Preload conversation open data

Co-authored-by: Scott Nonnenberg <scott@signal.org>

ts/components/AnnouncementsOnlyGroupBanner.tsx

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import React, { useState } from 'react';
+import { noop } from 'lodash';
 import type {
   ConversationType,
   ShowConversationType,
@@ -45,6 +46,7 @@ export function AnnouncementsOnlyGroupBanner({
               onClick={() => {
                 showConversation({ conversationId: admin.id });
               }}
+              onMouseDown={noop}
               theme={theme}
             />
           ))}

ts/components/ConversationList.stories.tsx

@@ -68,6 +68,7 @@ function Wrapper({
       shouldRecomputeRowHeights={false}
       i18n={i18n}
       blockConversation={action('blockConversation')}
+      onPreloadConversation={action('onPreloadConversation')}
       onSelectConversation={action('onSelectConversation')}
       onOutgoingAudioCallInConversation={action(
         'onOutgoingAudioCallInConversation'

ts/components/ConversationList.tsx

@@ -197,6 +197,7 @@ export type PropsType = {
     conversationId: string,
     disabledReason: undefined | ContactCheckboxDisabledReason
   ) => void;
+  onPreloadConversation: (conversationId: string, messageId?: string) => void;
   onSelectConversation: (conversationId: string, messageId?: string) => void;
   onOutgoingAudioCallInConversation: (conversationId: string) => void;
   onOutgoingVideoCallInConversation: (conversationId: string) => void;
@@ -220,6 +221,7 @@ export function ConversationList({
   blockConversation,
   onClickArchiveButton,
   onClickContactCheckbox,
+  onPreloadConversation,
   onSelectConversation,
   onOutgoingAudioCallInConversation,
   onOutgoingVideoCallInConversation,
@@ -411,6 +413,7 @@ export function ConversationList({
               })}
               key={key}
               badge={getPreferredBadge(badges)}
+              onMouseDown={onPreloadConversation}
               onClick={onSelectConversation}
               i18n={i18n}
               theme={theme}
@@ -527,6 +530,7 @@ export function ConversationList({
       onClickContactCheckbox,
       onOutgoingAudioCallInConversation,
       onOutgoingVideoCallInConversation,
+      onPreloadConversation,
       onSelectConversation,
       removeConversation,
       renderMessageSearchResult,

ts/components/ForwardMessagesModal.tsx

@@ -400,6 +400,7 @@ export function ForwardMessagesModal({
                       showConversation={shouldNeverBeCalled}
                       showUserNotFoundModal={shouldNeverBeCalled}
                       setIsFetchingUUID={shouldNeverBeCalled}
+                      onPreloadConversation={shouldNeverBeCalled}
                       onSelectConversation={shouldNeverBeCalled}
                       blockConversation={shouldNeverBeCalled}
                       removeConversation={shouldNeverBeCalled}

ts/components/LeftPane.stories.tsx

@@ -172,6 +172,7 @@ const useProps = (overrideProps: OverridePropsType = {}): PropsType => {
       makeFakeLookupConversationWithoutServiceId(),
     showUserNotFoundModal: action('showUserNotFoundModal'),
     setIsFetchingUUID,
+    preloadConversation: action('preloadConversation'),
     showConversation: action('showConversation'),
     blockConversation: action('blockConversation'),
     onOutgoingAudioCallInConversation: action(

ts/components/LeftPane.tsx

@@ -139,6 +139,7 @@ export type PropsType = {
   showFindByUsername: () => void;
   showFindByPhoneNumber: () => void;
   showConversation: ShowConversationType;
+  preloadConversation: (conversationId: string) => void;
   showInbox: () => void;
   startComposing: () => void;
   startSearch: () => unknown;
@@ -205,6 +206,7 @@ export function LeftPane({
 
   openUsernameReservationModal,
   preferredWidthFromStorage,
+  preloadConversation,
   removeConversation,
   renderCaptchaDialog,
   renderCrashReportDialog,
@@ -776,6 +778,7 @@ export function LeftPane({
                 }
                 showConversation={showConversation}
                 blockConversation={blockConversation}
+                onPreloadConversation={preloadConversation}
                 onSelectConversation={onSelectConversation}
                 onOutgoingAudioCallInConversation={
                   onOutgoingAudioCallInConversation

