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[mediawiki.git] / includes / libs / CSSMin.php

<?php
/**
 * Minification of CSS stylesheets.
 *
 * Copyright 2010 Wikimedia Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *              http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed
 * under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS
 * OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License.
 *
 * @file
 * @version 0.1.1 -- 2010-09-11
 * @author Trevor Parscal <tparscal@wikimedia.org>
 * @copyright Copyright 2010 Wikimedia Foundation
 * @license http://www.apache.org/licenses/LICENSE-2.0
 */

/**
 * Transforms CSS data
 *
 * This class provides minification, URL remapping, URL extracting, and data-URL embedding.
 */
class CSSMin {

        /* Constants */

        /** @var string Strip marker for comments. **/
        const PLACEHOLDER = "\x7fPLACEHOLDER\x7f";

        /**
         * Internet Explorer data URI length limit. See encodeImageAsDataURI().
         */
        const DATA_URI_SIZE_LIMIT = 32768;
        const URL_REGEX = 'url\(\s*[\'"]?(?P<file>[^\?\)\'"]*?)(?P<query>\?[^\)\'"]*?|)[\'"]?\s*\)';
        const EMBED_REGEX = '\/\*\s*\@embed\s*\*\/';
        const COMMENT_REGEX = '\/\*.*?\*\/';

        /* Protected Static Members */

        /** @var array List of common image files extensions and MIME-types */
        protected static $mimeTypes = [
                'gif' => 'image/gif',
                'jpe' => 'image/jpeg',
                'jpeg' => 'image/jpeg',
                'jpg' => 'image/jpeg',
                'png' => 'image/png',
                'tif' => 'image/tiff',
                'tiff' => 'image/tiff',
                'xbm' => 'image/x-xbitmap',
                'svg' => 'image/svg+xml',
        ];

        /* Static Methods */

        /**
         * Get a list of local files referenced in a stylesheet (includes non-existent files).
         *
         * @param string $source CSS stylesheet source to process
         * @param string $path File path where the source was read from
         * @return array List of local file references
         */
        public static function getLocalFileReferences( $source, $path ) {
                $stripped = preg_replace( '/' . self::COMMENT_REGEX . '/s', '', $source );
                $path = rtrim( $path, '/' ) . '/';
                $files = [];

                $rFlags = PREG_OFFSET_CAPTURE | PREG_SET_ORDER;
                if ( preg_match_all( '/' . self::URL_REGEX . '/', $stripped, $matches, $rFlags ) ) {
                        foreach ( $matches as $match ) {
                                $url = $match['file'][0];

                                // Skip fully-qualified and protocol-relative URLs and data URIs
                                if ( substr( $url, 0, 2 ) === '//' || parse_url( $url, PHP_URL_SCHEME ) ) {
                                        break;
                                }

                                $files[] = $path . $url;
                        }
                }
                return $files;
        }

        /**
         * Encode an image file as a data URI.
         *
         * If the image file has a suitable MIME type and size, encode it as a data URI, base64-encoded
         * for binary files or just percent-encoded otherwise. Return false if the image type is
         * unfamiliar or file exceeds the size limit.
         *
         * @param string $file Image file to encode.
         * @param string|null $type File's MIME type or null. If null, CSSMin will
         *     try to autodetect the type.
         * @param bool $ie8Compat By default, a data URI will only be produced if it can be made short
         *     enough to fit in Internet Explorer 8 (and earlier) URI length limit (32,768 bytes). Pass
         *     `false` to remove this limitation.
         * @return string|bool Image contents encoded as a data URI or false.
         */
        public static function encodeImageAsDataURI( $file, $type = null, $ie8Compat = true ) {
                // Fast-fail for files that definitely exceed the maximum data URI length
                if ( $ie8Compat && filesize( $file ) >= self::DATA_URI_SIZE_LIMIT ) {
                        return false;
                }

                if ( $type === null ) {
                        $type = self::getMimeType( $file );
                }
                if ( !$type ) {
                        return false;
                }

                return self::encodeStringAsDataURI( file_get_contents( $file ), $type, $ie8Compat );
        }

