Home > Articles > Programming > PHP

This chapter is from the book

This chapter is from the book

PHP and WDDX

As previously stated, a WDDX module has been available for PHP since version 4.0 of the language. Created by Andrei Zmievski, this WDDX module includes standard serialization and deserialization functions to convert PHP variables and arrays into WDDX-compatible data structures.

If you're using a stock PHP binary, it's quite likely that you'll need to recompile PHP to add support for this library to your PHP build (detailed instructions for accomplishing this are available in Appendix A, "Recompiling PHP to Add XML Support").

Encoding Data with WDDX

PHP's WDDX module offers a number of different ways to encode data into WDDX. The following sections demonstrate this by using the following:

  • The wddx_serialize_value() function

  • The wddx_serialize_vars() function

  • The wddx_add_vars() function

The wddx_serialize_value() Function

The simplest way to encode data into WDDX (and the one I will use most frequently in this chapter) is via the wddx_serialize_value() function, which is used to encode a single variable into WDDX. Listing 5.3 demonstrates its application.

Listing 5.3 Serializing a Single Variable with wddx_serialize_value()

<?php
$flavor = "strawberry";

print wddx_serialize_value($flavor);
?>

Listing 5.4 demonstrates the result.

Listing 5.4 A WDDX Packet Generated via wddx_serialize_value()

<wddxPacket version='1.0'>
   <header/>
   <data>
      <string>strawberry</string>
   </data>
</wddxPacket>

Manual Labor

Note that PHP typically generates the WDDX packet as one long string. This can sometimes get confusing, so I manually indented and spaced out some of the output listings in this chapter for greater readability. Whitespace within a WDDX packet, but outside WDDX elements, is ignored by the WDDX deserializer; whitespace embedded within a WDDX element is, obviously, preserved.

As Listings 5.5 and 5.6 demonstrate, this works with arrays, too.

Listing 5.5 Serializing a PHP Array with wddx_serialize_value()

<?php
$flavors = array("strawberry", "chocolate", "raspberry", "peach");

print wddx_serialize_value($flavors);
?>

Listing 5.6 A WDDX Packet Representing an Array

<wddxPacket version='1.0'>
   <header/>
   <data>
      <array length='4'>
         <string>strawberry</string>
         <string>chocolate</string>
         <string>raspberry</string>
         <string>peach</string>
      </array>
   </data>
</wddxPacket>

An optional second parameter to wddx_serialize_value() lets you add a human- readable comment to the resulting packet. Listing 5.7 is a variant of Listing 5.5 that demonstrates this, with the output shown in Listing 5.8.

Going to the Source

If you're using your web browser to view the examples in the section, you may wonder why the output you see on your screen doesn't match the output shown here. Well, that's because web browsers tend to hide tags that they don't know about; consequently, the WDDX tags generated during the serialization process are not displayed in the rendered web page.

The solution is fairly simple: use the browser's View Source command to view the raw source for the web page, and you should see the full uncensored output.

Listing 5.7 Adding a Comment to a WDDX Packet

<?php
$flavors = array("strawberry", "chocolate", "raspberry", "peach");

print wddx_serialize_value($flavors, "A WDDX representation of my favorite
icecream flavors"); ?>

Listing 5.8 A WDDX Packet with a Human-Readable Comment in the Header

<wddxPacket version='1.0'>
   <header>
      <comment>A WDDX representation of my favorite icecream flavors</comment>
   </header>
    <data>
      <array length='4'>
         <string>strawberry</string>
         <string>chocolate</string>
         <string>raspberry</string>
         <string>peach</string>
      </array>
   </data>
</wddxPacket>

The wddx_serialize_vars() Function

The wddx_serialize_value() function cannot accept more than a single variable. However, it's also possible to serialize more than one variable at a time with the wddx_serialize_vars() function, which can accept multiple variables for serialization as function arguments. Listing 5.9 demonstrates how this works.

Listing 5.9 Serializing Multiple Values with wddx_serialize_vars()

<?php
$phrase = "The game's afoot";
$animals = array("parrot" => "Polly", "hippo" => "Hal", "dog" => "Rover",
"squirrel" => "Sparky"); print wddx_serialize_vars("phrase", "animals"); ?>

Note that wddx_serialize_vars() requires the names of the variables to be serialized as string arguments.

Listing 5.10 displays the result of a wddx_serialize_vars() run.

Listing 5.10 A WDDX Packet Generated via wddx_serialize_vars()

<wddxPacket version='1.0'>
<header/>
   <data>
      <struct>
         <var name='phrase'>
            <string>The game's afoot</string>
         </var>
         <var name='animals'>
            <struct>
               <var name='parrot'>
                  <string>Polly</string>
               </var>
               <var name='hippo'>
                  <string>Hal</string>
               </var>
               <var name='dog'>
                  <string>Rover</string>
               </var>
               <var name='squirrel'>
                  <string>Sparky</string>
               </var>
            </struct>
         </var>
      </struct>
   </data>
</wddxPacket>

It's interesting to note, also, that wddx_serialize_value() and wddx_serialize_vars() generate significantly different (though valid) WDDX packets. Consider Listing 5.11, which creates a WDDX packet containing the same variable-value pair as Listing 5.3, and compare the resulting output in Listing 5.12 with that in Listing 5.4.

