/mod/assign/feedback/editpdf/fpdi/pdf_parser.php

<?php

/**

 * This file is part of FPDI

 *

 * @package   FPDI

 * @copyright Copyright (c) 2015 Setasign - Jan Slabon (http://www.setasign.com)

 * @license   http://opensource.org/licenses/mit-license The MIT License

 * @version   1.6.1

 */



/**

 * Class pdf_parser

 */

class pdf_parser

{

    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_NULL = 0;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_NUMERIC = 1;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_TOKEN = 2;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_HEX = 3;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_STRING = 4;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_DICTIONARY = 5;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_ARRAY = 6;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_OBJDEC = 7;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_OBJREF = 8;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_OBJECT = 9;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_STREAM = 10;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_BOOLEAN = 11;



    /**

     * Type constant

     *

     * @var integer

     */

    const TYPE_REAL = 12;



    /**

     * Define the amount of byte in which the initial keyword of a PDF document should be searched.

     *

     * @var int

     */

    static public $searchForStartxrefLength = 5500;



    /**

     * Filename

     *

     * @var string

     */

    public $filename;



    /**

     * File resource

     *

     * @var resource

     */

    protected $_f;



    /**

     * PDF Context

     *

     * @var pdf_context

     */

    protected $_c;



    /**

     * xref-Data

     *

     * @var array

     */

    protected $_xref;



    /**

     * Data of the Root object

     *

     * @var array

     */

    protected $_root;



    /**

     * PDF version of the loaded document

     *

     * @var string

     */

    protected $_pdfVersion;



    /**

     * For reading encrypted documents and xref/object streams are in use

     *

     * @var boolean

     */

    protected $_readPlain = true;



    /**

     * The current read object

     *

     * @var array

     */

    protected $_currentObj;



    /**

     * Constructor

     *

     * @param string $filename Source filename

     * @throws InvalidArgumentException

     */

    public function __construct($filename)

    {

        $this->filename = $filename;



        $this->_f = @fopen($this->filename, 'rb');



        if (!$this->_f) {

            throw new InvalidArgumentException(sprintf('Cannot open %s !', $filename));

        }



        $this->getPdfVersion();



        if (!class_exists('pdf_context')) {

            require_once('pdf_context.php');

        }

        $this->_c = new pdf_context($this->_f);



        // Read xref-Data

        $this->_xref = array();

        $this->_readXref($this->_xref, $this->_findXref());



        // Check for Encryption

        $this->getEncryption();



        // Read root

        $this->_readRoot();

    }



    /**

     * Destructor

     */

    public function __destruct()

    {

        $this->closeFile();

    }



    /**

     * Close the opened file

     */

    public function closeFile()

    {

        if (isset($this->_f) && is_resource($this->_f)) {

            fclose($this->_f);

            unset($this->_f);

        }

    }



    /**

     * Check Trailer for Encryption

     *

     * @throws Exception

     */

    public function getEncryption()

    {

        if (isset($this->_xref['trailer'][1]['/Encrypt'])) {

            throw new Exception('File is encrypted!');

        }

    }



    /**

     * Get PDF-Version

     *

     * @return string

     */

    public function getPdfVersion()

    {

        if ($this->_pdfVersion === null) {

            fseek($this->_f, 0);

            preg_match('/\d\.\d/', fread($this->_f, 16), $m);

            if (isset($m[0]))

                $this->_pdfVersion = $m[0];

        }



        return $this->_pdfVersion;

    }



    /**

     * Read the /Root dictionary

     */

    protected function _readRoot()

    {

        if ($this->_xref['trailer'][1]['/Root'][0] != self::TYPE_OBJREF) {

            throw new Exception('Wrong Type of Root-Element! Must be an indirect reference');

        }



        $this->_root = $this->resolveObject($this->_xref['trailer'][1]['/Root']);

    }



    /**

     * Find the xref table

     *

     * @return integer

     * @throws Exception

     */

    protected function _findXref()

    {

        $toRead = self::$searchForStartxrefLength;



        $stat = fseek($this->_f, -$toRead, SEEK_END);

        if ($stat === -1) {

            fseek($this->_f, 0);

        }



        $data = fread($this->_f, $toRead);



        $keywordPos = strpos(strrev($data), strrev('startxref'));

        if (false === $keywordPos) {

            $keywordPos = strpos(strrev($data), strrev('startref'));

