Decoding Data with WDDX - Page 5

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);
?>

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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];
?>	?>

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PHP and WDDX - Page 4
XML and PHP
A Few Examples - Page 6