IEContentAnalyzer.php

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<?php
class IEContentAnalyzer {
    protected $baseTypeTable = [
        'ambiguous' /*1*/ => [
            'text/plain',
            'application/octet-stream',
            'application/x-netcdf', // [sic]
        ],
        'text' /*3*/ => [
            'text/richtext', 'image/x-bitmap', 'application/postscript', 'application/base64',
            'application/macbinhex40', 'application/x-cdf', 'text/scriptlet'
        ],
        'binary' /*4*/ => [
            'application/pdf', 'audio/x-aiff', 'audio/basic', 'audio/wav', 'image/gif',
            'image/pjpeg', 'image/jpeg', 'image/tiff', 'image/x-png', 'image/png', 'image/bmp',
            'image/x-jg', 'image/x-art', 'image/x-emf', 'image/x-wmf', 'video/avi',
            'video/x-msvideo', 'video/mpeg', 'application/x-compressed',
            'application/x-zip-compressed', 'application/x-gzip-compressed', 'application/java',
            'application/x-msdownload'
        ],
        'html' /*5*/ => [ 'text/html' ],
    ];

    protected $addedTypes = [
        'ie07' => [
            'text' => [ 'text/xml', 'application/xml' ]
        ],
    ];

    protected $registry = [
        '.323' => 'text/h323',
        '.3g2' => 'video/3gpp2',
        '.3gp' => 'video/3gpp',
        '.3gp2' => 'video/3gpp2',
        '.3gpp' => 'video/3gpp',
        '.aac' => 'audio/aac',
        '.ac3' => 'audio/ac3',
        '.accda' => 'application/msaccess',
        '.accdb' => 'application/msaccess',
        '.accdc' => 'application/msaccess',
        '.accde' => 'application/msaccess',
        '.accdr' => 'application/msaccess',
        '.accdt' => 'application/msaccess',
        '.ade' => 'application/msaccess',
        '.adp' => 'application/msaccess',
        '.adts' => 'audio/aac',
        '.ai' => 'application/postscript',
        '.aif' => 'audio/aiff',
        '.aifc' => 'audio/aiff',
        '.aiff' => 'audio/aiff',
        '.amc' => 'application/x-mpeg',
        '.application' => 'application/x-ms-application',
        '.asf' => 'video/x-ms-asf',
        '.asx' => 'video/x-ms-asf',
        '.au' => 'audio/basic',
        '.avi' => 'video/avi',
        '.bmp' => 'image/bmp',
        '.caf' => 'audio/x-caf',
        '.cat' => 'application/vnd.ms-pki.seccat',
        '.cbo' => 'application/sha',
        '.cdda' => 'audio/aiff',
        '.cer' => 'application/x-x509-ca-cert',
        '.conf' => 'text/plain',
        '.crl' => 'application/pkix-crl',
        '.crt' => 'application/x-x509-ca-cert',
        '.css' => 'text/css',
        '.csv' => 'application/vnd.ms-excel',
        '.der' => 'application/x-x509-ca-cert',
        '.dib' => 'image/bmp',
        '.dif' => 'video/x-dv',
        '.dll' => 'application/x-msdownload',
        '.doc' => 'application/msword',
        '.docm' => 'application/vnd.ms-word.document.macroEnabled.12',
        '.docx' => 'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
        '.dot' => 'application/msword',
        '.dotm' => 'application/vnd.ms-word.template.macroEnabled.12',
        '.dotx' => 'application/vnd.openxmlformats-officedocument.wordprocessingml.template',
        '.dv' => 'video/x-dv',
        '.dwfx' => 'model/vnd.dwfx+xps',
        '.edn' => 'application/vnd.adobe.edn',
        '.eml' => 'message/rfc822',
        '.eps' => 'application/postscript',
        '.etd' => 'application/x-ebx',
        '.exe' => 'application/x-msdownload',
        '.fdf' => 'application/vnd.fdf',
        '.fif' => 'application/fractals',
        '.gif' => 'image/gif',
        '.gsm' => 'audio/x-gsm',
        '.hqx' => 'application/mac-binhex40',
        '.hta' => 'application/hta',
        '.htc' => 'text/x-component',
        '.htm' => 'text/html',
