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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\StreamReader;
/**
* Class FixedReader
*
* This reader allows a very less overhead parsing of single entries of the cross-reference, because the main entries
* are only read when needed and not in a single run.
*/
class FixedReader extends AbstractReader implements ReaderInterface
{
/**
* @var StreamReader
*/
protected $reader;
/**
* Data of subsections.
*
* @var array
*/
protected $subSections;
/**
* FixedReader constructor.
*
* @param PdfParser $parser
* @throws CrossReferenceException
*/
public function __construct(PdfParser $parser)
{
$this->reader = $parser->getStreamReader();
$this->read();
parent::__construct($parser);
}
/**
* Get all subsection data.
*
* @return array
*/
public function getSubSections()
{
return $this->subSections;
}
/**
* @inheritdoc
* @return int|false
*/
public function getOffsetFor($objectNumber)
{
foreach ($this->subSections as $offset => list($startObject, $objectCount)) {
/**
* @var int $startObject
* @var int $objectCount
*/
if ($objectNumber >= $startObject && $objectNumber < ($startObject + $objectCount)) {
$position = $offset + 20 * ($objectNumber - $startObject);
$this->reader->ensure($position, 20);
$line = $this->reader->readBytes(20);
if ($line === false || $line[17] === 'f') {
return false;
}
return (int) \substr($line, 0, 10);
}
}
return false;
}
/**
* Read the cross-reference.
*
* This reader will only read the subsections in this method. The offsets were resolved individually by this
* information.
*
* @throws CrossReferenceException
*/
protected function read()
{
$subSections = [];
$startObject = $entryCount = $lastLineStart = null;
$validityChecked = false;
while (($line = $this->reader->readLine(20)) !== false) {
if (\strpos($line, 'trailer') !== false) {
$this->reader->reset($lastLineStart);
break;
}
// jump over if line content doesn't match the expected string
if (\sscanf($line, '%d %d', $startObject, $entryCount) !== 2) {
continue;
}
$oldPosition = $this->reader->getPosition();
$position = $oldPosition + $this->reader->getOffset();
if (!$validityChecked && $entryCount > 0) {
$nextLine = $this->reader->readBytes(21);
/* Check the next line for maximum of 20 bytes and not longer
* By catching 21 bytes and trimming the length should be still 21.
*/
if (\strlen(\trim($nextLine)) !== 21) {
throw new CrossReferenceException(
'Cross-reference entries are larger than 20 bytes.',
CrossReferenceException::ENTRIES_TOO_LARGE
);
}
/* Check for less than 20 bytes: cut the line to 20 bytes and trim; have to result in exactly 18 bytes.
* If it would have less bytes the substring would get the first bytes of the next line which would
* evaluate to a 20 bytes long string after trimming.
*/
if (\strlen(\trim(\substr($nextLine, 0, 20))) !== 18) {
throw new CrossReferenceException(
'Cross-reference entries are less than 20 bytes.',
CrossReferenceException::ENTRIES_TOO_SHORT
);
}
$validityChecked = true;
}
$subSections[$position] = [$startObject, $entryCount];
$lastLineStart = $position + $entryCount * 20;
$this->reader->reset($lastLineStart);
}
// reset after the last correct parsed line
$this->reader->reset($lastLineStart);
if (\count($subSections) === 0) {
throw new CrossReferenceException(
'No entries found in cross-reference.',
CrossReferenceException::NO_ENTRIES
);
}
$this->subSections = $subSections;
}
/**
* Fixes an invalid object number shift.
*
* This method can be used to repair documents with an invalid subsection header:
*
* <code>
* xref
* 1 7
* 0000000000 65535 f
* 0000000009 00000 n
* 0000412075 00000 n
* 0000412172 00000 n
* 0000412359 00000 n
* 0000412417 00000 n
* 0000412468 00000 n
* </code>
*
* It shall only be called on the first table.
*
* @return bool
*/
public function fixFaultySubSectionShift()
{
$subSections = $this->getSubSections();
if (\count($subSections) > 1) {
return false;
}
$subSection = \current($subSections);
if ($subSection[0] != 1) {
return false;
}
if ($this->getOffsetFor(1) === false) {
foreach ($subSections as $offset => list($startObject, $objectCount)) {
$this->subSections[$offset] = [$startObject - 1, $objectCount];
}
return true;
}
return false;
}
}
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