Never return broken notifications #409

Since notifications are stored in Redis, we can't expect relational
integrity: deleting a user will *not* delete notifications that
mention it.

But if we return notifications with missing bits (a `follow` without a
`user`, for example), the frontend will get very confused and throw an
exception while trying to render them.

This change makes sure we never expose those broken notifications. For
uniformity, I've applied the same logic to notes and roles mentioned
in notifications, even if nobody reported breakage in those cases.

Tested by creating a few types of notifications with a `notifierId`,
then deleting their user.

1 files changed, 59 insertions, 16 deletions

diff --git a/packages/backend/src/core/entities/NotificationEntityService.ts b/packages/backend/src/core/entities/NotificationEntityService.ts
index a620acc2dc..a196871f8a 100644
--- a/packages/backend/src/core/entities/NotificationEntityService.ts
+++ b/packages/backend/src/core/entities/NotificationEntityService.ts
@@ -64,21 +64,38 @@ export class NotificationEntityService implements OnModuleInit {
 			packedNotes: Map<MiNote['id'], Packed<'Note'>>;
 			packedUsers: Map<MiUser['id'], Packed<'UserLite'>>;
 		},
-	): Promise<Packed<'Notification'>> {
+	): Promise<Packed<'Notification'> | null> {
 		const notification = src;
-		const noteIfNeed = NOTE_REQUIRED_NOTIFICATION_TYPES.has(notification.type) && 'noteId' in notification ? (
+		const needsNote = NOTE_REQUIRED_NOTIFICATION_TYPES.has(notification.type) && 'noteId' in notification;
+		const noteIfNeed = needsNote ? (
 			hint?.packedNotes != null
 				? hint.packedNotes.get(notification.noteId)
 				: this.noteEntityService.pack(notification.noteId, { id: meId }, {
 					detail: true,
 				})
 		) : undefined;
-		const userIfNeed = 'notifierId' in notification ? (
+		// if the note has been deleted, don't show this notification
+		if (needsNote && !noteIfNeed) {
+			return null;
+		}
+
+		const needsUser = 'notifierId' in notification;
+		const userIfNeed = needsUser ? (
 			hint?.packedUsers != null
 				? hint.packedUsers.get(notification.notifierId)
 				: this.userEntityService.pack(notification.notifierId, { id: meId })
 		) : undefined;
-		const role = notification.type === 'roleAssigned' ? await this.roleEntityService.pack(notification.roleId) : undefined;
+		// if the user has been deleted, don't show this notification
+		if (needsUser && !userIfNeed) {
+			return null;
+		}
+
+		const needsRole = notification.type === 'roleAssigned';
+		const role = needsRole ? await this.roleEntityService.pack(notification.roleId) : undefined;
+		// if the role has been deleted, don't show this notification
+		if (needsRole && !role) {
+			return null;
+		}
 
 		return await awaitAll({
 			id: notification.id,
@@ -141,10 +158,10 @@ export class NotificationEntityService implements OnModuleInit {
 			validNotifications = validNotifications.filter(x => (x.type !== 'receiveFollowRequest') || reqs.some(r => r.followerId === x.notifierId));
 		}
 
-		return await Promise.all(validNotifications.map(x => this.pack(x, meId, {}, {
+		return (await Promise.all(validNotifications.map(x => this.pack(x, meId, {}, {
 			packedNotes,
 			packedUsers,
-		})));
+		})))).filter(n => n);
 	}
 