        '.html' => 'text/html',
        '.htt' => 'text/webviewhtml',
        '.hxa' => 'application/xml',
        '.hxc' => 'application/xml',
        '.hxd' => 'application/octet-stream',
        '.hxe' => 'application/xml',
        '.hxf' => 'application/xml',
        '.hxh' => 'application/octet-stream',
        '.hxi' => 'application/octet-stream',
        '.hxk' => 'application/xml',
        '.hxq' => 'application/octet-stream',
        '.hxr' => 'application/octet-stream',
        '.hxs' => 'application/octet-stream',
        '.hxt' => 'application/xml',
        '.hxv' => 'application/xml',
        '.hxw' => 'application/octet-stream',
        '.ico' => 'image/x-icon',
        '.iii' => 'application/x-iphone',
        '.ins' => 'application/x-internet-signup',
        '.iqy' => 'text/x-ms-iqy',
        '.isp' => 'application/x-internet-signup',
        '.jfif' => 'image/jpeg',
        '.jnlp' => 'application/x-java-jnlp-file',
        '.jpe' => 'image/jpeg',
        '.jpeg' => 'image/jpeg',
        '.jpg' => 'image/jpeg',
        '.jtx' => 'application/x-jtx+xps',
        '.latex' => 'application/x-latex',
        '.log' => 'text/plain',
        '.m1v' => 'video/mpeg',
        '.m2v' => 'video/mpeg',
        '.m3u' => 'audio/x-mpegurl',
        '.mac' => 'image/x-macpaint',
        '.man' => 'application/x-troff-man',
        '.mda' => 'application/msaccess',
        '.mdb' => 'application/msaccess',
        '.mde' => 'application/msaccess',
        '.mfp' => 'application/x-shockwave-flash',
        '.mht' => 'message/rfc822',
        '.mhtml' => 'message/rfc822',
        '.mid' => 'audio/mid',
        '.midi' => 'audio/mid',
        '.mod' => 'video/mpeg',
        '.mov' => 'video/quicktime',
        '.mp2' => 'video/mpeg',
        '.mp2v' => 'video/mpeg',
        '.mp3' => 'audio/mpeg',
        '.mp4' => 'video/mp4',
        '.mpa' => 'video/mpeg',
        '.mpe' => 'video/mpeg',
        '.mpeg' => 'video/mpeg',
        '.mpf' => 'application/vnd.ms-mediapackage',
        '.mpg' => 'video/mpeg',
        '.mpv2' => 'video/mpeg',
        '.mqv' => 'video/quicktime',
        '.NMW' => 'application/nmwb',
        '.nws' => 'message/rfc822',
        '.odc' => 'text/x-ms-odc',
        '.ols' => 'application/vnd.ms-publisher',
        '.p10' => 'application/pkcs10',
        '.p12' => 'application/x-pkcs12',
        '.p7b' => 'application/x-pkcs7-certificates',
        '.p7c' => 'application/pkcs7-mime',
        '.p7m' => 'application/pkcs7-mime',
        '.p7r' => 'application/x-pkcs7-certreqresp',
        '.p7s' => 'application/pkcs7-signature',
        '.pct' => 'image/pict',
        '.pdf' => 'application/pdf',
        '.pdx' => 'application/vnd.adobe.pdx',
        '.pfx' => 'application/x-pkcs12',
        '.pic' => 'image/pict',
        '.pict' => 'image/pict',
        '.pinstall' => 'application/x-picasa-detect',
        '.pko' => 'application/vnd.ms-pki.pko',
        '.png' => 'image/png',
        '.pnt' => 'image/x-macpaint',
        '.pntg' => 'image/x-macpaint',
        '.pot' => 'application/vnd.ms-powerpoint',
        '.potm' => 'application/vnd.ms-powerpoint.template.macroEnabled.12',
        '.potx' => 'application/vnd.openxmlformats-officedocument.presentationml.template',
        '.ppa' => 'application/vnd.ms-powerpoint',
        '.ppam' => 'application/vnd.ms-powerpoint.addin.macroEnabled.12',
        '.pps' => 'application/vnd.ms-powerpoint',
        '.ppsm' => 'application/vnd.ms-powerpoint.slideshow.macroEnabled.12',
        '.ppsx' => 'application/vnd.openxmlformats-officedocument.presentationml.slideshow',
        '.ppt' => 'application/vnd.ms-powerpoint',
        '.pptm' => 'application/vnd.ms-powerpoint.presentation.macroEnabled.12',
