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[mediawiki.git] / includes / json / FormatJson.php

<?php
/**
 * Wrapper for json_encode and json_decode.
 *
 * 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
 */

/**
 * JSON formatter wrapper class
 */
class FormatJson {
        /**
         * Skip escaping most characters above U+007F for readability and compactness.
         * This encoding option saves 3 to 8 bytes (uncompressed) for each such character;
         * however, it could break compatibility with systems that incorrectly handle UTF-8.
         *
         * @since 1.22
         */
        const UTF8_OK = 1;

        /**
         * Skip escaping the characters '<', '>', and '&', which have special meanings in
         * HTML and XML.
         *
         * @warning Do not use this option for JSON that could end up in inline scripts.
         * - HTML5, §4.3.1.2 Restrictions for contents of script elements
         * - XML 1.0 (5th Ed.), §2.4 Character Data and Markup
         *
         * @since 1.22
         */
        const XMLMETA_OK = 2;

        /**
         * Skip escaping as many characters as reasonably possible.
         *
         * @warning When generating inline script blocks, use FormatJson::UTF8_OK instead.
         *
         * @since 1.22
         */
        const ALL_OK = 3;

        /**
         * Regex that matches whitespace inside empty arrays and objects.
         *
         * This doesn't affect regular strings inside the JSON because those can't
         * have a real line break (\n) in them, at this point they are already escaped
         * as the string "\n" which this doesn't match.
         *
         * @private
         */
        const WS_CLEANUP_REGEX = '/(?<=[\[{])\n\s*+(?=[\]}])/';

        /**
         * Characters problematic in JavaScript.
         *
         * @note These are listed in ECMA-262 (5.1 Ed.), §7.3 Line Terminators along with U+000A (LF)
         *       and U+000D (CR). However, PHP already escapes LF and CR according to RFC 4627.
         */
        private static $badChars = array(
                "\xe2\x80\xa8", // U+2028 LINE SEPARATOR
                "\xe2\x80\xa9", // U+2029 PARAGRAPH SEPARATOR
        );

        /**
         * Escape sequences for characters listed in FormatJson::$badChars.
         */
        private static $badCharsEscaped = array(
                '\u2028', // U+2028 LINE SEPARATOR
                '\u2029', // U+2029 PARAGRAPH SEPARATOR
        );

        /**
         * Returns the JSON representation of a value.
         *
         * @note Empty arrays are encoded as numeric arrays, not as objects, so cast any associative
         *       array that might be empty to an object before encoding it.
         *
         * @note In pre-1.22 versions of MediaWiki, using this function for generating inline script
         *       blocks may result in an XSS vulnerability, and quite likely will in XML documents
         *       (cf. FormatJson::XMLMETA_OK). Use Xml::encodeJsVar() instead in such cases.
         *
         * @param mixed $value The value to encode. Can be any type except a resource.
         * @param string|bool $pretty If a string, add non-significant whitespace to improve
         *   readability, using that string for indentation. If true, use the default indent
         *   string (four spaces).
         * @param int $escaping Bitfield consisting of _OK class constants
         * @return string|bool: String if successful; false upon failure
         */
        public static function encode( $value, $pretty = false, $escaping = 0 ) {
                if ( !is_string( $pretty ) ) {
                        $pretty = $pretty ? '    ' : false;
                }

                if ( defined( 'JSON_UNESCAPED_UNICODE' ) ) {
                        return self::encode54( $value, $pretty, $escaping );
                }

                return self::encode53( $value, $pretty, $escaping );
        }

        /**
         * Decodes a JSON string.
         *
         * @param string $value The JSON string being decoded
         * @param bool $assoc When true, returned objects will be converted into associative arrays.
         *
         * @return mixed The value encoded in JSON in appropriate PHP type.
         * `null` is returned if the JSON cannot be decoded or if the encoded data is deeper than
         * the recursion limit.
         */
        public static function decode( $value, $assoc = false ) {
                return json_decode( $value, $assoc );
        }

        /**
         * JSON encoder wrapper for PHP >= 5.4, which supports useful encoding options.
         *
         * @param mixed $value
         * @param string|bool $pretty
         * @param int $escaping
         * @return string|bool
         */
        private static function encode54( $value, $pretty, $escaping ) {
                static $bug66021;
                if ( $pretty !== false && $bug66021 === null ) {
                        $bug66021 = json_encode( array(), JSON_PRETTY_PRINT ) !== '[]';
                }

