When working with XML-based applications, developers often find themselves facing the requirement to generate XML-encoded data structures on the fly. Examples of this include an XML order template based on user input in a Web form, or an XML representation of a server request or client response based on run-time parameters.

Although this task might seem intimidating, it’s actually quite simple when one takes into account PHP’s sophisticated DOM API for dynamic node construction and manipulation. Over the course of this article, I’ll be introducing you to the main functions in this API, showing you how to programmatically generate a complete well-formed XML document from scratch and save it to disk.

Note: This article assumes a working Apache/PHP5 installation with the DOM functions enabled, and a working knowledge of basic XML constructs such as elements, attributes and CDATA blocks. You can obtain an introduction to these topics from the introductory material at Melonfire (http://melonfire.com/community/columns/trog/article.php?id=78 and http://melonfire.com/community/columns/trog/article.php?id=79)

Creating the Doctype declaration

Let’s start right at the top, with the XML declaration. In PHP, this is fairly simple; it only requires you to instantiate an object of the DOMDocument class and supply it with a version number. To see it in action type out the example script in Listing A.

Listing A

<?php
// create doctype
$dom = new DOMDocument("1.0");
 
// display document in browser as plain text
// for readability purposes
header("Content-Type: text/plain");
 
// save and display tree
echo $dom->saveXML();
?>

Notice the saveXML() method of the DOMDocument object — I’ll come back to this later, but for the moment simply realise that this is the method used to output a current snapshot of the XML tree, either to a file or to the browser. In this case, I’ve sent the output directly to the browser as ASCII text for readability purposes; in real-world applications, you would probably send this with a Content-Type: text/xml header.

When you view the output in your browser, you should see something like this:

<?xml version="1.0"?>

Adding elements and text nodes

Now that’s all very pretty and fine, but the real power of XML comes from its elements and the content they enclose. Fortunately, once you’ve got the basic DOMDocument initialised, this becomes extremely simple. There are two steps to the process:

1. For each element or text node you wish to add, call the DOMDocument object’s createElement() or createTextNode() method with the element name or text content. This will result in the creation of a new object corresponding to the element or text node.
2. Append the element or text node to a parent node in the XML tree by calling that node’s appendChild() method and passing it the object produced in the previous step.

An example will make this clearer. Consider the script in Listing B.

Listing B

<?php
// create doctype
$dom = new DOMDocument("1.0");
 
// display document in browser as plain text
// for readability purposes
header("Content-Type: text/plain");
 
// create root element
$root = $dom->createElement("toppings");
$dom->appendChild($root);
 
// create child element
$item = $dom->createElement("item");
$root->appendChild($item);
 
// create text node
$text = $dom->createTextNode("pepperoni");
$item->appendChild($text);
 
// save and display tree
echo $dom->saveXML();
?>

Here, I’ve first created a root element named and attached it to the XML header. Next, I’ve created an element named and attached it to the root element. And finally, I’ve created a text node with the value “pepperoni” and attached it to the element. The result should look like this:

<?xml version="1.0"?>
<toppings>
<item>pepperoni</item>
</toppings>

If you’d like to add another topping, simply create another and populate it with different content (Listing C).

Listing C

<?php
// create doctype
$dom = new DOMDocument("1.0");
 
// display document in browser as plain text
// for readability purposes
header("Content-Type: text/plain");
 
// create root element
$root = $dom->createElement("toppings");
$dom->appendChild($root);
 
// create child element
$item = $dom->createElement("item");
$root->appendChild($item);
 
// create text node
$text = $dom->createTextNode("pepperoni");
$item->appendChild($text);
 
// create child element
$item = $dom->createElement("item");
$root->appendChild($item);
 
// create another text node
$text = $dom->createTextNode("tomato");
$item->appendChild($text);
 
// save and display tree
echo $dom->saveXML();
?>

And here’s the revised output:

<?xml version="1.0"?>
<toppings>
<item>pepperoni</item>
<item>tomato</item>
</toppings>

Adding attributes

You can also add qualifying information to your elements, through the thoughtful use of attributes. With the PHP DOM API, attributes are added in a two-step process: first create an attribute node holding the name of the attribute with the DOMDocument object’s createAttribute() method, and then append a text node to it holding the attribute value. Listing D is an example.