        }



        if (false === $keywordPos) {

            throw new Exception('Unable to find "startxref" keyword.');

        }



        $pos = strlen($data) - $keywordPos;

        $data = substr($data, $pos);



        if (!preg_match('/\s*(\d+).*$/s', $data, $matches)) {

            throw new Exception('Unable to find pointer to xref table.');

        }



        return (int) $matches[1];

    }



    /**

     * Read the xref table

     *

     * @param array $result Array of xref table entries

     * @param integer $offset of xref table

     * @return boolean

     * @throws Exception

     */

    protected function _readXref(&$result, $offset)

    {

        $tempPos = $offset - min(20, $offset);

        fseek($this->_f, $tempPos); // set some bytes backwards to fetch corrupted docs



        $data = fread($this->_f, 100);



        $xrefPos = strrpos($data, 'xref');



        if ($xrefPos === false) {

            $this->_c->reset($offset);

            $xrefStreamObjDec = $this->_readValue($this->_c);



            if (is_array($xrefStreamObjDec) && isset($xrefStreamObjDec[0]) && $xrefStreamObjDec[0] == self::TYPE_OBJDEC) {

                throw new Exception(

                    sprintf(

                        'This document (%s) probably uses a compression technique which is not supported by the ' .

                        'free parser shipped with FPDI. (See https://www.setasign.com/fpdi-pdf-parser for more details)',

                        $this->filename

                    )

                );

            } else {

                throw new Exception('Unable to find xref table.');

            }

        }



        if (!isset($result['xrefLocation'])) {

            $result['xrefLocation'] = $tempPos + $xrefPos;

            $result['maxObject'] = 0;

        }



        $cycles = -1;

        $bytesPerCycle = 100;



        fseek($this->_f, $tempPos = $tempPos + $xrefPos + 4); // set the handle directly after the "xref"-keyword

        $data = fread($this->_f, $bytesPerCycle);



        while (($trailerPos = strpos($data, 'trailer', max($bytesPerCycle * $cycles++, 0))) === false && !feof($this->_f)) {

            $data .= fread($this->_f, $bytesPerCycle);

        }



        if ($trailerPos === false) {

            throw new Exception('Trailer keyword not found after xref table');

        }



        $data = ltrim(substr($data, 0, $trailerPos));



        // get Line-Ending

        $found = preg_match_all("/(\r\n|\n|\r)/", substr($data, 0, 100), $m); // check the first 100 bytes for line breaks

        if ($found === 0) {

            throw new Exception('Xref table seems to be corrupted.');

        }

        $differentLineEndings = count(array_unique($m[0]));

        if ($differentLineEndings > 1) {

            $lines = preg_split("/(\r\n|\n|\r)/", $data, -1, PREG_SPLIT_NO_EMPTY);

        } else {

            $lines = explode($m[0][0], $data);

        }



        $data = $differentLineEndings = $m = null;

        unset($data, $differentLineEndings, $m);



        $linesCount = count($lines);



        $start = 1;



        for ($i = 0; $i < $linesCount; $i++) {

            $line = trim($lines[$i]);

            if ($line) {

                $pieces = explode(' ', $line);

                $c = count($pieces);

                switch($c) {

                    case 2:

                        $start = (int)$pieces[0];

                        $end   = $start + (int)$pieces[1];

                        if ($end > $result['maxObject'])

                            $result['maxObject'] = $end;

                        break;

                    case 3:

                        if (!isset($result['xref'][$start]))

                            $result['xref'][$start] = array();



                        if (!array_key_exists($gen = (int) $pieces[1], $result['xref'][$start])) {

                            $result['xref'][$start][$gen] = $pieces[2] == 'n' ? (int) $pieces[0] : null;

                        }

                        $start++;

                        break;

                    default:

                        throw new Exception('Unexpected data in xref table');

                }

            }

        }



        $lines = $pieces = $line = $start = $end = $gen = null;

        unset($lines, $pieces, $line, $start, $end, $gen);



        $this->_c->reset($tempPos + $trailerPos + 7);

        $trailer = $this->_readValue($this->_c);



        if (!isset($result['trailer'])) {

            $result['trailer'] = $trailer;

        }



        if (isset($trailer[1]['/Prev'])) {

            $this->_readXref($result, $trailer[1]['/Prev'][1]);

        }



        $trailer = null;

        unset($trailer);



        return true;

    }



    /**

     * Reads a PDF value

     *

     * @param pdf_context $c

     * @param string $token A token

     * @return mixed

     * @throws Exception

     */

    protected function _readValue(&$c, $token = null)

    {

        if (is_null($token)) {

            $token = $this->_readToken($c);

        }



        if ($token === false) {

            return false;

        }



        switch ($token) {

            case '<':

                // This is a hex string.

