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diff --git a/includes/libs/StringUtils.php b/includes/libs/StringUtils.php
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+<?php
+/**
+ * Methods to play with strings.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+/**
+ * A collection of static methods to play with strings.
+ */
+class StringUtils {
+	/**
+	 * Test whether a string is valid UTF-8.
+	 *
+	 * The function check for invalid byte sequences, overlong encoding but
+	 * not for different normalisations.
+	 *
+	 * This relies internally on the mbstring function mb_check_encoding()
+	 * hardcoded to check against UTF-8. Whenever the function is not available
+	 * we fallback to a pure PHP implementation. Setting $disableMbstring to
+	 * true will skip the use of mb_check_encoding, this is mostly intended for
+	 * unit testing our internal implementation.
+	 *
+	 * @since 1.21
+	 * @note In MediaWiki 1.21, this function did not provide proper UTF-8 validation.
+	 * In particular, the pure PHP code path did not in fact check for overlong forms.
+	 * Beware of this when backporting code to that version of MediaWiki.
+	 *
+	 * @param string $value String to check
+	 * @param bool $disableMbstring Whether to use the pure PHP
+	 * implementation instead of trying mb_check_encoding. Intended for unit
+	 * testing. Default: false
+	 *
+	 * @return bool Whether the given $value is a valid UTF-8 encoded string
+	 */
+	static function isUtf8( $value, $disableMbstring = false ) {
+		$value = (string)$value;
+
+		// If the mbstring extension is loaded, use it. However, before PHP 5.4, values above
+		// U+10FFFF are incorrectly allowed, so we have to check for them separately.
+		if ( !$disableMbstring && function_exists( 'mb_check_encoding' ) ) {
+			static $newPHP;
+			if ( $newPHP === null ) {
+				$newPHP = !mb_check_encoding( "\xf4\x90\x80\x80", 'UTF-8' );
+			}
+
+			return mb_check_encoding( $value, 'UTF-8' ) &&
+				( $newPHP || preg_match( "/\xf4[\x90-\xbf]|[\xf5-\xff]/S", $value ) === 0 );
+		}
+
+		if ( preg_match( "/[\x80-\xff]/S", $value ) === 0 ) {
+			// String contains only ASCII characters, has to be valid
+			return true;
+		}
+
+		// PCRE implements repetition using recursion; to avoid a stack overflow (and segfault)
+		// for large input, we check for invalid sequences (<= 5 bytes) rather than valid
+		// sequences, which can be as long as the input string is. Multiple short regexes are
+		// used rather than a single long regex for performance.
+		static $regexes;
+		if ( $regexes === null ) {
+			$cont = "[\x80-\xbf]";
+			$after = "(?!$cont)"; // "(?:[^\x80-\xbf]|$)" would work here
+			$regexes = array(
+				// Continuation byte at the start
+				"/^$cont/",
+
+				// ASCII byte followed by a continuation byte
+				"/[\\x00-\x7f]$cont/S",
+
+				// Illegal byte
+				"/[\xc0\xc1\xf5-\xff]/S",
+
+				// Invalid 2-byte sequence, or valid one then an extra continuation byte
+				"/[\xc2-\xdf](?!$cont$after)/S",
+
+				// Invalid 3-byte sequence, or valid one then an extra continuation byte
+				"/\xe0(?![\xa0-\xbf]$cont$after)/",
+				"/[\xe1-\xec\xee\xef](?!$cont{2}$after)/S",
+				"/\xed(?![\x80-\x9f]$cont$after)/",
+
+				// Invalid 4-byte sequence, or valid one then an extra continuation byte
+				"/\xf0(?![\x90-\xbf]$cont{2}$after)/",
+				"/[\xf1-\xf3](?!$cont{3}$after)/S",
+				"/\xf4(?![\x80-\x8f]$cont{2}$after)/",
+			);
+		}
+
+		foreach ( $regexes as $regex ) {
+			if ( preg_match( $regex, $value ) !== 0 ) {
+				return false;
+			}
+		}
+
+		return true;
+	}
+
+	/**
+	 * Perform an operation equivalent to
+	 *
+	 *     preg_replace( "!$startDelim(.*?)$endDelim!", $replace, $subject );
+	 *
+	 * except that it's worst-case O(N) instead of O(N^2)
+	 *
+	 * Compared to delimiterReplace(), this implementation is fast but memory-
+	 * hungry and inflexible. The memory requirements are such that I don't
+	 * recommend using it on anything but guaranteed small chunks of text.
