SVGMetadataExtractor.php

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<?php
class SVGMetadataExtractor {
        static function getMetadata( $filename ) {
                $svg = new SVGReader( $filename );
                return $svg->getMetadata();
        }
}

class SVGReader {
        const DEFAULT_WIDTH = 512;
        const DEFAULT_HEIGHT = 512;
        const NS_SVG = 'http://www.w3.org/2000/svg';

        private $reader = null;
        private $mDebug = false;
        private $metadata = Array();

        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 );
        }

        public function getMetadata() {
                return $this->metadata;
        }

        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" );

                                if ( !isset( $this->metadata['animated'] ) ) {
                                        // Recurse into children of current tag, looking for animation.
                                        $this->animateFilter( $tag );
                                }
                        }

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

                $this->reader->close();

                return true;
        }

        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();
                }
        }

        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();
        }

        private function animateFilter( $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 ) {
                                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();
                }
        }

        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" );
                }
        }

        private function warn( $data ) {
                wfDebug( "SVGReader: $data\n" );
        }

        private function notice( $data ) {
                wfDebug( "SVGReader WARN: $data\n" );
        }

        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 ) );
                }
        }

        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 );
                }
        }
}