ARC: Ariadne Component Library

A flexible component library for PHP

The Ariadne Component Library is a spinoff from the Ariadne Web Application Framework and Content Management System [ http://www.ariadne-cms.org/ ]

arc/xml

This component provides a unified xml parser and writer. The writer allows for readable and always correct xml in code, without using templates. The parser is a wrapper around both DOMDocument and SimpleXML.

The parser and writer also work on fragments of XML. The parser also makes sure that the output is identical to the input. When converting a node to a string, \arc\xml will return the full xml string, including tags. If you don't want that, you can always access the 'nodeValue' property to get the original SimpleXMLElement.

Finally the parser also adds the ability to use basic CSS selectors to find elements in the XML.

Example code:

    use \arc\xml as x;
    $xmlString = 
        x::preamble()
        .x::rss(['version'=>'2.0'],
             x::channel(
                 x::title('Wikipedia'),
                 x::link('http://www.wikipedia.org'),
                 x::description('This feed notifies you of new articles on Wikipedia.')
             )
        );

And parsing it:

    $xml = \arc\xml::parse($xmlString);
    $title = $xml->channel->title->nodeValue; // SimpleXMLElement 'Wikipedia'
    $titleTag = $xml->channel->title; // <title>Wikipedia</title>
    echo $title;

Installation

This library requires PHP 7.1 or higher. It is installable and autoloadable via Composer as arc/xml.

    composer require arc/xml

Parsing XML

Examples

For these examples we'll use the following XML

<rdf:RDF 
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" 
    xmlns:dc="http://purl.org/dc/elements/1.1/">
    <channel rdf:about="http://slashdot.org/">
        <title>Slashdot</title>
        <link>http://slashdot.org/</link>
        <description>News for nerds, stuff that matters</description>
        <dc:language>en-us</dc:language>
        <dc:date>2016-01-30T20:38:08+00:00</dc:date>
    </channel>
    <item rdf:about="http://hardware.slashdot.org/story/1757209/">
        <title>Drone Races To Be Broadcast To VR Headsets</title>
        <link>http://hardware.slashdot.org/story/1757209/</link>
    </item>
    <item rdf:about="http://it.slashdot.org/story/1720259/">
        <title>FTDI Driver Breaks Hardware Again</title>
        <link>http://it.slashdot.org/story/1720259/</link>
    </item>
</rdf:RDF>

Getting the title

    $xml = \arc\xml::parse( $xmlString );
    $title = $xml->channel->title;
    echo $title;

result:

<title>Slashdot</title>

The parser returns the full XML element by default. If you just want the contents, you must be explicit:

    $title = $xml->channel->title->nodeValue;
    echo $title;

result:

Slashdot

Instead of the default in SimpleXML, arc\xml must be explicitly told to get the value of the node using the nodeValue property.

Setting the title

    $xml->channel->title = 'Update title';

As you can see, there is no need to mention the nodeValue here, the name 'title' is enough to select the correct element. It would not make sense to turn the title into another tag entirely here. You can still use the nodeValue if you prefer though.

Getting attributes

    $about = $xml->channel['rdf:about'];

result

http://slashdot.org/

Just what you would expect, even though there is a namespace in there. When you use a namespace that the parser hasn't been told about before, it will simply look it up in the document and re-use it.

Since attributes aren't XML nodes, there is no nodeValue. Attributes are always returned as just a string.

Setting attributes

    $xml->channel['title-attribute'] = 'This is a title attribute'; 

This adds the title-attribute if it wasn't there before, or updates it if it was.

Removing attributes

   unset($xml->channel['title-attribute']);

Searching the document

    $items = $xml->find('item');
    echo implode($items);

result:

    <item rdf:about="http://hardware.slashdot.org/story/1757209/">
        <title>Drone Races To Be Broadcast To VR Headsets</title>
        <link>http://hardware.slashdot.org/story/1757209/</link>
    </item>
    <item rdf:about="http://it.slashdot.org/story/1720259/">
        <title>FTDI Driver Breaks Hardware Again</title>
        <link>http://it.slashdot.org/story/1720259/</link>
    </item>

Again, you get the full XML of the result and it is just an array. (Its been joined here using implode for clarity).

The find() method accepts most CSS2.0 selectors. For now you can't enter more than one selector, so you can't select 'item, channel' for instance. Either use the SimpleXML xpath() method or run multiple queries.

Searching using namespaces

    $xml->registerNamespace('dublincore','http://purl.org/dc/elements/1.1/');
    $date = current($xml->find('dublincore|date));
    echo $date;

result:

    <dc:date>2016-01-30T20:38:08+00:00</dc:date>

Again, you get the full XML by default. But in addition, though you've used a namespace alias not known in the document ( dublincore ), find() returns the <dc:date> element for you. The alias is different, but the namespace is the same and that is what matters.

The find() method always returns an array, which may be empty. By using current() you get the first element found, or null if nothing was found.

Supported CSS Selectors

The following CSS selectors are supported:

• tag1 tag2
  This matches tag2 which is a descendant of tag1.
• tag1 > tag2
  This matches tag2 which is a direct child of tag1.
• tag:first-child
  This matches tag only if its the first child.
• tag1 + tag2
  This matches tag2 only if its immediately preceded by tag1.
• tag1 ~ tag2
  This matches tag2 only if it has a previous sibling tag1.
• tag[attr]
  This matches tag if it has the attribute attr.
• tag[attr="foo"]
  This matches tag if it has the attribute attr with the value foo in its value list.
• tag#id
  This matches any tag with id id.
• #id
  This matches any element with id id.
• ns|tag
  This matches ns:tag or more generally tag in the namespace indicated by the alias ns

SimpleXML

The parsed XML behaves almost identical to a SimpleXMLElement, with the exceptions noted above. So you can access attributes just like SimpleXMLElement allows:

    $version = $xml['version'];
    $version = $xml->attributes('version');

You can walk through the node tree:

    $title = $xml->channel->title;

Any method or property available in SimpleXMLElement is included in \arc\xml parsed data.

DOMElement methods

In addition to SimpleXMLElement methods, you can also call any method that is available in DOMElement.

    $version = $xml->getAttributes('version');
    $title = $xml->getElementsByTagName('channel')[0]
        ->getElementsByTagName('title')[0];

Parsing fragments

The arc\xml parser accepts partial XML content. It doesn't require a single root element.

    $xmlString = <<< EOF
<item>
    <title>An item</title>
</item>
<item>
    <title>Another item</title>
</item>
EOF;
    $xml = \arc\xml::parse($xmlString);
    echo $xml;

result:

<item>
    <title>An item</title>
</item>
<item>
    <title>Another item</title>
</item>