I turned in the manuscript for the book, which had already gone through technical editing, back in April 2009. That’s right, 14 months ago. After going through proofreading and layout, having a cover designed, getting an ISBN, and so forth, the digital version of the book finally went up for sale about three months ago.

At that point, I asked if print copies would be available at php|tek. The publisher sounded unsure, but told me that they would see what they could do. I was later told that the book had gone through printing and that arrangements had been made for a box to be shipped to the hotel on the Monday prior to the conference starting. It didn’t arrive at any point before or during the conference.

After the conference was over (now about two months ago), I was told that the box had finally arrived at the hotel the following Wednesday. I’m not sure how this was known, because the box was never recovered from the hotel to be shipped elsewhere.

The publisher then resolved to request another box from the printer. This box would have to be shipped to someone to proof the printed copies for quality assurance, then the books would go on sale. I was told about this resolution in early June, about five or six weeks ago. I’ve been in touch with the person responsible for proofing the books; they haven’t been received yet.

I have no direct contact with the printer, so all I’ve been able to do is e-mail the publisher repeatedly (six times and counting) since then asking for an update. Through an instant messenger conversation, I was told that a call was supposed to be placed to the printer early last week to determine what the status of things was. So far as I know, that call was never made, or at least I was never told of the result.

I’m as frustrated with this situation as anyone. I want the book to be available to people who want to read it in the format they prefer. If you are in this audience, please contact the publisher to voice your opinion. You can do so by using this contact form on their web site or by sending them a tweet on Twitter. Thank you all very much for your continued support.

I recently wrote a PHP script to scrape data from a .NET application. In the process of developing this script, I noticed something interesting that I thought I’d share. In this case, I was using the cURL extension, but the tip isn’t necessarily specific to that. One thing my script did was submit a POST request to simulate a form submission. The code looked something like the sample below.

$ch = curl_init();
curl_setopt_array($ch, array(
    CURLOPT_URL => 'http://...',
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => array(
        'field1' => 'value1',
        // ...
    ),
    // ...
));

The issue I ran into had to do with a behavior of the CURLOPT_POSTFIELDS setting that’s easy to overlook. This is a segment of its description from the PHP manual page for the curl_setopt() function.

If value is an array, the Content-Type header will be set to multipart/form-data.

If the form being submitted is not set to have an enctype attribute value of multipart/form-data in the form’s markup, .NET returns a 500-level HTTP response with no further information on what causes the error (for security purposes). This presumably happens because it’s expecting one value for the Content-Type request header and getting another.

Setting CURLOPT_HEADER and CURLOPT_VERBOSE to true helped to reveal that this was the issue. The fix is pretty simple: instead of passing the array itself for CURLOPT_POSTFIELDS, pass the result of wrapping it in a call to the  http_build_query() function (see its PHP manual page). This converts it to a properly formatted query string, which causes cURL to use the default Content-Type header value of application/x-www-form-urlencoded instead.

Tools like Firebug can help you to examine requests made by a browser. Together with these settings for cURL, you can modify your script’s requests to match those of your browser as closely as possible, making gotchas like this less likely to trip you up.

The SPL, or Standard PHP Library, is an often overlooked extension in the PHP core. It first came on the scene in PHP 5 and a variety of iterators constituted the majority of its initial offerings. Though the iterator offerings were expanded in PHP 5.3, the particularly interesting additions to the SPL were several specialized data structure classes, the foundational concepts for which originate in the field of computer science. In this post, I will provide an overview of these new classes and explain why and when they should be used.

Arrays

While PHP has several data types, the ones that likely see the most frequent and varied use are strings and arrays. They are the proverbial duct tape and WD-40 of PHP, respectively. Like arrays, SPL data structure classes are used to store composite (i.e. non-scalar) data.

Now, that’s not to say that every instance of an array in existing codebases should be replaced with an SPL container object. There are cases where it’s appropriate to use one over the other. Knowing the difference requires an understanding of how arrays work.

Within the C code that makes up the PHP interpreter, arrays are implemented as a data structure called a hash table or hash map. When a value contained within an array is referenced by its index, PHP uses a hashing function to convert that index into a unique hash representing the location of the corresponding value within the array.

