Revision: Remove some unnecessary temporary variables for returns

[mediawiki.git] / thumb.php

<?php
/**
 * The web entry point for retrieving media thumbnails, created by a MediaHandler
 * subclass or proxy request if FileRepo::getThumbProxyUrl is configured.
 *
 * This script may also resize an image on-demand, if it isn't found in the
 * configured FileBackend storage.
 *
 * 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
 * @ingroup entrypoint
 * @ingroup Media
 */

use MediaWiki\Logger\LoggerFactory;
use MediaWiki\MediaWikiServices;

define( 'MW_NO_OUTPUT_COMPRESSION', 1 );
// T241340: thumb.php is included by thumb_handler.php which already defined
// MW_ENTRY_POINT to 'thumb_handler'
if ( !defined( 'MW_ENTRY_POINT' ) ) {
        define( 'MW_ENTRY_POINT', 'thumb' );
}
require __DIR__ . '/includes/WebStart.php';

wfThumbMain();

function wfThumbMain() {
        global $wgTrivialMimeDetection, $wgRequest;

        // Don't use fancy MIME detection, just check the file extension for jpg/gif/png
        $wgTrivialMimeDetection = true;

        if ( defined( 'THUMB_HANDLER' ) ) {
                // Called from thumb_handler.php via 404; extract params from the URI...
                wfThumbHandle404();
        } else {
                // Called directly, use $_GET params
                wfStreamThumb( $wgRequest->getQueryValuesOnly() );
        }

        $mediawiki = new MediaWiki();
        $mediawiki->doPostOutputShutdown();
}

/**
 * Handle a thumbnail request via thumbnail file URL
 *
 * @return void
 */
function wfThumbHandle404() {
        // Determine the request path relative to the thumbnail zone base
        $repo = MediaWikiServices::getInstance()->getRepoGroup()->getLocalRepo();
        $baseUrl = $repo->getZoneUrl( 'thumb' );
        if ( substr( $baseUrl, 0, 1 ) === '/' ) {
                $basePath = $baseUrl;
        } else {
                $basePath = parse_url( $baseUrl, PHP_URL_PATH );
        }
        $relPath = WebRequest::getRequestPathSuffix( $basePath );

        $params = wfExtractThumbRequestInfo( $relPath ); // basic wiki URL param extracting
        if ( $params == null ) {
                wfThumbError( 400, 'The specified thumbnail parameters are not recognized.' );
                return;
        }

        wfStreamThumb( $params ); // stream the thumbnail
}

/**
 * Stream a thumbnail specified by parameters
 *
 * @param array $params List of thumbnailing parameters. In addition to parameters
 *  passed to the MediaHandler, this may also includes the keys:
 *   f (for filename), archived (if archived file), temp (if temp file),
 *   w (alias for width), p (alias for page), r (ignored; historical),
 *   rel404 (path for render on 404 to verify hash path correct),
 *   thumbName (thumbnail name to potentially extract more parameters from
 *   e.g. 'lossy-page1-120px-Foo.tiff' would add page, lossy and width
 *   to the parameters)
 * @return void
 */
function wfStreamThumb( array $params ) {
        global $wgVaryOnXFP;
        $permissionManager = MediaWikiServices::getInstance()->getPermissionManager();

        $headers = []; // HTTP headers to send

        $fileName = $params['f'] ?? '';

        // Backwards compatibility parameters
        if ( isset( $params['w'] ) ) {
                $params['width'] = $params['w'];
                unset( $params['w'] );
        }
        if ( isset( $params['width'] ) && substr( $params['width'], -2 ) == 'px' ) {
                // strip the px (pixel) suffix, if found
                $params['width'] = substr( $params['width'], 0, -2 );
        }
        if ( isset( $params['p'] ) ) {
                $params['page'] = $params['p'];
        }

        // Is this a thumb of an archived file?
        $isOld = ( isset( $params['archived'] ) && $params['archived'] );
        unset( $params['archived'] ); // handlers don't care

        // Is this a thumb of a temp file?
        $isTemp = ( isset( $params['temp'] ) && $params['temp'] );
        unset( $params['temp'] ); // handlers don't care

        // Some basic input validation
        $fileName = strtr( $fileName, '\\/', '__' );
        $localRepo = MediaWikiServices::getInstance()->getRepoGroup()->getLocalRepo();

