JpegMetadataExtractor.php

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<?php
class JpegMetadataExtractor {

        const MAX_JPEG_SEGMENTS = 200;
        // the max segment is a sanity check.
        // A jpeg file should never even remotely have
        // that many segments. Your average file has about 10.

        static function segmentSplitter ( $filename ) {
                $showXMP = function_exists( 'xml_parser_create_ns' );

                $segmentCount = 0;

                $segments = array(
                        'XMP_ext' => array(),
                        'COM' => array(),
                        'PSIR' => array(),
                );

                if ( !$filename ) {
                        throw new MWException( "No filename specified for " . __METHOD__ );
                }
                if ( !file_exists( $filename ) || is_dir( $filename ) ) {
                        throw new MWException( "Invalid file $filename passed to " . __METHOD__ );
                }

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

                if ( !$fh ) {
                        throw new MWException( "Could not open file $filename" );
                }

                $buffer = fread( $fh, 2 );
                if ( $buffer !== "\xFF\xD8" ) {
                        throw new MWException( "Not a jpeg, no SOI" );
                }
                while ( !feof( $fh ) ) {
                        $buffer = fread( $fh, 1 );
                        $segmentCount++;
                        if ( $segmentCount > self::MAX_JPEG_SEGMENTS ) {
                                // this is just a sanity check
                                throw new MWException( 'Too many jpeg segments. Aborting' );
                        }
                        if ( $buffer !== "\xFF" ) {
                                throw new MWException( "Error reading jpeg file marker. Expected 0xFF but got " . bin2hex( $buffer ) );
                        }

                        $buffer = fread( $fh, 1 );
                        while( $buffer === "\xFF" && !feof( $fh ) ) {
                                // Skip through any 0xFF padding bytes.
                                $buffer = fread( $fh, 1 );
                        }
                        if ( $buffer === "\xFE" ) {

                                // COM section -- file comment
                                // First see if valid utf-8,
                                // if not try to convert it to windows-1252.
                                $com = $oldCom = trim( self::jpegExtractMarker( $fh ) );
                                UtfNormal::quickIsNFCVerify( $com );
                                // turns $com to valid utf-8.
                                // thus if no change, its utf-8, otherwise its something else.
                                if ( $com !== $oldCom ) {
                                        wfSuppressWarnings();
                                        $com = $oldCom = iconv( 'windows-1252', 'UTF-8//IGNORE', $oldCom );
                                        wfRestoreWarnings();
                                }
                                // Try it again, if its still not a valid string, then probably
                                // binary junk or some really weird encoding, so don't extract.
                                UtfNormal::quickIsNFCVerify( $com );
                                if ( $com === $oldCom ) {
                                        $segments["COM"][] = $oldCom;
                                } else {
                                        wfDebug( __METHOD__ . ' Ignoring JPEG comment as is garbage.' );
                                }

                        } elseif ( $buffer === "\xE1" ) {
                                // APP1 section (Exif, XMP, and XMP extended)
                                // only extract if XMP is enabled.
                                $temp = self::jpegExtractMarker( $fh );
                                // check what type of app segment this is.
                                if ( substr( $temp, 0, 29 ) === "http://ns.adobe.com/xap/1.0/\x00" && $showXMP ) {
                                        $segments["XMP"] = substr( $temp, 29 );
                                } elseif ( substr( $temp, 0, 35 ) === "http://ns.adobe.com/xmp/extension/\x00" && $showXMP ) {
                                        $segments["XMP_ext"][] = substr( $temp, 35 );
                                } elseif ( substr( $temp, 0, 29 ) === "XMP\x00://ns.adobe.com/xap/1.0/\x00" && $showXMP ) {
                                        // Some images (especially flickr images) seem to have this.
                                        // I really have no idea what the deal is with them, but
                                        // whatever...
                                        $segments["XMP"] = substr( $temp, 29 );
                                        wfDebug( __METHOD__ . ' Found XMP section with wrong app identifier '
                                                . "Using anyways.\n" ); 
                                } elseif ( substr( $temp, 0, 6 ) === "Exif\0\0" ) {
                                        // Just need to find out what the byte order is.
                                        // because php's exif plugin sucks...
                                        // This is a II for little Endian, MM for big. Not a unicode BOM.
                                        $byteOrderMarker = substr( $temp, 6, 2 );
                                        if ( $byteOrderMarker === 'MM' ) {
                                                $segments['byteOrder'] = 'BE';
                                        } elseif ( $byteOrderMarker === 'II' ) {
                                                $segments['byteOrder'] = 'LE';
                                        } else {
                                                wfDebug( __METHOD__ . ' Invalid byte ordering?!' );
                                        }
                                }
                        } elseif ( $buffer === "\xED" ) {
                                // APP13 - PSIR. IPTC and some photoshop stuff
                                $temp = self::jpegExtractMarker( $fh );
                                if ( substr( $temp, 0, 14 ) === "Photoshop 3.0\x00" ) {
                                        $segments["PSIR"][] = $temp;
                                }
                        } elseif ( $buffer === "\xD9" || $buffer === "\xDA" ) {
                                // EOI - end of image or SOS - start of scan. either way we're past any interesting segments
                                return $segments;
                        } else {
                                // segment we don't care about, so skip
                                $size = wfUnpack( "nint", fread( $fh, 2 ), 2 );
                                if ( $size['int'] <= 2 ) throw new MWException( "invalid marker size in jpeg" );
                                fseek( $fh, $size['int'] - 2, SEEK_CUR );
                        }