        /**
         * Encode file contents as a data URI with chosen MIME type.
         *
         * The URI will be base64-encoded for binary files or just percent-encoded otherwise.
         *
         * @since 1.25
         *
         * @param string $contents File contents to encode.
         * @param string $type File's MIME type.
         * @param bool $ie8Compat See encodeImageAsDataURI().
         * @return string|bool Image contents encoded as a data URI or false.
         */
        public static function encodeStringAsDataURI( $contents, $type, $ie8Compat = true ) {
                // Try #1: Non-encoded data URI
                // The regular expression matches ASCII whitespace and printable characters.
                if ( preg_match( '/^[\r\n\t\x20-\x7e]+$/', $contents ) ) {
                        // Do not base64-encode non-binary files (sane SVGs).
                        // (This often produces longer URLs, but they compress better, yielding a net smaller size.)
                        $uri = 'data:' . $type . ',' . rawurlencode( $contents );
                        if ( !$ie8Compat || strlen( $uri ) < self::DATA_URI_SIZE_LIMIT ) {
                                return $uri;
                        }
                }

                // Try #2: Encoded data URI
                $uri = 'data:' . $type . ';base64,' . base64_encode( $contents );
                if ( !$ie8Compat || strlen( $uri ) < self::DATA_URI_SIZE_LIMIT ) {
                        return $uri;
                }

                // A data URI couldn't be produced
                return false;
        }

        /**
         * Serialize a string (escape and quote) for use as a CSS string value.
         * http://www.w3.org/TR/2013/WD-cssom-20131205/#serialize-a-string
         *
         * @param string $value
         * @return string
         * @throws Exception
         */
        public static function serializeStringValue( $value ) {
                if ( strstr( $value, "\0" ) ) {
                        throw new Exception( "Invalid character in CSS string" );
                }
                $value = strtr( $value, [ '\\' => '\\\\', '"' => '\\"' ] );
                $value = preg_replace_callback( '/[\x01-\x1f\x7f-\x9f]/', function ( $match ) {
                        return '\\' . base_convert( ord( $match[0] ), 10, 16 ) . ' ';
                }, $value );
                return '"' . $value . '"';
        }

        /**
         * @param string $file
         * @return bool|string
         */
        public static function getMimeType( $file ) {
                $realpath = realpath( $file );
                if (
                        $realpath
                        && function_exists( 'finfo_file' )
                        && function_exists( 'finfo_open' )
                        && defined( 'FILEINFO_MIME_TYPE' )
                ) {
                        return finfo_file( finfo_open( FILEINFO_MIME_TYPE ), $realpath );
                }

                // Infer the MIME-type from the file extension
                $ext = strtolower( pathinfo( $file, PATHINFO_EXTENSION ) );
                if ( isset( self::$mimeTypes[$ext] ) ) {
                        return self::$mimeTypes[$ext];
                }

                return false;
        }

        /**
         * Build a CSS 'url()' value for the given URL, quoting parentheses (and other funny characters)
         * and escaping quotes as necessary.
         *
         * See http://www.w3.org/TR/css-syntax-3/#consume-a-url-token
         *
         * @param string $url URL to process
         * @return string 'url()' value, usually just `"url($url)"`, quoted/escaped if necessary
         */
        public static function buildUrlValue( $url ) {
                // The list below has been crafted to match URLs such as:
                //   scheme://user@domain:port/~user/fi%20le.png?query=yes&really=y+s
                //   data:image/png;base64,R0lGODlh/+==
                if ( preg_match( '!^[\w\d:@/~.%+;,?&=-]+$!', $url ) ) {
                        return "url($url)";
                } else {
                        return 'url("' . strtr( $url, [ '\\' => '\\\\', '"' => '\\"' ] ) . '")';
                }
        }

        /**
         * Remaps CSS URL paths and automatically embeds data URIs for CSS rules
         * or url() values preceded by an / * @embed * / comment.
         *
         * @param string $source CSS data to remap
         * @param string $local File path where the source was read from
         * @param string $remote URL path to the file
         * @param bool $embedData If false, never do any data URI embedding,
         *   even if / * @embed * / is found.
         * @return string Remapped CSS data
         */
        public static function remap( $source, $local, $remote, $embedData = true ) {
                // High-level overview:
                // * For each CSS rule in $source that includes at least one url() value:
                //   * Check for an @embed comment at the start indicating that all URIs should be embedded
                //   * For each url() value:
                //     * Check for an @embed comment directly preceding the value
                //     * If either @embed comment exists:
                //       * Embedding the URL as data: URI, if it's possible / allowed
                //       * Otherwise remap the URL to work in generated stylesheets