                // Read the value, then the terminator



                $pos = $c->offset;



                while(1) {



                    $match = strpos($c->buffer, '>', $pos);



                    // If you can't find it, try

                    // reading more data from the stream



                    if ($match === false) {

                        if (!$c->increaseLength()) {

                            return false;

                        } else {

                            continue;

                        }

                    }



                    $result = substr($c->buffer, $c->offset, $match - $c->offset);

                    $c->offset = $match + 1;



                    return array (self::TYPE_HEX, $result);

                }

                break;



            case '<<':

                // This is a dictionary.



                $result = array();



                // Recurse into this function until we reach

                // the end of the dictionary.

                while (($key = $this->_readToken($c)) !== '>>') {

                    if ($key === false) {

                        return false;

                    }



                    if (($value =   $this->_readValue($c)) === false) {

                        return false;

                    }



                    // Catch missing value

                    if ($value[0] == self::TYPE_TOKEN && $value[1] == '>>') {

                        $result[$key] = array(self::TYPE_NULL);

                        break;

                    }



                    $result[$key] = $value;

                }



                return array (self::TYPE_DICTIONARY, $result);



            case '[':

                // This is an array.



                $result = array();



                // Recurse into this function until we reach

                // the end of the array.

                while (($token = $this->_readToken($c)) !== ']') {

                    if ($token === false) {

                        return false;

                    }



                    if (($value = $this->_readValue($c, $token)) === false) {

                        return false;

                    }



                    $result[] = $value;

                }



                return array (self::TYPE_ARRAY, $result);



            case '(':

                // This is a string

                $pos = $c->offset;



                $openBrackets = 1;

                do {

                    for (; $openBrackets != 0 && $pos < $c->length; $pos++) {

                        switch (ord($c->buffer[$pos])) {

                            case 0x28: // '('

                                $openBrackets++;

                                break;

                            case 0x29: // ')'

                                $openBrackets--;

                                break;

                            case 0x5C: // backslash

                                $pos++;

                        }

                    }

                } while($openBrackets != 0 && $c->increaseLength());



                $result = substr($c->buffer, $c->offset, $pos - $c->offset - 1);

                $c->offset = $pos;



                return array (self::TYPE_STRING, $result);



            case 'stream':

                $tempPos = $c->getPos() - strlen($c->buffer);

                $tempOffset = $c->offset;



                $c->reset($startPos = $tempPos + $tempOffset);



                // Find the first "newline"

                while ($c->buffer[0] !== chr(10) && $c->buffer[0] !== chr(13)) {

                    $c->reset(++$startPos);

                    if ($c->ensureContent() === false) {

                        throw new Exception(

                            'Unable to parse stream data. No newline followed the stream keyword.'

                        );

                    }

                }



                $e = 0; // ensure line breaks in front of the stream

                if ($c->buffer[0] == chr(10) || $c->buffer[0] == chr(13))

                    $e++;

                if ($c->buffer[1] == chr(10) && $c->buffer[0] != chr(10))

                    $e++;



                if ($this->_currentObj[1][1]['/Length'][0] == self::TYPE_OBJREF) {

                    $tmpLength = $this->resolveObject($this->_currentObj[1][1]['/Length']);

                    $length = $tmpLength[1][1];

                } else {

                    $length = $this->_currentObj[1][1]['/Length'][1];

                }



                if ($length > 0) {

                    $c->reset($startPos + $e, $length);

                    $v = $c->buffer;

                } else {

                    $v = '';

                }



                $c->reset($startPos + $e + $length);

                $endstream = $this->_readToken($c);



                if ($endstream != 'endstream') {

                    $c->reset($startPos + $e + $length + 9); // 9 = strlen("endstream")

                    // We don't throw an error here because the next

                    // round trip will start at a new offset

                }



                return array(self::TYPE_STREAM, $v);



            default:

                if (is_numeric($token)) {

                    // A numeric token. Make sure that

                    // it is not part of something else.

                    if (($tok2 = $this->_readToken($c)) !== false) {

                        if (is_numeric($tok2)) {



                            // Two numeric tokens in a row.