 	@bindThis
@@ -159,23 +176,34 @@ export class NotificationEntityService implements OnModuleInit {
 			packedNotes: Map<MiNote['id'], Packed<'Note'>>;
 			packedUsers: Map<MiUser['id'], Packed<'UserLite'>>;
 		},
-	): Promise<Packed<'Notification'>> {
+	): Promise<Packed<'Notification'> | null> {
 		const notification = src;
-		const noteIfNeed = NOTE_REQUIRED_GROUPED_NOTIFICATION_TYPES.has(notification.type) && 'noteId' in notification ? (
+		const needsNote = NOTE_REQUIRED_GROUPED_NOTIFICATION_TYPES.has(notification.type) && 'noteId' in notification;
+		const noteIfNeed = needsNote ? (
 			hint?.packedNotes != null
 				? hint.packedNotes.get(notification.noteId)
 				: this.noteEntityService.pack(notification.noteId, { id: meId }, {
 					detail: true,
 				})
 		) : undefined;
-		const userIfNeed = 'notifierId' in notification ? (
+		// if the note has been deleted, don't show this notification
+		if (needsNote && !noteIfNeed) {
+			return null;
+		}
+
+		const needsUser = 'notifierId' in notification;
+		const userIfNeed = needsUser ? (
 			hint?.packedUsers != null
 				? hint.packedUsers.get(notification.notifierId)
 				: this.userEntityService.pack(notification.notifierId, { id: meId })
 		) : undefined;
+		// if the user has been deleted, don't show this notification
+		if (needsUser && !userIfNeed) {
+			return null;
+		}
 
 		if (notification.type === 'reaction:grouped') {
-			const reactions = await Promise.all(notification.reactions.map(async reaction => {
+			const reactions = (await Promise.all(notification.reactions.map(async reaction => {
 				const user = hint?.packedUsers != null
 					? hint.packedUsers.get(reaction.userId)!
 					: await this.userEntityService.pack(reaction.userId, { id: meId });
@@ -183,7 +211,12 @@ export class NotificationEntityService implements OnModuleInit {
 					user,
 					reaction: reaction.reaction,
 				};
-			}));
+			}))).filter(r => r.user);
+			// if all users have been deleted, don't show this notification
+			if (!reactions.length) {
+				return null;
+			}
+
 			return await awaitAll({
 				id: notification.id,
 				createdAt: new Date(notification.createdAt).toISOString(),
@@ -192,14 +225,19 @@ export class NotificationEntityService implements OnModuleInit {
 				reactions,
 			});
 		} else if (notification.type === 'renote:grouped') {
-			const users = await Promise.all(notification.userIds.map(userId => {
+			const users = (await Promise.all(notification.userIds.map(userId => {
 				const packedUser = hint?.packedUsers != null ? hint.packedUsers.get(userId) : null;
 				if (packedUser) {
 					return packedUser;
 				}
 
 				return this.userEntityService.pack(userId, { id: meId });
-			}));
+			}))).filter(u => u);
+			// if all users have been deleted, don't show this notification
+			if (!users.length) {
+				return null;
+			}
+
 			return await awaitAll({
 				id: notification.id,
 				createdAt: new Date(notification.createdAt).toISOString(),
@@ -209,7 +247,12 @@ export class NotificationEntityService implements OnModuleInit {
 			});
 		}
 
-		const role = notification.type === 'roleAssigned' ? await this.roleEntityService.pack(notification.roleId) : undefined;
+		const needsRole = notification.type === 'roleAssigned';
+		const role = needsRole ? await this.roleEntityService.pack(notification.roleId) : undefined;
+		// if the role has been deleted, don't show this notification
+		if (needsRole && !role) {
+			return null;
+		}
 
 		return await awaitAll({
 			id: notification.id,
@@ -277,9 +320,9 @@ export class NotificationEntityService implements OnModuleInit {
 			validNotifications = validNotifications.filter(x => (x.type !== 'receiveFollowRequest') || reqs.some(r => r.followerId === x.notifierId));
 		}
 
-		return await Promise.all(validNotifications.map(x => this.packGrouped(x, meId, {}, {
+		return (await Promise.all(validNotifications.map(x => this.packGrouped(x, meId, {}, {
 			packedNotes,
 			packedUsers,
-		})));
+		})))).filter(n => n);
 	}
 }