Category Archives: PHP Programming

PHP Dark Arts: References

Remember the first time you dabbled in C?  Oh, the glorious typing, functions, and structs!  Now do you remember the first time you ran in to a pointer?  ‘*’, ‘&’, ‘->’ all made your hurt, but eventually you figured it out.  It’s fortunate (depending how you look at it) that we don’t have need to dabble with pointers or references while web programming these days.  However, PHP does allow us to passing things around by reference.  It’s not used often, but when used correctly can be very beneficial to the quality of your code.

What are PHP references?

The first thing you need to know about PHP references is that they are not C references.  You can’t do pointer arithmetic on them because they aren’t actually addresses.  In PHP references are actually symbol table aliases.  This means that you can have 2 variable names sharing the same variable content.

What can you do with references?

There are 3 things that you can do with PHP references.

  • Assign by reference.
  • Pass by reference.
  • Return by reference.
$x =& $y;
$x = 3;
echo "X: $x, Y: $y";

The above code sets $x and $y’s references to the same content area. Therefore, when $x is assigned 3, $y has access to the same data.

function add_item(&$item) {
   	$item++;
}
 
$totalItems = 0;
for($i = 0; $i <; 5; $i++) {
	add_item($totalItems);
}
echo "Total items: $totalItems";

This code allows you to modify a variable’s value without ever returning anything. In this example I made a simple counter, but you can set the value of $item to anything and it should work out just fine.

class Test {
	public $count = 0;
 
	public function &getCount() {
		return $this->count;
	}
}
 
$t = new Test();
$value = &$t->getCount();
$t->count = 25;
echo $value;

This code returns a reference to the public $count variable of the Test class. Generally this isn’t best practice, as it lowers the readability of the code.

Unsetting References

In the event that you want to free a variable from it’s reference to another, you can simply use the unset function.

$x =& $y;
unset($x);

HTML 5 Canvas: Saving to a File with PHP

So you’ve finally discovered the wonder that is the HTML5 Canvas element. Great! If you’re like me, the first thing I wanted to do with it was doodle on it. I eventually worked out how to map touch/mouse events to the canvas and draw lines, but I wanted to save my creations!

As it turns out, the Canvas element has a method called toDataURL(), which base64 encodes the entire Canvas element and returns it as a string. From there, you can just pump it over to a server and handle it from there. Here’s the step-by-step, which assumes you are also running jQuery on your site.

Step 1: Save the canvas and POST the data

var data = document.getElementById("myCanvasID").toDataURL();
$.post("process.php", {
	imageData : data
}, function(data) {
	window.location = data;
});

Step 2: Process the POST data, and save it to a file.

$data = substr($_POST['imageData'], strpos($_POST['imageData'], ",") + 1);
$decodedData = base64_decode($data);
$fp = fopen("canvas.png", 'wb');
fwrite($fp, $decodedData);
fclose();
echo "/canvas.png";

Note: The first line of this script removes the header information that is sent with the encoded data.

Thats all there is to it. You can now easily save your HTML 5 awesomeness.

Caching WordPress Data with the Transients API

If you’re a plugin or theme developer, there may come a time when you need to execute a long running operation. It doesn’t need to be anything complicated, but something as simple as fetching a Twitter feed can take a significant amount of time. When you come across these types of situations, it’s handy to be able to store the data on your own server and then fetch a new copy of it every X hours. This is called caching, and WordPress convieniently comes packages with an excellent caching API called Transients .
Wordpress Transients API

The Transients API is surprisingly simple to use. In fact, it’s very much like using set_option and get_option except with an expiration time. If you aren’t familiar with caching at all, here’s the general workflow:

  1. If the data exists in the cache and isn’t expired, get it.
  2. If the data doesn’t exist in the cache or is expired, perform the necessary actions to get the data.
  3. Store the data in the cache if it doesn’t already exist or is expired.
  4. Continue from here using data.

When attempting to use the Transients API for caching, there are three functions that you need to be aware of: set_transient, get_transient, and delete_transient.