        // Actually fetch the image. Method depends on whether it is archived or not.
        if ( $isTemp ) {
                $repo = $localRepo->getTempRepo();
                $img = new UnregisteredLocalFile( null, $repo,
                        # Temp files are hashed based on the name without the timestamp.
                        # The thumbnails will be hashed based on the entire name however.
                        # @todo fix this convention to actually be reasonable.
                        $repo->getZonePath( 'public' ) . '/' . $repo->getTempHashPath( $fileName ) . $fileName
                );
        } elseif ( $isOld ) {
                // Format is <timestamp>!<name>
                $bits = explode( '!', $fileName, 2 );
                if ( count( $bits ) != 2 ) {
                        wfThumbError( 404, wfMessage( 'badtitletext' )->parse() );
                        return;
                }
                $title = Title::makeTitleSafe( NS_FILE, $bits[1] );
                if ( !$title ) {
                        wfThumbError( 404, wfMessage( 'badtitletext' )->parse() );
                        return;
                }
                $img = $localRepo->newFromArchiveName( $title, $fileName );
        } else {
                $img = $localRepo->newFile( $fileName );
        }

        // Check the source file title
        if ( !$img ) {
                wfThumbError( 404, wfMessage( 'badtitletext' )->parse() );
                return;
        }

        // Check permissions if there are read restrictions
        $varyHeader = [];
        if ( !in_array( 'read', $permissionManager->getGroupPermissions( [ '*' ] ), true ) ) {
                $user = RequestContext::getMain()->getUser();
                $imgTitle = $img->getTitle();

                if ( !$imgTitle || !$permissionManager->userCan( 'read', $user, $imgTitle ) ) {
                        wfThumbError( 403, 'Access denied. You do not have permission to access ' .
                                'the source file.' );
                        return;
                }
                $headers[] = 'Cache-Control: private';
                $varyHeader[] = 'Cookie';
        }

        // Check if the file is hidden
        if ( $img->isDeleted( File::DELETED_FILE ) ) {
                wfThumbErrorText( 404, "The source file '$fileName' does not exist." );
                return;
        }

        // Do rendering parameters extraction from thumbnail name.
        if ( isset( $params['thumbName'] ) ) {
                $params = wfExtractThumbParams( $img, $params );
        }
        if ( $params == null ) {
                wfThumbError( 400, 'The specified thumbnail parameters are not recognized.' );
                return;
        }

        // Check the source file storage path
        if ( !$img->exists() ) {
                $redirectedLocation = false;
                if ( !$isTemp ) {
                        // Check for file redirect
                        // Since redirects are associated with pages, not versions of files,
                        // we look for the most current version to see if its a redirect.
                        $possRedirFile = $localRepo->findFile( $img->getName() );
                        if ( $possRedirFile && $possRedirFile->getRedirected() !== null ) {
                                $redirTarget = $possRedirFile->getName();
                                $targetFile = $localRepo->newFile( Title::makeTitleSafe( NS_FILE, $redirTarget ) );
                                if ( $targetFile->exists() ) {
                                        $newThumbName = $targetFile->thumbName( $params );
                                        if ( $isOld ) {
                                                /** @var array $bits */
                                                $newThumbUrl = $targetFile->getArchiveThumbUrl(
                                                        $bits[0] . '!' . $targetFile->getName(), $newThumbName );
                                        } else {
                                                $newThumbUrl = $targetFile->getThumbUrl( $newThumbName );
                                        }
                                        $redirectedLocation = wfExpandUrl( $newThumbUrl, PROTO_CURRENT );
                                }
                        }
                }

                if ( $redirectedLocation ) {
                        // File has been moved. Give redirect.
                        $response = RequestContext::getMain()->getRequest()->response();
                        $response->statusHeader( 302 );
                        $response->header( 'Location: ' . $redirectedLocation );
                        $response->header( 'Expires: ' .
                                gmdate( 'D, d M Y H:i:s', time() + 12 * 3600 ) . ' GMT' );
                        if ( $wgVaryOnXFP ) {
                                $varyHeader[] = 'X-Forwarded-Proto';
                        }
                        if ( count( $varyHeader ) ) {
                                $response->header( 'Vary: ' . implode( ', ', $varyHeader ) );
                        }
                        $response->header( 'Content-Length: 0' );
                        return;
                }

                // If its not a redirect that has a target as a local file, give 404.
                wfThumbErrorText( 404, "The source file '$fileName' does not exist." );
                return;
        } elseif ( $img->getPath() === false ) {
                wfThumbErrorText( 400, "The source file '$fileName' is not locally accessible." );
                return;
        }

