diff --git a/keyserver/src/session/cookies.js b/keyserver/src/session/cookies.js
index a1e124140..2233788de 100644
--- a/keyserver/src/session/cookies.js
+++ b/keyserver/src/session/cookies.js
@@ -1,877 +1,898 @@
 // @flow
 
 import crypto from 'crypto';
 import type { $Response, $Request } from 'express';
 import invariant from 'invariant';
 import bcrypt from 'twin-bcrypt';
 import url from 'url';
 
 import { hasMinCodeVersion } from 'lib/shared/version-utils.js';
 import type { Shape } from 'lib/types/core.js';
 import type { SignedIdentityKeysBlob } from 'lib/types/crypto-types.js';
 import { isWebPlatform } from 'lib/types/device-types.js';
 import type { Platform, PlatformDetails } from 'lib/types/device-types.js';
 import type { CalendarQuery } from 'lib/types/entry-types.js';
 import {
   type ServerSessionChange,
   cookieLifetime,
   cookieSources,
   type CookieSource,
   cookieTypes,
   sessionIdentifierTypes,
   type SessionIdentifierType,
 } from 'lib/types/session-types.js';
 import type { SIWESocialProof } from 'lib/types/siwe-types.js';
 import type { InitialClientSocketMessage } from 'lib/types/socket-types.js';
 import type { UserInfo } from 'lib/types/user-types.js';
 import { values } from 'lib/utils/objects.js';
 import { promiseAll } from 'lib/utils/promises.js';
 
 import { Viewer } from './viewer.js';
 import type { AnonymousViewerData, UserViewerData } from './viewer.js';
 import createIDs from '../creators/id-creator.js';
 import { createSession } from '../creators/session-creator.js';
 import { dbQuery, SQL } from '../database/database.js';
 import { deleteCookie } from '../deleters/cookie-deleters.js';
 import { handleAsyncPromise } from '../responders/handlers.js';
 import { clearDeviceToken } from '../updaters/device-token-updaters.js';
 import { updateThreadMembers } from '../updaters/thread-updaters.js';
 import { assertSecureRequest } from '../utils/security-utils.js';
 import {
   type AppURLFacts,
   getAppURLFactsFromRequestURL,
 } from '../utils/urls.js';
 
 function cookieIsExpired(lastUsed: number) {
   return lastUsed + cookieLifetime <= Date.now();
 }
 
 type SessionParameterInfo = {
   isSocket: boolean,
   sessionID: ?string,
   sessionIdentifierType: SessionIdentifierType,
   ipAddress: string,
   userAgent: ?string,
 };
 
 type FetchViewerResult =
   | { type: 'valid', viewer: Viewer }
   | InvalidFetchViewerResult;
 
 type InvalidFetchViewerResult =
   | {
       type: 'nonexistant',
       cookieName: ?string,
       cookieSource: ?CookieSource,
       sessionParameterInfo: SessionParameterInfo,
     }
   | {
       type: 'invalidated',
       cookieName: string,
       cookieID: string,
       cookieSource: CookieSource,
       sessionParameterInfo: SessionParameterInfo,
       platformDetails: ?PlatformDetails,
       deviceToken: ?string,
     };
 
 async function fetchUserViewer(
   cookie: string,
   cookieSource: CookieSource,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   const [cookieID, cookiePassword] = cookie.split(':');
   if (!cookieID || !cookiePassword) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.USER,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   const query = SQL`
     SELECT hash, user, last_used, platform, device_token, versions
     FROM cookies
     WHERE id = ${cookieID} AND user IS NOT NULL
   `;
   const [[result], allSessionInfo] = await Promise.all([
     dbQuery(query),
     fetchSessionInfo(sessionParameterInfo, cookieID),
   ]);
   if (result.length === 0) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.USER,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   let sessionID = null,
     sessionInfo = null;
   if (allSessionInfo) {
     ({ sessionID, ...sessionInfo } = allSessionInfo);
   }
 
   const cookieRow = result[0];
   let platformDetails = null;
   if (cookieRow.versions) {
     const versions = JSON.parse(cookieRow.versions);
     platformDetails = {
       platform: cookieRow.platform,
       codeVersion: versions.codeVersion,
       stateVersion: versions.stateVersion,
     };
   } else {
     platformDetails = { platform: cookieRow.platform };
   }
   const deviceToken = cookieRow.device_token;
 
