408 lines
13 KiB
PHP
408 lines
13 KiB
PHP
<?php
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namespace Laminas\Xml;
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use DOMDocument;
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use SimpleXMLElement;
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class Security
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{
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const ENTITY_DETECT = 'Detected use of ENTITY in XML, disabled to prevent XXE/XEE attacks';
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/**
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* Heuristic scan to detect entity in XML
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*
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* @param string $xml
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* @throws Exception\RuntimeException If entity expansion or external entity declaration was discovered.
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*/
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protected static function heuristicScan($xml)
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{
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foreach (self::getEntityComparison($xml) as $compare) {
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if (strpos($xml, $compare) !== false) {
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throw new Exception\RuntimeException(self::ENTITY_DETECT);
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}
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}
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}
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/**
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* Scan XML string for potential XXE and XEE attacks
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*
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* @param string $xml
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* @param DomDocument $dom
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* @param int $libXmlConstants additional libxml constants to pass in
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* @param callable $callback the callback to use to create the dom element
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* @throws Exception\RuntimeException
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* @return SimpleXMLElement|DomDocument|boolean
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*/
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private static function scanString($xml, DOMDocument $dom = null, $libXmlConstants, callable $callback)
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{
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// If running with PHP-FPM we perform an heuristic scan
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// We cannot use libxml_disable_entity_loader because of this bug
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// @see https://bugs.php.net/bug.php?id=64938
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if (self::isPhpFpm()) {
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self::heuristicScan($xml);
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}
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if (null === $dom) {
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$simpleXml = true;
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$dom = new DOMDocument();
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}
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if (! self::isPhpFpm()) {
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if (\PHP_VERSION_ID < 80000) {
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$loadEntities = libxml_disable_entity_loader(true);
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}
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$useInternalXmlErrors = libxml_use_internal_errors(true);
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}
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// Load XML with network access disabled (LIBXML_NONET)
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// error disabled with @ for PHP-FPM scenario
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set_error_handler(function ($errno, $errstr) {
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if (substr_count($errstr, 'DOMDocument::loadXML()') > 0) {
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return true;
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}
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return false;
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}, E_WARNING);
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$result = $callback($xml, $dom, LIBXML_NONET | $libXmlConstants);
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restore_error_handler();
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if (! $result) {
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// Entity load to previous setting
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if (! self::isPhpFpm()) {
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if (\PHP_VERSION_ID < 80000) {
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libxml_disable_entity_loader($loadEntities);
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}
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libxml_use_internal_errors($useInternalXmlErrors);
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}
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return false;
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}
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// Scan for potential XEE attacks using ENTITY, if not PHP-FPM
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if (! self::isPhpFpm()) {
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foreach ($dom->childNodes as $child) {
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if ($child->nodeType === XML_DOCUMENT_TYPE_NODE) {
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if ($child->entities->length > 0) {
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throw new Exception\RuntimeException(self::ENTITY_DETECT);
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}
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}
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}
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}
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// Entity load to previous setting
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if (! self::isPhpFpm()) {
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if (\PHP_VERSION_ID < 80000) {
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libxml_disable_entity_loader($loadEntities);
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}
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libxml_use_internal_errors($useInternalXmlErrors);
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}
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if (isset($simpleXml)) {
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$result = simplexml_import_dom($dom);
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if (! $result instanceof SimpleXMLElement) {
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return false;
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}
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return $result;
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}
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return $dom;
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}
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/**
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* Scan XML string for potential XXE and XEE attacks
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*
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* @param string $xml
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* @param DomDocument $dom
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* @param int $libXmlConstants additional libxml constants to pass in
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* @throws Exception\RuntimeException
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* @return SimpleXMLElement|DomDocument|boolean
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*/
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public static function scan($xml, DOMDocument $dom = null, $libXmlConstants = 0)
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{
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$callback = function ($xml, $dom, $constants) {
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return $dom->loadXml($xml, $constants);
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};
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return self::scanString($xml, $dom, $libXmlConstants, $callback);
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}
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/**
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* Scan HTML string for potential XXE and XEE attacks
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*
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* @param string $xml
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* @param DomDocument $dom
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* @param int $libXmlConstants additional libxml constants to pass in
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* @throws Exception\RuntimeException
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* @return SimpleXMLElement|DomDocument|boolean
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*/