+	 *
+	 * @param string $startDelim
+	 * @param string $endDelim
+	 * @param string $replace
+	 * @param string $subject
+	 *
+	 * @return string
+	 */
+	static function hungryDelimiterReplace( $startDelim, $endDelim, $replace, $subject ) {
+		$segments = explode( $startDelim, $subject );
+		$output = array_shift( $segments );
+		foreach ( $segments as $s ) {
+			$endDelimPos = strpos( $s, $endDelim );
+			if ( $endDelimPos === false ) {
+				$output .= $startDelim . $s;
+			} else {
+				$output .= $replace . substr( $s, $endDelimPos + strlen( $endDelim ) );
+			}
+		}
+
+		return $output;
+	}
+
+	/**
+	 * Perform an operation equivalent to
+	 *
+	 *   preg_replace_callback( "!$startDelim(.*)$endDelim!s$flags", $callback, $subject )
+	 *
+	 * This implementation is slower than hungryDelimiterReplace but uses far less
+	 * memory. The delimiters are literal strings, not regular expressions.
+	 *
+	 * If the start delimiter ends with an initial substring of the end delimiter,
+	 * e.g. in the case of C-style comments, the behavior differs from the model
+	 * regex. In this implementation, the end must share no characters with the
+	 * start, so e.g. /*\/ is not considered to be both the start and end of a
+	 * comment. /*\/xy/*\/ is considered to be a single comment with contents /xy/.
+	 *
+	 * @param string $startDelim Start delimiter
+	 * @param string $endDelim End delimiter
+	 * @param callable $callback Function to call on each match
+	 * @param string $subject
+	 * @param string $flags Regular expression flags
+	 * @throws InvalidArgumentException
+	 * @return string
+	 */
+	static function delimiterReplaceCallback( $startDelim, $endDelim, $callback,
+		$subject, $flags = ''
+	) {
+		$inputPos = 0;
+		$outputPos = 0;
+		$output = '';
+		$foundStart = false;
+		$encStart = preg_quote( $startDelim, '!' );
+		$encEnd = preg_quote( $endDelim, '!' );
+		$strcmp = strpos( $flags, 'i' ) === false ? 'strcmp' : 'strcasecmp';
+		$endLength = strlen( $endDelim );
+		$m = array();
+
+		while ( $inputPos < strlen( $subject ) &&
+			preg_match( "!($encStart)|($encEnd)!S$flags", $subject, $m, PREG_OFFSET_CAPTURE, $inputPos )
+		) {
+			$tokenOffset = $m[0][1];
+			if ( $m[1][0] != '' ) {
+				if ( $foundStart &&
+					$strcmp( $endDelim, substr( $subject, $tokenOffset, $endLength ) ) == 0
+				) {
+					# An end match is present at the same location
+					$tokenType = 'end';
+					$tokenLength = $endLength;
+				} else {
+					$tokenType = 'start';
+					$tokenLength = strlen( $m[0][0] );
+				}
+			} elseif ( $m[2][0] != '' ) {
+				$tokenType = 'end';
+				$tokenLength = strlen( $m[0][0] );
+			} else {
+				throw new InvalidArgumentException( 'Invalid delimiter given to ' . __METHOD__ );
+			}
+
+			if ( $tokenType == 'start' ) {
+				# Only move the start position if we haven't already found a start
+				# This means that START START END matches outer pair
+				if ( !$foundStart ) {
+					# Found start
+					$inputPos = $tokenOffset + $tokenLength;
+					# Write out the non-matching section
+					$output .= substr( $subject, $outputPos, $tokenOffset - $outputPos );
+					$outputPos = $tokenOffset;
+					$contentPos = $inputPos;
+					$foundStart = true;
+				} else {
+					# Move the input position past the *first character* of START,
