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<?php
/**
* This file is part of FPDI
*
* @package setasign\Fpdi
* @copyright Copyright (c) 2024 Setasign GmbH & Co. KG (https://www.setasign.com)
* @license http://opensource.org/licenses/mit-license The MIT License
*/
namespace setasign\Fpdi\PdfParser\CrossReference;
use setasign\Fpdi\PdfParser\PdfParser;
use setasign\Fpdi\PdfParser\Type\PdfDictionary;
use setasign\Fpdi\PdfParser\Type\PdfIndirectObject;
use setasign\Fpdi\PdfParser\Type\PdfNumeric;
use setasign\Fpdi\PdfParser\Type\PdfStream;
use setasign\Fpdi\PdfParser\Type\PdfToken;
use setasign\Fpdi\PdfParser\Type\PdfTypeException;
/**
* Class CrossReference
*
* This class processes the standard cross reference of a PDF document.
*/
class CrossReference
{
/**
* The byte length in which the "startxref" keyword should be searched.
*
* @var int
*/
public static $trailerSearchLength = 5500;
/**
* @var int
*/
protected $fileHeaderOffset = 0;
/**
* @var PdfParser
*/
protected $parser;
/**
* @var ReaderInterface[]
*/
protected $readers = [];
/**
* CrossReference constructor.
*
* @param PdfParser $parser
* @throws CrossReferenceException
* @throws PdfTypeException
*/
public function __construct(PdfParser $parser, $fileHeaderOffset = 0)
{
$this->parser = $parser;
$this->fileHeaderOffset = $fileHeaderOffset;
$offset = $this->findStartXref();
$reader = null;
/** @noinspection TypeUnsafeComparisonInspection */
while ($offset != false) { // By doing an unsafe comparsion we ignore faulty references to byte offset 0
try {
$reader = $this->readXref($offset + $this->fileHeaderOffset);
} catch (CrossReferenceException $e) {
// sometimes the file header offset is part of the byte offsets, so let's retry by resetting it to zero.
if ($e->getCode() === CrossReferenceException::INVALID_DATA && $this->fileHeaderOffset !== 0) {
$this->fileHeaderOffset = 0;
$reader = $this->readXref($offset);
} else {
throw $e;
}
}
$trailer = $reader->getTrailer();
$this->checkForEncryption($trailer);
$this->readers[] = $reader;
if (isset($trailer->value['Prev'])) {
$offset = $trailer->value['Prev']->value;
} else {
$offset = false;
}
}
// fix faulty sub-section header
if ($reader instanceof FixedReader) {
/**
* @var FixedReader $reader
*/
$reader->fixFaultySubSectionShift();
}
if ($reader === null) {
throw new CrossReferenceException('No cross-reference found.', CrossReferenceException::NO_XREF_FOUND);
}
}
/**
* Get the size of the cross reference.
*
* @return integer
*/
public function getSize()
{
return $this->getTrailer()->value['Size']->value;
}
/**
* Get the trailer dictionary.
*
* @return PdfDictionary
*/
public function getTrailer()
{
return $this->readers[0]->getTrailer();
}
/**
* Get the cross reference readser instances.
*
* @return ReaderInterface[]
*/
public function getReaders()
{
return $this->readers;
}
/**
* Get the offset by an object number.
*
* @param int $objectNumber
* @return integer|bool
*/
public function getOffsetFor($objectNumber)
{
foreach ($this->getReaders() as $reader) {
$offset = $reader->getOffsetFor($objectNumber);
if ($offset !== false) {
return $offset;
}
}
return false;
}
/**
* Get an indirect object by its object number.