Listing D

<?php
// create doctype
$dom = new DOMDocument("1.0");
 
// display document in browser as plain text
// for readability purposes
header("Content-Type: text/plain");
 
// create root element
$root = $dom->createElement("toppings");
$dom->appendChild($root);
 
// create child element
$item = $dom->createElement("item");
$root->appendChild($item);
 
// create text node
$text = $dom->createTextNode("pepperoni");
$item->appendChild($text);
 
// create attribute node
$price = $dom->createAttribute("price");
$item->appendChild($price);
 
// create attribute value node
$priceValue = $dom->createTextNode("4");
$price->appendChild($priceValue);
 
// save and display tree
echo $dom->saveXML();
?>

And here’s what the output will look like:

<?xml version="1.0"?>
<toppings>
<item price="4">pepperoni</item>
</toppings>

Adding CDATA blocks and processing instructions

While not used quite as often, CDATA blocks and processing instructions (PI) are also well-supported by the PHP API, through the DOMDocument object’s createCDATASection() and createProcessingInstruction() methods. Listing E shows you an example.

Listing E

<?php
// create doctype
$dom = new DOMDocument("1.0");
 
// display document in browser as plain text
// for readability purposes
header("Content-Type: text/plain");
 
// create root element
$root = $dom->createElement("toppings");
$dom->appendChild($root);
 
// create child element
$item = $dom->createElement("item");
$root->appendChild($item);
 
// create text node
$text = $dom->createTextNode("pepperoni");
$item->appendChild($text);
 
// create attribute node
$price = $dom->createAttribute("price");
$item->appendChild($price);
 
// create attribute value node
$priceValue = $dom->createTextNode("4");
$price->appendChild($priceValue);
 
// create CDATA section
$cdata = $dom->createCDATASection("\nCustomer requests that pizza be sliced into 16 square pieces\n");
$root->appendChild($cdata);
 
// create PI
$pi = $dom->createProcessingInstruction("pizza", "bake()");
$root->appendChild($pi);
 
// save and display tree
echo $dom->saveXML();
?>

And here’s the output:

<?xml version="1.0"?>
<toppings>
<item price="4">pepperoni</item>
<![CDATA[
Customer requests that pizza be sliced into 16 square pieces
]]>
<?pizza bake()?>
</toppings>

Saving the results

Once you’ve got the tree the way you want it, you can either save it to a file or store it in a PHP variable. The former function is performed by calling the save() method with a file name, while the latter is performed by calling the saveXML() method and assigning the result to a string. Here’s an example (Listing F).

Listing F

<?php
// create doctype
$dom = new DOMDocument("1.0");
 
// create root element
$root = $dom->createElement("toppings");
$dom->appendChild($root);
$dom->formatOutput=true;
 
// create child element
$item = $dom->createElement("item");
$root->appendChild($item);
 
// create text node
$text = $dom->createTextNode("pepperoni");
$item->appendChild($text);
 
// create attribute node
$price = $dom->createAttribute("price");
$item->appendChild($price);
 
// create attribute value node
$priceValue = $dom->createTextNode("4");
$price->appendChild($priceValue);
 
// create CDATA section
$cdata = $dom->createCDATASection("\nCustomer requests that pizza be sliced into 16 square pieces\n");
$root->appendChild($cdata);
 
// create PI
$pi = $dom->createProcessingInstruction("pizza", "bake()");
$root->appendChild($pi);
 
// save tree to file
$dom->save("order.xml");
 
// save tree to string
$order = $dom->save("order.xml");
?>

And that’s about it. Hopefully you found this article interesting, and will be able to use these techniques in your daily work with XML. Happy coding!

XPath is a language that allows you to address parts of an XML document, making XSLT transformations practically necessary. It also makes it an invaluable tool for managing XML data in applications such as Web applications.

Microsoft provides XPath functionality through the selectSingleNode() and selectNodes() methods on DOM nodes and documents. However, PHP uses functions that provide XPath functionality through contexts. In the following example, I’ll show sample XML data and PHP code to grab different parts of the XML document. I’ll also explain how the PHP code works.

In the example code, I use the following XML data to provide the functionality. (Note: This code was developed and run successfully using PHP 4.3.4, Windows XP, and IIS 5.1.)