                            // In this case, we're probably in

                            // front of either an object reference

                            // or an object specification.

                            // Determine the case and return the data

                            if (($tok3 = $this->_readToken($c)) !== false) {

                                switch ($tok3) {

                                    case 'obj':

                                        return array(self::TYPE_OBJDEC, (int)$token, (int)$tok2);

                                    case 'R':

                                        return array(self::TYPE_OBJREF, (int)$token, (int)$tok2);

                                }

                                // If we get to this point, that numeric value up

                                // there was just a numeric value. Push the extra

                                // tokens back into the stack and return the value.

                                array_push($c->stack, $tok3);

                            }

                        }



                        array_push($c->stack, $tok2);

                    }



                    if ($token === (string)((int)$token))

                        return array(self::TYPE_NUMERIC, (int)$token);

                    else

                        return array(self::TYPE_REAL, (float)$token);

                } else if ($token == 'true' || $token == 'false') {

                    return array(self::TYPE_BOOLEAN, $token == 'true');

                } else if ($token == 'null') {

                   return array(self::TYPE_NULL);

                } else {

                    // Just a token. Return it.

                    return array(self::TYPE_TOKEN, $token);

                }

         }

    }



    /**

     * Resolve an object

     *

     * @param array $objSpec The object-data

     * @return array|boolean

     * @throws Exception

     */

    public function resolveObject($objSpec)

    {

        $c = $this->_c;



        // Exit if we get invalid data

        if (!is_array($objSpec)) {

            return false;

        }



        if ($objSpec[0] == self::TYPE_OBJREF) {



            // This is a reference, resolve it

            if (isset($this->_xref['xref'][$objSpec[1]][$objSpec[2]])) {



                // Save current file position

                // This is needed if you want to resolve

                // references while you're reading another object

                // (e.g.: if you need to determine the length

                // of a stream)



                $oldPos = $c->getPos();



                // Reposition the file pointer and

                // load the object header.



                $c->reset($this->_xref['xref'][$objSpec[1]][$objSpec[2]]);



                $header = $this->_readValue($c);



                if ($header[0] != self::TYPE_OBJDEC || $header[1] != $objSpec[1] || $header[2] != $objSpec[2]) {

                    $toSearchFor = $objSpec[1] . ' ' . $objSpec[2] . ' obj';

                    if (preg_match('/' . $toSearchFor . '/', $c->buffer)) {

                        $c->offset = strpos($c->buffer, $toSearchFor) + strlen($toSearchFor);

                        // reset stack

                        $c->stack = array();

                    } else {

                        throw new Exception(

                            sprintf("Unable to find object (%s, %s) at expected location.", $objSpec[1], $objSpec[2])

                        );

                    }

                }



                // If we're being asked to store all the information

                // about the object, we add the object ID and generation

                // number for later use

                $result = array (

                    self::TYPE_OBJECT,

                    'obj' => $objSpec[1],

                    'gen' => $objSpec[2]

                );



                $this->_currentObj =& $result;



                // Now simply read the object data until

                // we encounter an end-of-object marker

                while (true) {

                    $value = $this->_readValue($c);

                    if ($value === false || count($result) > 4) {

                        // in this case the parser couldn't find an "endobj" so we break here

                        break;

                    }



                    if ($value[0] == self::TYPE_TOKEN && $value[1] === 'endobj') {

                        break;

                    }



                    $result[] = $value;

                }



                $c->reset($oldPos);



                if (isset($result[2][0]) && $result[2][0] == self::TYPE_STREAM) {

                    $result[0] = self::TYPE_STREAM;

                }



            } else {

                throw new Exception(

                    sprintf("Unable to find object (%s, %s) at expected location.", $objSpec[1], $objSpec[2])

                );

            }



            return $result;

        } else {

            return $objSpec;

        }

    }



    /**

     * Reads a token from the context

     *

     * @param pdf_context $c

     * @return mixed

     */

    protected function _readToken($c)

    {

        // If there is a token available

        // on the stack, pop it out and

        // return it.



        if (count($c->stack)) {

            return array_pop($c->stack);

        }



        // Strip away any whitespace



        do {

            if (!$c->ensureContent()) {

                return false;

            }

            $c->offset += strspn($c->buffer, "\x20\x0A\x0C\x0D\x09\x00", $c->offset);

        } while ($c->offset >= $c->length - 1);



        // Get the first character in the stream



        $char = $c->buffer[$c->offset++];



        switch ($char) {



            case '[':

            case ']':

            case '(':

            case ')':



                // This is either an array or literal string

                // delimiter, Return it



                return $char;



            case '<':

            case '>':



                // This could either be a hex string or

                // dictionary delimiter. Determine the

                // appropriate case and return the token



                if ($c->buffer[$c->offset] == $char) {

                    if (!$c->ensureContent()) {

                        return false;

                    }

                    $c->offset++;

                    return $char . $char;

                } else {

                    return $char;

                }



            case '%':



                // This is a comment - jump over it!