*
* @param int $objectNumber
* @return PdfIndirectObject
* @throws CrossReferenceException
*/
public function getIndirectObject($objectNumber)
{
$offset = $this->getOffsetFor($objectNumber);
if ($offset === false) {
throw new CrossReferenceException(
\sprintf('Object (id:%s) not found.', $objectNumber),
CrossReferenceException::OBJECT_NOT_FOUND
);
}
$parser = $this->parser;
$parser->getTokenizer()->clearStack();
$parser->getStreamReader()->reset($offset + $this->fileHeaderOffset);
try {
/** @var PdfIndirectObject $object */
$object = $parser->readValue(null, PdfIndirectObject::class);
} catch (PdfTypeException $e) {
throw new CrossReferenceException(
\sprintf('Object (id:%s) not found at location (%s).', $objectNumber, $offset),
CrossReferenceException::OBJECT_NOT_FOUND,
$e
);
}
if ($object->objectNumber !== $objectNumber) {
throw new CrossReferenceException(
\sprintf('Wrong object found, got %s while %s was expected.', $object->objectNumber, $objectNumber),
CrossReferenceException::OBJECT_NOT_FOUND
);
}
return $object;
}
/**
* Read the cross-reference table at a given offset.
*
* Internally the method will try to evaluate the best reader for this cross-reference.
*
* @param int $offset
* @return ReaderInterface
* @throws CrossReferenceException
* @throws PdfTypeException
*/
protected function readXref($offset)
{
$this->parser->getStreamReader()->reset($offset);
$this->parser->getTokenizer()->clearStack();
$initValue = $this->parser->readValue();
return $this->initReaderInstance($initValue);
}
/**
* Get a cross-reference reader instance.
*
* @param PdfToken|PdfIndirectObject $initValue
* @return ReaderInterface|bool
* @throws CrossReferenceException
* @throws PdfTypeException
*/
protected function initReaderInstance($initValue)
{
$position = $this->parser->getStreamReader()->getPosition()
+ $this->parser->getStreamReader()->getOffset() + $this->fileHeaderOffset;
if ($initValue instanceof PdfToken && $initValue->value === 'xref') {
try {
return new FixedReader($this->parser);
} catch (CrossReferenceException $e) {
$this->parser->getStreamReader()->reset($position);
$this->parser->getTokenizer()->clearStack();
return new LineReader($this->parser);
}
}
if ($initValue instanceof PdfIndirectObject) {
try {
$stream = PdfStream::ensure($initValue->value);
} catch (PdfTypeException $e) {
throw new CrossReferenceException(
'Invalid object type at xref reference offset.',
CrossReferenceException::INVALID_DATA,
$e
);
}
$type = PdfDictionary::get($stream->value, 'Type');
if ($type->value !== 'XRef') {
throw new CrossReferenceException(
'The xref position points to an incorrect object type.',
CrossReferenceException::INVALID_DATA
);
}
$this->checkForEncryption($stream->value);
throw new CrossReferenceException(
'This PDF document 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)',
CrossReferenceException::COMPRESSED_XREF
);
}
throw new CrossReferenceException(
'The xref position points to an incorrect object type.',
CrossReferenceException::INVALID_DATA
);
}
/**
* Check for encryption.
*
* @param PdfDictionary $dictionary
* @throws CrossReferenceException
*/
protected function checkForEncryption(PdfDictionary $dictionary)
{
if (isset($dictionary->value['Encrypt'])) {
throw new CrossReferenceException(
'This PDF document is encrypted and cannot be processed with FPDI.',
CrossReferenceException::ENCRYPTED
);
}
}
/**
* Find the start position for the first cross-reference.
*
* @return int The byte-offset position of the first cross-reference.
* @throws CrossReferenceException
*/
protected function findStartXref()
{
$reader = $this->parser->getStreamReader();
$reader->reset(-self::$trailerSearchLength, self::$trailerSearchLength);
$buffer = $reader->getBuffer(false);
$pos = \strrpos($buffer, 'startxref');
$addOffset = 9;
if ($pos === false) {
// Some corrupted documents uses startref, instead of startxref
$pos = \strrpos($buffer, 'startref');
if ($pos === false) {
throw new CrossReferenceException(
'Unable to find pointer to xref table',
CrossReferenceException::NO_STARTXREF_FOUND
);
}
$addOffset = 8;
}
$reader->setOffset($pos + $addOffset);
try {
$value = $this->parser->readValue(null, PdfNumeric::class);
} catch (PdfTypeException $e) {
throw new CrossReferenceException(
'Invalid data after startxref keyword.',
CrossReferenceException::INVALID_DATA,
$e
);
}
return $value->value;
}
}
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