<?xml version="1.0"?>
<x:root xmlns:x="http://www.someplace.com">
<x:row>
<x:dog
color="yellow">Marmaduke</x:dog>
<x:cat>Garfield</x:cat>
</x:row>
<x:row>
<x:dog color="white">Snoopy</x:dog>
<x:cat>Heathcliff</x:cat>
</x:row>
<x:row>
<x:dog color="gray">Spike</x:dog>
<x:cat>Sylvester</x:cat>
</x:row>
</x:root>

This XML data contains a few elements and some attributes including a namespace declaration — some basic XML. This results in varied queries for me to test.

<?php
$sxml = '<?xml version="1.0"?>
    <x:root xmlns:x="http://www.someplace.com">
        <x:row>
            <x:dog color="yellow">Marmaduke</x:dog>
            <x:cat>Garfield</x:cat>
        </x:row>
        <x:row>
            <x:dog color="white">Snoopy</x:dog>
            <x:cat>Heathcliff</x:cat>
        </x:row>
        <x:row>
            <x:dog color="gray">Spike</x:dog>
            <x:cat>Sylvester</x:cat>
        </x:row>
    </x:root>';
 
$xml = domxml_open_mem($sxml);
 
$xpc = xpath_new_context($xml);
xpath_register_ns($xpc, "x", "http://www.someplace.com");
 
$nodes = xpath_eval($xpc, "//x:row/x:dog[@color='yellow']/text()");
foreach ($nodes->nodeset as $node) {
    print $node->content . "\n";
}
 
$nodes = xpath_eval($xpc, "//x:row/x:dog");
foreach ($nodes->nodeset as $node) {
    print $xml->dump_node($node) . "\n";
}
 
$nodes = xpath_eval($xpc, "//x:cat/child::text()|//x:dog[@color='white' or
@color='gray']/text()");
foreach ($nodes->nodeset as $node) {
    print $node->content . "\n";
}
 
$xml->free();
?>

First, I create a local variable to hold the XML string. This information could have been passed in as part of a POST HTTP request. However, for this example, I’m going to include it in the code. The next step is to create a DOM Document by using the domxml_open_mem() function. This function creates a DOM Document object in memory from a valid XML string. It accepts one parameter: the XML string. Another way to accomplish this is to store the XML in a separate file and use the domxml_open_file() function to load the XML from a file. This function takes one parameter: the filename of the XML file.

Once I create the DOM Document object, I can create an XPath context with this object through the xpath_new_context() function, which takes one parameter: the current DOM Document object. This context is used to evaluate the XPath expression and is also used to register namespaces, if needed. Since my XML includes a namespace, I register the namespace with the xpath_register_ns() function. This makes it possible to create XPath queries using prefixes. The xpath_register_ns() function takes three parameters: the XPath context, the prefix, and the namespace, respectively.

Now I can run XPath queries. This is done with the xpath_eval() function, whose first parameter is the XPath context and second parameter is the XPath expression. The function returns an array of DOM Nodes. In my code, I step through the nodeset and produce some form of output.

In the first XPath example, I grab all the x:dog text elements under the x:row nodes, where the ‘color’ attribute equals ‘yellow’. This is where the XPath expression in PHP differs slightly from an XPath expression using MSXML. I include the ‘/text()’ part of the expression to return the text nodes only. With MSXML, you access the text node with the ‘text’ property. Using the ‘content’ property on the returned text node, I can get the content of the text node.

In the second example, I grab all the x:dog elements under the x:row nodes. However, I use the dump_node() method on the DOM Document object to print out the complete XML of the appropriate node. The dump_node() method accepts one parameter: the DOM Node of which you wish to dump the contents.

In the last example, I grab all the x:cat text nodes and all the x:dog text nodes where the ‘color’ attribute is ‘white’ or ‘gray’. Once again, I step through the nodeset and print out the content of each text node. Finally, I free up the DOM Document object.

Following are the websites list who provide free php scripts. You can find lots of information about PHP as well as free code samples, code galleries, and free scripts for download at these and other sites. There may be some premium php scripts which may come for a price but overall the list is good enough.

http://www.scripts.com/php-scripts/

http://www.best-php-scripts.com/

http://gscripts.net/

http://www.phpjunkyard.com/

http://www.free-php.net/

http://coding.phpground.net/

http://www.atomicphp.com/

http://www.thefreecountry.com/php/index.shtml

http://www.phpbuilder.com/snippet/

http://phpwizard.net/

http://www.phpclasses.org/

http://px.sklar.com/

http://zend.com/codex.php

http://www.weberdev.com/

http://www.hotscripts.com/PHP/

http://www.phpresourceindex.com/

I would be adding more to the list soon….

