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[mediawiki.git] / includes / media / PNGMetadataExtractor.php

<?php
/**
 * PNG frame counter and metadata extractor.
 *
 * Slightly derived from GIFMetadataExtractor.php
 * Deliberately not using MWExceptions to avoid external dependencies, encouraging
 * redistribution.
 *
 * 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
 */

/**
 * PNG frame counter.
 *
 * @ingroup Media
 */
class PNGMetadataExtractor {
        /** @var string */
        private static $pngSig;

        /** @var int */
        private static $crcSize;

        /** @var array */
        private static $textChunks;

        const VERSION = 1;
        const MAX_CHUNK_SIZE = 3145728; // 3 megabytes

        static function getMetadata( $filename ) {
                self::$pngSig = pack( "C8", 137, 80, 78, 71, 13, 10, 26, 10 );
                self::$crcSize = 4;
                /* based on list at http://owl.phy.queensu.ca/~phil/exiftool/TagNames/PNG.html#TextualData
                 * and http://www.w3.org/TR/PNG/#11keywords
                 */
                self::$textChunks = array(
                        'xml:com.adobe.xmp' => 'xmp',
                        # Artist is unofficial. Author is the recommended
                        # keyword in the PNG spec. However some people output
                        # Artist so support both.
                        'artist' => 'Artist',
                        'model' => 'Model',
                        'make' => 'Make',
                        'author' => 'Artist',
                        'comment' => 'PNGFileComment',
                        'description' => 'ImageDescription',
                        'title' => 'ObjectName',
                        'copyright' => 'Copyright',
                        # Source as in original device used to make image
                        # not as in who gave you the image
                        'source' => 'Model',
                        'software' => 'Software',
                        'disclaimer' => 'Disclaimer',
                        'warning' => 'ContentWarning',
                        'url' => 'Identifier', # Not sure if this is best mapping. Maybe WebStatement.
                        'label' => 'Label',
                        'creation time' => 'DateTimeDigitized',
                        /* Other potentially useful things - Document */
                );

                $frameCount = 0;
                $loopCount = 1;
                $text = array();
                $duration = 0.0;
                $bitDepth = 0;
                $colorType = 'unknown';

                if ( !$filename ) {
                        throw new Exception( __METHOD__ . ": No file name specified" );
                } elseif ( !file_exists( $filename ) || is_dir( $filename ) ) {
                        throw new Exception( __METHOD__ . ": File $filename does not exist" );
                }

                $fh = fopen( $filename, 'rb' );

                if ( !$fh ) {
                        throw new Exception( __METHOD__ . ": Unable to open file $filename" );
                }

                // Check for the PNG header
                $buf = fread( $fh, 8 );
                if ( $buf != self::$pngSig ) {
                        throw new Exception( __METHOD__ . ": Not a valid PNG file; header: $buf" );
                }

                // Read chunks
                while ( !feof( $fh ) ) {
                        $buf = fread( $fh, 4 );
                        if ( !$buf || strlen( $buf ) < 4 ) {
                                throw new Exception( __METHOD__ . ": Read error" );
                        }
                        $chunk_size = unpack( "N", $buf );
                        $chunk_size = $chunk_size[1];

                        if ( $chunk_size < 0 ) {
                                throw new Exception( __METHOD__ . ": Chunk size too big for unpack" );
                        }

                        $chunk_type = fread( $fh, 4 );
                        if ( !$chunk_type || strlen( $chunk_type ) < 4 ) {
                                throw new Exception( __METHOD__ . ": Read error" );
                        }

