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SVGReader.php
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	<?php

	/**
	* Extraction of SVG image metadata.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
	* http://www.gnu.org/copyleft/gpl.html
	*
	* @file
	* @ingroup Media
	* @author "Derk-Jan Hartman <hartman _at_ videolan d0t org>"
	* @author Brooke Vibber
	* @copyright Copyright © 2010-2010 Brooke Vibber, Derk-Jan Hartman
	* @license GPL-2.0-or-later
	*/

	use MediaWiki\Language\LanguageCode;
	use MediaWiki\MainConfigNames;
	use MediaWiki\MediaWikiServices;
	use Wikimedia\AtEase\AtEase;

	/**
	* @ingroup Media
	*/
	class SVGReader {
	private const DEFAULT_WIDTH = 512;
	private const DEFAULT_HEIGHT = 512;
	private const NS_SVG = 'http://www.w3.org/2000/svg';
	public const LANG_PREFIX_MATCH = 1;
	public const LANG_FULL_MATCH = 2;

	/** @var XMLReader */
	private $reader;

	/** @var bool */
	private $mDebug = false;

	/** @var array */
	private $metadata = [];
	/** @var int[] */
	private $languages = [];
	/** @var int[] */
	private $languagePrefixes = [];

	/**
	* Creates an SVGReader drawing from the source provided
	* @param string $source URI from which to read
	* @throws InvalidSVGException
	*/
	public function __construct( $source ) {
	$svgMetadataCutoff = MediaWikiServices::getInstance()->getMainConfig()
	->get( MainConfigNames::SVGMetadataCutoff );
	$this->reader = new XMLReader();

	// Don't use $file->getSize() since file object passed to SVGHandler::getMetadata is bogus.
	$size = filesize( $source );
	if ( $size === false ) {
	throw new InvalidSVGException( "Error getting filesize of SVG." );
	}

	if ( $size > $svgMetadataCutoff ) {
	$this->debug( "SVG is $size bytes, which is bigger than {$svgMetadataCutoff}. Truncating." );
	$contents = file_get_contents( $source, false, null, 0, $svgMetadataCutoff );
	if ( $contents === false ) {
	throw new InvalidSVGException( 'Error reading SVG file.' );
	}
	$status = $this->reader->XML( $contents, null, LIBXML_NOERROR \| LIBXML_NOWARNING );
	} else {
	$status = $this->reader->open( $source, null, LIBXML_NOERROR \| LIBXML_NOWARNING );
	}
	if ( !$status ) {
	throw new InvalidSVGException( "Error getting xml of SVG." );
	}

	// Expand entities, since Adobe Illustrator uses them for xmlns
	// attributes (T33719). Note that libxml2 has some protection
	// against large recursive entity expansions so this is not as
	// insecure as it might appear to be. However, it is still extremely
	// insecure. It's necessary to wrap any read() calls with
	// libxml_disable_entity_loader() to avoid arbitrary local file
	// inclusion, or even arbitrary code execution if the expect
	// extension is installed (T48859).
	// phpcs:ignore Generic.PHP.NoSilencedErrors -- suppress deprecation per T268847
	$oldDisable = @libxml_disable_entity_loader( true );
	$this->reader->setParserProperty( XMLReader::SUBST_ENTITIES, true );

	$this->metadata['width'] = self::DEFAULT_WIDTH;
	$this->metadata['height'] = self::DEFAULT_HEIGHT;

	// The size in the units specified by the SVG file
	// (for the metadata box)
	// Per the SVG spec, if unspecified, default to '100%'
	$this->metadata['originalWidth'] = '100%';
	$this->metadata['originalHeight'] = '100%';

	// Because we cut off the end of the svg making an invalid one. Complicated
	// try catch thing to make sure warnings get restored. Seems like there should
	// be a better way.
	AtEase::suppressWarnings();
	try {
	// Note: if this throws, the width/height will be taken to be 0x0.
	// Should we consider it the default 512x512 instead?
	$this->read();
	} finally {
	libxml_disable_entity_loader( $oldDisable );
	AtEase::restoreWarnings();
	}
	}

	/**
	* @return array Array with the known metadata
	*/
	public function getMetadata() {
	return $this->metadata;
	}

	/**
	* Read the SVG
	* @throws InvalidSVGException
	* @return bool
	*/
	protected function read() {
	$keepReading = $this->reader->read();

	/* Skip until first element */
	while ( $keepReading && $this->reader->nodeType !== XMLReader::ELEMENT ) {
	$keepReading = $this->reader->read();
	}

	if ( $this->reader->localName !== 'svg' \|\| $this->reader->namespaceURI !== self::NS_SVG ) {
	throw new InvalidSVGException( "Expected <svg> tag, got " .
	$this->reader->localName . " in NS " . $this->reader->namespaceURI );
	}
	$this->debug( '<svg> tag is correct.' );
	$this->handleSVGAttribs();