        // Check IMS against the source file
        // This means that clients can keep a cached copy even after it has been deleted on the server
        if ( !empty( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ) {
                // Fix IE brokenness
                $imsString = preg_replace( '/;.*$/', '', $_SERVER["HTTP_IF_MODIFIED_SINCE"] );
                // Calculate time
                Wikimedia\suppressWarnings();
                $imsUnix = strtotime( $imsString );
                Wikimedia\restoreWarnings();
                if ( wfTimestamp( TS_UNIX, $img->getTimestamp() ) <= $imsUnix ) {
                        HttpStatus::header( 304 );
                        return;
                }
        }

        $rel404 = $params['rel404'] ?? null;
        unset( $params['r'] ); // ignore 'r' because we unconditionally pass File::RENDER
        unset( $params['f'] ); // We're done with 'f' parameter.
        unset( $params['rel404'] ); // moved to $rel404

        // Get the normalized thumbnail name from the parameters...
        try {
                $thumbName = $img->thumbName( $params );
                if ( !strlen( $thumbName ) ) { // invalid params?
                        throw new MediaTransformInvalidParametersException(
                                'Empty return from File::thumbName'
                        );
                }
                $thumbName2 = $img->thumbName( $params, File::THUMB_FULL_NAME ); // b/c; "long" style
        } catch ( MediaTransformInvalidParametersException $e ) {
                wfThumbError(
                        400,
                        'The specified thumbnail parameters are not valid: ' . $e->getMessage()
                );
                return;
        } catch ( MWException $e ) {
                wfThumbError( 500, $e->getHTML(), 'Exception caught while extracting thumb name',
                        [ 'exception' => $e ] );
                return;
        }

        // For 404 handled thumbnails, we only use the base name of the URI
        // for the thumb params and the parent directory for the source file name.
        // Check that the zone relative path matches up so CDN caches won't pick
        // up thumbs that would not be purged on source file deletion (T36231).
        if ( $rel404 !== null ) { // thumbnail was handled via 404
                if ( rawurldecode( $rel404 ) === $img->getThumbRel( $thumbName ) ) {
                        // Request for the canonical thumbnail name
                } elseif ( rawurldecode( $rel404 ) === $img->getThumbRel( $thumbName2 ) ) {
                        // Request for the "long" thumbnail name; redirect to canonical name
                        $response = RequestContext::getMain()->getRequest()->response();
                        $response->statusHeader( 301 );
                        $response->header( 'Location: ' .
                                wfExpandUrl( $img->getThumbUrl( $thumbName ), PROTO_CURRENT ) );
                        $response->header( 'Expires: ' .
                                gmdate( 'D, d M Y H:i:s', time() + 7 * 86400 ) . ' GMT' );
                        if ( $wgVaryOnXFP ) {
                                $varyHeader[] = 'X-Forwarded-Proto';
                        }
                        if ( count( $varyHeader ) ) {
                                $response->header( 'Vary: ' . implode( ', ', $varyHeader ) );
                        }
                        return;
                } else {
                        wfThumbErrorText( 404, "The given path of the specified thumbnail is incorrect;
                                expected '" . $img->getThumbRel( $thumbName ) . "' but got '" .
                                rawurldecode( $rel404 ) . "'." );
                        return;
                }
        }

        $dispositionType = isset( $params['download'] ) ? 'attachment' : 'inline';

        // Suggest a good name for users downloading this thumbnail
        $headers[] =
                "Content-Disposition: {$img->getThumbDisposition( $thumbName, $dispositionType )}";

        if ( count( $varyHeader ) ) {
                $headers[] = 'Vary: ' . implode( ', ', $varyHeader );
        }

        // Stream the file if it exists already...
        $thumbPath = $img->getThumbPath( $thumbName );
        if ( $img->getRepo()->fileExists( $thumbPath ) ) {
                $starttime = microtime( true );
                $status = $img->getRepo()->streamFileWithStatus( $thumbPath, $headers );
                $streamtime = microtime( true ) - $starttime;

                if ( $status->isOK() ) {
                        MediaWikiServices::getInstance()->getStatsdDataFactory()->timing(
                                'media.thumbnail.stream', $streamtime
                        );
                } else {
                        wfThumbError( 500, 'Could not stream the file', null, [ 'file' => $thumbName,
                                'path' => $thumbPath, 'error' => $status->getWikiText( false, false, 'en' ) ] );
                }
                return;
        }

