MM-38774 - partial fix for: Community running out of memory (#18445)

* prevent invalid images from entering generateMiniPreview in the future

* fixing err, err2, imgErr

* linting

* load actual pngs and gifs in tests

* consistent style

app/file.go

@@ -1118,28 +1118,38 @@ func (a *App) generatePreviewImage(img image.Image, previewPath string) {
 // will save fileinfo with the preview added
 func (a *App) generateMiniPreview(fi *model.FileInfo) {
 	if fi.IsImage() && fi.MiniPreview == nil {
-		file, err := a.FileReader(fi.Path)
-		if err != nil {
-			mlog.Debug("error reading image file", mlog.Err(err))
+		file, appErr := a.FileReader(fi.Path)
+		if appErr != nil {
+			mlog.Debug("error reading image file", mlog.Err(appErr))
 			return
 		}
 		defer file.Close()
-		img, release, imgErr := prepareImage(a.srv.imgDecoder, file)
-		if imgErr != nil {
-			mlog.Debug("generateMiniPreview: prepareImage failed", mlog.Err(imgErr),
+		img, release, err := prepareImage(a.srv.imgDecoder, file)
+		if err != nil {
+			mlog.Debug("generateMiniPreview: prepareImage failed", mlog.Err(err),
 				mlog.String("fileinfo_id", fi.Id), mlog.String("channel_id", fi.ChannelId),
 				mlog.String("creator_id", fi.CreatorId))
+
+			// Since this file is not a valid image (for whatever reason), prevent this fileInfo
+			// from entering generateMiniPreview in the future
+			fi.UpdateAt = model.GetMillis()
+			fi.MimeType = "invalid-" + fi.MimeType
+			if _, err = a.Srv().Store.FileInfo().Upsert(fi); err != nil {
+				mlog.Debug("Invalidating FileInfo failed", mlog.Err(err))
+			}
+
 			return
 		}
 		defer release()
-		if miniPreview, err := imaging.GenerateMiniPreviewImage(img,
+		var miniPreview []byte
+		if miniPreview, err = imaging.GenerateMiniPreviewImage(img,
 			miniPreviewImageWidth, miniPreviewImageHeight, jpegEncQuality); err != nil {
 			mlog.Info("Unable to generate mini preview image", mlog.Err(err))
 		} else {
 			fi.MiniPreview = &miniPreview
 		}
-		if _, appErr := a.Srv().Store.FileInfo().Upsert(fi); appErr != nil {
-			mlog.Debug("creating mini preview failed", mlog.Err(appErr))
+		if _, err = a.Srv().Store.FileInfo().Upsert(fi); err != nil {
+			mlog.Debug("creating mini preview failed", mlog.Err(err))
 		} else {
 			a.Srv().Store.FileInfo().InvalidateFileInfosForPostCache(fi.PostId, false)
 		}