                // PHP escapes '/' to prevent breaking out of inline script blocks using '</script>',
                // which is hardly useful when '<' and '>' are escaped (and inadequate), and such
                // escaping negatively impacts the human readability of URLs and similar strings.
                $options = JSON_UNESCAPED_SLASHES;
                $options |= $pretty !== false ? JSON_PRETTY_PRINT : 0;
                $options |= ( $escaping & self::UTF8_OK ) ? JSON_UNESCAPED_UNICODE : 0;
                $options |= ( $escaping & self::XMLMETA_OK ) ? 0 : ( JSON_HEX_TAG | JSON_HEX_AMP );
                $json = json_encode( $value, $options );
                if ( $json === false ) {
                        return false;
                }

                if ( $pretty !== false ) {
                        // Workaround for <https://bugs.php.net/bug.php?id=66021>
                        if ( $bug66021 ) {
                                $json = preg_replace( self::WS_CLEANUP_REGEX, '', $json );
                        }
                        if ( $pretty !== '    ' ) {
                                // Change the four-space indent to a tab indent
                                $json = str_replace( "\n    ", "\n\t", $json );
                                while ( strpos( $json, "\t    " ) !== false ) {
                                        $json = str_replace( "\t    ", "\t\t", $json );
                                }

                                if ( $pretty !== "\t" ) {
                                        // Change the tab indent to the provided indent
                                        $json = str_replace( "\t", $pretty, $json );
                                }
                        }
                }
                if ( $escaping & self::UTF8_OK ) {
                        $json = str_replace( self::$badChars, self::$badCharsEscaped, $json );
                }

                return $json;
        }

        /**
         * JSON encoder wrapper for PHP 5.3, which lacks native support for some encoding options.
         * Therefore, the missing options are implemented here purely in PHP code.
         *
         * @param mixed $value
         * @param string|bool $pretty
         * @param int $escaping
         * @return string|bool
         */
        private static function encode53( $value, $pretty, $escaping ) {
                $options = ( $escaping & self::XMLMETA_OK ) ? 0 : ( JSON_HEX_TAG | JSON_HEX_AMP );
                $json = json_encode( $value, $options );
                if ( $json === false ) {
                        return false;
                }

                // Emulate JSON_UNESCAPED_SLASHES. Because the JSON contains no unescaped slashes
                // (only escaped slashes), a simple string replacement works fine.
                $json = str_replace( '\/', '/', $json );

                if ( $escaping & self::UTF8_OK ) {
                        // JSON hex escape sequences follow the format \uDDDD, where DDDD is four hex digits
                        // indicating the equivalent UTF-16 code unit's value. To most efficiently unescape
                        // them, we exploit the JSON extension's built-in decoder.
                        // * We escape the input a second time, so any such sequence becomes \\uDDDD.
                        // * To avoid interpreting escape sequences that were in the original input,
                        //   each double-escaped backslash (\\\\) is replaced with \\\u005c.
                        // * We strip one of the backslashes from each of the escape sequences to unescape.
                        // * Then the JSON decoder can perform the actual unescaping.
                        $json = str_replace( "\\\\\\\\", "\\\\\\u005c", addcslashes( $json, '\"' ) );
                        $json = json_decode( preg_replace( "/\\\\\\\\u(?!00[0-7])/", "\\\\u", "\"$json\"" ) );
                        $json = str_replace( self::$badChars, self::$badCharsEscaped, $json );
                }

                if ( $pretty !== false ) {
                        return self::prettyPrint( $json, $pretty );
                }

                return $json;
        }

        /**
         * Adds non-significant whitespace to an existing JSON representation of an object.
         * Only needed for PHP < 5.4, which lacks the JSON_PRETTY_PRINT option.
         *
         * @param string $json
         * @param string $indentString
         * @return string
         */
        private static function prettyPrint( $json, $indentString ) {
                $buf = '';
                $indent = 0;
                $json = strtr( $json, array( '\\\\' => '\\\\', '\"' => "\x01" ) );
                for ( $i = 0, $n = strlen( $json ); $i < $n; $i += $skip ) {
                        $skip = 1;
                        switch ( $json[$i] ) {
                                case ':':
                                        $buf .= ': ';
                                        break;
                                case '[':
                                case '{':
                                        ++$indent;
                                        // falls through
                                case ',':
                                        $buf .= $json[$i] . "\n" . str_repeat( $indentString, $indent );
                                        break;
                                case ']':
                                case '}':
                                        $buf .= "\n" . str_repeat( $indentString, --$indent ) . $json[$i];
                                        break;
                                case '"':
                                        $skip = strcspn( $json, '"', $i + 1 ) + 2;
                                        $buf .= substr( $json, $i, $skip );
                                        break;
                                default:
                                        $skip = strcspn( $json, ',]}"', $i + 1 ) + 1;
                                        $buf .= substr( $json, $i, $skip );
                        }
                }
                $buf = preg_replace( self::WS_CLEANUP_REGEX, '', $buf );

                return str_replace( "\x01", '\"', $buf );
        }
}