  • set_transient($identifier, $data, $expiration_in_minutes): This function stores your data into the database. The identifier is a string that uniquely identifies your data. Your data can be any sort of complex object, so long as it is serializable. The expiration is how long your want your data to be valid (ex: 12 hours would be 60*60*12).
  • get_transient($identifier): This retrieves your data. If the data doesn’t exist or the expiration time has passed, false is returned. Otherwise, the same data you stored will be returned.
  • delete_transient($identifier): This will delete your data before it’s expiration time. This is handy if you are storing post-dependent data because you can hook it into the save action so that every time you save a post, your cached data is cleared.

Now that we’ve covered the basics, how about a quick example?

if (false === ( $my_data = get_transient('super_expensive_operation_data') ) ) {
     $my_data = do_stuff();
     set_transient('super_expensive_operation_data', $my_data, 60*60*12);
}
 
echo $my_data;
 
function do_stuff() {
     $x = 0;
     for($i = 0; $i != 999999999; $i++) {
          $x = $x * $i;
     }
     return $x;
}

The example is pretty straight forward. We first check to see if there is a cached copy of the data, if not, we fetch the data from the “do_stuff” function, and store it in the database. Simple, right?

One of the benefits of using the Transients API (aside from speeding your site up) is that plugins like WP Super Cache or WP Total Cache will auto-magically cache your data into memcached if you have it set up. For you, this means an even faster site! If you have any questions about caching techniques or the Transients API, leave a comment and I’d be happy to help.

Tracking Email Open Time with PHP

You can download my code for this article here.
Some time ago I had great aspirations of launching a web company that does email tracking and analytics. One of the things that I really wanted to figure out but wasn’t well documented on the web was how to track how long a user had a particular email open. When a company like MailChimp wants to track emails that they are sending out, they put a small image in the email called a “beacon”. When the user opens the email, the beacon image is requested from the server. The server sends the image, but not before it gathers information about the computer requesting it. The works great for checking if an email was opened, or what platform the person is on, but it doesn’t work at all for determining how long the email was open for.

One option that came to mind for checking the open time of an email was long polling.  Long polling (in this case) would use Javascript to contact the server every X seconds after the email was loaded.  Using those requests, it’d be trivial to find out how long it was open for.  Unfortunately, most (if not all) email clients don’t allow the execution of Javascript within emails, so that idea was completely sank.  The only option I had left was to use the beacon image to somehow determine open time.

The only option I could think of for using the image beacon without any Javascript was to redirect the image back to itself.  After much trial and error, I came up with the following.

//Open the file, and send to user.
$fileName = "../img/beacon.gif";
$fp = fopen($fileName, "r");
header("Content-type: image/gif");
while(!feof($fp)) {
    //Do a redirect for the timing.?
    sleep(2);
    if(isset($_GET['clientID'])) {
    	$redirect = $_SERVER['REQUEST_URI'];
    } else {
    	$redirect = $_SERVER['REQUEST_URI'] . "?clientID=" . $clientID;
    }
    header("Location: $redirect");
}

So what’s happening in this code?  First of all, we’re opening a small GIF file that we’re going to pretend to send to the user.  The second step is to send a header for an image file to the user so that their mail client expects one to be delivered.  This step is important because if the header isn’t sent, the browser/mail client will close the connection.  After that, you make the request sleep for a few seconds (as few or as many as you want depending on how granular you want your timing data to be) and then redirect back to the same page.  The “if” statement within the while loop is there so you can identify incoming requests and log the data accordingly.

So there you have it.  If you’ve ever wondered how people track the open time of an email, it’s probably a method very similar to this.  The only caveat to this method is that it relies on the user loading images in an email.  However, if you have a large enough sample you can just take the average open time from the users that did open it and be fairly confident with that.

Note: There has been some discussion over on Stack Overflow about this article. You may find it helpful.