        '.pptx' => 'application/vnd.openxmlformats-officedocument.presentationml.presentation',
        '.prf' => 'application/pics-rules',
        '.ps' => 'application/postscript',
        '.pub' => 'application/vnd.ms-publisher',
        '.pwz' => 'application/vnd.ms-powerpoint',
        '.py' => 'text/plain',
        '.pyw' => 'text/plain',
        '.qht' => 'text/x-html-insertion',
        '.qhtm' => 'text/x-html-insertion',
        '.qt' => 'video/quicktime',
        '.qti' => 'image/x-quicktime',
        '.qtif' => 'image/x-quicktime',
        '.qtl' => 'application/x-quicktimeplayer',
        '.rat' => 'application/rat-file',
        '.rmf' => 'application/vnd.adobe.rmf',
        '.rmi' => 'audio/mid',
        '.rqy' => 'text/x-ms-rqy',
        '.rtf' => 'application/msword',
        '.sct' => 'text/scriptlet',
        '.sd2' => 'audio/x-sd2',
        '.sdp' => 'application/sdp',
        '.shtml' => 'text/html',
        '.sit' => 'application/x-stuffit',
        '.sldm' => 'application/vnd.ms-powerpoint.slide.macroEnabled.12',
        '.sldx' => 'application/vnd.openxmlformats-officedocument.presentationml.slide',
        '.slk' => 'application/vnd.ms-excel',
        '.snd' => 'audio/basic',
        '.so' => 'application/x-apachemodule',
        '.sol' => 'text/plain',
        '.sor' => 'text/plain',
        '.spc' => 'application/x-pkcs7-certificates',
        '.spl' => 'application/futuresplash',
        '.sst' => 'application/vnd.ms-pki.certstore',
        '.stl' => 'application/vnd.ms-pki.stl',
        '.swf' => 'application/x-shockwave-flash',
        '.thmx' => 'application/vnd.ms-officetheme',
        '.tif' => 'image/tiff',
        '.tiff' => 'image/tiff',
        '.txt' => 'text/plain',
        '.uls' => 'text/iuls',
        '.vcf' => 'text/x-vcard',
        '.vdx' => 'application/vnd.ms-visio.viewer',
        '.vsd' => 'application/vnd.ms-visio.viewer',
        '.vss' => 'application/vnd.ms-visio.viewer',
        '.vst' => 'application/vnd.ms-visio.viewer',
        '.vsx' => 'application/vnd.ms-visio.viewer',
        '.vtx' => 'application/vnd.ms-visio.viewer',
        '.wav' => 'audio/wav',
        '.wax' => 'audio/x-ms-wax',
        '.wbk' => 'application/msword',
        '.wdp' => 'image/vnd.ms-photo',
        '.wiz' => 'application/msword',
        '.wm' => 'video/x-ms-wm',
        '.wma' => 'audio/x-ms-wma',
        '.wmd' => 'application/x-ms-wmd',
        '.wmv' => 'video/x-ms-wmv',
        '.wmx' => 'video/x-ms-wmx',
        '.wmz' => 'application/x-ms-wmz',
        '.wpl' => 'application/vnd.ms-wpl',
        '.wsc' => 'text/scriptlet',
        '.wvx' => 'video/x-ms-wvx',
        '.xaml' => 'application/xaml+xml',
        '.xbap' => 'application/x-ms-xbap',
        '.xdp' => 'application/vnd.adobe.xdp+xml',
        '.xfdf' => 'application/vnd.adobe.xfdf',
        '.xht' => 'application/xhtml+xml',
        '.xhtml' => 'application/xhtml+xml',
        '.xla' => 'application/vnd.ms-excel',
        '.xlam' => 'application/vnd.ms-excel.addin.macroEnabled.12',
        '.xlk' => 'application/vnd.ms-excel',
        '.xll' => 'application/vnd.ms-excel',
        '.xlm' => 'application/vnd.ms-excel',
        '.xls' => 'application/vnd.ms-excel',
        '.xlsb' => 'application/vnd.ms-excel.sheet.binary.macroEnabled.12',
        '.xlsm' => 'application/vnd.ms-excel.sheet.macroEnabled.12',
        '.xlsx' => 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
        '.xlt' => 'application/vnd.ms-excel',
        '.xltm' => 'application/vnd.ms-excel.template.macroEnabled.12',
        '.xltx' => 'application/vnd.openxmlformats-officedocument.spreadsheetml.template',
        '.xlw' => 'application/vnd.ms-excel',
        '.xml' => 'text/xml',
        '.xps' => 'application/vnd.ms-xpsdocument',
        '.xsl' => 'text/xml',
    ];