                }
                // shouldn't get here.
                throw new MWException( "Reached end of jpeg file unexpectedly" );
        }

        private static function jpegExtractMarker( &$fh ) {
                $size = wfUnpack( "nint", fread( $fh, 2 ), 2 );
                if ( $size['int'] <= 2 ) {
                        throw new MWException( "invalid marker size in jpeg" );
                }
                $segment = fread( $fh, $size['int'] - 2 );
                if ( strlen( $segment ) !== $size['int'] - 2 ) {
                        throw new MWException( "Segment shorter than expected" );
                }
                return $segment;
        }

        public static function doPSIR ( $app13 ) {
                if ( !$app13 ) {
                        throw new MWException( "No App13 segment given" );
                }
                // First compare hash with real thing
                // 0x404 contains IPTC, 0x425 has hash
                // This is used to determine if the iptc is newer than
                // the xmp data, as xmp programs update the hash,
                // where non-xmp programs don't.

                $offset = 14; // skip past PHOTOSHOP 3.0 identifier. should already be checked.
                $appLen = strlen( $app13 );
                $realHash = "";
                $recordedHash = "";

                // the +12 is the length of an empty item.
                while ( $offset + 12 <= $appLen ) {
                        $valid = true;
                        if ( substr( $app13, $offset, 4 ) !== '8BIM' ) {
                                // its supposed to be 8BIM
                                // but apparently sometimes isn't esp. in
                                // really old jpg's
                                $valid = false;
                        }
                        $offset += 4;
                        $id = substr( $app13, $offset, 2 );
                        // id is a 2 byte id number which identifies
                        // the piece of info this record contains.

                        $offset += 2;

                        // some record types can contain a name, which
                        // is a pascal string 0-padded to be an even
                        // number of bytes. Most times (and any time
                        // we care) this is empty, making it two null bytes.

                        $lenName = ord( substr( $app13, $offset, 1 ) ) + 1;
                        // we never use the name so skip it. +1 for length byte
                        if ( $lenName % 2 == 1 ) {
                                $lenName++;
                        } // pad to even.
                        $offset += $lenName;

                        // now length of data (unsigned long big endian)
                        $lenData = wfUnpack( 'Nlen', substr( $app13, $offset, 4 ), 4 );
                        // PHP can take issue with very large unsigned ints and make them negative.
                        // Which should never ever happen, as this has to be inside a segment
                        // which is limited to a 16 bit number.
                        if ( $lenData['len'] < 0 ) throw new MWException( "Too big PSIR (" . $lenData['len'] . ')' );

                        $offset += 4; // 4bytes length field;

                        // this should not happen, but check.
                        if ( $lenData['len'] + $offset > $appLen ) {
                                throw new MWException( "PSIR data too long. (item length=" . $lenData['len']
                                        . "; offset=$offset; total length=$appLen)" );
                        }

                        if ( $valid ) {
                                switch ( $id ) {
                                        case "\x04\x04":
                                                // IPTC block
                                                $realHash = md5( substr( $app13, $offset, $lenData['len'] ), true );
                                                break;
                                        case "\x04\x25":
                                                $recordedHash = substr( $app13, $offset, $lenData['len'] );
                                                break;
                                }
                        }

                        // if odd, add 1 to length to account for
                        // null pad byte.
                        if ( $lenData['len'] % 2 == 1 ) $lenData['len']++;
                        $offset += $lenData['len'];

                }

                if ( !$realHash || !$recordedHash ) {
                        return 'iptc-no-hash';
                } elseif ( $realHash === $recordedHash ) {
                        return 'iptc-good-hash';
                } else { /*$realHash !== $recordedHash */
                        return 'iptc-bad-hash';
                }
        }
}