This hash map implementation enables arrays to store an arbitrary number of elements and provide access to all of those elements simultaneously using either numeric or string keys. Arrays are extremely fast for the capabilities they provide and are an excellent general purpose data structure.

Fixed Arrays

In contrast to arrays, SplFixedArray functions more like C arrays or Java arrays than PHP arrays. The maximum number of elements that it may contain is specified upon instantiation. While it is possible to change it later via the setSize() method, this negates the performance advantages of using it: because its size is fixed, it doesn’t need to use a hashing function to resolve the position of elements within the array. It makes sense to use fixed arrays when the number of elements to be stored is known in advance and the elements only need to be accessed by sequential position.

SplFixedArray implements the Iterator, ArrayAccess, and Countable interfaces. Iterator allows it to be iterated using a foreach loop. ArrayAccess provides access to its elements using array syntax where elements are referred to using integer positions beginning at 0 as with enumerated arrays. Countable enables a list to be passed to the count() function like an array.

Aside from the inability to use it in place of arrays with array functions, instances of SplFixedArray function just like arrays for all intents and purposes. It’s even possible to convert them to and from arrays using the toArray() and fromArray() methods respectively. However, it generally makes more sense to use SplFixedArray exclusively for each individual use case.

Lists

In computer science, a list is defined as an ordered collection of values. A linked list is a data structure in which each element in the list includes a reference to one or both of the elements on either side of it within the list. The term “doubly-linked list” is used to refer to the latter case. In the SPL, this takes the form of the class SplDoublyLinkedList.

Like SplFixedArray, SplDoublyLinkedList also implements the Iterator, ArrayAccess, and Countable interfaces. In addition to the methods that come with these interface implementations, elements can be added to or removed from the start or end of the list using its push(), pop(), shift() and unshift() methods, which correspond to the array_push(), array_pop(), array_shift(), and array_unshift() functions respectively. Unfortunately, as of PHP 5.3.2, there’s no way to insert an element anywhere in the list other than at the beginning or the end. A feature request has been filed for this. Add a comment or vote to show support for its addition.

The elements at the start and end of the list are accessible via its top() and bottom() methods respectively, which correspond to the reset() and end() functions. Like SplFixedArray, elements can also be accessed arbitrarily by positional index using the array syntax granted by ArrayAccess. It makes sense to use lists when the number of elements to be stored is not known in advance and the elements only need to be accessed by sequential position.

Stacks

Stacks are similar to lists with two major differences. First, elements can only be added to the top of the stack. Second, an element can only be accessed by taking it off the top of the stack. Because of these differences, the stack is often referred to as a Last-In-First-Out or LIFO data structure. SplStack is the SPL stack implementation.

SplStack is a bit removed from the traditional definition of a stack. It extends SplDoublyLinkedList and inherits its abilities, some of which don’t really apply to stacks. In order to enforce its restriction on how elements are accessed, SplStack overrides the setIteratorMode() method of its parent class and implements its own to prevent modification of the iteration direction. Both methods allow elements to be retained or removed as they are iterated.

Use of stacks makes sense when the number of elements to be stored is not known in advance and the only element that must be accessible is the last one stored. However, as of PHP 5.3.2, the performance of SplStack leaves something to be desired. Benchmarks included later in this provide an objective illustration of this, though the cause of the behavior remains unknown.

Queues

Queues are also similar to lists, again with two major differences. First, elements can only be added (or “enqueued”) to the end of the queue. Second, an element can only be accessed by removing (or “dequeueing”) it from the beginning of the queue. For these reasons the queue is referred to as a First-In-First-Out or FIFO data structure. The SplQueue class implements this data structure in the SPL.

SplQueue follows suit with SplStack in extending SplDoublyLinkedList. Just as SplStack resultingly inherits some operations with at least questionable applicability, so too does SplQueue. Likewise, it overrides setIteratorMode() with its own version to restrict how elements are accessed. Use of queues makes sense when the number of elements to be stored is not known in advance and the only element that must be accessible is the remaining element that was stored earliest.

One minor difference between SplQueue and SplStack is that the former contains two method aliases named after conceptual queue operations: dequeue() aliases SplDoublyLinkedList::shift() and enqueue() aliases SplDoublyLinkedList::push(). This makes sense because while push() and pop() share similar applicability to conceptual stack operations, they are already present in its parent class.