ts/components/StoriesSettingsModal.tsx

@@ -1220,6 +1220,7 @@ export function EditDistributionListModal({
                 onClickContactCheckbox={(conversationId: string) => {
                   toggleSelectedConversation(conversationId);
                 }}
+                onPreloadConversation={shouldNeverBeCalled}
                 onSelectConversation={shouldNeverBeCalled}
                 blockConversation={shouldNeverBeCalled}
                 removeConversation={shouldNeverBeCalled}

ts/components/conversationList/BaseConversationListItem.tsx

@@ -50,6 +50,7 @@ type PropsType = {
   messageText?: ReactNode;
   messageTextIsAlwaysFullSize?: boolean;
   onClick?: () => void;
+  onMouseDown?: () => void;
   shouldShowSpinner?: boolean;
   unreadCount?: number;
   unreadMentionsCount?: number;
@@ -100,6 +101,7 @@ export const BaseConversationListItem: FunctionComponent<PropsType> =
       messageText,
       messageTextIsAlwaysFullSize,
       onClick,
+      onMouseDown,
       phoneNumber,
       profileName,
       sharedGroupNames,
@@ -289,6 +291,7 @@ export const BaseConversationListItem: FunctionComponent<PropsType> =
           data-testid={testId}
           disabled={disabled}
           onClick={onClick}
+          onMouseDown={onMouseDown}
           type="button"
         >
           {contents}

ts/components/conversationList/ConversationListItem.tsx

@@ -74,6 +74,7 @@ type PropsHousekeeping = {
   buttonAriaLabel?: string;
   i18n: LocalizerType;
   onClick: (id: string) => void;
+  onMouseDown: (id: string) => void;
   theme: ThemeType;
 };
 
@@ -98,6 +99,7 @@ export const ConversationListItem: FunctionComponent<Props> = React.memo(
     markedUnread,
     muteExpiresAt,
     onClick,
+    onMouseDown,
     phoneNumber,
     profileName,
     removalStage,
@@ -202,6 +204,10 @@ export const ConversationListItem: FunctionComponent<Props> = React.memo(
     }
 
     const onClickItem = useCallback(() => onClick(id), [onClick, id]);
+    const onMouseDownItem = useCallback(
+      () => onMouseDown(id),
+      [onMouseDown, id]
+    );
 
     return (
       <BaseConversationListItem
@@ -223,6 +229,7 @@ export const ConversationListItem: FunctionComponent<Props> = React.memo(
         messageText={messageText}
         messageTextIsAlwaysFullSize
         onClick={onClickItem}
+        onMouseDown={onMouseDownItem}
         phoneNumber={phoneNumber}
         profileName={profileName}
         sharedGroupNames={sharedGroupNames}

ts/models/conversations.ts

@@ -137,6 +137,7 @@ import {
   isIncoming,
   isStory,
 } from '../state/selectors/message';
+import { getPreloadedConversationId } from '../state/selectors/conversations';
 import {
   conversationJobQueue,
   conversationQueueJobEnum,
@@ -180,6 +181,7 @@ import {
   getConversationToDelete,
   getMessageToDelete,
 } from '../util/deleteForMe';
+import { explodePromise } from '../util/explodePromise';
 import { getCallHistorySelector } from '../state/selectors/callHistory';
 
 /* eslint-disable more/no-then */
@@ -1503,24 +1505,32 @@ export class ConversationModel extends window.Backbone
     }
   }
 
-  private setInProgressFetch(): () => unknown {
+  private async setInProgressFetch(): Promise<() => void> {
     const logId = `setInProgressFetch(${this.idForLogging()})`;
+    while (this.inProgressFetch != null) {
+      log.warn(`${logId}: blocked, waiting`);
+      // eslint-disable-next-line no-await-in-loop
+      await this.inProgressFetch;
+    }
     const start = Date.now();
 
-    let resolvePromise: (value?: unknown) => void;
+    const { resolve, promise } = explodePromise<void>();
-    this.inProgressFetch = new Promise(resolve => {
+    this.inProgressFetch = promise;
-      resolvePromise = resolve;
-    });
 