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public static function scanHtml($html, DOMDocument $dom = null, $libXmlConstants = 0)
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{
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$callback = function ($html, $dom, $constants) {
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return $dom->loadHtml($html, $constants);
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};
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return self::scanString($html, $dom, $libXmlConstants, $callback);
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}
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/**
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* Scan XML file for potential XXE/XEE attacks
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*
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* @param string $file
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* @param DOMDocument $dom
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* @throws Exception\InvalidArgumentException
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* @return SimpleXMLElement|DomDocument
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*/
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public static function scanFile($file, DOMDocument $dom = null)
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{
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if (! file_exists($file)) {
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throw new Exception\InvalidArgumentException(
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"The file $file specified doesn't exist"
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);
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}
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return self::scan(file_get_contents($file), $dom);
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}
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/**
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* Return true if PHP is running with PHP-FPM
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*
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* This method is mainly used to determine whether or not heuristic checks
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* (vs libxml checks) should be made, due to threading issues in libxml;
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* under php-fpm, threading becomes a concern.
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*
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* However, PHP versions 5.6.6+ contain a patch to the
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* libxml support in PHP that makes the libxml checks viable; in such
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* versions, this method will return false to enforce those checks, which
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* are more strict and accurate than the heuristic checks.
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*
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* @return boolean
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*/
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public static function isPhpFpm()
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{
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$isVulnerableVersion = version_compare(PHP_VERSION, '5.6', 'ge')
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&& version_compare(PHP_VERSION, '5.6.6', 'lt');
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if (0 === strpos(php_sapi_name(), 'fpm') && $isVulnerableVersion) {
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return true;
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}
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return false;
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}
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/**
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* Determine and return the string(s) to use for the <!ENTITY comparison.
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*
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* @param string $xml
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* @return string[]
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*/
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protected static function getEntityComparison($xml)
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{
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$encodingMap = self::getAsciiEncodingMap();
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return array_map(function ($encoding) use ($encodingMap) {
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$generator = isset($encodingMap[$encoding]) ? $encodingMap[$encoding] : $encodingMap['UTF-8'];
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return $generator('<!ENTITY');
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}, self::detectXmlEncoding($xml, self::detectStringEncoding($xml)));
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}
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/**
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* Determine the string encoding.
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*
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* Determines string encoding from either a detected BOM or a
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* heuristic.
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*
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* @param string $xml
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* @return string File encoding
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*/
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protected static function detectStringEncoding($xml)
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{
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return self::detectBom($xml) ?: self::detectXmlStringEncoding($xml);
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}
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/**
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* Attempt to match a known BOM.
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*
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* Iterates through the return of getBomMap(), comparing the initial bytes
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* of the provided string to the BOM of each; if a match is determined,
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* it returns the encoding.
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*
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* @param string $string
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* @return false|string Returns encoding on success.
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*/
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protected static function detectBom($string)
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{
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foreach (self::getBomMap() as $criteria) {
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if (0 === strncmp($string, $criteria['bom'], $criteria['length'])) {
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return $criteria['encoding'];
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}
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}
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return false;
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}
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/**
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* Attempt to detect the string encoding of an XML string.
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*
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* @param string $xml
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* @return string Encoding
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*/
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protected static function detectXmlStringEncoding($xml)
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{
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foreach (self::getAsciiEncodingMap() as $encoding => $generator) {
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$prefix = $generator('<' . '?xml');
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if (0 === strncmp($xml, $prefix, strlen($prefix))) {
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return $encoding;
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}
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}
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// Fallback
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return 'UTF-8';
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}
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/**
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* Attempt to detect the specified XML encoding.
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*
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* Using the file's encoding, determines if an "encoding" attribute is
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* present and well-formed in the XML declaration; if so, it returns a
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* list with both the ASCII representation of that declaration and the
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* original file encoding.
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*
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* If not, a list containing only the provided file encoding is returned.