Despite their common ancestry, SplQueue appears to have better performance than SplStack as of PHP 5.3.2. Benchmarks included later in this post review this in more detail.

Heaps

Up to this point, the data structures discussed have resembled lists insofar as they contain elements in the order in which they were added. By contrast, when an element is added to a heap, a comparison function is used to compare the new element to other elements already in the heap and element is placed appropriately within the heap based on that function’s return value. The beauty of heaps is that their underlying algorithm does this with minimal element comparisons, so it’s extremely efficient. Using heaps makes sense when the number of elements to be stored is not known in advance and elements must be accessed in an order based on how they compare to each other.

SplHeap is an abstract class used to create a heap by extending it and providing a comparison function in the form of its compare() method. Only the root element of a heap, the one yielding the highest comparison function return value, may be accessed or removed from the heap at any given time. This is done using the extract() method of SplHeap. SplHeap implements the Iterator and Countable interfaces but, because only the root element can be extracted, it does not implement the ArrayAccess interface like the previously discussed data structure classes.

In addition to the abstract SplHeap class, two concrete implementations are also included in the SPL, namely SplMinHeap and SplMaxHeap. The compare() method of SplMinHeap returns a value such that the smallest element in the heap is the root element. Likewise, the compare() method of SplMaxHeap returns a value such that the largest element in the heap is the root element.

At first glance, using a subclass of SplHeap may seem equivalent to calling sort() or a similar function on an array and accessing the elements in sequence. This is indeed the case if all elements are added to the array prior to it being sorted. However, situations such as elements arriving over time or inadequate memory to store all elements simultaneously may preclude this approach. Use of arrays in such situations would require repeated resorting of the entire array as new elements are added, which is inefficient. This is why using the corresponding heap class makes a lot more sense in that situation than repeated calls to sort(), min() or max(). Additionally, SplHeap can be used to implement the heapsort algorithm, which has better worst case performance versus the quicksort algorithm implementation used by arrays.

Priority Queues

Priority queues are somewhat similar to heaps. In fact, while it doesn’t extend SplHeap, SplPriorityQueue does make use of a heap structure internally to implement its functionality. The difference is that the insert() method of SplPriorityQueue queue accepts both a value and an associated priority, removing the need to use an array or object to store both of these and define an appropriate comparison function in an SplHeap instance. Elements with the highest priority, like those in SplMaxHeap with the highest value, are the ones that come out first when extract() is called. Note that elements with equal priority are returned in no particular order.

For reasons similar to those of SplHeap, SplPriorityQueue implements both Iterator and Countable interfaces and does not implement the ArrayAccess interface. Because it stores a value and priority per element, SplPriorityQueue includes a setExtractFlags() method that modifies the behavior of extract() to return the stored value, the stored priority, or an array containing both. Priorities are not bound to a particular data type: strings, integers, or even composite data types can be used. SplPriorityQueue can be extended and its compare() method overridden to customize the comparison logic.

It makes sense to use a priority queue when the number of elements to be stored is not known in advance and elements must be accessed in an order based on how a value associated with each element (versus the element value itself) compares to the same associated values of other elements.

Sets and Composite Hash Maps

SplObjectStorage combines some of the properties of two different data structures. First, it provides the same functionality of a hash table that a normal array has, but without its associated inability to use objects as keys unless the spl_object_hash() function is used. In other words, it implements a composite hash map. Second, it can be used as a set to store objects as data without a meaningful corresponding key or concept of sequential order.

Its attach() method accepts an object key and the data to associate with it and its detach() method allows data to be removed using its associated object key. To use the object as a set, simply exclude the $data parameter for attach() as it’s optional. The set operations implemented by SplObjectStorage all have array function counterparts. For example, the addAll() method and array_merge() function both correspond to the union set operation. The difference operation is available using the removeAll() method and array_diff() function and its variants. The contains() method and in_array() function both implement the element_of operation. Sadly, only arrays have an implementation of the intersection operation in the form of array_intersect() and its variants. Tobias Schlitt has a more in-depth analysis of this data structure that includes implementations of the set operations lacking in the SPL itself.

