2 files changed, 17 insertions, 12 deletions

diff --git a/apps/files_sharing/lib/Controller/PublicPreviewController.php b/apps/files_sharing/lib/Controller/PublicPreviewController.php
index 9678aa67888..da71aca904c 100644
--- a/apps/files_sharing/lib/Controller/PublicPreviewController.php
+++ b/apps/files_sharing/lib/Controller/PublicPreviewController.php
@@ -78,6 +78,8 @@ class PublicPreviewController extends PublicShareController {
 		int $y = 32,
 		$a = false,
 	) {
+		$cacheForSeconds = 60 * 60 * 24; // 1 day
+
 		if ($token === '' || $x === 0 || $y === 0) {
 			return new DataResponse([], Http::STATUS_BAD_REQUEST);
 		}
@@ -93,7 +95,17 @@ class PublicPreviewController extends PublicShareController {
 		}
 
 		$attributes = $share->getAttributes();
-		if ($attributes !== null && $attributes->getAttribute('permissions', 'download') === false) {
+		// Only explicitly set to false will forbid the download!
+		$downloadForbidden = $attributes?->getAttribute('permissions', 'download') === false;
+		// Is this header is set it means our UI is doing a preview for no-download shares
+		// we check a header so we at least prevent people from using the link directly (obfuscation)
+		$isPublicPreview = $this->request->getHeader('X-NC-Preview') === 'true';
+
+		if ($isPublicPreview && $downloadForbidden) {
+			// Only cache for 15 minutes on public preview requests to quickly remove from cache
+			$cacheForSeconds = 15 * 60;
+		} elseif ($downloadForbidden) {
+			// This is not a public share preview so we only allow a preview if download permissions are granted
 			return new DataResponse([], Http::STATUS_FORBIDDEN);
 		}
 
@@ -107,7 +119,7 @@ class PublicPreviewController extends PublicShareController {
 
 			$f = $this->previewManager->getPreview($file, $x, $y, !$a);
 			$response = new FileDisplayResponse($f, Http::STATUS_OK, ['Content-Type' => $f->getMimeType()]);
-			$response->cacheFor(3600 * 24);
+			$response->cacheFor($cacheForSeconds);
 			return $response;
 		} catch (NotFoundException $e) {
 			return new DataResponse([], Http::STATUS_NOT_FOUND);
diff --git a/apps/files_sharing/lib/ViewOnly.php b/apps/files_sharing/lib/ViewOnly.php
index 9cd18f968f6..2204d26388b 100644
--- a/apps/files_sharing/lib/ViewOnly.php
+++ b/apps/files_sharing/lib/ViewOnly.php
@@ -89,17 +89,10 @@ class ViewOnly {
 		/** @var SharedStorage $storage */
 		$share = $storage->getShare();
 
-		$canDownload = true;
-
-		// Check if read-only and on whether permission can download is both set and disabled.
+		// Check whether download-permission was denied (granted if not set)
 		$attributes = $share->getAttributes();
-		if ($attributes !== null) {
-			$canDownload = $attributes->getAttribute('permissions', 'download');
-		}
+		$canDownload = $attributes?->getAttribute('permissions', 'download');
 
-		if ($canDownload !== null && !$canDownload) {
-			return false;
-		}
-		return true;
+		return $canDownload !== false;
 	}
 }