+    let isFinished = false;
     let timeout: NodeJS.Timeout;
     const finish = () => {
+      strictAssert(!isFinished, 'inProgressFetch.finish called twice');
+      isFinished = true;
+
       const duration = Date.now() - start;
       if (duration > 500) {
         log.warn(`${logId}: in progress fetch took ${duration}ms`);
       }
 
-      resolvePromise();
+      resolve();
       clearTimeout(timeout);
+      strictAssert(this.inProgressFetch === promise, `${logId}: conflict`);
       this.inProgressFetch = undefined;
     };
     timeout = setTimeout(() => {
@@ -1531,13 +1541,85 @@ export class ConversationModel extends window.Backbone
     return finish;
   }
 
+  async preloadNewestMessages(): Promise<void> {
+    const logId = `preloadNewestMessages/${this.idForLogging()}`;
+
+    const { addPreloadData } = window.reduxActions.conversations;
+
+    // Bail-out of complex paths
+    if (!this.getAccepted()) {
+      log.info(`${logId}: not accepted, skipping`);
+      return;
+    }
+
+    const finish = await this.setInProgressFetch();
+    log.info(`${logId}: starting`);
+    try {
+      let metrics = await getMessageMetricsForConversation({
+        conversationId: this.id,
+        includeStoryReplies: !isGroup(this.attributes),
+      });
+
+      let messages: ReadonlyArray<MessageAttributesType>;
+      if (metrics.oldestUnseen) {
+        const unseen = await getMessageById(metrics.oldestUnseen.id);
+        if (!unseen) {
+          throw new Error(
+            `preloadNewestMessages: failed to load oldestUnseen ${metrics.oldestUnseen.id}`
+          );
+        }
+
+        const receivedAt = unseen.received_at;
+        const sentAt = unseen.sent_at;
+        const {
+          older,
+          newer,
+          metrics: freshMetrics,
+        } = await getConversationRangeCenteredOnMessage({
+          conversationId: this.id,
+          includeStoryReplies: !isGroup(this.attributes),
+          limit: MESSAGE_LOAD_CHUNK_SIZE,
+          messageId: unseen.id,
+          receivedAt,
+          sentAt,
+          storyId: undefined,
+        });
+        messages = [...older, unseen, ...newer];
+
+        metrics = freshMetrics;
+      } else {
+        messages = await getOlderMessagesByConversation({
+          conversationId: this.id,
+          includeStoryReplies: !isGroup(this.attributes),
+          limit: MESSAGE_LOAD_CHUNK_SIZE,
+          storyId: undefined,
+        });
+      }
+
+      const cleaned = await this.cleanAttributes(messages);
+
+      log.info(
+        `${logId}: preloaded ${cleaned.length} messages, ` +
+          `latest timestamp=${cleaned.at(-1)?.sent_at}`
+      );
+
+      addPreloadData({
+        conversationId: this.id,
+        messages: cleaned,
+        metrics,
+      });
+    } finally {
+      finish();
+    }
+  }
+
   async loadNewestMessages(
     newestMessageId: string | undefined,
     setFocus: boolean | undefined
   ): Promise<void> {
     const logId = `loadNewestMessages/${this.idForLogging()}`;
 
-    const { messagesReset, setMessageLoadingState } =
+    const { messagesReset, setMessageLoadingState, consumePreloadData } =
       window.reduxActions.conversations;
     const conversationId = this.id;
 
@@ -1545,11 +1627,29 @@ export class ConversationModel extends window.Backbone
       conversationId,
       TimelineMessageLoadingState.DoingInitialLoad
     );
-    const finish = this.setInProgressFetch();
+    let finish: undefined | (() => void) = await this.setInProgressFetch();
 
+    const preloadedId = getPreloadedConversationId(
+      window.reduxStore.getState()
+    );
     try {
       let scrollToLatestUnread = true;
 