                        if ( $chunk_type == "IHDR" ) {
                                $buf = self::read( $fh, $chunk_size );
                                if ( !$buf || strlen( $buf ) < $chunk_size ) {
                                        throw new Exception( __METHOD__ . ": Read error" );
                                }
                                $bitDepth = ord( substr( $buf, 8, 1 ) );
                                // Detect the color type in British English as per the spec
                                // http://www.w3.org/TR/PNG/#11IHDR
                                switch ( ord( substr( $buf, 9, 1 ) ) ) {
                                        case 0:
                                                $colorType = 'greyscale';
                                                break;
                                        case 2:
                                                $colorType = 'truecolour';
                                                break;
                                        case 3:
                                                $colorType = 'index-coloured';
                                                break;
                                        case 4:
                                                $colorType = 'greyscale-alpha';
                                                break;
                                        case 6:
                                                $colorType = 'truecolour-alpha';
                                                break;
                                        default:
                                                $colorType = 'unknown';
                                                break;
                                }
                        } elseif ( $chunk_type == "acTL" ) {
                                $buf = fread( $fh, $chunk_size );
                                if ( !$buf || strlen( $buf ) < $chunk_size || $chunk_size < 4 ) {
                                        throw new Exception( __METHOD__ . ": Read error" );
                                }

                                $actl = unpack( "Nframes/Nplays", $buf );
                                $frameCount = $actl['frames'];
                                $loopCount = $actl['plays'];
                        } elseif ( $chunk_type == "fcTL" ) {
                                $buf = self::read( $fh, $chunk_size );
                                if ( !$buf || strlen( $buf ) < $chunk_size ) {
                                        throw new Exception( __METHOD__ . ": Read error" );
                                }
                                $buf = substr( $buf, 20 );
                                if ( strlen( $buf ) < 4 ) {
                                        throw new Exception( __METHOD__ . ": Read error" );
                                }

                                $fctldur = unpack( "ndelay_num/ndelay_den", $buf );
                                if ( $fctldur['delay_den'] == 0 ) {
                                        $fctldur['delay_den'] = 100;
                                }
                                if ( $fctldur['delay_num'] ) {
                                        $duration += $fctldur['delay_num'] / $fctldur['delay_den'];
                                }
                        } elseif ( $chunk_type == "iTXt" ) {
                                // Extracts iTXt chunks, uncompressing if necessary.
                                $buf = self::read( $fh, $chunk_size );
                                $items = array();
                                if ( preg_match(
                                        '/^([^\x00]{1,79})\x00(\x00|\x01)\x00([^\x00]*)(.)[^\x00]*\x00(.*)$/Ds',
                                        $buf, $items )
                                ) {
                                        /* $items[1] = text chunk name, $items[2] = compressed flag,
                                         * $items[3] = lang code (or ""), $items[4]= compression type.
                                         * $items[5] = content
                                         */

                                        // Theoretically should be case-sensitive, but in practise...
                                        $items[1] = strtolower( $items[1] );
                                        if ( !isset( self::$textChunks[$items[1]] ) ) {
                                                // Only extract textual chunks on our list.
                                                fseek( $fh, self::$crcSize, SEEK_CUR );
                                                continue;
                                        }

                                        $items[3] = strtolower( $items[3] );
                                        if ( $items[3] == '' ) {
                                                // if no lang specified use x-default like in xmp.
                                                $items[3] = 'x-default';
                                        }

                                        // if compressed
                                        if ( $items[2] == "\x01" ) {
                                                if ( function_exists( 'gzuncompress' ) && $items[4] === "\x00" ) {
                                                        wfSuppressWarnings();
                                                        $items[5] = gzuncompress( $items[5] );
                                                        wfRestoreWarnings();

                                                        if ( $items[5] === false ) {
                                                                // decompression failed
                                                                wfDebug( __METHOD__ . ' Error decompressing iTxt chunk - ' . $items[1] . "\n" );
                                                                fseek( $fh, self::$crcSize, SEEK_CUR );
                                                                continue;
                                                        }
                                                } else {
                                                        wfDebug( __METHOD__ . ' Skipping compressed png iTXt chunk due to lack of zlib,'
                                                                . " or potentially invalid compression method\n" );
                                                        fseek( $fh, self::$crcSize, SEEK_CUR );
                                                        continue;
                                                }
                                        }
                                        $finalKeyword = self::$textChunks[$items[1]];
                                        $text[$finalKeyword][$items[3]] = $items[5];
                                        $text[$finalKeyword]['_type'] = 'lang';
                                } else {
                                        // Error reading iTXt chunk
                                        throw new Exception( __METHOD__ . ": Read error on iTXt chunk" );
                                }
                        } elseif ( $chunk_type == 'tEXt' ) {
                                $buf = self::read( $fh, $chunk_size );