        $user = RequestContext::getMain()->getUser();
        if ( !wfThumbIsStandard( $img, $params ) && $user->pingLimiter( 'renderfile-nonstandard' ) ) {
                wfThumbError( 429, wfMessage( 'actionthrottledtext' )->parse() );
                return;
        } elseif ( $user->pingLimiter( 'renderfile' ) ) {
                wfThumbError( 429, wfMessage( 'actionthrottledtext' )->parse() );
                return;
        }

        $thumbProxyUrl = $img->getRepo()->getThumbProxyUrl();

        if ( strlen( $thumbProxyUrl ) ) {
                wfProxyThumbnailRequest( $img, $thumbName );
                // No local fallback when in proxy mode
                return;
        } else {
                // Generate the thumbnail locally
                list( $thumb, $errorMsg ) = wfGenerateThumbnail( $img, $params, $thumbName, $thumbPath );
        }

        /** @var MediaTransformOutput|MediaTransformError|bool $thumb */

        // Check for thumbnail generation errors...
        $msg = wfMessage( 'thumbnail_error' );
        $errorCode = 500;

        if ( !$thumb ) {
                $errorMsg = $errorMsg ?: $msg->rawParams( 'File::transform() returned false' )->escaped();
                if ( $errorMsg instanceof MessageSpecifier &&
                        $errorMsg->getKey() === 'thumbnail_image-failure-limit'
                ) {
                        $errorCode = 429;
                }
        } elseif ( $thumb->isError() ) {
                $errorMsg = $thumb->getHtmlMsg();
                $errorCode = $thumb->getHttpStatusCode();
        } elseif ( !$thumb->hasFile() ) {
                $errorMsg = $msg->rawParams( 'No path supplied in thumbnail object' )->escaped();
        } elseif ( $thumb->fileIsSource() ) {
                $errorMsg = $msg
                        ->rawParams( 'Image was not scaled, is the requested width bigger than the source?' )
                        ->escaped();
                $errorCode = 400;
        }

        if ( $errorMsg !== false ) {
                wfThumbError( $errorCode, $errorMsg, null, [ 'file' => $thumbName, 'path' => $thumbPath ] );
        } else {
                // Stream the file if there were no errors
                $status = $thumb->streamFileWithStatus( $headers );
                if ( !$status->isOK() ) {
                        wfThumbError( 500, 'Could not stream the file', null, [
                                'file' => $thumbName, 'path' => $thumbPath,
                                'error' => $status->getWikiText( false, false, 'en' ) ] );
                }
        }
}

/**
 * Proxies thumbnail request to a service that handles thumbnailing
 *
 * @param File $img
 * @param string $thumbName
 */
function wfProxyThumbnailRequest( $img, $thumbName ) {
        $thumbProxyUrl = $img->getRepo()->getThumbProxyUrl();

        // Instead of generating the thumbnail ourselves, we proxy the request to another service
        $thumbProxiedUrl = $thumbProxyUrl . $img->getThumbRel( $thumbName );

        $req = MWHttpRequest::factory( $thumbProxiedUrl );
        $secret = $img->getRepo()->getThumbProxySecret();

        // Pass a secret key shared with the proxied service if any
        if ( strlen( $secret ) ) {
                $req->setHeader( 'X-Swift-Secret', $secret );
        }

        // Send request to proxied service
        $status = $req->execute();

        MediaWiki\HeaderCallback::warnIfHeadersSent();

        // Simply serve the response from the proxied service as-is
        header( 'HTTP/1.1 ' . $req->getStatus() );

        $headers = $req->getResponseHeaders();

        foreach ( $headers as $key => $values ) {
                foreach ( $values as $value ) {
                        header( $key . ': ' . $value, false );
                }
        }

        echo $req->getContent();
}

/**
 * Actually try to generate a new thumbnail
 *
 * @param File $file
 * @param array $params
 * @param string $thumbName
 * @param string $thumbPath
 * @return array (MediaTransformOutput|bool, string|bool error message HTML)
 */
function wfGenerateThumbnail( File $file, array $params, $thumbName, $thumbPath ) {
        global $wgAttemptFailureEpoch;

        $cache = ObjectCache::getLocalClusterInstance();
        $key = $cache->makeKey(
                'attempt-failures',
                $wgAttemptFailureEpoch,
                $file->getRepo()->getName(),
                $file->getSha1(),
                md5( $thumbName )
        );

        // Check if this file keeps failing to render
        if ( $cache->get( $key ) >= 4 ) {
                return [ false, wfMessage( 'thumbnail_image-failure-limit', 4 ) ];
        }