+      if (
+        // Arguments provided by onConversationOpened
+        newestMessageId == null &&
+        !setFocus &&
+        // Cache conditions for preloadNewestMessages above (in case they are
+        // invalidated after loading cache)
+        this.getAccepted() &&
+        // Existing preload
+        preloadedId === conversationId
+      ) {
+        log.info(`${logId}: preload cache still valid, skipping`);
+        consumePreloadData(preloadedId);
+        return;
+      }
+
       if (newestMessageId) {
         const newestInMemoryMessage = await getMessageById(newestMessageId);
         if (newestInMemoryMessage) {
@@ -1581,7 +1681,11 @@ export class ConversationModel extends window.Backbone
         metrics.oldest
       ) {
         log.info(`${logId}: scrolling to oldest ${metrics.oldest.sent_at}`);
-        void this.loadAndScroll(metrics.oldest.id, { disableScroll: true });
+        void this.loadAndScroll(metrics.oldest.id, {
+          disableScroll: true,
+          onFinish: finish,
+        });
+        finish = undefined;
         return;
       }
 
@@ -1591,7 +1695,9 @@ export class ConversationModel extends window.Backbone
         );
         void this.loadAndScroll(metrics.oldestUnseen.id, {
           disableScroll: !setFocus,
+          onFinish: finish,
         });
+        finish = undefined;
         return;
       }
 
@@ -1628,7 +1734,7 @@ export class ConversationModel extends window.Backbone
       setMessageLoadingState(conversationId, undefined);
       throw error;
     } finally {
-      finish();
+      finish?.();
     }
   }
   async loadOlderMessages(oldestMessageId: string): Promise<void> {
@@ -1642,7 +1748,7 @@ export class ConversationModel extends window.Backbone
       conversationId,
       TimelineMessageLoadingState.LoadingOlderMessages
     );
-    const finish = this.setInProgressFetch();
+    const finish = await this.setInProgressFetch();
 
     try {
       const message = await getMessageById(oldestMessageId);
@@ -1699,7 +1805,7 @@ export class ConversationModel extends window.Backbone
       conversationId,
       TimelineMessageLoadingState.LoadingNewerMessages
     );
-    const finish = this.setInProgressFetch();
+    const finish = await this.setInProgressFetch();
 
     try {
       const message = await getMessageById(newestMessageId);
@@ -1744,7 +1850,7 @@ export class ConversationModel extends window.Backbone
 
   async loadAndScroll(
     messageId: string,
-    options?: { disableScroll?: boolean }
+    options: { disableScroll?: boolean; onFinish?: () => void } = {}
   ): Promise<void> {
     const { messagesReset, setMessageLoadingState } =
       window.reduxActions.conversations;
@@ -1754,7 +1860,10 @@ export class ConversationModel extends window.Backbone
       conversationId,
       TimelineMessageLoadingState.DoingInitialLoad
     );
-    const finish = this.setInProgressFetch();
+    let { onFinish: finish } = options;
+    if (!finish) {
+      finish = await this.setInProgressFetch();
+    }
 
     try {
       const message = await getMessageById(messageId);

ts/sql/Server.ts

@@ -3443,11 +3443,9 @@ function getMessageMetricsForConversation(
   );
 
   return {
-    oldest: oldest ? pick(oldest, ['received_at', 'sent_at', 'id']) : undefined,
+    oldest,
-    newest: newest ? pick(newest, ['received_at', 'sent_at', 'id']) : undefined,
+    newest,
-    oldestUnseen: oldestUnseen
+    oldestUnseen,
-      ? pick(oldestUnseen, ['received_at', 'sent_at', 'id'])
-      : undefined,
     totalUnseen,
   };
 }

ts/state/ducks/conversations.ts

@@ -435,6 +435,11 @@ export type ConversationMessageType = ReadonlyDeep<{
   scrollToMessageId?: string;
   scrollToMessageCounter: number;
 }>;
+export type ConversationPreloadDataType = ReadonlyDeep<{
+  conversationId: string;
+  messages: ReadonlyArray<ReadonlyMessageAttributesType>;
+  metrics: MessageMetricsType;
+}>;
 
 export type MessagesByConversationType = ReadonlyDeep<{
   [key: string]: ConversationMessageType | undefined;
@@ -550,6 +555,8 @@ export type ConversationsStateType = ReadonlyDeep<{
   // Note: it's very important that both of these locations are always kept up to date
   messagesLookup: MessageLookupType;
   messagesByConversation: MessagesByConversationType;
+
+  preloadData?: ConversationPreloadDataType;
 }>;
 