Like some of the other data structures in the SPL, SplObjectStorage implements the Iterator, Countable, and ArrayAccess interfaces. Oddly, it also implements the Traversable interface (which is limited to internally defined classes and negates the need for implementation of the Iterator interface) and the Serializable interface (and it is the only SPL data structure class to do so).

Using this class makes sense when data must be stored using composite keys or the ability to access data using set operations is more important than accessing data in a specific order.

Benchmarks

Standard disclaimer: There are lies, damned lies, and benchmarks. YMMV.

Platform

• System: Sony Vaio VGN-NR298E
• CPU: Intel Core2Duo 1.83GHz
• RAM: 4 GB DDR2
• OS: Ubuntu 9.10 Karmic Koala Desktop Edition 64-bit
• PHP: Custom build of 5.3.2 (here’s how to create one) using this configuration: --without-pear --without-sqlite --without-sqlite3 --without-pdo-sqlite

Process

Code used is located in this GitHub repository.

1. Modify constant declarations at the top of runner.php as appropriate (50 executions per test were used to get the results below), then execute it from the command line. It will in turn execute each of the scripts in the tests directory, measuring execution time and memory usage. Results will be recorded in results/raw.csv.
2. To generate graphs, run graphs.php. This uses the Graph component from the ezComponents library. Resulting images will be written to the results directory in PNG format.

Results

		Code Array SPL
		Code Array SPL
		Code Array SPL
		Code Array SPL
		Code Array SPL
		Code Array SPL
		Code Array SPL

Other Data Structures

If you have an interest in other data structure implementations for PHP outside of SPL offerings, check out the bloomy PECL extension, which is an implementation of a bloom filter created by Andrei Zmievski.

It’s currently only available in PDF format due to a delay with the printer; a dead tree version should become available within the next few weeks. To my knowledge, there are plans to offer the paper and PDF bundle as has been done in the past with their other books.

Many of you reading this post probably have a personal to-do list of goals that you want to accomplish within your lifetime.  Becoming the published author of a book has been an item on my own list for some time, one that seeing this accomplishment through to its completion has helped me to cross out. I think anyone who has achieved a similar victory can relate to its significance, if only to oneself.

I do of course encourage you to purchase the book. I have no naïve notions that this will result in any substantial monetary return. Even if it did, that was not my reason for writing the book. I did it because I have knowledge that I believe is worth knowing and sharing with you. There were a number of people who contributed to this and I encourage you to read about them in the pages of the book that credit them.

It is also worth restating here that I have many family members, friends, and colleagues who helped to make this possible. There are too many to name, but I would like to thank each and every one of you from the bottom of my heart. I consider this a milestone in my life and my only hope is that it has as profound an effect on your life as it has on my own.

More than one way to skin a cat

First, there is no one “correct” way to design a model. If there were, the framework would probably have an actual model component. It doesn’t, and as Bill Karwin — former Project Manager for Zend Framework — has said, the reason for this because designing the model is your job. There are pros and cons to any approach. It’s all about finding a method that works for you, is appropriate for the situation at hand, and mitigates difficulty in long-term application maintenance.

The Model section of the Quick Start Guide and this blog post by Michelangelo van Dam includes examples of a Data Mapper approach. Zend_Db uses a Table Data Gateway and Row Data Gateway approach. Doctrine, a popular ORM library that is gaining traction in the ZF community, uses an Active Record approach. And available approaches don’t stop there. As a general rule of thumb when designing models and components in general, I recommend favoring composition over inheritance. You’ll get a better sense of what I mean by that later in the post.

Defining the model

The Wikipedia article on the MVC architectural pattern isn’t all-encompassing, but isn’t a bad place to start either. In particular, it drives home a few important points about the model that you should bear in mind.

The model is a “domain-specific representation of the data upon which the application operates.”

In a nutshell, the model handles data: storing it, retrieving it, filtering and validating it, and providing access to it.

The model contains “domain logic” that “adds meaning to raw data.”

In other words, it handles the conversion from raw data in a data source to semantically meaningful PHP objects and back again.

“MVC does not specifically mention the data access layer because it is understood to be underneath or encapsulated by the model.”