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*
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* @param string $xml
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* @param string $fileEncoding
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* @return string[] Potential XML encodings
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*/
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protected static function detectXmlEncoding($xml, $fileEncoding)
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{
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$encodingMap = self::getAsciiEncodingMap();
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$generator = $encodingMap[$fileEncoding];
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$encAttr = $generator('encoding="');
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$quote = $generator('"');
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$close = $generator('>');
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$closePos = strpos($xml, $close);
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if (false === $closePos) {
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return [$fileEncoding];
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}
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$encPos = strpos($xml, $encAttr);
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if (false === $encPos
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|| $encPos > $closePos
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) {
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return [$fileEncoding];
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}
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$encPos += strlen($encAttr);
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$quotePos = strpos($xml, $quote, $encPos);
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if (false === $quotePos) {
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return [$fileEncoding];
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}
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$encoding = self::substr($xml, $encPos, $quotePos);
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return [
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// Following line works because we're only supporting 8-bit safe encodings at this time.
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str_replace('\0', '', $encoding), // detected encoding
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$fileEncoding, // file encoding
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];
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}
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/**
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* Return a list of BOM maps.
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*
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* Returns a list of common encoding -> BOM maps, along with the character
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* length to compare against.
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*
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* @link https://en.wikipedia.org/wiki/Byte_order_mark
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* @return array
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*/
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protected static function getBomMap()
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{
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return [
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[
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'encoding' => 'UTF-32BE',
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'bom' => pack('CCCC', 0x00, 0x00, 0xfe, 0xff),
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'length' => 4,
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],
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[
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'encoding' => 'UTF-32LE',
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'bom' => pack('CCCC', 0xff, 0xfe, 0x00, 0x00),
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'length' => 4,
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],
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[
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'encoding' => 'GB-18030',
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'bom' => pack('CCCC', 0x84, 0x31, 0x95, 0x33),
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'length' => 4,
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],
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[
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'encoding' => 'UTF-16BE',
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'bom' => pack('CC', 0xfe, 0xff),
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'length' => 2,
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],
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[
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'encoding' => 'UTF-16LE',
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'bom' => pack('CC', 0xff, 0xfe),
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'length' => 2,
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],
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[
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'encoding' => 'UTF-8',
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'bom' => pack('CCC', 0xef, 0xbb, 0xbf),
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'length' => 3,
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],
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];
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}
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/**
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* Return a map of encoding => generator pairs.
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*
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* Returns a map of encoding => generator pairs, where the generator is a
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* callable that accepts a string and returns the appropriate byte order
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* sequence of that string for the encoding.
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*
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* @return array
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*/
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protected static function getAsciiEncodingMap()
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{
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return [
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'UTF-32BE' => function ($ascii) {
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return preg_replace('/(.)/', "\0\0\0\\1", $ascii);
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},
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'UTF-32LE' => function ($ascii) {
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return preg_replace('/(.)/', "\\1\0\0\0", $ascii);
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},
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'UTF-32odd1' => function ($ascii) {
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return preg_replace('/(.)/', "\0\\1\0\0", $ascii);
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},
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'UTF-32odd2' => function ($ascii) {
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return preg_replace('/(.)/', "\0\0\\1\0", $ascii);
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},
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'UTF-16BE' => function ($ascii) {
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return preg_replace('/(.)/', "\0\\1", $ascii);
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},
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'UTF-16LE' => function ($ascii) {
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return preg_replace('/(.)/', "\\1\0", $ascii);
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},
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'UTF-8' => function ($ascii) {
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return $ascii;
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},
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'GB-18030' => function ($ascii) {
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return $ascii;
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},
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];
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}
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/**
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* Binary-safe substr.
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*
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* substr() is not binary-safe; this method loops by character to ensure
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* multi-byte characters are aggregated correctly.
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*
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* @param string $string
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* @param int $start
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* @param int $end
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* @return string
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*/
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protected static function substr($string, $start, $end)
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{
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$substr = '';
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for ($i = $start; $i < $end; $i += 1) {
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$substr .= $string[$i];
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}
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return $substr;
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}
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}
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