No need to construct the image in memory

lib/Controller/Preview.php

@@ -87,9 +87,15 @@ private function getThumbnail($fileId, $square, $scale) {
 			);
 		if ($preview === null) {
 			$preview = $this->prepareEmptyThumbnail($file, $status);
+			return [$preview, $status];
 		}
 
-		return [$preview, $status];
+		$result = [
+			'preview' => $base64Encode ? base64_encode($preview->getContent()) : $preview->getContent(),
+			'mimetype' => $file->getMimeType()
+		];
+
+		return [$result, $status];
 	}
 
 	/**
@@ -156,7 +162,7 @@ private function getFile($fileId) {
 	 * @param bool $keepAspect
 	 * @param bool $base64Encode
 	 *
-	 * @return array<\OC_Image|string, int>
+	 * @return array<File|ISimpleFile, int>
 	 */
 	private function getPreviewData(
 		$file, $animatedPreview, $width, $height, $keepAspect, $base64Encode

lib/Controller/PreviewController.php

@@ -121,7 +121,7 @@ public function getThumbnails($ids, $square, $scale) {
 	 * @param int $width
 	 * @param int $height
 	 *
-	 * @return ImageResponse|Http\JSONResponse
+	 * @return Http\FileDisplayResponse|Http\JSONResponse
 	 */
 	public function getPreview($fileId, $width, $height) {
 		/** @type File $file */
@@ -135,9 +135,21 @@ public function getPreview($fileId, $width, $height) {
 				], $status
 			);
 		}
-		$preview['name'] = $file->getName();
 
-		return new ImageResponse($preview, $status);
+		$response = new Http\FileDisplayResponse($preview, Http::STATUS_OK, ['Content-Type' => $preview->getMimeType()]);
+
+		// Let cache this!
+		$response->addHeader('Pragma', 'public');
+
+		// Cache previews for 24H
+		$response->cacheFor(3600 * 24);
+		$expires = new \DateTime();
+		$expires->add(new \DateInterval('P1D'));
+		$response->addHeader('Expires', $expires->format(\DateTime::RFC2822));
+		$response->addHeader('Content-Disposition', 'attachment; filename*=UTF-8\'\'' . rawurlencode($file->getName()) . '; filename="'
+			. rawurlencode($file->getName()) . '"');
+		return $response;
+
 	}
 
 }

lib/Service/DownloadService.php

@@ -28,26 +28,16 @@ class DownloadService extends Service {
 	 * Downloads the requested file
 	 *
 	 * @param File $file
-	 * @param bool $base64Encode
 	 *
-	 * @return array|false
+	 * @return File
 	 * @throws NotFoundServiceException
 	 */
-	public function downloadFile($file, $base64Encode = false) {
+	public function downloadFile($file) {
 		try {
 			$this->logger->debug(
 				"[DownloadService] File to Download: {name}", ['name' => $file->getName()]
 			);
-			$download = [
-				'preview'  => $file->getContent(),
-				'mimetype' => $file->getMimeType()
-			];
-
-			if ($base64Encode) {
-				$download['preview'] = $this->encode($download['preview']);
-			}
-
-			return $download;
+			return $file;
 		} catch (\Exception $exception) {
 			throw new NotFoundServiceException('There was a problem accessing the file');
 		}

lib/Service/PreviewService.php

@@ -13,6 +13,7 @@
 namespace OCA\Gallery\Service;
 
 use OCP\Files\File;
+use OCP\Files\SimpleFS\ISimpleFile;
 use OCP\Image;
 use OCP\IPreview;
 use OCP\ILogger;
@@ -94,26 +95,14 @@ public function isPreviewRequired($file, $animatedPreview) {
 	 * @param int $maxX asked width for the preview
 	 * @param int $maxY asked height for the preview
 	 * @param bool $keepAspect
-	 * @param bool $base64Encode
 	 *
-	 * @return string|\OC_Image|string|false preview data
+	 * @return ISimpleFile preview
 	 * @throws InternalServerErrorServiceException
 	 */
-	public function createPreview(
-		$file, $maxX = 0, $maxY = 0, $keepAspect = true, $base64Encode = false
+	public function createPreview(File $file, $maxX = 0, $maxY = 0, $keepAspect = true
 	) {
 		try {
-			$preview = $this->previewManager->getPreview($file, $maxX, $maxY, !$keepAspect);
-			$img = new Image($preview->getContent());
-			$mimeType = $img->mimeType();
-			if ($img && $base64Encode) {
-				$img = $this->encode($img);
-			}
-
-			return [
-				'preview'  => $img,
-				'mimetype' => $mimeType
-			];
+			return $this->previewManager->getPreview($file, $maxX, $maxY, !$keepAspect);
 		} catch (\Exception $exception) {
 			throw new InternalServerErrorServiceException('Preview generation has failed');
 		}