                                // In case there is no \x00 which will make explode fail.
                                if ( strpos( $buf, "\x00" ) === false ) {
                                        throw new Exception( __METHOD__ . ": Read error on tEXt chunk" );
                                }

                                list( $keyword, $content ) = explode( "\x00", $buf, 2 );
                                if ( $keyword === '' || $content === '' ) {
                                        throw new Exception( __METHOD__ . ": Read error on tEXt chunk" );
                                }

                                // Theoretically should be case-sensitive, but in practise...
                                $keyword = strtolower( $keyword );
                                if ( !isset( self::$textChunks[$keyword] ) ) {
                                        // Don't recognize chunk, so skip.
                                        fseek( $fh, self::$crcSize, SEEK_CUR );
                                        continue;
                                }
                                wfSuppressWarnings();
                                $content = iconv( 'ISO-8859-1', 'UTF-8', $content );
                                wfRestoreWarnings();

                                if ( $content === false ) {
                                        throw new Exception( __METHOD__ . ": Read error (error with iconv)" );
                                }

                                $finalKeyword = self::$textChunks[$keyword];
                                $text[$finalKeyword]['x-default'] = $content;
                                $text[$finalKeyword]['_type'] = 'lang';
                        } elseif ( $chunk_type == 'zTXt' ) {
                                if ( function_exists( 'gzuncompress' ) ) {
                                        $buf = self::read( $fh, $chunk_size );

                                        // In case there is no \x00 which will make explode fail.
                                        if ( strpos( $buf, "\x00" ) === false ) {
                                                throw new Exception( __METHOD__ . ": Read error on zTXt chunk" );
                                        }

                                        list( $keyword, $postKeyword ) = explode( "\x00", $buf, 2 );
                                        if ( $keyword === '' || $postKeyword === '' ) {
                                                throw new Exception( __METHOD__ . ": Read error on zTXt chunk" );
                                        }
                                        // Theoretically should be case-sensitive, but in practise...
                                        $keyword = strtolower( $keyword );

                                        if ( !isset( self::$textChunks[$keyword] ) ) {
                                                // Don't recognize chunk, so skip.
                                                fseek( $fh, self::$crcSize, SEEK_CUR );
                                                continue;
                                        }
                                        $compression = substr( $postKeyword, 0, 1 );
                                        $content = substr( $postKeyword, 1 );
                                        if ( $compression !== "\x00" ) {
                                                wfDebug( __METHOD__ . " Unrecognized compression method in zTXt ($keyword). Skipping.\n" );
                                                fseek( $fh, self::$crcSize, SEEK_CUR );
                                                continue;
                                        }

                                        wfSuppressWarnings();
                                        $content = gzuncompress( $content );
                                        wfRestoreWarnings();

                                        if ( $content === false ) {
                                                // decompression failed
                                                wfDebug( __METHOD__ . ' Error decompressing zTXt chunk - ' . $keyword . "\n" );
                                                fseek( $fh, self::$crcSize, SEEK_CUR );
                                                continue;
                                        }

                                        wfSuppressWarnings();
                                        $content = iconv( 'ISO-8859-1', 'UTF-8', $content );
                                        wfRestoreWarnings();

                                        if ( $content === false ) {
                                                throw new Exception( __METHOD__ . ": Read error (error with iconv)" );
                                        }

                                        $finalKeyword = self::$textChunks[$keyword];
                                        $text[$finalKeyword]['x-default'] = $content;
                                        $text[$finalKeyword]['_type'] = 'lang';
                                } else {
                                        wfDebug( __METHOD__ . " Cannot decompress zTXt chunk due to lack of zlib. Skipping.\n" );
                                        fseek( $fh, $chunk_size, SEEK_CUR );
                                }
                        } elseif ( $chunk_type == 'tIME' ) {
                                // last mod timestamp.
                                if ( $chunk_size !== 7 ) {
                                        throw new Exception( __METHOD__ . ": tIME wrong size" );
                                }
                                $buf = self::read( $fh, $chunk_size );
                                if ( !$buf || strlen( $buf ) < $chunk_size ) {
                                        throw new Exception( __METHOD__ . ": Read error" );
                                }

