fix(app): distrust windows loaded across a connection gap (#2574)

fluxer_app/src/features/messaging/commands/MessageCommands.tsx

@@ -8,6 +8,7 @@ import {Endpoints} from '@app/features/app/constants/Endpoints';
 import Authentication from '@app/features/auth/state/Authentication';
 import Channels from '@app/features/channel/state/Channels';
 import DeveloperOptions from '@app/features/devtools/state/DeveloperOptions';
+import GatewayConnection from '@app/features/gateway/transport/GatewayConnection';
 import GuildMatureContentAgree from '@app/features/guild/state/GuildMatureContentAgree';
 import {DELETE_MESSAGE_DESCRIPTOR} from '@app/features/i18n/utils/CommonMessageDescriptors';
 import GuildMembers from '@app/features/member/state/GuildMembers';
@@ -15,6 +16,7 @@ import {
 	type MessageFetchCacheHit,
 	resolveMessageFetchExecutionDecision,
 	resolveMessageFetchPreflightDecision,
+	resolveMessageFetchWindowCached,
 } from '@app/features/messaging/commands/MessageFetchStateMachine';
 import {resolveMessagePageState} from '@app/features/messaging/commands/MessagePageStateMachine';
 import {MessageDeleteFailedModal} from '@app/features/messaging/components/alerts/MessageDeleteFailedModal';
@@ -258,6 +260,7 @@ function handleMessageFetchSuccess(
 	channelId: string,
 	messages: Array<WireMessage>,
 	pageState: MessagePageState,
+	cached: boolean,
 	jump?: JumpOptions,
 	tailProbe?: TailProbeContext,
 ): void {
@@ -268,7 +271,7 @@ function handleMessageFetchSuccess(
 		isAfter: pageState.isAfter,
 		hasMoreBefore: pageState.hasMoreBefore,
 		hasMoreAfter: pageState.hasMoreAfter,
-		cached: false,
+		cached,
 		jump,
 		tailProbe: tailProbe != null,
 	});
@@ -466,17 +469,25 @@ export async function fetchMessages(
 			const started = Messages.getMessages(channelId);
 			probeEpoch = {loadGeneration: started.loadGeneration, jumpTicket: started.jumpTicket};
 		}
+		const connectedAtRequest = GatewayConnection.isConnected;
+		const epochAtRequest = GatewayConnection.connectionEpoch;
 		try {
 			const timeStart = Date.now();
 			logger.debug(`Fetching messages for channel ${channelId}`);
 			const messages = await requestChannelMessages(channelId, before, after, limit, jump);
+			const cached = resolveMessageFetchWindowCached({
+				connectedAtRequest,
+				connectedAtResponse: GatewayConnection.isConnected,
+				epochAtRequest,
+				epochAtResponse: GatewayConnection.connectionEpoch,
+			});
 			if (probeEpoch != null && !isTailProbeApplicable(channelId, probeEpoch, after)) {
 				settleTailProbe(options, 'retry');
 				return [];
 			}
 			const pageState = calculateMessagePageState(channelId, before, after, limit, messages, jump);
 			logger.info(`Fetched ${messages.length} messages for channel ${channelId}, took ${Date.now() - timeStart}ms`);
-			handleMessageFetchSuccess(channelId, messages, pageState, jump, options?.tailProbe);
+			handleMessageFetchSuccess(channelId, messages, pageState, cached, jump, options?.tailProbe);
 			settleTailProbe(options, 'applied');
 			return messages;
 		} catch (error) {