    protected $versions = [ 'ie05', 'ie06', 'ie07', 'ie07.strict', 'ie07.nohtml' ];

    protected $typeTable = [];

    function __construct() {
        // Construct versioned type arrays from the base type array plus additions
        $types = $this->baseTypeTable;
        foreach ( $this->versions as $version ) {
            if ( isset( $this->addedTypes[$version] ) ) {
                foreach ( $this->addedTypes[$version] as $format => $addedTypes ) {
                    $types[$format] = array_merge( $types[$format], $addedTypes );
                }
            }
            $this->typeTable[$version] = $types;
        }
    }

    public function getRealMimesFromData( $fileName, $chunk, $proposed ) {
        $types = $this->getMimesFromData( $fileName, $chunk, $proposed );
        $types = array_map( [ $this, 'translateMimeType' ], $types );
        return $types;
    }

    public function translateMimeType( $type ) {
        static $table = [
            'image/pjpeg' => 'image/jpeg',
            'image/x-png' => 'image/png',
            'image/x-wmf' => 'application/x-msmetafile',
            'image/bmp' => 'image/x-bmp',
            'application/x-zip-compressed' => 'application/zip',
            'application/x-compressed' => 'application/x-compress',
            'application/x-gzip-compressed' => 'application/x-gzip',
            'audio/mid' => 'audio/midi',
        ];
        if ( isset( $table[$type] ) ) {
            $type = $table[$type];
        }
        return $type;
    }

    public function getMimesFromData( $fileName, $chunk, $proposed ) {
        $types = [];
        foreach ( $this->versions as $version ) {
            $types[$version] = $this->getMimeTypeForVersion( $version, $fileName, $chunk, $proposed );
        }
        return $types;
    }

    protected function getMimeTypeForVersion( $version, $fileName, $chunk, $proposed ) {
        // Strip text after a semicolon
        $semiPos = strpos( $proposed, ';' );
        if ( $semiPos !== false ) {
            $proposed = substr( $proposed, 0, $semiPos );
        }

        $proposedFormat = $this->getDataFormat( $version, $proposed );
        if ( $proposedFormat == 'unknown'
            && $proposed != 'multipart/mixed'
            && $proposed != 'multipart/x-mixed-replace' )
        {
            return $proposed;
        }
        if ( strval( $chunk ) === '' ) {
            return $proposed;
        }

        // Truncate chunk at 255 bytes
        $chunk = substr( $chunk, 0, 255 );

        // IE does the Check*Headers() calls last, and instead does the following image
        // type checks by directly looking for the magic numbers. What I do here should
        // have the same effect since the magic number checks are identical in both cases.
        $result = $this->sampleData( $version, $chunk );
        $sampleFound = $result['found'];
        $counters = $result['counters'];
        $binaryType = $this->checkBinaryHeaders( $version, $chunk );
        $textType = $this->checkTextHeaders( $version, $chunk );

        if ( $proposed == 'text/html' && isset( $sampleFound['html'] ) ) {
            return 'text/html';
        }
        if ( $proposed == 'image/gif' && $binaryType == 'image/gif' ) {
            return 'image/gif';
        }
        if ( ( $proposed == 'image/pjpeg' || $proposed == 'image/jpeg' )
            && $binaryType == 'image/pjpeg' )
        {
            return $proposed;
        }
        // PNG check added in IE 7
        if ( $version >= 'ie07'
            && ( $proposed == 'image/x-png' || $proposed == 'image/png' )
            && $binaryType == 'image/x-png' )
        {
            return $proposed;
        }

        // CDF was removed in IE 7 so it won't be in $sampleFound for later versions
        if ( isset( $sampleFound['cdf'] ) ) {
            return 'application/x-cdf';
        }