                $pos = $c->offset;

                while(1) {

                    $match = preg_match("/(\r\n|\r|\n)/", $c->buffer, $m, PREG_OFFSET_CAPTURE, $pos);

                    if ($match === 0) {

                        if (!$c->increaseLength()) {

                            return false;

                        } else {

                            continue;

                        }

                    }



                    $c->offset = $m[0][1] + strlen($m[0][0]);



                    return $this->_readToken($c);

                }



            default:



                // This is "another" type of token (probably

                // a dictionary entry or a numeric value)

                // Find the end and return it.



                if (!$c->ensureContent()) {

                    return false;

                }



                while(1) {



                    // Determine the length of the token



                    $pos = strcspn($c->buffer, "\x20%[]<>()/\x0A\x0C\x0D\x09\x00", $c->offset);



                    if ($c->offset + $pos <= $c->length - 1) {

                        break;

                    } else {

                        // If the script reaches this point,

                        // the token may span beyond the end

                        // of the current buffer. Therefore,

                        // we increase the size of the buffer

                        // and try again--just to be safe.



                        $c->increaseLength();

                    }

                }



                $result = substr($c->buffer, $c->offset - 1, $pos + 1);



                $c->offset += $pos;



                return $result;

        }

    }



    /**

     * Un-filter a stream object

     *

     * @param array $obj

     * @return string

     * @throws Exception

     */

    protected function _unFilterStream($obj)

    {

        $filters = array();



        if (isset($obj[1][1]['/Filter'])) {

            $filter = $obj[1][1]['/Filter'];



            if ($filter[0] == pdf_parser::TYPE_OBJREF) {

                $tmpFilter = $this->resolveObject($filter);

                $filter = $tmpFilter[1];

            }



            if ($filter[0] == pdf_parser::TYPE_TOKEN) {

                $filters[] = $filter;

            } else if ($filter[0] == pdf_parser::TYPE_ARRAY) {

                $filters = $filter[1];

            }

        }



        $stream = $obj[2][1];



        foreach ($filters AS $filter) {

            switch ($filter[1]) {

                case '/FlateDecode':

                case '/Fl':

                    if (function_exists('gzuncompress')) {

                        $oStream = $stream;

                        $stream = (strlen($stream) > 0) ? @gzuncompress($stream) : '';

                    } else {

                        throw new Exception(

                            sprintf('To handle %s filter, please compile php with zlib support.', $filter[1])

                        );

                    }



                    if ($stream === false) {

                        $tries = 0;

                        while ($tries < 8 && ($stream === false || strlen($stream) < strlen($oStream))) {

                            $oStream = substr($oStream, 1);

                            $stream = @gzinflate($oStream);

                            $tries++;

                        }



                        if ($stream === false) {

                            throw new Exception('Error while decompressing stream.');

                        }

                    }

                    break;

                case '/LZWDecode':

                    if (!class_exists('FilterLZW')) {

                        require_once('filters/FilterLZW.php');

                    }

                    $decoder = new FilterLZW();

                    $stream = $decoder->decode($stream);

                    break;

                case '/ASCII85Decode':

                    if (!class_exists('FilterASCII85')) {

                        require_once('filters/FilterASCII85.php');

                    }

                    $decoder = new FilterASCII85();

                    $stream = $decoder->decode($stream);

                    break;

                case '/ASCIIHexDecode':

                    if (!class_exists('FilterASCIIHexDecode')) {

                        require_once('filters/FilterASCIIHexDecode.php');

                    }

                    $decoder = new FilterASCIIHexDecode();

                    $stream = $decoder->decode($stream);

                    break;

                case null:

                    break;

                default:

                    throw new Exception(sprintf('Unsupported Filter: %s', $filter[1]));

            }

        }



        return $stream;

    }

}