 

If you liked this article, then you may like:

  • PHP Dark Arts: Multi-Processing (Part 1)
  • PHP Dark Arts: Multi-Processing (Part 2)
  • PHP Dark Arts: Shared Memory Segments (IPC)
  • PHP Dark Arts: Semaphores
  • PHP Dark Arts: GUI Programming with GTK
  • PHP Dark Arts: Sockets
  • PHP Dark Arts: Daemonizing a Process
  • WordPress Development as a Team

    At my day job I’m really the only person that knows how to write WordPress plugins, so when I write one it’s usually sand-boxed on my machine where nobody can touch it. However, in a side endeavor I’m part of we have a team of 3 people developing on one plugin. As I’m the most experienced plugin developer amongst our team, I was tasked with coming up with a development style and plugin architecture that would work for us.

    Development Style

    Everyone will be running a local copy of WordPress and making their changes to the plugin locally. The plugin itself will be under version control using Git, and developers will push/pull changes from either a self-hosted Git server or Git Hub. Database schema will be tracked in a file called schema.sql. When someone makes a change to the schema, it goes into that file at the bottom with a comment about why the schema changed. We’ll being jQuery as our Javascript framework of choice, and we’ll be writing all of our Javascript in CoffeeScript (see my previous entries).

    Plugin Architecture

    The more difficult aspect of developing this plugin as a team is the sheer size of the plugin. Realistically this could probably be split into about 6 different plugins by functionality, but we want to keep everything together in one tidy package. To illustrate the architecture, I made a quick drawing.

    The first layer of the plugin is essentially a wrapper. It initializes the ORM that we are using to access the database (we are using a separate database for this plugin’s data), and includes the wrapper class. The wrapper class is where developers drop their sub-plugin include file and instantiate it’s main object. For instance, for each sub plugin there will probably be two classes instantiated in the wrapper. One being admin related functionality, and the other being for front-end display functionality. My thinking with this architecture was that we could all work on separate sub-plugins without crossing paths too frequently. This also allows us to separate the different functionality areas of the plugin in a logical manner. The other benefit to architecting the plugin like this is that it will be very easy to port to a different architecture in the future. I’m well aware that WordPress probably isn’t the best tool for the job, but it is the best tool for the team with the deadline that we have.

    Thoughts

    While thinking about WordPress Plugin Architecture, I cruised the source code of a lot of plugins and it seems that everyone goes about it in a different way. If you’ve ever developed a large-scale plugin with a team, how did you go about doing it? Did you run in to any problems that you didn’t foresee at the beginning of the process?

    Getting Web Scale with Memcached

    The web is huge, and there are a lot of people on it. Day and night, millions upon millions of people are on the web surfing, commenting, and contributing. Normally your blog gets a few hundred visitors a day ( a few thousand on a good day ), but what happens when that number increases? Can your database server handle all that load? Will Apache come screeching to a halt due to all of the requests? The answer is probably yes, unless you implement some form of caching. Many years ago this wasn’t a huge problem, but as the web and it’s user base has grown, so has the problem of “web scale”.

    Memcached

    Memcached is a pretty simple concept. Just as the name implies, it’s a caching system that stores stuff in memory. That’s really all you need to know to get started. If you’re interested in learning more, check out the Memcached home page.

    PHP Memcache

    As this is mostly a PHP blog, I’m going to show you how to use Memcached with the PHP Memcache module. While this tutorial is language specific, the concepts here can be applied to any language to increase the speed of your web pages. That being said, the first step is to get Memcached installed on your machine. There are a ton of tutorials out there on the web for this, so I’m going to leave that as an exercise for you. Once that’s installed, you should check out my guide for getting the PHP Memcache module installed on XAMPP, that way you can run this tutorial locally.

    Step 1: Make the connection

    This step is pretty straight forward. If you can’t connect to your caching server, you can’t cache. If the connection is successful, continue trying to cache. Otherwise, just query your database as normal.

    $memcache = new Memcache;
    $memcache->connect("my.memcached.server", 11211);

    Step 2: Cache something

    For this step, the only potential “gotch-ya” is that the your identifier must be unique, and time to expire is in seconds.