        // RSS and Atom were added in IE 7 so they won't be in $sampleFound for
        // previous versions
        if ( isset( $sampleFound['rss'] ) ) {
            return 'application/rss+xml';
        }
        if ( isset( $sampleFound['rdf-tag'] )
            && isset( $sampleFound['rdf-url'] )
            && isset( $sampleFound['rdf-purl'] ) )
        {
            return 'application/rss+xml';
        }
        if ( isset( $sampleFound['atom'] ) ) {
            return 'application/atom+xml';
        }

        if ( isset( $sampleFound['xml'] ) ) {
            // TODO: I'm not sure under what circumstances this flag is enabled
            if ( strpos( $version, 'strict' ) !== false ) {
                if ( $proposed == 'text/html' || $proposed == 'text/xml' ) {
                    return 'text/xml';
                }
            } else {
                return 'text/xml';
            }
        }
        if ( isset( $sampleFound['html'] ) ) {
            // TODO: I'm not sure under what circumstances this flag is enabled
            if ( strpos( $version, 'nohtml' ) !== false ) {
                if ( $proposed == 'text/plain' ) {
                    return 'text/html';
                }
            } else {
                return 'text/html';
            }
        }
        if ( isset( $sampleFound['xbm'] ) ) {
            return 'image/x-bitmap';
        }
        if ( isset( $sampleFound['binhex'] ) ) {
            return 'application/macbinhex40';
        }
        if ( isset( $sampleFound['scriptlet'] ) ) {
            if ( strpos( $version, 'strict' ) !== false ) {
                if ( $proposed == 'text/plain' || $proposed == 'text/scriptlet' ) {
                    return 'text/scriptlet';
                }
            } else {
                return 'text/scriptlet';
            }
        }

        // Freaky heuristics to determine if the data is text or binary
        // The heuristic is of course broken for non-ASCII text
        if ( $counters['ctrl'] != 0 && ( $counters['ff'] + $counters['low'] )
            < ( $counters['ctrl'] + $counters['high'] ) * 16 )
        {
            $kindOfBinary = true;
            $type = $binaryType ? $binaryType : $textType;
            if ( $type === false ) {
                $type = 'application/octet-stream';
            }
        } else {
            $kindOfBinary = false;
            $type = $textType ? $textType : $binaryType;
            if ( $type === false ) {
                $type = 'text/plain';
            }
        }

        // Check if the output format is ambiguous
        // This generally means that detection failed, real types aren't ambiguous
        $detectedFormat = $this->getDataFormat( $version, $type );
        if ( $detectedFormat != 'ambiguous' ) {
            return $type;
        }

        if ( $proposedFormat != 'ambiguous' ) {
            // FormatAgreesWithData()
            if ( $proposedFormat == 'text' && !$kindOfBinary ) {
                return $proposed;
            }
            if ( $proposedFormat == 'binary' && $kindOfBinary ) {
                return $proposed;
            }
            if ( $proposedFormat == 'html' ) {
                return $proposed;
            }
        }

        // Find a MIME type by searching the registry for the file extension.
        $dotPos = strrpos( $fileName, '.' );
        if ( $dotPos === false ) {
            return $type;
        }
        $ext = substr( $fileName, $dotPos );
        if ( isset( $this->registry[$ext] ) ) {
            return $this->registry[$ext];
        }

        // TODO: If the extension has an application registered to it, IE will return
        // application/octet-stream. We'll skip that, so we could erroneously
        // return text/plain or application/x-netcdf where application/octet-stream
        // would be correct.

        return $type;
    }

    private function checkTextHeaders( $version, $chunk ) {
        $chunk2 = substr( $chunk, 0, 2 );
        $chunk4 = substr( $chunk, 0, 4 );
        $chunk5 = substr( $chunk, 0, 5 );
        if ( $chunk4 == '%PDF' ) {
            return 'application/pdf';
        }
        if ( $chunk2 == '%!' ) {
            return 'application/postscript';
        }
        if ( $chunk5 == '{\\rtf' ) {
            return 'text/richtext';
        }
        if ( $chunk5 == 'begin' ) {
            return 'application/base64';
        }
        return false;
    }