        $done = false;
        // Record failures on PHP fatals in addition to caching exceptions
        register_shutdown_function( function () use ( $cache, &$done, $key ) {
                if ( !$done ) { // transform() gave a fatal
                        // Randomize TTL to reduce stampedes
                        $cache->incrWithInit( $key, $cache::TTL_HOUR + mt_rand( 0, 300 ) );
                }
        } );

        $thumb = false;
        $errorHtml = false;

        // guard thumbnail rendering with PoolCounter to avoid stampedes
        // expensive files use a separate PoolCounter config so it is possible
        // to set up a global limit on them
        if ( $file->isExpensiveToThumbnail() ) {
                $poolCounterType = 'FileRenderExpensive';
        } else {
                $poolCounterType = 'FileRender';
        }

        // Thumbnail isn't already there, so create the new thumbnail...
        try {
                $work = new PoolCounterWorkViaCallback( $poolCounterType, sha1( $file->getName() ),
                        [
                                'doWork' => function () use ( $file, $params ) {
                                        return $file->transform( $params, File::RENDER_NOW );
                                },
                                'doCachedWork' => function () use ( $file, $params, $thumbPath ) {
                                        // If the worker that finished made this thumbnail then use it.
                                        // Otherwise, it probably made a different thumbnail for this file.
                                        return $file->getRepo()->fileExists( $thumbPath )
                                                ? $file->transform( $params, File::RENDER_NOW )
                                                : false; // retry once more in exclusive mode
                                },
                                'error' => function ( Status $status ) {
                                        return wfMessage( 'generic-pool-error' )->parse() . '<hr>' . $status->getHTML();
                                }
                        ]
                );
                $result = $work->execute();
                if ( $result instanceof MediaTransformOutput ) {
                        $thumb = $result;
                } elseif ( is_string( $result ) ) { // error
                        $errorHtml = $result;
                }
        } catch ( Exception $e ) {
                // Tried to select a page on a non-paged file?
        }

        /** @noinspection PhpUnusedLocalVariableInspection */
        $done = true; // no PHP fatal occurred

        if ( !$thumb || $thumb->isError() ) {
                // Randomize TTL to reduce stampedes
                $cache->incrWithInit( $key, $cache::TTL_HOUR + mt_rand( 0, 300 ) );
        }

        return [ $thumb, $errorHtml ];
}

/**
 * Convert pathinfo type parameter, into normal request parameters
 *
 * So for example, if the request was redirected from
 * /w/images/thumb/a/ab/Foo.png/120px-Foo.png. The $thumbRel parameter
 * of this function would be set to "a/ab/Foo.png/120px-Foo.png".
 * This method is responsible for turning that into an array
 * with the following keys:
 *  * f => the filename (Foo.png)
 *  * rel404 => the whole thing (a/ab/Foo.png/120px-Foo.png)
 *  * archived => 1 (If the request is for an archived thumb)
 *  * temp => 1 (If the file is in the "temporary" zone)
 *  * thumbName => the thumbnail name, including parameters (120px-Foo.png)
 *
 * Transform specific parameters are set later via wfExtractThumbParams().
 *
 * @param string $thumbRel Thumbnail path relative to the thumb zone
 * @return array|null Associative params array or null
 */
function wfExtractThumbRequestInfo( $thumbRel ) {
        $repo = MediaWikiServices::getInstance()->getRepoGroup()->getLocalRepo();

        $hashDirReg = $subdirReg = '';
        $hashLevels = $repo->getHashLevels();
        for ( $i = 0; $i < $hashLevels; $i++ ) {
                $subdirReg .= '[0-9a-f]';
                $hashDirReg .= "$subdirReg/";
        }

        // Check if this is a thumbnail of an original in the local file repo
        if ( preg_match( "!^((archive/)?$hashDirReg([^/]*)/([^/]*))$!", $thumbRel, $m ) ) {
                list( /*all*/, $rel, $archOrTemp, $filename, $thumbname ) = $m;
        // Check if this is a thumbnail of an temp file in the local file repo
        } elseif ( preg_match( "!^(temp/)($hashDirReg([^/]*)/([^/]*))$!", $thumbRel, $m ) ) {
                list( /*all*/, $archOrTemp, $rel, $filename, $thumbname ) = $m;
        } else {
                return null; // not a valid looking thumbnail request
        }

        $params = [ 'f' => $filename, 'rel404' => $rel ];
        if ( $archOrTemp === 'archive/' ) {
                $params['archived'] = 1;
        } elseif ( $archOrTemp === 'temp/' ) {
                $params['temp'] = 1;
        }

