regression: thread jump-to-reply pagination skips a page when Max Record Amount is set

apps/meteor/client/views/room/contextualBar/Threads/hooks/useThreadMessagesQuery.spec.ts

@@ -37,19 +37,21 @@ const newestPageIds = idsOf(allReplies.slice(TOTAL - PAGE_SIZE));
 
 type GetThreadMessagesParams = { tmid: string; offset?: number; count?: number; aroundId?: string; sort?: string };
 
-const setup = () => {
+const setup = ({ serverLimit = Infinity }: { serverLimit?: number } = {}) => {
 	const getThreadMessages = jest.fn(({ offset = 0, count = PAGE_SIZE, aroundId }: GetThreadMessagesParams) => {
+		const effectiveCount = Math.min(count, serverLimit);
+
 		if (aroundId) {
 			const index = allReplies.findIndex(({ _id }) => _id === aroundId);
-			const start = Math.max(0, index - Math.floor(count / 2));
+			const start = Math.max(0, index - Math.floor(effectiveCount / 2));
 
-			return { messages: allReplies.slice(start, start + count), count, offset: start, total: TOTAL };
+			return { messages: allReplies.slice(start, start + effectiveCount), count: effectiveCount, offset: start, total: TOTAL };
 		}
 
 		const end = TOTAL - offset;
-		const start = Math.max(0, end - count);
+		const start = Math.max(0, end - effectiveCount);
 
-		return { messages: allReplies.slice(start, end), count, offset, total: TOTAL };
+		return { messages: allReplies.slice(start, end), count: effectiveCount, offset, total: TOTAL };
 	});
 
 	const wrapper = mockAppRoot()
@@ -129,4 +131,55 @@ describe('useThreadMessagesQuery', () => {
 			expect(idsOf(result.current.data?.messages ?? [])).toEqual(newestPageIds);
 		});
 	});
+
+	describe('when the server clamps the response size (e.g. "Max Record Amount")', () => {
+		const SERVER_LIMIT = 20;
+		const AROUND_INDEX = 60;
+
+		it('does not skip a batch of messages when loading the next page after jumping to an old reply', async () => {
+			const { result } = setup({ serverLimit: SERVER_LIMIT });
+
+			await waitForLoaded(result);
+
+			await act(async () => {
+				await result.current.loadMessageAround(`reply-${AROUND_INDEX}`);
+			});
+			await waitFor(() => expect(result.current.hasNextPage).toBe(true));
+
+			const idsBeforeNextPage = idsOf(result.current.data?.messages ?? []);
+			const oldestLoadedIndex = allReplies.findIndex(({ _id }) => _id === idsBeforeNextPage[0]);
+			const newestLoadedIndex = allReplies.findIndex(({ _id }) => _id === idsBeforeNextPage[idsBeforeNextPage.length - 1]);
+
+			await act(async () => {
+				await result.current.fetchNextPage();
+			});
+			await waitFor(() => expect(result.current.isFetchingNextPage).toBe(false));
+
+			// The newly-loaded batch must continue immediately after the previously loaded one, with no gap.
+			const idsAfterNextPage = idsOf(result.current.data?.messages ?? []);
+			expect(idsAfterNextPage).toEqual(idsOf(allReplies.slice(oldestLoadedIndex, newestLoadedIndex + 1 + SERVER_LIMIT)));
+		});
+
+		it('reaches the newest message without gaps after repeatedly loading next pages', async () => {
+			const { result } = setup({ serverLimit: SERVER_LIMIT });
+
+			await waitForLoaded(result);
+
+			await act(async () => {
+				await result.current.loadMessageAround(`reply-${AROUND_INDEX}`);
+			});
+			await waitFor(() => expect(result.current.hasNextPage).toBe(true));
+
+			const oldestLoadedIndex = allReplies.findIndex(({ _id }) => _id === (result.current.data?.messages ?? [])[0]._id);
+
+			while (result.current.hasNextPage) {
+				await act(async () => {
+					await result.current.fetchNextPage();
+				});
+				await waitFor(() => expect(result.current.isFetchingNextPage).toBe(false));
+			}
+
+			expect(idsOf(result.current.data?.messages ?? [])).toEqual(idsOf(allReplies.slice(oldestLoadedIndex)));
+		});
+	});
 });

apps/meteor/client/views/room/contextualBar/Threads/hooks/useThreadMessagesQuery.ts

@@ -128,7 +128,8 @@ export const useThreadMessagesQuery = (tmid: IThreadMainMessage['_id'], rid?: IR
 			const filtered = filterThreadMessages(messages, tmid);
 			const processed = (await processMessages(filtered)) as IThreadMessage[];
 
-			const pageParam = Math.max(0, total - offset - count);
+			const pageSize = Math.min(processed.length, count);
+			const pageParam = Math.max(0, total - offset - pageSize);
 
 			queryClient.setQueryData<ThreadMessagesInfiniteData>(currentQueryKey, {
 				pages: [{ items: processed, itemCount: total }],
@@ -178,8 +179,15 @@ export const useThreadMessagesQuery = (tmid: IThreadMainMessage['_id'], rid?: IR
 			};
 		},
 		initialPageParam: 0,
-		getNextPageParam: (_lastPage, _allPages, lastPageParam) => {
-			return lastPageParam > 0 ? Math.max(0, lastPageParam - count) : undefined;
+		getNextPageParam: (lastPage, _allPages, lastPageParam) => {
+			if (lastPageParam <= 0) {
+				return undefined;
+			}
+			const pageSize = Math.min(lastPage.items.length, count);
+			if (pageSize <= 0) {
+				return undefined;
+			}
+			return Math.max(0, lastPageParam - pageSize);
 		},
 		getPreviousPageParam: (firstPage, _allPages, firstPageParam) => {
 			const pageSize = Math.min(firstPage.items.length, count);