The shorter version: $model != $database. This is one point that trips a lot of people up. The model and your database are not congruent, synonymous, or in any way equivalent. Yes, 99% of the time, your model will use a database for its data source. However, models can be more complex than that: they can serve as clients to web services, limit access to data using an ACL, access data caching resources like memcached or APC, and so forth.

Designing the model

“So which approach do you use?”

Generally, the answer is none of the above. My personal preference is to keep data, in the form of plain old PHP arrays and objects, separate from logic to handle that data. Many common PHP tasks result in data already being present in either of these forms such as in its superglobal arrays, so it seems natural to just take it in the form in which it’s provided.

I define a model class that composes some other object to access the data I need, generally a Zend_Db_Adapter instance. Any methods of that model class return data using scalar types or classes that PHP supports natively. What’s great about this is that it’s fairly easy to convert data to and from these forms using type juggling regardless of the data’s origin.

“But wait, how can I encapsulate the data source within my model if I need a dependency like a Zend_Db_Adapter instance for it to be able to interact with that data source?”

This is another major question that people tend to ask. If any code calling your model first has to handle injecting its dependencies, that muddies up separation of concerns because calling code then must have some knowledge of how your model operates internally. This is a problem because, if the data source of the model needs to change in the future, all calling code needs to change as well versus only model code. There are a few ways to approach this problem in Zend Framework.

The first method involves storing your dependencies in Zend_Registry. Declare accessor methods in the model for dependencies that retrieve them from the registry only if they are not explicitly injected from calling code. This bypasses the need for dependency injection from application code, thus preserving separation of concerns, but still allows injection to be performed for unit testing purposes.

The second method is a variation of the first and is specific to the case of Zend_Db_Adapter instances. This approach involves setting your adapter as the default adapter to use for Zend_Db_Table instances in lieu of using the registry to store it. Note that this doesn’t require actually using Zend_Db_Table in order to work. This can be set from the bootstrap or application configuration file, then retrieved using the getDefaultAdapter() method of the Zend_Db_Table_Abstract class. Again, don’t forget your accessor methods so dependencies can be injected from unit tests.

Another method might be to use a service locator as a dependency in models. This serves as a layer of abstraction between models and their dependencies when it comes to controllers dealing with both. To my knowledge, the closest thing to an implementation of this in ZF is the Zend_Application_Bootstrap classes. From a controller, the bootstrap instance can be accessed as in the code example below.

$bootstrap = $this->getInvokeArg('bootstrap');

Where to go from here

Service layers are another frequent topic related to models. Those aside, I mainly suggest picking a simple model that you can prototype and try several approaches to see which you prefer. If you’ve got some ZF experience under your belt, I’d be interested in hearing about your own modeling approaches and experiences and encourage you to leave a comment on this post.

Version 3 of the DOM standard introduces a renameNode() method, but the PHP DOM extension doesn’t currently support it.

The $nodeName property of the DOMNode class is read-only, so it can’t be changed that way.

A node can be created with a different name in the same document, but if you specify a value to go along with it, any entities in that value are automatically encoded, so it’s not possible to pass in the intended inner content of a node if it contains other nodes.

The only method I’ve found that works is to replicate the attributes and child nodes of the original node. Attributes are fairly easy, but I ran into an issue replicating children where only the first child of any given node was replicated within its intended replacement and the remaining children were omitted. Here’s the original code that was exhibiting this behavior.

foreach ($oldNode->childNodes as $childNode) {
    $newNode->appendChild($childNode);
}

The reason for this behavior is that the $childNodes property of $oldNode is implicitly modified when $childNode is transferred from it to $newNode, so the internal pointer of $childNodes to the next child in the list is no longer accurate.

To get around this, I took advantage of the fact that any node with any child nodes will always have a $firstChild property pointing to the first one. The modified code that takes this approach is below and has the behavior I originally set out to implement.

while ($oldNode->firstChild) {
    $newNode->appendChild($oldNode->firstChild);
}

If you’re curious, below is the full code segment for renaming a node.