The following example illustrates how to use an external entity reference handler to include and parse other documents, as well as how PIs can be processed, and a way of determining "trust" for PIs containing code.

Consider the following XML’s

< ?xml version=’1.0′?>
< !DOCTYPE chapter SYSTEM "/just/a/test.dtd" [
<!ENTITY plainEntity "FOO entity">
< !ENTITY systemEntity SYSTEM "xmltest2.xml">
]>
<chapter>
 <title>Title &plainEntity;</title>
 <para>
  <informaltable>
   <tgroup cols="3">
    <tbody>
     <row><entry>a1</entry><entry morerows="1">b1</entry><entry>c1</entry></row>
     <row><entry>a2</entry><entry>c2</entry></row>
     <row><entry>a3</entry><entry>b3</entry><entry>c3</entry></row>
    </tbody>
   </tgroup>
  </informaltable>
 </para>
 &systemEntity;
 <section id="about">
  <title>About this Document</title>
  <para>
   <!– this is a comment –>
   < ?php echo ‘Hi!  This is PHP version ‘ . phpversion(); ?>
  </para>
 </section>
</chapter>

<?xml version="1.0"?>
<!DOCTYPE foo [
<!ENTITY testEnt "test entity">
]>
<foo>
<element attrib="value"/>
&testEnt;
<?php echo "This is some more PHP code being executed."; ?>
</foo>

The following code shows how we can parse the above XML file using PHP

< ?php
$file = "xmltest.xml";

function trustedFile($file)
{
    // only trust local files owned by ourselves
    if (!eregi("^([a-z]+)://", $file)
        && fileowner($file) == getmyuid()) {
            return true;
    }
    return false;
}

function startElement($parser, $name, $attribs)
{
    echo "&lt;<font color=\"#0000cc\">$name";
    if (count($attribs)) {
        foreach ($attribs as $k => $v) {
            echo " <font color=\"#009900\">$k</font>=\"<font color=\"#990000\">$v</font>\"";
        }
    }
    echo "&gt;";
}

function endElement($parser, $name)
{
    echo "&lt;/<font color=\"#0000cc\">$name</font>&gt;";
}

function characterData($parser, $data)
{
    echo "<b>$data</b>";
}

function PIHandler($parser, $target, $data)
{
    switch (strtolower($target)) {
        case "php":
            global $parser_file;
            // If the parsed document is "trusted", we say it is safe
            // to execute PHP code inside it.  If not, display the code
            // instead.
            if (trustedFile($parser_file[$parser])) {
                eval($data);
            } else {
                printf("Untrusted PHP code: <i>%s</i>",
                        htmlspecialchars($data));
            }
            break;
    }
}

function defaultHandler($parser, $data)
{
    if (substr($data, 0, 1) == "&" && substr($data, -1, 1) == ";") {
        printf(’<font color="#aa00aa">%s</font>’,
                htmlspecialchars($data));
    } else {
        printf(’<font size="-1">%s</font>’,
                htmlspecialchars($data));
    }
}

function externalEntityRefHandler($parser, $openEntityNames, $base, $systemId,
                                  $publicId) {
    if ($systemId) {
        if (!list($parser, $fp) = new_xml_parser($systemId)) {
            printf("Could not open entity %s at %s\n", $openEntityNames,
                   $systemId);
            return false;
        }
        while ($data = fread($fp, 4096)) {
            if (!xml_parse($parser, $data, feof($fp))) {
                printf("XML error: %s at line %d while parsing entity %s\n",
                       xml_error_string(xml_get_error_code($parser)),
                       xml_get_current_line_number($parser), $openEntityNames);
                xml_parser_free($parser);
                return false;
            }
        }
        xml_parser_free($parser);
        return true;
    }
    return false;
}

function new_xml_parser($file)
{
    global $parser_file;