fluxer_app/src/features/messaging/commands/MessageFetchStateMachine.test.ts

@@ -8,6 +8,7 @@ import {
 	type MessageFetchPreflightInput,
 	resolveMessageFetchExecutionDecision,
 	resolveMessageFetchPreflightDecision,
+	resolveMessageFetchWindowCached,
 	selectMessageFetchExecutionDecision,
 	selectMessageFetchPreflightDecision,
 	transitionMessageFetchExecutionSnapshot,
@@ -104,3 +105,31 @@ describe('messageFetchExecutionMachine', () => {
 		expect(selectMessageFetchExecutionDecision(networkSnapshot)).toEqual({type: 'requestNetwork'});
 	});
 });
+
+describe('resolveMessageFetchWindowCached', () => {
+	function trust(overrides: Partial<Parameters<typeof resolveMessageFetchWindowCached>[0]> = {}) {
+		return {
+			connectedAtRequest: true,
+			connectedAtResponse: true,
+			epochAtRequest: 7,
+			epochAtResponse: 7,
+			...overrides,
+		};
+	}
+
+	it('trusts a window loaded inside one uninterrupted connection', () => {
+		expect(resolveMessageFetchWindowCached(trust())).toBe(false);
+	});
+
+	it('distrusts a window whose request left while the socket was down', () => {
+		expect(resolveMessageFetchWindowCached(trust({connectedAtRequest: false}))).toBe(true);
+	});
+
+	it('distrusts a window whose response landed while the socket was down', () => {
+		expect(resolveMessageFetchWindowCached(trust({connectedAtResponse: false}))).toBe(true);
+	});
+
+	it('distrusts a window whose connection epoch moved under it', () => {
+		expect(resolveMessageFetchWindowCached(trust({epochAtResponse: 8}))).toBe(true);
+	});
+});

fluxer_app/src/features/messaging/commands/MessageFetchStateMachine.ts

@@ -197,3 +197,15 @@ export function selectMessageFetchExecutionDecision(
 export function resolveMessageFetchExecutionDecision(input: MessageFetchExecutionInput): MessageFetchExecutionDecision {
 	return buildExecutionDecision(input);
 }
+
+export interface MessageFetchWindowTrustInput {
+	connectedAtRequest: boolean;
+	connectedAtResponse: boolean;
+	epochAtRequest: number;
+	epochAtResponse: number;
+}
+
+export function resolveMessageFetchWindowCached(input: MessageFetchWindowTrustInput): boolean {
+	if (!input.connectedAtRequest || !input.connectedAtResponse) return true;
+	return input.epochAtRequest !== input.epochAtResponse;
+}

fluxer_app/src/features/messaging/state/ChannelMessages.ts

@@ -3,7 +3,10 @@
 import {Message} from '@app/features/messaging/models/MessagingMessage';
 import {UploadingAttachment} from '@app/features/messaging/models/UploadingAttachment';
 import {resolveChannelIncomingMessageDecision} from '@app/features/messaging/state/ChannelIncomingMessageStateMachine';
-import {resolveChannelMessagesLoadDecision} from '@app/features/messaging/state/ChannelMessagesLoadStateMachine';
+import {
+	resolveChannelMessagesLoadDecision,
+	selectChannelMessagesLoadRestoresTrust,
+} from '@app/features/messaging/state/ChannelMessagesLoadStateMachine';
 import MessageReactions from '@app/features/messaging/state/MessageReactions';
 import {mergeAscendingById} from '@app/features/messaging/utils/MessagePaginationUtils';
 import SelectedChannel from '@app/features/navigation/state/SelectedChannel';
@@ -358,6 +361,10 @@ export class ChannelMessages {
 		ChannelMessages.retainedChannelIds.delete(channelId);
 	}
 
+	static isRetained(channelId: string): boolean {
+		return ChannelMessages.retainedChannelIds.has(channelId);
+	}
+
 	static dropBuffers(channelId: string): void {
 		const instance = ChannelMessages.channelCache.get(channelId);
 		if (!instance) return;
@@ -900,6 +907,11 @@ export class ChannelMessages {
 					jumpReturnChannelId: jump?.returnToMessageId ? (jump.returnChannelId ?? this.channelId) : null,
 					jumpReturnGuildId: jump?.returnToMessageId ? (jump.returnGuildId ?? null) : null,
 				};
+		const reachesLiveEdge = selectChannelMessagesLoadRestoresTrust({
+			mode: loadDecision.mode,
+			isAfter,
+			hasMoreAfter,
+		});
 		next = next.cloneAnd({
 			ready: true,
 			loadingMore: false,
@@ -907,7 +919,7 @@ export class ChannelMessages {
 			...jumpPatch,
 			hasMoreBefore: loadDecision.preserveHasMoreBefore ? next.hasMoreBefore : hasMoreBefore,
 			hasMoreAfter: loadDecision.preserveHasMoreAfter ? next.hasMoreAfter : hasMoreAfter,
-			cached,
+			cached: reachesLiveEdge ? cached : next.cached || cached,
 			error: false,
 		});
 		return next;