	$exitDepth = $this->reader->depth;
	$keepReading = $this->reader->read();
	while ( $keepReading ) {
	$tag = $this->reader->localName;
	$type = $this->reader->nodeType;
	$isSVG = ( $this->reader->namespaceURI === self::NS_SVG );

	$this->debug( "$tag" );

	if ( $isSVG && $tag === 'svg' && $type === XMLReader::END_ELEMENT
	&& $this->reader->depth <= $exitDepth
	) {
	break;
	}

	if ( $isSVG && $tag === 'title' ) {
	$this->readField( $tag, 'title' );
	} elseif ( $isSVG && $tag === 'desc' ) {
	$this->readField( $tag, 'description' );
	} elseif ( $isSVG && $tag === 'metadata' && $type === XMLReader::ELEMENT ) {
	$this->readXml( 'metadata' );
	} elseif ( $isSVG && $tag === 'script' ) {
	// We normally do not allow scripted svgs.
	// However its possible to configure MW to let them
	// in, and such files should be considered animated.
	$this->metadata['animated'] = true;
	} elseif ( $tag !== '#text' ) {
	$this->debug( "Unhandled top-level XML tag $tag" );

	// Recurse into children of current tag, looking for animation and languages.
	$this->animateFilterAndLang( $tag );
	}

	// Goto next element, which is sibling of current (Skip children).
	$keepReading = $this->reader->next();
	}

	$this->reader->close();

	$this->metadata['translations'] = $this->languages + $this->languagePrefixes;

	return true;
	}

	/**
	* Read a textelement from an element
	*
	* @param string $name Name of the element that we are reading from
	* @param string\|null $metafield Field that we will fill with the result
	*/
	private function readField( $name, $metafield = null ) {
	$this->debug( "Read field $metafield" );
	if ( !$metafield \|\| $this->reader->nodeType !== XMLReader::ELEMENT ) {
	return;
	}
	$keepReading = $this->reader->read();
	while ( $keepReading ) {
	if ( $this->reader->localName === $name
	&& $this->reader->namespaceURI === self::NS_SVG
	&& $this->reader->nodeType === XMLReader::END_ELEMENT
	) {
	break;
	}

	if ( $this->reader->nodeType === XMLReader::TEXT ) {
	$this->metadata[$metafield] = trim( $this->reader->value );
	}
	$keepReading = $this->reader->read();
	}
	}

	/**
	* Read an XML snippet from an element
	*
	* @param string\|null $metafield Field that we will fill with the result
	*/
	private function readXml( $metafield = null ) {
	$this->debug( "Read top level metadata" );
	if ( !$metafield \|\| $this->reader->nodeType !== XMLReader::ELEMENT ) {
	return;
	}
	// @todo Find and store type of xml snippet. metadata['metadataType'] = "rdf"
	$this->metadata[$metafield] = trim( $this->reader->readInnerXml() );

	$this->reader->next();
	}

	/**
	* Filter all children, looking for animated elements.
	* Also get a list of languages that can be targeted.
	*
	* @param string $name Name of the element that we are reading from
	*/
	private function animateFilterAndLang( $name ) {
	$this->debug( "animate filter for tag $name" );
	if ( $this->reader->nodeType !== XMLReader::ELEMENT ) {
	return;
	}
	if ( $this->reader->isEmptyElement ) {
	return;
	}
	$exitDepth = $this->reader->depth;
	$keepReading = $this->reader->read();
	while ( $keepReading ) {
	if ( $this->reader->localName === $name && $this->reader->depth <= $exitDepth
	&& $this->reader->nodeType === XMLReader::END_ELEMENT
	) {
	break;
	}

	if ( $this->reader->namespaceURI === self::NS_SVG
	&& $this->reader->nodeType === XMLReader::ELEMENT
	) {
	$sysLang = $this->reader->getAttribute( 'systemLanguage' );
	if ( $sysLang !== null && $sysLang !== '' ) {
	// See https://www.w3.org/TR/SVG/struct.html#SystemLanguageAttribute
	$langList = explode( ',', $sysLang );
	foreach ( $langList as $langItem ) {
	$langItem = trim( $langItem );
	if ( LanguageCode::isWellFormedLanguageTag( $langItem ) ) {
	$this->languages[$langItem] = self::LANG_FULL_MATCH;
	}
	// Note, the standard says that any prefix should work,
	// here we do only the initial prefix, since that will catch
	// 99% of cases, and we are going to compare against fallbacks.
	// This differs mildly from how the spec says languages should be
	// handled, however it matches better how the MediaWiki language
	// preference is generally handled.
	$dash = strpos( $langItem, '-' );
	// Intentionally checking both !false and > 0 at the same time.
	if ( $dash ) {
	$itemPrefix = substr( $langItem, 0, $dash );
	if ( LanguageCode::isWellFormedLanguageTag( $itemPrefix ) ) {
	$this->languagePrefixes[$itemPrefix] = self::LANG_PREFIX_MATCH;
	}
	}
	}
	}
	switch ( $this->reader->localName ) {
	case 'style':
	$styleContents = $this->reader->readString();
	if (
	str_contains( $styleContents, 'animated' ) \|\|
	str_contains( $styleContents, '@keyframes' )
	) {
	$this->debug( "HOUSTON WE HAVE ANIMATION" );
	$this->metadata['animated'] = true;
	}
	break;
	case 'script':
	// Normally we disallow files with
	// <script>, but its possible
	// to configure MW to disable
	// such checks.
	case 'animate':
	case 'set':
	case 'animateMotion':
	case 'animateColor':
	case 'animateTransform':
	$this->debug( "HOUSTON WE HAVE ANIMATION" );
	$this->metadata['animated'] = true;
	break;
	}
	}
	$keepReading = $this->reader->read();
	}
	}

