OutputHandler.php

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<?php
namespace MediaWiki;

class OutputHandler {
    public static function handle( $s ) {
        global $wgDisableOutputCompression, $wgMangleFlashPolicy;
        if ( $wgMangleFlashPolicy ) {
            $s = self::mangleFlashPolicy( $s );
        }
        if ( !$wgDisableOutputCompression && !ini_get( 'zlib.output_compression' ) ) {
            if ( !defined( 'MW_NO_OUTPUT_COMPRESSION' ) ) {
                $s = self::handleGzip( $s );
            }
            if ( !ini_get( 'output_handler' ) ) {
                self::emitContentLength( strlen( $s ) );
            }
        }
        return $s;
    }

    private static function findUriExtension() {
        if ( isset( $_SERVER['REQUEST_URI'] ) ) {
            // Strip the query string...
            $path = explode( '?', $_SERVER['REQUEST_URI'], 2 )[0];
        } elseif ( isset( $_SERVER['SCRIPT_NAME'] ) ) {
            // Probably IIS. QUERY_STRING appears separately.
            $path = $_SERVER['SCRIPT_NAME'];
        } else {
            // Can't get the path from the server? :(
            return '';
        }

        $period = strrpos( $path, '.' );
        if ( $period !== false ) {
            return strtolower( substr( $path, $period ) );
        }
        return '';
    }

    private static function handleGzip( $s ) {
        if ( !function_exists( 'gzencode' ) ) {
            wfDebug( __METHOD__ . "() skipping compression (gzencode unavailable)\n" );
            return $s;
        }
        if ( headers_sent() ) {
            wfDebug( __METHOD__ . "() skipping compression (headers already sent)\n" );
            return $s;
        }

        $ext = self::findUriExtension();
        if ( $ext == '.gz' || $ext == '.tgz' ) {
            // Don't do gzip compression if the URL path ends in .gz or .tgz
            // This confuses Safari and triggers a download of the page,
            // even though it's pretty clearly labeled as viewable HTML.
            // Bad Safari! Bad!
            return $s;
        }

        if ( wfClientAcceptsGzip() ) {
            wfDebug( __METHOD__ . "() is compressing output\n" );
            header( 'Content-Encoding: gzip' );
            $s = gzencode( $s, 6 );
        }

        // Set vary header if it hasn't been set already
        $headers = headers_list();
        $foundVary = false;
        foreach ( $headers as $header ) {
            $headerName = strtolower( substr( $header, 0, 5 ) );
            if ( $headerName == 'vary:' ) {
                $foundVary = true;
                break;
            }
        }
        if ( !$foundVary ) {
            header( 'Vary: Accept-Encoding' );
            global $wgUseKeyHeader;
            if ( $wgUseKeyHeader ) {
                header( 'Key: Accept-Encoding;match=gzip' );
            }
        }
        return $s;
    }

    private static function mangleFlashPolicy( $s ) {
        # Avoid weird excessive memory usage in PCRE on big articles
        if ( preg_match( '/<\s*cross-domain-policy(?=\s|>)/i', $s ) ) {
            return preg_replace( '/<(\s*)(cross-domain-policy(?=\s|>))/i', '<$1NOT-$2', $s );
        } else {
            return $s;
        }
    }

    private static function emitContentLength( $length ) {
        if ( !headers_sent()
            && isset( $_SERVER['SERVER_PROTOCOL'] )
            && $_SERVER['SERVER_PROTOCOL'] == 'HTTP/1.0'
        ) {
            header( "Content-Length: $length" );
        }
    }
}