 // Helpers
@@ -979,9 +986,20 @@ type ReplaceAvatarsActionType = ReadonlyDeep<{
     avatars: ReadonlyArray<AvatarDataType>;
   };
 }>;
+export type AddPreloadDataActionType = ReadonlyDeep<{
+  type: 'ADD_PRELOAD_DATA';
+  payload: ConversationPreloadDataType;
+}>;
+export type ConsumePreloadDataActionType = ReadonlyDeep<{
+  type: 'CONSUME_PRELOAD_DATA';
+  payload: {
+    conversationId: string;
+  };
+}>;
 
 // eslint-disable-next-line local-rules/type-alias-readonlydeep
 export type ConversationActionType =
+  | AddPreloadDataActionType
   | CancelVerificationDataByConversationActionType
   | ClearCancelledVerificationActionType
   | ClearGroupCreationErrorActionType
@@ -997,6 +1015,7 @@ export type ConversationActionType =
   | ComposeDeleteAvatarActionType
   | ComposeReplaceAvatarsActionType
   | ComposeSaveAvatarActionType
+  | ConsumePreloadDataActionType
   | ConversationAddedActionType
   | ConversationChangedActionType
   | ConversationRemovedActionType
@@ -1057,6 +1076,7 @@ export const actions = {
   acceptConversation,
   acknowledgeGroupMemberNameCollisions,
   addMembersToGroup,
+  addPreloadData,
   approvePendingMembershipFromGroupV2,
   reportSpam,
   blockAndReportSpam,
@@ -1076,6 +1096,7 @@ export const actions = {
   composeDeleteAvatarFromDisk,
   composeReplaceAvatar,
   composeSaveAvatarToDisk,
+  consumePreloadData,
   conversationAdded,
   conversationChanged,
   conversationRemoved,
@@ -3028,6 +3049,33 @@ function messagesReset({
     },
   };
 }
+function addPreloadData(
+  preloadData: ConversationPreloadDataType
+): AddPreloadDataActionType {
+  const { messages, conversationId } = preloadData;
+  for (const message of messages) {
+    strictAssert(
+      message.conversationId === conversationId,
+      `addPreloadData(${conversationId}): invalid message conversationId ` +
+        `${message.conversationId}`
+    );
+  }
+
+  return {
+    type: 'ADD_PRELOAD_DATA',
+    payload: preloadData,
+  };
+}
+function consumePreloadData(
+  conversationId: string
+): ConsumePreloadDataActionType {
+  return {
+    type: 'CONSUME_PRELOAD_DATA',
+    payload: {
+      conversationId,
+    },
+  };
+}
 function setMessageLoadingState(
   conversationId: string,
   messageLoadingState: undefined | TimelineMessageLoadingState
@@ -4795,6 +4843,94 @@ function updateNicknameAndNote(
   };
 }
 
