’ve been having:

Adding text and signature (image) to a PDF (definitely more practical then print + fill it in + sign + scan and send it back).

PDF-XChange Viewer (v 2.5 free, for windows) is a simpler alternative to PDF editing software, and is able to add images (including your scanned signature) and text into a PDF, and save the changes. If the link is broken or not available, or the app is not free anymore, maybe I still have a copy on my dropbox.

Steps to add a signature

  • (only the first time) Tools -> Comment and markup tools -> show Stamps Palette. Create new collection -> From Image
  • Tools -> Comment and markup tools -> Stamp Tool -> [select your signature]

Steps to add text

  •  Tools -> Comment and markup tool -> Typewriter tool

Last time I found a free sofware able to do that I then forgot the name and I was unable to find a valid one. Next time it happens I’ll search in my blog first :)

Feb 13

Firefox user preferences with selenium (behat+mink) to bypass a proxy or disable cache

At work we are testing an existing application with behat+mink. We normally use goutte driver, but in some cases (when javascript is needed) we need to use selenium server piloting firefox.

When using firefox, the page is loaded including external javascript (google analytics, network ads etc..) so it needs connetivity. An alternative is disabling external requests on the testing environment or use a fake DNS entry, but that wasn’t a viable solution for us.

A small problem I had was bypassing the office network proxy, that requires a proxy auto config file (PAC) when firefox was running. You can find many links online mentioning the various firefox preferences you can set, for example network.proxy.http and network.proxy.http_port to specify a proxy, or network.http.use-cache to enable/disable the browser cache.

In my configuration (ubuntu 12.04, with selenium 2.28, firefox 18.0.1), the preferences file read by firefox is located at /usr/lib/firefox/defaults/pref/proxy.js, where you can add the various calls to user_pref([settings], [value]) .

Here an example of how I changed the puppet manifest of the box to make things working for us

file { "/usr/lib/firefox/defaults/pref/proxy.js":
 content =>
'user_pref("network.proxy.autoconfig_url", "http://chante-with-your-value/default.pac");
user_pref("network.http.use-cache", false);
user_pref("network.dnsCacheExpiration", 1);
user_pref("network.proxy.type", 2);'