    private function checkBinaryHeaders( $version, $chunk ) {
        $chunk2 = substr( $chunk, 0, 2 );
        $chunk3 = substr( $chunk, 0, 3 );
        $chunk4 = substr( $chunk, 0, 4 );
        $chunk5 = substr( $chunk, 0, 5 );
        $chunk5uc = strtoupper( $chunk5 );
        $chunk8 = substr( $chunk, 0, 8 );
        if ( $chunk5uc == 'GIF87' || $chunk5uc == 'GIF89' ) {
            return 'image/gif';
        }
        if ( $chunk2 == "\xff\xd8" ) {
            return 'image/pjpeg'; // actually plain JPEG but this is what IE returns
        }

        if ( $chunk2 == 'BM'
            && substr( $chunk, 6, 2 ) == "\000\000"
            && substr( $chunk, 8, 2 ) == "\000\000" )
        {
            return 'image/bmp'; // another non-standard MIME
        }
        if ( $chunk4 == 'RIFF'
            && substr( $chunk, 8, 4 ) == 'WAVE' )
        {
            return 'audio/wav';
        }
        // These were integer literals in IE
        // Perhaps the author was not sure what the target endianness was
        if ( $chunk4 == ".sd\000"
            || $chunk4 == ".snd"
            || $chunk4 == "\000ds."
            || $chunk4 == "dns." )
        {
            return 'audio/basic';
        }
        if ( $chunk3 == "MM\000" ) {
            return 'image/tiff';
        }
        if ( $chunk2 == 'MZ' ) {
            return 'application/x-msdownload';
        }
        if ( $chunk8 == "\x89PNG\x0d\x0a\x1a\x0a" ) {
            return 'image/x-png'; // [sic]
        }
        if ( strlen( $chunk ) >= 5 ) {
            $byte2 = ord( $chunk[2] );
            $byte4 = ord( $chunk[4] );
            if ( $byte2 >= 3 && $byte2 <= 31 && $byte4 == 0 && $chunk2 == 'JG' ) {
                return 'image/x-jg';
            }
        }
        // More endian confusion?
        if ( $chunk4 == 'MROF' ) {
            return 'audio/x-aiff';
        }
        $chunk4_8 = substr( $chunk, 8, 4 );
        if ( $chunk4 == 'FORM' && ( $chunk4_8 == 'AIFF' || $chunk4_8 == 'AIFC' ) ) {
            return 'audio/x-aiff';
        }
        if ( $chunk4 == 'RIFF' && $chunk4_8 == 'AVI ' ) {
            return 'video/avi';
        }
        if ( $chunk4 == "\x00\x00\x01\xb3" || $chunk4 == "\x00\x00\x01\xba" ) {
            return 'video/mpeg';
        }
        if ( $chunk4 == "\001\000\000\000"
            && substr( $chunk, 40, 4 ) == ' EMF' )
        {
            return 'image/x-emf';
        }
        if ( $chunk4 == "\xd7\xcd\xc6\x9a" ) {
            return 'image/x-wmf';
        }
        if ( $chunk4 == "\xca\xfe\xba\xbe" ) {
            return 'application/java';
        }
        if ( $chunk2 == 'PK' ) {
            return 'application/x-zip-compressed';
        }
        if ( $chunk2 == "\x1f\x9d" ) {
            return 'application/x-compressed';
        }
        if ( $chunk2 == "\x1f\x8b" ) {
            return 'application/x-gzip-compressed';
        }
        // Skip redundant check for ZIP
        if ( $chunk5 == "MThd\000" ) {
            return 'audio/mid';
        }
        if ( $chunk4 == '%PDF' ) {
            return 'application/pdf';
        }
        return false;
    }

    protected function sampleData( $version, $chunk ) {
        $found = [];
        $counters = [
            'ctrl' => 0,
            'high' => 0,
            'low' => 0,
            'lf' => 0,
            'cr' => 0,
            'ff' => 0
        ];
        $htmlTags = [
            'html',
            'head',
            'title',
            'body',
            'script',
            'a href',
            'pre',
            'img',
            'plaintext',
            'table'
        ];
        $rdfUrl = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#';
        $rdfPurl = 'http://purl.org/rss/1.0/';
        $xbmMagic1 = '#define';
        $xbmMagic2 = '_width';
        $xbmMagic3 = '_bits';
        $binhexMagic = 'converted with BinHex';
        $chunkLength = strlen( $chunk );

        for ( $offset = 0; $offset < $chunkLength; $offset++ ) {
            $curChar = $chunk[$offset];
            if ( $curChar == "\x0a" ) {
                $counters['lf']++;
                continue;
            } elseif ( $curChar == "\x0d" ) {
                $counters['cr']++;
                continue;
            } elseif ( $curChar == "\x0c" ) {
                $counters['ff']++;
                continue;
            } elseif ( $curChar == "\t" ) {
                $counters['low']++;
                continue;
            } elseif ( ord( $curChar ) < 32 ) {
                $counters['ctrl']++;
                continue;
            } elseif ( ord( $curChar ) >= 128 ) {
                $counters['high']++;
                continue;
            }