	private function debug( $data ) {
	if ( $this->mDebug ) {
	wfDebug( "SVGReader: $data" );
	}
	}

	/**
	* Parse the attributes of an SVG element
	*
	* The parser has to be in the start element of "<svg>"
	*/
	private function handleSVGAttribs() {
	$defaultWidth = self::DEFAULT_WIDTH;
	$defaultHeight = self::DEFAULT_HEIGHT;
	$aspect = 1.0;
	$width = null;
	$height = null;

	if ( $this->reader->getAttribute( 'viewBox' ) ) {
	// min-x min-y width height
	$viewBox = preg_split( '/\s[\s,]\s/', trim( $this->reader->getAttribute( 'viewBox' ) ?? '' ) );
	if ( count( $viewBox ) === 4 ) {
	$viewWidth = self::scaleSVGUnit( $viewBox[2] );
	$viewHeight = self::scaleSVGUnit( $viewBox[3] );
	if ( $viewWidth > 0 && $viewHeight > 0 ) {
	$aspect = $viewWidth / $viewHeight;
	$defaultHeight = $defaultWidth / $aspect;
	}
	}
	}
	if ( $this->reader->getAttribute( 'width' ) ) {
	$width = self::scaleSVGUnit( $this->reader->getAttribute( 'width' ) ?? '', $defaultWidth );
	$this->metadata['originalWidth'] = $this->reader->getAttribute( 'width' );
	}
	if ( $this->reader->getAttribute( 'height' ) ) {
	$height = self::scaleSVGUnit( $this->reader->getAttribute( 'height' ) ?? '', $defaultHeight );
	$this->metadata['originalHeight'] = $this->reader->getAttribute( 'height' );
	}

	if ( !isset( $width ) && !isset( $height ) ) {
	$width = $defaultWidth;
	$height = $width / $aspect;
	} elseif ( isset( $width ) && !isset( $height ) ) {
	$height = $width / $aspect;
	} elseif ( isset( $height ) && !isset( $width ) ) {
	$width = $height * $aspect;
	}

	if ( $width > 0 && $height > 0 ) {
	$this->metadata['width'] = (int)round( $width );
	$this->metadata['height'] = (int)round( $height );
	}
	}

	/**
	* Return a rounded pixel equivalent for a labeled CSS/SVG length.
	* https://www.w3.org/TR/SVG11/coords.html#Units
	* https://www.w3.org/TR/css-values-3/#lengths
	*
	* @param string $length CSS/SVG length.
	* @param float\|int $viewportSize Optional scale for percentage units...
	* @return float Length in pixels
	*/
	public static function scaleSVGUnit( $length, $viewportSize = 512 ) {
	// Per CSS values spec, assume 96dpi.
	static $unitLength = [
	'px' => 1.0,
	'pt' => 1.333333,
	'pc' => 16.0,
	'mm' => 3.7795275,
	'q' => 0.944881,
	'cm' => 37.795275,
	'in' => 96.0,
	'em' => 16.0, // Browser default font size if unspecified
	'rem' => 16.0,
	'ch' => 8.0, // Spec says 1em if impossible to determine
	'ex' => 8.0, // Spec says 0.5em if impossible to determine
	'' => 1.0, // "User units" pixels by default
	];
	// TODO: Does not support vw, vh, vmin, vmax.
	$matches = [];
	if ( preg_match(
	'/^\s([-+]?\d(?:\.\d+\|\d+)(?:[Ee][-+]?\d+)?)\s*' .
	'(rem\|em\|ex\|px\|pt\|pc\|cm\|mm\|in\|ch\|q\|%)\s*$/i',
	$length,
	$matches
	) ) {
	$length = (float)$matches[1];
	$unit = strtolower( $matches[2] );
	if ( $unit === '%' ) {
	return $length * 0.01 * $viewportSize;
	}

	return $length * $unitLength[$unit];
	}

	// Assume pixels
	return (float)$length;
	}
	}

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