Listing 5.11 Serializing a Single Variable with wddx_serialize_vars()

<?php
$flavor = "strawberry";

print wddx_serialize_vars("flavor");
?>

Listing 5.12 A WDDX Packet Generated via wddx_serialize_vars()

<wddxPacket version='1.0'>
   <header/>
   <data>
      <struct>
         <var name='flavor'>
            <string>strawberry</string>
         </var>
      </struct>
   </data>
</wddxPacket>

The wddx_add_vars() Function

PHP also allows you to build a WDDX packet incrementally, adding variables to it as they become available, with the wddx_add_vars() function. Listing 5.13 demonstrates this approach, building a WDDX packet from the results of a form POST operation.

Listing 5.13 Building a WDDX Packet Incrementally with wddx_add_vars()

<?php

// create a packet handle
// the argument here is an optional comment
$wp = wddx_packet_start("A packet containing a list of form fields with values");

// iterate through POSTed fields
// add variables to packet
wddx_add_vars($wp, "HTTP_POST_VARS");

// end the packet
// you can now assign the generated packet to a variable
// and print it 
wddx_packet_end($wp);
?>

This is a slightly more complicated technique than the ones described previously. Let's go through it step by step:

  1. The first order of business is to create an empty WDDX packet to hold the data; this is accomplished with the aptly named wddx_packet_start() function, which returns a handle for the newly minted packet.

  2. $wp = wddx_packet_start("A packet containing a list of form fields with  _values");

    This handle is used in all subsequent operations. Note that the wddx_packet_start() function can be passed an optional comment string, which is used to add a comment to the header of the generated packet.

  3. With the packet created, the next step is to add data to it. In Listing 5.13, the data is generated dynamically from a form submission, and each value is then added to the packet via the wddx_add_vars() function.

  4. wddx_add_vars($wp, "HTTP_POST_VARS");

    This function works in much the same way as wddx_serialize_vars()—it accepts multiple variable names as argument (although I've only used one here), serializes these variables into WDDX structures, and adds them to the packet. Note, however, that wddx_add_vars() requires, as first argument, the handle representing the packet to which the data is to be added.

  5. After all the required data has been inserted into the packet, the final step is to close the packet, accomplished via the wddx_packet_end() function. Again, the packet handle is used to identify the packet to be closed.

  6. wddx_packet_end($wp);

    Note that the wddx_packet_end() function returns the contents of the newly minted packet; this return value can be assigned to a variable and used in subsequent lines of the PHP script.

    This approach comes in particularly handy if you're dealing with dynamically generated data, either from a database or elsewhere.

With your data now safely encoded into WDDX, let's now look at how you can convert it back into usable PHP data structures.

Decoding Data with WDDX

Although there are five different functions available to encode data into WDDX, PHP has only a single function to perform the deserialization of WDDX packets. This function is named wddx_deserialize(), and it accepts a string containing a WDDX packet as its only argument.

Listing 5.14 demonstrates how a PHP variable encoded in WDDX can be deserialized by wddx_deserialize().

Listing 5.14 Deserializing a WDDX Packet into a Native PHP Structure

<?php

$flavor = "blueberry";

// print value before converting to WDDX 
echo "Before serialization, \$flavor = $flavor <br>";

// serialize into WDDX packet
$packet = wddx_serialize_value($flavor);

// deserialize generated packet and display value
echo "After serialization, \$flavor = " . wddx_deserialize($packet);
?>

This works with arrays, too—in Listing 5.15, the deserialized result $output is an array containing the same elements as the original array $stooges.

Listing 5.15 Deserializing a WDDX Packet into a PHP Array

<?php

$stooges = array("larry", "curly", "moe");

// serialize into WDDX packet
$packet = wddx_serialize_value($stooges);

// deserialize generated packet
$output = wddx_deserialize($packet);

// view it
print_r($output);
?>

Buyer Beware!

There's an important caveat to keep in mind when using PHP's WDDX module. As shown in Listings 5.4 and 5.12, the wddx_serialize_vars() and wddx_add_vars() functions work in a slightly different manner from the wddx_serialize_value() function. Both wddx_serialize_vars() and wddx_add_vars() use WDDX structures (represented by <struct> elements) to store variables and their values, regardless of whether the variable is a string, number, or array. On the other hand, wddx_serialize_value() uses a <struct> only if the variable is an associative array.

This variation in the serialization process can significantly impact the deserialization process because PHP's wddx_deserialize() function automatically converts <struct>s into associative arrays. Consequently, the manner in which you access the original value of the variable will change, depending on how it was originally serialized.

Consider Table 5.1, which demonstrates the difference.

Table 5.1 A Comparison of Serialization with wddx_serialize_value() and wddx_serialize_vars()

wddx_serialize_value()

wddx_serialize_vars()

<?php

<?php

$lang = array("PHP", "Perl", "Python", "XML", "JSP");

$lang = array("PHP", "Perl", "Python", "XML", "JSP");

$alpha = wddx_serialize_value($lang);

$alpha = wddx_serialize_vars("lang");

$beta = wddx_deserialize($alpha)

$beta = wddx_deserialize($alpha);

// returns "PHP"

// returns "PHP"

print $beta[0];

print $beta["lang"][0];

// returns "Python"

// returns "Python"

print $beta[2];

print $beta["lang"][2];

?>

?>


InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020