   if (
     !bcrypt.compareSync(cookiePassword, cookieRow.hash) ||
     cookieIsExpired(cookieRow.last_used)
   ) {
     return {
       type: 'invalidated',
       cookieName: cookieTypes.USER,
       cookieID,
       cookieSource,
       sessionParameterInfo,
       platformDetails,
       deviceToken,
     };
   }
   const userID = cookieRow.user.toString();
   const viewer = new Viewer({
     isSocket: sessionParameterInfo.isSocket,
     loggedIn: true,
     id: userID,
     platformDetails,
     deviceToken,
     userID,
     cookieSource,
     cookieID,
     cookiePassword,
     sessionIdentifierType: sessionParameterInfo.sessionIdentifierType,
     sessionID,
     sessionInfo,
     isScriptViewer: false,
     ipAddress: sessionParameterInfo.ipAddress,
     userAgent: sessionParameterInfo.userAgent,
   });
   return { type: 'valid', viewer };
 }
 
 async function fetchAnonymousViewer(
   cookie: string,
   cookieSource: CookieSource,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   const [cookieID, cookiePassword] = cookie.split(':');
   if (!cookieID || !cookiePassword) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.ANONYMOUS,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   const query = SQL`
     SELECT last_used, hash, platform, device_token, versions
     FROM cookies
     WHERE id = ${cookieID} AND user IS NULL
   `;
   const [[result], allSessionInfo] = await Promise.all([
     dbQuery(query),
     fetchSessionInfo(sessionParameterInfo, cookieID),
   ]);
   if (result.length === 0) {
     return {
       type: 'nonexistant',
       cookieName: cookieTypes.ANONYMOUS,
       cookieSource,
       sessionParameterInfo,
     };
   }
 
   let sessionID = null,
     sessionInfo = null;
   if (allSessionInfo) {
     ({ sessionID, ...sessionInfo } = allSessionInfo);
   }
 
   const cookieRow = result[0];
   let platformDetails = null;
   if (cookieRow.platform && cookieRow.versions) {
     const versions = JSON.parse(cookieRow.versions);
     platformDetails = {
       platform: cookieRow.platform,
       codeVersion: versions.codeVersion,
       stateVersion: versions.stateVersion,
     };
   } else if (cookieRow.platform) {
     platformDetails = { platform: cookieRow.platform };
   }
   const deviceToken = cookieRow.device_token;
 
   if (
     !bcrypt.compareSync(cookiePassword, cookieRow.hash) ||
     cookieIsExpired(cookieRow.last_used)
   ) {
     return {
       type: 'invalidated',
       cookieName: cookieTypes.ANONYMOUS,
       cookieID,
       cookieSource,
       sessionParameterInfo,
       platformDetails,
       deviceToken,
     };
   }
   const viewer = new Viewer({
     isSocket: sessionParameterInfo.isSocket,
     loggedIn: false,
     id: cookieID,
     platformDetails,
     deviceToken,
     cookieSource,
     cookieID,
     cookiePassword,
     sessionIdentifierType: sessionParameterInfo.sessionIdentifierType,
     sessionID,
     sessionInfo,
     isScriptViewer: false,
     ipAddress: sessionParameterInfo.ipAddress,
     userAgent: sessionParameterInfo.userAgent,
   });
   return { type: 'valid', viewer };
 }
 
 type SessionInfo = {
   +sessionID: ?string,
   +lastValidated: number,
   +lastUpdate: number,
   +calendarQuery: CalendarQuery,
 };
 async function fetchSessionInfo(
   sessionParameterInfo: SessionParameterInfo,
   cookieID: string,
 ): Promise<?SessionInfo> {
   const { sessionID } = sessionParameterInfo;
   const session = sessionID !== undefined ? sessionID : cookieID;
   if (!session) {
     return null;
   }
   const query = SQL`
     SELECT query, last_validated, last_update
     FROM sessions
     WHERE id = ${session} AND cookie = ${cookieID}
   `;
   const [result] = await dbQuery(query);
   if (result.length === 0) {
     return null;
   }
   return {
     sessionID,
     lastValidated: result[0].last_validated,
     lastUpdate: result[0].last_update,
     calendarQuery: JSON.parse(result[0].query),
   };
 }
 