            $counters['low']++;
            if ( $curChar == '<' ) {
                // XML
                $remainder = substr( $chunk, $offset + 1 );
                if ( !strncasecmp( $remainder, '?XML', 4 ) ) {
                    $nextChar = substr( $chunk, $offset + 5, 1 );
                    if ( $nextChar == ':' || $nextChar == ' ' || $nextChar == "\t" ) {
                        $found['xml'] = true;
                    }
                }
                // Scriptlet (JSP)
                if ( !strncasecmp( $remainder, 'SCRIPTLET', 9 ) ) {
                    $found['scriptlet'] = true;
                    break;
                }
                // HTML
                foreach ( $htmlTags as $tag ) {
                    if ( !strncasecmp( $remainder, $tag, strlen( $tag ) ) ) {
                        $found['html'] = true;
                    }
                }
                // Skip broken check for additional tags (HR etc.)

                // CHANNEL replaced by RSS, RDF and FEED in IE 7
                if ( $version < 'ie07' ) {
                    if ( !strncasecmp( $remainder, 'CHANNEL', 7 ) ) {
                        $found['cdf'] = true;
                    }
                } else {
                    // RSS
                    if ( !strncasecmp( $remainder, 'RSS', 3 ) ) {
                        $found['rss'] = true;
                        break; // return from SampleData
                    }
                    if ( !strncasecmp( $remainder, 'rdf:RDF', 7 ) ) {
                        $found['rdf-tag'] = true;
                        // no break
                    }
                    if ( !strncasecmp( $remainder, 'FEED', 4 ) ) {
                        $found['atom'] = true;
                        break;
                    }
                }
                continue;
            }
            // Skip broken check for -->

            // RSS URL checks
            // For some reason both URLs must appear before it is recognised
            $remainder = substr( $chunk, $offset );
            if ( !strncasecmp( $remainder, $rdfUrl, strlen( $rdfUrl ) ) ) {
                $found['rdf-url'] = true;
                if ( isset( $found['rdf-tag'] )
                    && isset( $found['rdf-purl'] ) ) // [sic]
                {
                    break;
                }
                continue;
            }

            if ( !strncasecmp( $remainder, $rdfPurl, strlen( $rdfPurl ) ) ) {
                if ( isset( $found['rdf-tag'] )
                    && isset( $found['rdf-url'] ) ) // [sic]
                {
                    break;
                }
                continue;
            }

            // XBM checks
            if ( !strncasecmp( $remainder, $xbmMagic1, strlen( $xbmMagic1 ) ) ) {
                $found['xbm1'] = true;
                continue;
            }
            if ( $curChar == '_' ) {
                if ( isset( $found['xbm2'] ) ) {
                    if ( !strncasecmp( $remainder, $xbmMagic3, strlen( $xbmMagic3 ) ) ) {
                        $found['xbm'] = true;
                        break;
                    }
                } elseif ( isset( $found['xbm1'] ) ) {
                    if ( !strncasecmp( $remainder, $xbmMagic2, strlen( $xbmMagic2 ) ) ) {
                        $found['xbm2'] = true;
                    }
                }
            }

            // BinHex
            if ( !strncmp( $remainder, $binhexMagic, strlen( $binhexMagic ) ) ) {
                $found['binhex'] = true;
            }
        }
        return [ 'found' => $found, 'counters' => $counters ];
    }

    protected function getDataFormat( $version, $type ) {
        $types = $this->typeTable[$version];
        if ( $type == '(null)' || strval( $type ) === '' ) {
            return 'ambiguous';
        }
        foreach ( $types as $format => $list ) {
            if ( in_array( $type, $list ) ) {
                return $format;
            }
        }
        return 'unknown';
    }
}