    $myValue = "hello world!";
    $memcache->set("Hello World", $myValue, false, 60*60*24);

    Step 3: Retrieve an item from the cache

    $myValue = $memcache->get("Hello World");
    echo $myValue;

    Step 4: Putting it all together

    So how does all this work in conjunction with your web app? The basic workflow for using caching is the following:

    1. Does my item exist in cache> (This satisfies determining if a connection to the cache has been made as well.)
    2. If so, get the item and store in a variable.
    3. If not, get the item from the database.
    4. Store the item for later use.
    $memcache = new Memcache;
    $memcache->connect("my.memcached.server", 11211);
     
    $arrayVals = $memcache->get("My Identifier");
    if(!$arrayVals) {
            //Note: This assumes that the data in the table doesn't change
           // and that it is fairly small in size.
    	$query = "SELECT * FROM myTable";
    	$result = mysql_query($query);
    	while($row = mysql_fetch_array($result)){
    		$arrayVals[] = $row;
    	}
    	$memcache->set("My Identifier", $arrayVals, false, 60*60*24);
    }
     
    foreach($arrayVals as $val) {
    	print_r($val);
    }

    If you’re following carefully, you can see that the first time through the data will get pulled out of the database. However, for the next 24 hours the data will be coming from the Memcached server. It’s little tricks like this that can help your site survive being featured on Reddit. Moral of the story: If your site is slow because of volume, try caching almost everything and you should have noticeable improvements.

    Installing Memcache on MAMP

    For the better part of 2 hours I tried and failed to get the Memcache extension installed on MAMP.  I tried following several guides, but everything fell flat on it’s face about 75% of the way through.  I eventually figured it out, and I wanted to share it so that other people don’t have to go through the pain and suffering that I did.  It turns out to be surprisingly easy, but YMMV.

    Step 1: Install XCode

    Step 2: Make the MAMP PHP binary files executable

    sudo chmod +xrw /Applications/MAMP/bin/php5.3/bin/p*

    Step 3: Get the Memcache extension source

    cd ~
    wget http://pecl.php.net/get/memcache-2.2.5.tgz
    tar -zxvf memcache-2.2.5.tgz
    cd memcache-2.2.5

    Step 4: PHPize the Memcache extension files

    /Applications/MAMP/bin/php5.3/bin/phpize

    Step 5: Compile the Memcache extension

    ./configure
    make

    Step 6: Add the extension to the PHP.ini file

    Add the following to the end of your PHP 5.3 ini file via the MAMP file menu.

    extension=memcache.so

    Step 7: Copy the memcache extension to the PHP extension folder

    cp modules/memcache.so /Applications/MAMP/bin/php5.3/lib/php/extensions/no-debug-non-zts-[yourtimestamp]/

    The “[yourtimestamp]” varies per installation, but you should just be able to tab complete that part.

    PHP Alternative Syntax

    Did you know that PHP has an alternative syntax structure?  Up until about two years ago, I didn’t either.  It wasn’t until I started poking around in the WordPress core that I saw it.  Intrigued, I popped over to PHP.net and read an entry on it.  In a nutshell, the alternative syntax can go far in making your PHP code much easier to read.  The control structures if, while, for, foreach, and switch can all be expressed in the alternative syntax form.  In general, I prefer to use the alternative syntax when mixing PHP in with HTML, and the standard syntax when writing pure PHP.

    If Example

    // This....
    if($myString == "foo"):
        echo "bar";
    else:
        echo "no-foo-bar";
    endif;
     
    //...is equal to this.
    if($myString == "food") {
        echo "bar";
    } else {
        echo "no-foo-bar";
    }

    ForEach Example

    $names = array("bob", "tom", "john");
     
    //This....
    foreach($names as $name):
        echo "Your name is: {$name}";
    endforeach;
     
    //...is equal to this.
    foreach($names as $name) {
        echo "Your name is: {$name}";
    }

    Resources

    If you’re looking for more resources on PHP’s alternative syntax, check out the documentation here, or the WordPress source code for examples.