+function updateMessageLookup(
+  state: ConversationsStateType,
+  {
+    conversationId,
+    messages,
+    metrics,
+    scrollToMessageId,
+    unboundedFetch,
+  }: {
+    conversationId: string;
+    messages: ReadonlyArray<ReadonlyMessageAttributesType>;
+    metrics: MessageMetricsType;
+    scrollToMessageId?: string | undefined;
+    unboundedFetch: boolean;
+  }
+): ConversationsStateType {
+  const { messagesByConversation, messagesLookup } = state;
+  const existingConversation = messagesByConversation[conversationId];
+
+  const lookup = fromPairs(messages.map(message => [message.id, message]));
+  const sorted = orderBy(
+    values(lookup),
+    ['received_at', 'sent_at'],
+    ['ASC', 'ASC']
+  );
+
+  let { newest, oldest } = metrics;
+
+  // If our metrics are a little out of date, we'll fix them up
+  if (sorted.length > 0) {
+    const first = sorted[0];
+    if (first && (!oldest || first.received_at <= oldest.received_at)) {
+      oldest = pick(first, ['id', 'received_at', 'sent_at']);
+    }
+
+    const last = sorted[sorted.length - 1];
+    if (
+      last &&
+      (!newest || unboundedFetch || last.received_at >= newest.received_at)
+    ) {
+      newest = pick(last, ['id', 'received_at', 'sent_at']);
+    }
+  }
+
+  const messageIds = sorted.map(message => message.id);
+
+  return {
+    ...state,
+    preloadData: undefined,
+    ...(state.selectedConversationId === conversationId
+      ? {
+          targetedMessage: scrollToMessageId,
+          targetedMessageCounter: state.targetedMessageCounter + 1,
+          targetedMessageSource: TargetedMessageSource.Reset,
+        }
+      : {}),
+    messagesLookup: {
+      ...messagesLookup,
+      ...lookup,
+    },
+    messagesByConversation: {
+      ...messagesByConversation,
+      [conversationId]: {
+        messageChangeCounter: 0,
+        scrollToMessageId,
+        scrollToMessageCounter: existingConversation
+          ? existingConversation.scrollToMessageCounter + 1
+          : 0,
+        messageIds,
+        metrics: {
+          ...metrics,
+          newest,
+          oldest,
+        },
+      },
+    },
+  };
+}
+
+function dropPreloadData(
+  state: ConversationsStateType
+): ConversationsStateType {
+  if (state.preloadData == null) {
+    return state;
+  }
+  return { ...state, preloadData: undefined };
+}
+
 export function reducer(
   state: Readonly<ConversationsStateType> = getEmptyState(),
   action: Readonly<
@@ -5395,7 +5531,7 @@ export function reducer(
     if (!existingConversation) {
       return maybeUpdateSelectedMessageForDetails(
         { messageId: id, targetedMessageForDetails: data },
-        state
+        dropPreloadData(state)
       );
     }
 
@@ -5404,14 +5540,14 @@ export function reducer(
     if (!existingMessage) {
       return maybeUpdateSelectedMessageForDetails(
         { messageId: id, targetedMessageForDetails: data },
-        state
+        dropPreloadData(state)
       );
     }
 
     const conversationAttrs = state.conversationLookup[conversationId];
     const isGroupStoryReply = isGroup(conversationAttrs) && data.storyId;
     if (isGroupStoryReply) {
-      return state;
+      return dropPreloadData(state);
     }
 
     const hasNewEdit =
@@ -5434,6 +5570,7 @@ export function reducer(
         },
         state
       ),
+      preloadData: undefined,
       messagesByConversation: {
         ...state.messagesByConversation,
         [conversationId]: {
@@ -5514,75 +5651,32 @@ export function reducer(
   }
 
   if (action.type === 'MESSAGES_RESET') {
-    const {
+    return updateMessageLookup(state, action.payload);
-      conversationId,
-      messages,
-      metrics,
-      scrollToMessageId,
-      unboundedFetch,
-    } = action.payload;
-    const { messagesByConversation, messagesLookup } = state;
-
-    const existingConversation = messagesByConversation[conversationId];
-
-    const lookup = fromPairs(messages.map(message => [message.id, message]));
-    const sorted = orderBy(
-      values(lookup),
-      ['received_at', 'sent_at'],
-      ['ASC', 'ASC']
-    );
-
-    let { newest, oldest } = metrics;
-
-    // If our metrics are a little out of date, we'll fix them up
-    if (sorted.length > 0) {
-      const first = sorted[0];
-      if (first && (!oldest || first.received_at <= oldest.received_at)) {
-        oldest = pick(first, ['id', 'received_at', 'sent_at']);
   }
-
+  if (action.type === 'ADD_PRELOAD_DATA') {
-      const last = sorted[sorted.length - 1];
-      if (
-        last &&
-        (!newest || unboundedFetch || last.received_at >= newest.received_at)
-      ) {
-        newest = pick(last, ['id', 'received_at', 'sent_at']);
-      }
-    }
-
-    const messageIds = sorted.map(message => message.id);
-
     return {
       ...state,
-      ...(state.selectedConversationId === conversationId
+      preloadData: action.payload,
-        ? {
-            targetedMessage: scrollToMessageId,
-            targetedMessageCounter: state.targetedMessageCounter + 1,
-            targetedMessageSource: TargetedMessageSource.Reset,
-          }
-        : {}),
-      messagesLookup: {
-        ...messagesLookup,
-        ...lookup,
-      },
-      messagesByConversation: {
-        ...messagesByConversation,
-        [conversationId]: {
-          messageChangeCounter: 0,
-          scrollToMessageId,
-          scrollToMessageCounter: existingConversation
-            ? existingConversation.scrollToMessageCounter + 1
-            : 0,
-          messageIds,
-          metrics: {
-            ...metrics,
-            newest,
-            oldest,
-          },
-        },
-      },
     };
   }
+  if (action.type === 'CONSUME_PRELOAD_DATA') {
+    const { preloadData, selectedConversationId } = state;
+    const { conversationId } = action.payload;
+    if (!preloadData) {
+      return state;
+    }
+    if (
+      preloadData.conversationId !== conversationId ||
+      selectedConversationId !== conversationId
+    ) {
+      return dropPreloadData(state);
+    }
+
+    return updateMessageLookup(state, {
+      ...preloadData,
+      unboundedFetch: true,
+    });
+  }
   if (action.type === 'SET_MESSAGE_LOADING_STATE') {
     const { payload } = action;
     const { conversationId, messageLoadingState } = payload;
@@ -5676,7 +5770,7 @@ export function reducer(
     if (!existingConversation) {
       return maybeUpdateSelectedMessageForDetails(
         { messageId: id, targetedMessageForDetails: undefined },
-        state
+        dropPreloadData(state)
       );
     }
 