+					# to protect against missing END when it overlaps with START
+					$inputPos = $tokenOffset + 1;
+				}
+			} elseif ( $tokenType == 'end' ) {
+				if ( $foundStart ) {
+					# Found match
+					$output .= call_user_func( $callback, array(
+						substr( $subject, $outputPos, $tokenOffset + $tokenLength - $outputPos ),
+						substr( $subject, $contentPos, $tokenOffset - $contentPos )
+					) );
+					$foundStart = false;
+				} else {
+					# Non-matching end, write it out
+					$output .= substr( $subject, $inputPos, $tokenOffset + $tokenLength - $outputPos );
+				}
+				$inputPos = $outputPos = $tokenOffset + $tokenLength;
+			} else {
+				throw new InvalidArgumentException( 'Invalid delimiter given to ' . __METHOD__ );
+			}
+		}
+		if ( $outputPos < strlen( $subject ) ) {
+			$output .= substr( $subject, $outputPos );
+		}
+
+		return $output;
+	}
+
+	/**
+	 * Perform an operation equivalent to
+	 *
+	 *   preg_replace( "!$startDelim(.*)$endDelim!$flags", $replace, $subject )
+	 *
+	 * @param string $startDelim Start delimiter regular expression
+	 * @param string $endDelim End delimiter regular expression
+	 * @param string $replace Replacement string. May contain $1, which will be
+	 *                 replaced by the text between the delimiters
+	 * @param string $subject String to search
+	 * @param string $flags Regular expression flags
+	 * @return string The string with the matches replaced
+	 */
+	static function delimiterReplace( $startDelim, $endDelim, $replace, $subject, $flags = '' ) {
+		$replacer = new RegexlikeReplacer( $replace );
+
+		return self::delimiterReplaceCallback( $startDelim, $endDelim,
+			$replacer->cb(), $subject, $flags );
+	}
+
+	/**
+	 * More or less "markup-safe" explode()
+	 * Ignores any instances of the separator inside <...>
+	 * @param string $separator
+	 * @param string $text
+	 * @return array
+	 */
+	static function explodeMarkup( $separator, $text ) {
+		$placeholder = "\x00";
+
+		// Remove placeholder instances
+		$text = str_replace( $placeholder, '', $text );
+
+		// Replace instances of the separator inside HTML-like tags with the placeholder
+		$replacer = new DoubleReplacer( $separator, $placeholder );
+		$cleaned = StringUtils::delimiterReplaceCallback( '<', '>', $replacer->cb(), $text );
+
+		// Explode, then put the replaced separators back in
+		$items = explode( $separator, $cleaned );
+		foreach ( $items as $i => $str ) {
+			$items[$i] = str_replace( $placeholder, $separator, $str );
+		}
+
+		return $items;
+	}
+
+	/**
+	 * Escape a string to make it suitable for inclusion in a preg_replace()
+	 * replacement parameter.
+	 *
+	 * @param string $string
+	 * @return string
+	 */
+	static function escapeRegexReplacement( $string ) {
+		$string = str_replace( '\\', '\\\\', $string );
+		$string = str_replace( '$', '\\$', $string );
+
+		return $string;
+	}
+
+	/**
+	 * Workalike for explode() with limited memory usage.
+	 * Returns an Iterator
+	 * @param string $separator
+	 * @param string $subject
+	 * @return ArrayIterator|ExplodeIterator
+	 */
+	static function explode( $separator, $subject ) {
+		if ( substr_count( $subject, $separator ) > 1000 ) {
+			return new ExplodeIterator( $separator, $subject );
+		} else {
+			return new ArrayIterator( explode( $separator, $subject ) );
+		}
+	}
+}