OutputHandler.php

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<?php
namespace MediaWiki;
 
use MediaWiki\Logger\LoggerFactory;
 
class OutputHandler {
    public static function handle( $s, $phase ) {
        global $wgDisableOutputCompression, $wgMangleFlashPolicy;
 
        // Don't send headers if output is being discarded (T278579)
        if ( ( $phase & PHP_OUTPUT_HANDLER_CLEAN ) === PHP_OUTPUT_HANDLER_CLEAN ) {
            $logger = LoggerFactory::getInstance( 'output' );
            $logger->debug( __METHOD__ . " entrypoint={entry}; size={size}; phase=$phase", [
                'entry' => MW_ENTRY_POINT,
                'size' => strlen( $s ),
            ] );
 
            return $s;
        }
 
        if ( $wgMangleFlashPolicy ) {
            $s = self::mangleFlashPolicy( $s );
        }
 
        // Sanity check if a compression output buffer is already enabled via php.ini. Such
        // buffers exists at the start of the request and are reflected by ob_get_level().
        $phpHandlesCompression = (
            ini_get( 'output_handler' ) === 'ob_gzhandler' ||
            ini_get( 'zlib.output_handler' ) === 'ob_gzhandler' ||
            !in_array(
                strtolower( ini_get( 'zlib.output_compression' ) ),
                [ '', 'off', '0' ]
            )
        );
 
        if (
            // Compression is not already handled by an internal PHP buffer
            !$phpHandlesCompression &&
            // Compression is not disabled by the application entry point
            !defined( 'MW_NO_OUTPUT_COMPRESSION' ) &&
            // Compression is not disabled by site configuration
            !$wgDisableOutputCompression
        ) {
            $s = self::handleGzip( $s );
        }
 
        if (
            // Response body length does not depend on internal PHP compression buffer
            !$phpHandlesCompression &&
            // Response body length does not depend on mangling by a custom buffer
            !ini_get( 'output_handler' ) &&
            !ini_get( 'zlib.output_handler' )
        ) {
            self::emitContentLength( strlen( $s ) );
        }
 
        return $s;
    }
 
    private static function findUriExtension() {
        // @todo FIXME: this sort of dupes some code in WebRequest::getRequestUrl()
        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)" );
            return $s;
        }
        if ( headers_sent() ) {
            wfDebug( __METHOD__ . "() skipping compression (headers already sent)" );
            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 ( $s === '' ) {
            // Do not gzip empty HTTP responses since that would not only bloat the body
            // length, but it would result in invalid HTTP responses when the HTTP status code
            // is one that must not be accompanied by a body (e.g. "204 No Content").
            return $s;
        }
 
        if ( wfClientAcceptsGzip() ) {
            wfDebug( __METHOD__ . "() is compressing output" );
            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' );
        }
        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() ) {
            wfDebug( __METHOD__ . "() headers already sent" );
            return;
        }
 
        if (
            in_array( http_response_code(), [ 200, 404 ], true ) ||
            ( $_SERVER['SERVER_PROTOCOL'] ?? null ) === 'HTTP/1.0'
        ) {
            header( "Content-Length: $length" );
        }
    }
}