$newNode = $oldNode->ownerDocument->createElement('new_element_name');
if ($oldNode->attributes->length) {
    foreach ($oldNode->attributes as $attribute) {
        $newNode->setAttribute($attribute->nodeName, $attribute->nodeValue);
    }
}
while ($oldNode->firstChild) {
    $newNode->appendChild($oldNode->firstChild);
}
$oldNode->ownerDocument->replaceChild($newNode, $oldNode);

Another potential “gotcha” is the argument order of the replaceChild() method, which is the new node followed by the old node rather than the reverse that most people might expect. Thanks to Joshua May for pointing that one out to me; I might never have understood why I was getting a “Not Found Error” DOMException otherwise.

The issue I ran into was due to all the generated PHP classes being housed in a single file. I had to process two WSDL files that had several identical user-defined types in common. As a result, I couldn’t simply include the two PHP files generated from them because PHP doesn’t allow you to define two classes with the same name.

Looking at its source code, modifying wsdl2php to change this behavior was not a very appealing option. Attempting to consolidate the two WSDL files into one with no redundant user-defined type declarations seemed futile as well. Instead, I resolved to split the generated PHP files such that each class was contained in its own file. This would also allow me to use an autoloader to determine which of the classes I actually needed for the particular service call I was making.

Due to the number of classes, splitting the classes into separate files by hand would have been tedious and time-consuming. I decided to tap into my previous experience with the tokenizer extension to throw together a CLI script that would handle this for me. Once I got it working, it clocked in at just over 50 LOC with comments and whitespace. You simply call it from a shell and pass it the PHP file you want to split and the destination for the split class files.

I thought it might be useful for others needed to process similarly formatted source code, so I threw it into a github repository for anyone who might like to take a look. I’m open to suggestions for improvements to implement if enough people find it useful. Feel free to file an issue on the repository if you happen to find a bug.

As for what’s next, I’ll be starting at K-fx². (Nope, no funemployment for me.) There, I’ll be developing Zend Framework applications and helping to streamline development processes and infrastructure.

Thanks to all my friends and family who’ve provided support during this transition. I’m looking forward to what the next year holds.

First, in addition to the other things you should do before attending, be ready to give your presentation before you get on the plane. You should start on your slides as far in advance as possible. Don’t put it off or wait until the last minute, because it will likely be more work than you anticipate. This includes making sure that any live demos you intend to give will run as expected. Syntax errors and crashing web servers look very bad to the audience.

One of the reasons for this is that you’ll want to practice your talk out loud. It’s one thing to put the material onto slides, but it may sound different when it’s actually coming out of your mouth and going into the crowd. You may find stumbling points, places where you stutter or get caught off-guard when transitioning from one topic to another. Try to organize the presentation such that it matches your natural flow when talking about the topic without any slides at all.

Which reminds me, learn from the masters. People like Marco Tabini have spoken before and have a wealth of knowledge that they’ll share fairly freely most of the time, especially if alcohol (or, in Marco’s case, an espresso) is involved. Look at books like Presentation Zen by Garr Reynolds. Take the time to hone your presentation skills before you have to make your delivery.

If you’ve been to a conference before, you’ve probably already learned about my next point the hard way. Don’t depend on wifi internet access availability. Why not? Because the vast majority of the time, it will suck. There won’t be enough IP addresses, someone will do something to hog bandwidth and make latency skyrocket, it will find some way to refuse to work. Save local copies of files, write a minimal daemon to simulate a remote server, do whatever you need to do to avoid it.

That point goes hand in hand with this one: test your equipment early and have a Plan B. In particular, hook your laptop up to the projector in the room in which you’ll be speaking (or to a test projector, if the conference hosts provide one and prefer you use that) to make sure it can display your slides. Ben Ramsey was gracious enough to loan me his Macbook at ZendCon because my Sony Vaio refused to work with the projector and the time-sensitive situation did nothing but add to my speaking nerves. Make sure you don’t end up in the same spot.

Lastly, don’t let critical reception deter you from speaking again. I got pretty negative feedback the first time around, but I took it in stride. While I know I have plenty of room for improvement, I’m still going to give it another shot. Do your very best, then strive to be better.

Hope you enjoyed this blog post and gleaned something useful from it. If you’ve got any of your own speaking tips, please feel free to add a comment on this post. If you’ll be attending php|tek, I look forward to seeing you there!