                // Guard against trailing slashes, because "some/remote/../foo.png"
                // resolves to "some/remote/foo.png" on (some?) clients (bug 27052).
                if ( substr( $remote, -1 ) == '/' ) {
                        $remote = substr( $remote, 0, -1 );
                }

                // Disallow U+007F DELETE, which is illegal anyway, and which
                // we use for comment placeholders.
                $source = str_replace( "\x7f", "?", $source );

                // Replace all comments by a placeholder so they will not interfere with the remapping.
                // Warning: This will also catch on anything looking like the start of a comment between
                // quotation marks (e.g. "foo /* bar").
                $comments = [];

                $pattern = '/(?!' . CSSMin::EMBED_REGEX . ')(' . CSSMin::COMMENT_REGEX . ')/s';

                $source = preg_replace_callback(
                        $pattern,
                        function ( $match ) use ( &$comments ) {
                                $comments[] = $match[ 0 ];
                                return CSSMin::PLACEHOLDER . ( count( $comments ) - 1 ) . 'x';
                        },
                        $source
                );

                // Note: This will not correctly handle cases where ';', '{' or '}'
                // appears in the rule itself, e.g. in a quoted string. You are advised
                // not to use such characters in file names. We also match start/end of
                // the string to be consistent in edge-cases ('@import url(…)').
                $pattern = '/(?:^|[;{])\K[^;{}]*' . CSSMin::URL_REGEX . '[^;}]*(?=[;}]|$)/';

                $source = preg_replace_callback(
                        $pattern,
                        function ( $matchOuter ) use ( $local, $remote, $embedData ) {
                                $rule = $matchOuter[0];

                                // Check for global @embed comment and remove it. Allow other comments to be present
                                // before @embed (they have been replaced with placeholders at this point).
                                $embedAll = false;
                                $rule = preg_replace(
                                        '/^((?:\s+|' .
                                                CSSMin::PLACEHOLDER .
                                                '(\d+)x)*)' .
                                                CSSMin::EMBED_REGEX .
                                                '\s*/',
                                        '$1',
                                        $rule,
                                        1,
                                        $embedAll
                                );

                                // Build two versions of current rule: with remapped URLs
                                // and with embedded data: URIs (where possible).
                                $pattern = '/(?P<embed>' . CSSMin::EMBED_REGEX . '\s*|)' . CSSMin::URL_REGEX . '/';

                                $ruleWithRemapped = preg_replace_callback(
                                        $pattern,
                                        function ( $match ) use ( $local, $remote ) {
                                                $remapped = CSSMin::remapOne( $match['file'], $match['query'], $local, $remote, false );

                                                return CSSMin::buildUrlValue( $remapped );
                                        },
                                        $rule
                                );

                                if ( $embedData ) {
                                        // Remember the occurring MIME types to avoid fallbacks when embedding some files.
                                        $mimeTypes = [];

                                        $ruleWithEmbedded = preg_replace_callback(
                                                $pattern,
                                                function ( $match ) use ( $embedAll, $local, $remote, &$mimeTypes ) {
                                                        $embed = $embedAll || $match['embed'];
                                                        $embedded = CSSMin::remapOne(
                                                                $match['file'],
                                                                $match['query'],
                                                                $local,
                                                                $remote,
                                                                $embed
                                                        );

                                                        $url = $match['file'] . $match['query'];
                                                        $file = "{$local}/{$match['file']}";
                                                        if (
                                                                !self::isRemoteUrl( $url ) && !self::isLocalUrl( $url )
                                                                && file_exists( $file )
                                                        ) {
                                                                $mimeTypes[ CSSMin::getMimeType( $file ) ] = true;
                                                        }

                                                        return CSSMin::buildUrlValue( $embedded );
                                                },
                                                $rule
                                        );

                                        // Are all referenced images SVGs?
                                        $needsEmbedFallback = $mimeTypes !== [ 'image/svg+xml' => true ];
                                }