    $xml_parser = xml_parser_create();
    xml_parser_set_option($xml_parser, XML_OPTION_CASE_FOLDING, 1);
    xml_set_element_handler($xml_parser, "startElement", "endElement");
    xml_set_character_data_handler($xml_parser, "characterData");
    xml_set_processing_instruction_handler($xml_parser, "PIHandler");
    xml_set_default_handler($xml_parser, "defaultHandler");
    xml_set_external_entity_ref_handler($xml_parser, "externalEntityRefHandler");
   
    if (!($fp = @fopen($file, "r"))) {
        return false;
    }
    if (!is_array($parser_file)) {
        settype($parser_file, "array");
    }
    $parser_file[$xml_parser] = $file;
    return array($xml_parser, $fp);
}

if (!(list($xml_parser, $fp) = new_xml_parser($file))) {
    die("could not open XML input");
}

echo "<pre>";
while ($data = fread($fp, 4096)) {
    if (!xml_parse($xml_parser, $data, feof($fp))) {
        die(sprintf("XML error: %s at line %d\n",
                    xml_error_string(xml_get_error_code($xml_parser)),
                    xml_get_current_line_number($xml_parser)));
    }
}
echo "</pre>";
echo "parse complete\n";
xml_parser_free($xml_parser);

?>

I hope this will help. Your comments are welcome.

Load an XML file as data using PHP

By handling mime-types and using browser detection, CodeHelp has already shown how to export XML using a PHP script. PHP can also receive XML as input - using the XML parser:

if (!($fp=@fopen("./contactsbare.xml", "r")))
        die ("Couldn’t open XML.");
$usercount=0;
$userdata=array();
$state=”;
if (!($xml_parser = xml_parser_create()))
        die("Couldn’t create parser.");

Each XML file can have it’s own DTD or structure. The PHP file using the XML parser must be tailored to one particular structure or DTD - it will then be able to read all files that are valid under that DTD. This example will use an over-simplified contacts format for XML - you will need to adapt the details of the tags (or nodes) for your own DTD. To follow the construction of the XML parser, load the example XML file into another window using the link in the Navigation Bar. (If the file doesn’t open in a new window in your browser, right click the link and choose Open in a New Window.) Multiple contacts can be specified by repeating the CONTACT tag and the PHP file therefore needs to keep track of the number of contacts used in this example. In the above code, $usercount is set to zero ready to hold the number of contacts found. $userdata will later be filled with data for each contact and $state is used to keep track of which node the parser is dealing with for each contact.

The PHP XML parser now needs two functions to be declared, one to handle the element data and one to handle the character data within the elements. This is where you need to change the code to reflect your own XML files - change the element and attribute names. I’ll start with the Element Handler. This is in two parts, a function to detect the start of real data and a function to detect when an element comes to an end - in this case to register when more than one contact is specified. Each function is called once for each node - use a switch statement to decide what action to take depending on which node is being processed. The parser will take care of the $name and $attrib variables.

function startElementHandler ($parser,$name,$attrib){
global $usercount;
global $userdata;
global $state;

switch ($name) {
        case $name=="NAME" : {
                $userdata[$usercount]["first"] = $attrib["FIRST"];
                $userdata[$usercount]["last"] = $attrib["LAST"];
                $userdata[$usercount]["nick"] = $attrib["NICK"];
                $userdata[$usercount]["title"] = $attrib["TITLE"];
                break;
                }
        }
}

function endElementHandler ($parser,$name){
global $usercount;
global $userdata;
global $state;
$state=”;
if($name=="CONTACT") {$usercount++;}
}

The function "startElementHandler()" has been abbreviated here by removing the other case $name=="" : {} statements, the full file will be looked at later.

Next, we need the character handler:

function characterDataHandler ($parser, $data) {
global $usercount;
global $userdata;
global $state;
if (!$state) {return;}
if ($state=="COMPANY") { $userdata[$usercount]["bcompany"] = $data;}
if ($state=="GENDER") { $userdata[$usercount]["gender"] = $data;}
}

Finally, tell the parser which functions to use, read the data from the opened file and parse the contents.

xml_set_element_handler($xml_parser,"startElementHandler","endElementHandler");
xml_set_character_data_handler( $xml_parser, "characterDataHandler");

while( $data = fread($fp, 4096)){
if(!xml_parse($xml_parser, $data, feof($fp))) {
break;}}
xml_parser_free($xml_parser);

The data from the XML file is now held in $userdata and can be accessed using a standard PHP loop:

for ($i=0;$i<$usercount; $i++) {
echo "Name: ".$userdata[$i]["title"]." ".
        ucfirst($userdata[$i]["first"])." ". ucfirst($userdata[$i]["last"]);
}