Pimcore\Controller\Plugin\Thumbnail::routeStartup PHP Method

    public function routeStartup(\Zend_Controller_Request_Abstract $request)
    {
        // this is a filter which checks for common used files (by browser, crawlers, ...) and prevent the default
        // error page, because this is more resource-intensive than exiting right here
        if (preg_match("@/image-thumbnails(.*)?/([0-9]+)/thumb__([a-zA-Z0-9_\\-]+)([^\\@]+)(\\@[0-9.]+x)?\\.([a-zA-Z]{2,5})@", rawurldecode($request->getPathInfo()), $matches)) {
            $assetId = $matches[2];
            $thumbnailName = $matches[3];
            if ($asset = Asset::getById($assetId)) {
                try {
                    $page = 1;
                    // default
                    $thumbnailFile = null;
                    $thumbnailConfig = null;
                    //get thumbnail for e.g. pdf page thumb__document_pdfPage-5
                    if (preg_match("|document_(.*)\\-(\\d+)\$|", $thumbnailName, $matchesThumbs)) {
                        $thumbnailName = $matchesThumbs[1];
                        $page = (int) $matchesThumbs[2];
                    }
                    // just check if the thumbnail exists -> throws exception otherwise
                    $thumbnailConfig = Asset\Image\Thumbnail\Config::getByName($thumbnailName);
                    if (!$thumbnailConfig) {
                        // check if there's an item in the TmpStore
                        $deferredConfigId = "thumb_" . $assetId . "__" . md5($matches[0]);
                        if ($thumbnailConfigItem = TmpStore::get($deferredConfigId)) {
                            $thumbnailConfig = $thumbnailConfigItem->getData();
                            TmpStore::delete($deferredConfigId);
                            if (!$thumbnailConfig instanceof Asset\Image\Thumbnail\Config) {
                                throw new \Exception("Deferred thumbnail config file doesn't contain a valid \\Asset\\Image\\Thumbnail\\Config object");
                            }
                        }
                    }
                    if (!$thumbnailConfig) {
                        throw new \Exception("Thumbnail '" . $thumbnailName . "' file doesn't exists");
                    }
                    if ($asset instanceof Asset\Document) {
                        $thumbnailConfig->setName(preg_replace("/\\-[\\d]+/", "", $thumbnailConfig->getName()));
                        $thumbnailConfig->setName(str_replace("document_", "", $thumbnailConfig->getName()));
                        $thumbnailFile = $asset->getImageThumbnail($thumbnailConfig, $page)->getFileSystemPath();
                    } elseif ($asset instanceof Asset\Image) {
                        //check if high res image is called
                        if (array_key_exists(5, $matches)) {
                            $highResFactor = (double) str_replace(["@", "x"], "", $matches[5]);
                            $thumbnailConfig->setHighResolution($highResFactor);
                        }
                        // check if a media query thumbnail was requested
                        if (preg_match("#~\\-~([\\d]+w)#", $matches[4], $mediaQueryResult)) {
                            $thumbnailConfig->selectMedia($mediaQueryResult[1]);
                        }
                        $thumbnailFile = $asset->getThumbnail($thumbnailConfig)->getFileSystemPath();
                    }
                    if ($thumbnailFile && file_exists($thumbnailFile)) {
                        // set appropriate caching headers
                        // see also: https://github.com/pimcore/pimcore/blob/1931860f0aea27de57e79313b2eb212dcf69ef13/.htaccess#L86-L86
                        $lifetime = 86400 * 7;
                        // 1 week lifetime, same as direct delivery in .htaccess
                        header("Cache-Control: public, max-age=" . $lifetime);
                        header("Expires: " . date("D, d M Y H:i:s T", time() + $lifetime));
                        $fileExtension = \Pimcore\File::getFileExtension($thumbnailFile);
                        if (in_array($fileExtension, ["gif", "jpeg", "jpeg", "png", "pjpeg"])) {
                            header("Content-Type: image/" . $fileExtension, true);
                        } else {
                            header("Content-Type: " . $asset->getMimetype(), true);
                        }
                        header("Content-Length: " . filesize($thumbnailFile), true);
                        while (@ob_end_flush()) {
                        }
                        flush();
                        readfile($thumbnailFile);
                        exit;
                    }
                } catch (\Exception $e) {
                    // nothing to do
                    Logger::error("Thumbnail with name '" . $thumbnailName . "' doesn't exist");
                }
            }
        }
    }