                                if ( !$embedData || $ruleWithEmbedded === $ruleWithRemapped ) {
                                        // We're not embedding anything, or we tried to but the file is not embeddable
                                        return $ruleWithRemapped;
                                } elseif ( $embedData && $needsEmbedFallback ) {
                                        // Build 2 CSS properties; one which uses a data URI in place of the @embed comment, and
                                        // the other with a remapped and versioned URL with an Internet Explorer 6 and 7 hack
                                        // making it ignored in all browsers that support data URIs
                                        return "$ruleWithEmbedded;$ruleWithRemapped!ie";
                                } else {
                                        // Look ma, no fallbacks! This is for files which IE 6 and 7 don't support anyway: SVG.
                                        return $ruleWithEmbedded;
                                }
                        }, $source );

                // Re-insert comments
                $pattern = '/' . CSSMin::PLACEHOLDER . '(\d+)x/';
                $source = preg_replace_callback( $pattern, function( $match ) use ( &$comments ) {
                        return $comments[ $match[1] ];
                }, $source );

                return $source;
        }

        /**
         * Is this CSS rule referencing a remote URL?
         *
         * @param string $maybeUrl
         * @return bool
         */
        protected static function isRemoteUrl( $maybeUrl ) {
                if ( substr( $maybeUrl, 0, 2 ) === '//' || parse_url( $maybeUrl, PHP_URL_SCHEME ) ) {
                        return true;
                }
                return false;
        }

        /**
         * Is this CSS rule referencing a local URL?
         *
         * @param string $maybeUrl
         * @return bool
         */
        protected static function isLocalUrl( $maybeUrl ) {
                if ( $maybeUrl !== '' && $maybeUrl[0] === '/' && !self::isRemoteUrl( $maybeUrl ) ) {
                        return true;
                }
                return false;
        }

        /**
         * Remap or embed a CSS URL path.
         *
         * @param string $file URL to remap/embed
         * @param string $query
         * @param string $local File path where the source was read from
         * @param string $remote URL path to the file
         * @param bool $embed Whether to do any data URI embedding
         * @return string Remapped/embedded URL data
         */
        public static function remapOne( $file, $query, $local, $remote, $embed ) {
                // The full URL possibly with query, as passed to the 'url()' value in CSS
                $url = $file . $query;

                // Expand local URLs with absolute paths like /w/index.php to possibly protocol-relative URL, if
                // wfExpandUrl() is available. (This will not be the case if we're running outside of MW.)
                if ( self::isLocalUrl( $url ) && function_exists( 'wfExpandUrl' ) ) {
                        return wfExpandUrl( $url, PROTO_RELATIVE );
                }

                // Pass thru fully-qualified and protocol-relative URLs and data URIs, as well as local URLs if
                // we can't expand them.
                if ( self::isRemoteUrl( $url ) || self::isLocalUrl( $url ) ) {
                        return $url;
                }

                if ( $local === false ) {
                        // Assume that all paths are relative to $remote, and make them absolute
                        $url = $remote . '/' . $url;
                } else {
                        // We drop the query part here and instead make the path relative to $remote
                        $url = "{$remote}/{$file}";
                        // Path to the actual file on the filesystem
                        $localFile = "{$local}/{$file}";
                        if ( file_exists( $localFile ) ) {
                                if ( $embed ) {
                                        $data = self::encodeImageAsDataURI( $localFile );
                                        if ( $data !== false ) {
                                                return $data;
                                        }
                                }
                                if ( method_exists( 'OutputPage', 'transformFilePath' ) ) {
                                        $url = OutputPage::transformFilePath( $remote, $local, $file );
                                } else {
                                        // Add version parameter as the first five hex digits
                                        // of the MD5 hash of the file's contents.
                                        $url .= '?' . substr( md5_file( $localFile ), 0, 5 );
                                }
                        }
                        // If any of these conditions failed (file missing, we don't want to embed it
                        // or it's not embeddable), return the URL (possibly with ?timestamp part)
                }
                if ( function_exists( 'wfRemoveDotSegments' ) ) {
                        $url = wfRemoveDotSegments( $url );
                }
                return $url;
        }

        /**
         * Removes whitespace from CSS data
         *
         * @param string $css CSS data to minify
         * @return string Minified CSS data
         */
        public static function minify( $css ) {
                return trim(
                        str_replace(
                                [ '; ', ': ', ' {', '{ ', ', ', '} ', ';}' ],
                                [ ';', ':', '{', '{', ',', '}', '}' ],
                                preg_replace( [ '/\s+/', '/\/\*.*?\*\//s' ], [ ' ', '' ], $css )
                        )
                );
        }
}