@@ -5725,6 +5819,7 @@ export function reducer(
         { messageId: id, targetedMessageForDetails: undefined },
         state
       ),
+      preloadData: undefined,
       messagesLookup: omit(messagesLookup, id),
       messagesByConversation: {
         [conversationId]: {
@@ -5863,7 +5958,7 @@ export function reducer(
           );
         }
 
-        return state;
+        return dropPreloadData(state);
       }
     }
 
@@ -5908,6 +6003,7 @@ export function reducer(
 
     return {
       ...state,
+      preloadData: undefined,
       messagesLookup: {
         ...messagesLookup,
         ...lookup,
@@ -5978,6 +6074,10 @@ export function reducer(
 
     const nextState = {
       ...state,
+      preloadData:
+        state.preloadData?.conversationId === conversationId
+          ? state.preloadData
+          : undefined,
       hasContactSpoofingReview: false,
       selectedConversationId: conversationId,
       targetedMessage: messageId,

ts/state/selectors/conversations.ts

@@ -1335,3 +1335,8 @@ export const getLastEditableMessageId = createSelector(
     return undefined;
   }
 );
+
+export const getPreloadedConversationId = createSelector(
+  getConversations,
+  ({ preloadData }): string | undefined => preloadData?.conversationId
+);

ts/state/smart/LeftPane.tsx

@@ -20,6 +20,7 @@ import { getCountryDataForLocale } from '../../util/getCountryData';
 import { lookupConversationWithoutServiceId } from '../../util/lookupConversationWithoutServiceId';
 import { missingCaseError } from '../../util/missingCaseError';
 import { isDone as isRegistrationDone } from '../../util/registration';
+import { drop } from '../../util/drop';
 import { useCallingActions } from '../ducks/calling';
 import { useConversationsActions } from '../ducks/conversations';
 import { ComposerStep, OneTimeModalState } from '../ducks/conversationsEnums';
@@ -256,6 +257,12 @@ const getModeSpecificProps = (
   }
 };
 
+function preloadConversation(conversationId: string): void {
+  drop(
+    window.ConversationController.get(conversationId)?.preloadNewestMessages()
+  );
+}
+
 export const SmartLeftPane = memo(function SmartLeftPane({
   hasFailedStorySends,
   hasPendingUpdate,
@@ -385,6 +392,7 @@ export const SmartLeftPane = memo(function SmartLeftPane({
       openUsernameReservationModal={openUsernameReservationModal}
       otherTabsUnreadStats={otherTabsUnreadStats}
       preferredWidthFromStorage={preferredWidthFromStorage}
+      preloadConversation={preloadConversation}
       removeConversation={removeConversation}
       renderCaptchaDialog={renderCaptchaDialog}
       renderCrashReportDialog={renderCrashReportDialog}