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mediawiki/includes/media/SVGMetadataExtractor.php
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SVGMetadataExtractor.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 Brion Vibber
* @copyright Copyright © 2010-2010 Brion Vibber, Derk-Jan Hartman
* @license http://www.gnu.org/copyleft/gpl.html GNU General Public License
*/
/**
* @ingroup Media
*/
class SVGMetadataExtractor {
static function getMetadata( $filename ) {
$svg = new SVGReader( $filename );
return $svg->getMetadata();
}
}
/**
* @ingroup Media
*/
class SVGReader {
const DEFAULT_WIDTH = 512;
const DEFAULT_HEIGHT = 512;
const NS_SVG = 'http://www.w3.org/2000/svg';
const LANG_PREFIX_MATCH = 1;
const LANG_FULL_MATCH = 2;
/** @var null|XMLReader */
private $reader = null;
/** @var bool */
private $mDebug = false;
/** @var array */
private $metadata = array();
private $languages = array();
private $languagePrefixes = array();
/**
* Constructor
*
* Creates an SVGReader drawing from the source provided
* @param string $source URI from which to read
* @throws MWException|Exception
*/
function __construct( $source ) {
global $wgSVGMetadataCutoff;
$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 MWException( "Error getting filesize of SVG." );
}
if ( $size > $wgSVGMetadataCutoff ) {
$this->debug( "SVG is $size bytes, which is bigger than $wgSVGMetadataCutoff. Truncating." );
$contents = file_get_contents( $source, false, null, -1, $wgSVGMetadataCutoff );
if ( $contents === false ) {
throw new MWException( 'Error reading SVG file.' );
}
$this->reader->XML( $contents, null, LIBXML_NOERROR | LIBXML_NOWARNING );
} else {
$this->reader->open( $source, null, LIBXML_NOERROR | LIBXML_NOWARNING );
}
// Expand entities, since Adobe Illustrator uses them for xmlns
// attributes (bug 31719). 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 (bug 46859).
$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.
wfSuppressWarnings();
try {
$this->read();
} catch ( Exception $e ) {
// Note, if this happens, the width/height will be taken to be 0x0.
// Should we consider it the default 512x512 instead?
wfRestoreWarnings();
libxml_disable_entity_loader( $oldDisable );
throw $e;
}
wfRestoreWarnings();
libxml_disable_entity_loader( $oldDisable );
}
/**
* @return array Array with the known metadata
*/
public function getMetadata() {
return $this->metadata;
}
/**
* Read the SVG
* @throws MWException
* @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 MWException( "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;
} elseif ( $isSVG && $tag == 'title' ) {
$this->readField( $tag, 'title' );
} elseif ( $isSVG && $tag == 'desc' ) {
$this->readField( $tag, 'description' );
} elseif ( $isSVG && $tag == 'metadata' && $type == XmlReader::ELEMENT ) {
$this->readXml( $tag, '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 $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;
} elseif ( $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 $metafield Field that we will fill with the result
* @throws MWException
*/
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"
if ( method_exists( $this->reader, 'readInnerXML' ) ) {
$this->metadata[$metafield] = trim( $this->reader->readInnerXML() );
} else {
throw new MWException( "The PHP XMLReader extension does not come " .
"with readInnerXML() method. Your libxml is probably out of " .
"date (need 2.6.20 or later)." );
}
$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;
} elseif ( $this->reader->namespaceURI == self::NS_SVG
&& $this->reader->nodeType == XmlReader::ELEMENT
) {
$sysLang = $this->reader->getAttribute( 'systemLanguage' );
if ( !is_null( $sysLang ) && $sysLang !== '' ) {
// See http://www.w3.org/TR/SVG/struct.html#SystemLanguageAttribute
$langList = explode( ',', $sysLang );
foreach ( $langList as $langItem ) {
$langItem = trim( $langItem );
if ( Language::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 ( Language::isWellFormedLanguageTag( $itemPrefix ) ) {
$this->languagePrefixes[$itemPrefix] = self::LANG_PREFIX_MATCH;
}
}
}
}
switch ( $this->reader->localName ) {
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();
}
}
// @todo FIXME: Unused, remove?
private function throwXmlError( $err ) {
$this->debug( "FAILURE: $err" );
wfDebug( "SVGReader XML error: $err\n" );
}
private function debug( $data ) {
if ( $this->mDebug ) {
wfDebug( "SVGReader: $data\n" );
}
}
// @todo FIXME: Unused, remove?
private function warn( $data ) {
wfDebug( "SVGReader: $data\n" );
}
// @todo FIXME: Unused, remove?
private function notice( $data ) {
wfDebug( "SVGReader WARN: $data\n" );
}
/**
* 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+/', trim( $this->reader->getAttribute( 'viewBox' ) ) );
if ( count( $viewBox ) == 4 ) {
$viewWidth = $this->scaleSVGUnit( $viewBox[2] );
$viewHeight = $this->scaleSVGUnit( $viewBox[3] );
if ( $viewWidth > 0 && $viewHeight > 0 ) {
$aspect = $viewWidth / $viewHeight;
$defaultHeight = $defaultWidth / $aspect;
}
}
}
if ( $this->reader->getAttribute( 'width' ) ) {
$width = $this->scaleSVGUnit( $this->reader->getAttribute( 'width' ), $defaultWidth );
$this->metadata['originalWidth'] = $this->reader->getAttribute( 'width' );
}
if ( $this->reader->getAttribute( 'height' ) ) {
$height = $this->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'] = intval( round( $width ) );
$this->metadata['height'] = intval( round( $height ) );
}
}
/**
* Return a rounded pixel equivalent for a labeled CSS/SVG length.
* http://www.w3.org/TR/SVG11/coords.html#UnitIdentifiers
*
* @param string $length CSS/SVG length.
* @param float|int $viewportSize Optional scale for percentage units...
* @return float Length in pixels
*/
static function scaleSVGUnit( $length, $viewportSize = 512 ) {
static $unitLength = array(
'px' => 1.0,
'pt' => 1.25,
'pc' => 15.0,
'mm' => 3.543307,
'cm' => 35.43307,
'in' => 90.0,
'em' => 16.0, // fake it?
'ex' => 12.0, // fake it?
'' => 1.0, // "User units" pixels by default
);
$matches = array();
if ( preg_match( '/^\s*(\d+(?:\.\d+)?)(em|ex|px|pt|pc|cm|mm|in|%|)\s*$/', $length, $matches ) ) {
$length = floatval( $matches[1] );
$unit = $matches[2];
if ( $unit == '%' ) {
return $length * 0.01 * $viewportSize;
} else {
return $length * $unitLength[$unit];
}
} else {
// Assume pixels
return floatval( $length );
}
}
}
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