        $params['thumbName'] = $thumbname;
        return $params;
}

/**
 * Convert a thumbnail name (122px-foo.png) to parameters, using
 * file handler.
 *
 * @param File $file File object for file in question
 * @param array $params Array of parameters so far
 * @return array Parameters array with more parameters
 */
function wfExtractThumbParams( $file, $params ) {
        if ( !isset( $params['thumbName'] ) ) {
                throw new InvalidArgumentException( "No thumbnail name passed to wfExtractThumbParams" );
        }

        $thumbname = $params['thumbName'];
        unset( $params['thumbName'] );

        // FIXME: Files in the temp zone don't set a MIME type, which means
        // they don't have a handler. Which means we can't parse the param
        // string. However, not a big issue as what good is a param string
        // if you have no handler to make use of the param string and
        // actually generate the thumbnail.
        $handler = $file->getHandler();

        // Based on UploadStash::parseKey
        $fileNamePos = strrpos( $thumbname, $params['f'] );
        if ( $fileNamePos === false ) {
                // Maybe using a short filename? (see FileRepo::nameForThumb)
                $fileNamePos = strrpos( $thumbname, 'thumbnail' );
        }

        if ( $handler && $fileNamePos !== false ) {
                $paramString = substr( $thumbname, 0, $fileNamePos - 1 );
                $extraParams = $handler->parseParamString( $paramString );
                if ( $extraParams !== false ) {
                        return $params + $extraParams;
                }
        }

        // As a last ditch fallback, use the traditional common parameters
        if ( preg_match( '!^(page(\d*)-)*(\d*)px-[^/]*$!', $thumbname, $matches ) ) {
                list( /* all */, /* pagefull */, $pagenum, $size ) = $matches;
                $params['width'] = $size;
                if ( $pagenum ) {
                        $params['page'] = $pagenum;
                }
                return $params; // valid thumbnail URL
        }
        return null;
}

/**
 * Output a thumbnail generation error message
 *
 * @param int $status
 * @param string $msgText Plain text (will be html escaped)
 * @return void
 */
function wfThumbErrorText( $status, $msgText ) {
        wfThumbError( $status, htmlspecialchars( $msgText, ENT_NOQUOTES ) );
}

/**
 * Output a thumbnail generation error message
 *
 * @param int $status
 * @param string $msgHtml HTML
 * @param string|null $msgText Short error description, for internal logging. Defaults to $msgHtml.
 *   Only used for HTTP 500 errors.
 * @param array $context Error context, for internal logging. Only used for HTTP 500 errors.
 * @return void
 */
function wfThumbError( $status, $msgHtml, $msgText = null, $context = [] ) {
        global $wgShowHostnames;

        MediaWiki\HeaderCallback::warnIfHeadersSent();

        if ( headers_sent() ) {
                LoggerFactory::getInstance( 'thumbnail' )->error(
                        'Error after output had been started. Output may be corrupt or truncated. ' .
                        'Original error: ' . ( $msgText ?: $msgHtml ) . " (Status $status)",
                        $context
                );
                return;
        }

        header( 'Cache-Control: no-cache' );
        header( 'Content-Type: text/html; charset=utf-8' );
        if ( $status == 400 || $status == 404 || $status == 429 ) {
                HttpStatus::header( $status );
        } elseif ( $status == 403 ) {
                HttpStatus::header( 403 );
                header( 'Vary: Cookie' );
        } else {
                LoggerFactory::getInstance( 'thumbnail' )->error( $msgText ?: $msgHtml, $context );
                HttpStatus::header( 500 );
        }
        if ( $wgShowHostnames ) {
                header( 'X-MW-Thumbnail-Renderer: ' . wfHostname() );
                $url = htmlspecialchars(
                        $_SERVER['REQUEST_URI'] ?? '',
                        ENT_NOQUOTES
                );
                $hostname = htmlspecialchars( wfHostname(), ENT_NOQUOTES );
                $debug = "<!-- $url -->\n<!-- $hostname -->\n";
        } else {
                $debug = '';
        }
        $content = <<<EOT
<!DOCTYPE html>
<html><head>
<meta charset="UTF-8" />
<title>Error generating thumbnail</title>
</head>
<body>
<h1>Error generating thumbnail</h1>
<p>
$msgHtml
</p>
$debug
</body>
</html>

EOT;
        header( 'Content-Length: ' . strlen( $content ) );
        echo $content;
}