fluxer_app/src/features/messaging/state/ChannelMessagesLoadStateMachine.test.ts

@@ -11,6 +11,7 @@ import {
 	resolveChannelMessagesWindowStatus,
 	selectChannelMessagesFillerVisible,
 	selectChannelMessagesLoadDecision,
+	selectChannelMessagesLoadRestoresTrust,
 	selectChannelMessagesSpacerHeight,
 	selectChannelMessagesTailGapId,
 	selectChannelMessagesTailProbeId,
@@ -518,3 +519,23 @@ describe('selectChannelMessagesTailProbeOutcome', () => {
 		expect(selectChannelMessagesTailProbeOutcome(outcomeInput({currentJumpTicket: 3}))).toBe('discard');
 	});
 });
+
+describe('selectChannelMessagesLoadRestoresTrust', () => {
+	it('trusts a window a replacement load rebuilt from scratch', () => {
+		expect(selectChannelMessagesLoadRestoresTrust({mode: 'replace', isAfter: false, hasMoreAfter: false})).toBe(true);
+	});
+
+	it('trusts a window whose tail merge caught up to the live edge', () => {
+		expect(selectChannelMessagesLoadRestoresTrust({mode: 'mergeAfter', isAfter: true, hasMoreAfter: false})).toBe(true);
+	});
+
+	it('keeps distrusting a tail merge that stopped short of the live edge', () => {
+		expect(selectChannelMessagesLoadRestoresTrust({mode: 'mergeAfter', isAfter: true, hasMoreAfter: true})).toBe(false);
+	});
+
+	it('keeps distrusting a page of older history', () => {
+		expect(selectChannelMessagesLoadRestoresTrust({mode: 'mergeBefore', isAfter: false, hasMoreAfter: false})).toBe(
+			false,
+		);
+	});
+});

fluxer_app/src/features/messaging/state/ChannelMessagesLoadStateMachine.ts

@@ -301,6 +301,15 @@ export function selectChannelMessagesTailProbeId(input: ChannelMessagesTailInput
 	return selectChannelMessagesTailGapId(input);
 }
 
+export function selectChannelMessagesLoadRestoresTrust(input: {
+	mode: ChannelMessagesLoadMode;
+	isAfter: boolean;
+	hasMoreAfter: boolean;
+}): boolean {
+	if (input.mode === 'replace') return true;
+	return input.isAfter && !input.hasMoreAfter;
+}
+
 export interface ChannelMessagesTailProbeResultInput {
 	probeGeneration: number;
 	currentGeneration: number;

fluxer_app/src/features/messaging/state/MessagingMessages.ts

@@ -201,7 +201,7 @@ class Messages {
 	}
 
 	private hasLoadedPage(messages: ChannelMessages): boolean {
-		return messages.ready && messages.length > 0;
+		return messages.ready && messages.length > 0 && !messages.cached;
 	}
 
 	shouldPreloadLatestPage(channelId: string): boolean {
@@ -209,7 +209,9 @@ class Messages {
 			return false;
 		}
 		const messages = ChannelMessages.get(channelId);
-		return !messages || (messages.length === 0 && !messages.loadingMore && !messages.ready);
+		if (!messages) return true;
+		if (messages.loadingMore || ChannelMessages.isRetained(channelId)) return false;
+		return messages.length === 0 ? !messages.ready : messages.cached;
 	}
 
 	@action
@@ -286,15 +288,6 @@ class Messages {
 		return true;
 	}
 
-	@action
-	handleResumed(): boolean {
-		ChannelMessages.forEach((messages) => {
-			this.commitMessages(messages.withPatch({ready: true}));
-		});
-		this.notifyChange();
-		return true;
-	}
-
 	@action
 	handleGatewayReady(): boolean {
 		const selectedChannelId = SelectedChannel.currentChannelId;
@@ -386,9 +379,10 @@ class Messages {
 		if (!isNonGuildChannel && !guildExists) {
 			return false;
 		}
+		const distrustedTailId = messages.ready && messages.cached ? (messages.last()?.id ?? null) : null;
 		this.commitMessages(messages.withPatch({loadingMore: true}));
 		this.notifyChange();
-		MessageCommands.fetchMessages(channelId, null, null, MAX_MESSAGES_PER_CHANNEL);
+		MessageCommands.fetchMessages(channelId, null, distrustedTailId, MAX_MESSAGES_PER_CHANNEL);
 		return false;
 	}