                                // Note: spec says this should be UTC.
                                $t = unpack( "ny/Cm/Cd/Ch/Cmin/Cs", $buf );
                                $strTime = sprintf( "%04d%02d%02d%02d%02d%02d",
                                        $t['y'], $t['m'], $t['d'], $t['h'],
                                        $t['min'], $t['s'] );

                                $exifTime = wfTimestamp( TS_EXIF, $strTime );

                                if ( $exifTime ) {
                                        $text['DateTime'] = $exifTime;
                                }
                        } elseif ( $chunk_type == 'pHYs' ) {
                                // how big pixels are (dots per meter).
                                if ( $chunk_size !== 9 ) {
                                        throw new Exception( __METHOD__ . ": pHYs wrong size" );
                                }

                                $buf = self::read( $fh, $chunk_size );
                                if ( !$buf || strlen( $buf ) < $chunk_size ) {
                                        throw new Exception( __METHOD__ . ": Read error" );
                                }

                                $dim = unpack( "Nwidth/Nheight/Cunit", $buf );
                                if ( $dim['unit'] == 1 ) {
                                        // Need to check for negative because php
                                        // doesn't deal with super-large unsigned 32-bit ints well
                                        if ( $dim['width'] > 0 && $dim['height'] > 0 ) {
                                                // unit is meters
                                                // (as opposed to 0 = undefined )
                                                $text['XResolution'] = $dim['width']
                                                        . '/100';
                                                $text['YResolution'] = $dim['height']
                                                        . '/100';
                                                $text['ResolutionUnit'] = 3;
                                                // 3 = dots per cm (from Exif).
                                        }
                                }
                        } elseif ( $chunk_type == "IEND" ) {
                                break;
                        } else {
                                fseek( $fh, $chunk_size, SEEK_CUR );
                        }
                        fseek( $fh, self::$crcSize, SEEK_CUR );
                }
                fclose( $fh );

                if ( $loopCount > 1 ) {
                        $duration *= $loopCount;
                }

                if ( isset( $text['DateTimeDigitized'] ) ) {
                        // Convert date format from rfc2822 to exif.
                        foreach ( $text['DateTimeDigitized'] as $name => &$value ) {
                                if ( $name === '_type' ) {
                                        continue;
                                }

                                // @todo FIXME: Currently timezones are ignored.
                                // possibly should be wfTimestamp's
                                // responsibility. (at least for numeric TZ)
                                $formatted = wfTimestamp( TS_EXIF, $value );
                                if ( $formatted ) {
                                        // Only change if we could convert the
                                        // date.
                                        // The png standard says it should be
                                        // in rfc2822 format, but not required.
                                        // In general for the exif stuff we
                                        // prettify the date if we can, but we
                                        // display as-is if we cannot or if
                                        // it is invalid.
                                        // So do the same here.

                                        $value = $formatted;
                                }
                        }
                }

                return array(
                        'frameCount' => $frameCount,
                        'loopCount' => $loopCount,
                        'duration' => $duration,
                        'text' => $text,
                        'bitDepth' => $bitDepth,
                        'colorType' => $colorType,
                );
        }

        /**
         * Read a chunk, checking to make sure its not too big.
         *
         * @param resource $fh The file handle
         * @param int $size Size in bytes.
         * @throws Exception If too big
         * @return string The chunk.
         */
        private static function read( $fh, $size ) {
                if ( $size > self::MAX_CHUNK_SIZE ) {
                        throw new Exception( __METHOD__ . ': Chunk size of ' . $size .
                                ' too big. Max size is: ' . self::MAX_CHUNK_SIZE );
                }

                return fread( $fh, $size );
        }
}