 // This function is meant to consume a cookie that has already been processed.
 // That means it doesn't have any logic to handle an invalid cookie, and it
 // doesn't update the cookie's last_used timestamp.
 async function fetchViewerFromCookieData(
   req: $Request,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   let viewerResult;
   const { user, anonymous } = req.cookies;
   if (user) {
     viewerResult = await fetchUserViewer(
       user,
       cookieSources.HEADER,
       sessionParameterInfo,
     );
   } else if (anonymous) {
     viewerResult = await fetchAnonymousViewer(
       anonymous,
       cookieSources.HEADER,
       sessionParameterInfo,
     );
   } else {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: null,
       sessionParameterInfo,
     };
   }
 
   // We protect against CSRF attacks by making sure that on web,
   // non-GET requests cannot use a bare cookie for session identification
   if (viewerResult.type === 'valid') {
     const { viewer } = viewerResult;
     invariant(
       req.method === 'GET' ||
         viewer.sessionIdentifierType !== sessionIdentifierTypes.COOKIE_ID ||
         !isWebPlatform(viewer.platform),
       'non-GET request from web using sessionIdentifierTypes.COOKIE_ID',
     );
   }
 
   return viewerResult;
 }
 
 async function fetchViewerFromRequestBody(
   body: mixed,
   sessionParameterInfo: SessionParameterInfo,
 ): Promise<FetchViewerResult> {
   if (!body || typeof body !== 'object') {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: null,
       sessionParameterInfo,
     };
   }
   const cookiePair = body.cookie;
   if (cookiePair === null || cookiePair === '') {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: cookieSources.BODY,
       sessionParameterInfo,
     };
   }
   if (!cookiePair || typeof cookiePair !== 'string') {
     return {
       type: 'nonexistant',
       cookieName: null,
       cookieSource: null,
       sessionParameterInfo,
     };
   }
   const [type, cookie] = cookiePair.split('=');
   if (type === cookieTypes.USER && cookie) {
     return await fetchUserViewer(
       cookie,
       cookieSources.BODY,
       sessionParameterInfo,
     );
   } else if (type === cookieTypes.ANONYMOUS && cookie) {
     return await fetchAnonymousViewer(
       cookie,
       cookieSources.BODY,
       sessionParameterInfo,
     );
   }
   return {
     type: 'nonexistant',
     cookieName: null,
     cookieSource: null,
     sessionParameterInfo,
   };
 }
 
 function getRequestIPAddress(req: $Request) {
   const { proxy } = getAppURLFactsFromRequestURL(req.originalUrl);
   let ipAddress;
   if (proxy === 'none') {
     ipAddress = req.socket.remoteAddress;
   } else if (proxy === 'apache') {
     ipAddress = req.get('X-Forwarded-For');
   }
   invariant(ipAddress, 'could not determine requesting IP address');
   return ipAddress;
 }
 
 function getSessionParameterInfoFromRequestBody(
   req: $Request,
 ): SessionParameterInfo {
   const body = (req.body: any);
   let sessionID =
     body.sessionID !== undefined || req.method !== 'GET'
       ? body.sessionID
       : null;
   if (sessionID === '') {
     sessionID = null;
   }
   const sessionIdentifierType =
     req.method === 'GET' || sessionID !== undefined
       ? sessionIdentifierTypes.BODY_SESSION_ID
       : sessionIdentifierTypes.COOKIE_ID;
   return {
     isSocket: false,
     sessionID,
     sessionIdentifierType,
     ipAddress: getRequestIPAddress(req),
     userAgent: req.get('User-Agent'),
   };
 }
 
 async function fetchViewerForJSONRequest(req: $Request): Promise<Viewer> {
   assertSecureRequest(req);
   const sessionParameterInfo = getSessionParameterInfoFromRequestBody(req);
   let result = await fetchViewerFromRequestBody(req.body, sessionParameterInfo);
   if (
     result.type === 'nonexistant' &&
     (result.cookieSource === null || result.cookieSource === undefined)
   ) {
     result = await fetchViewerFromCookieData(req, sessionParameterInfo);
   }
   return await handleFetchViewerResult(result);
 }
 
 const webPlatformDetails = { platform: 'web' };
 async function fetchViewerForHomeRequest(req: $Request): Promise<Viewer> {
   assertSecureRequest(req);
   const sessionParameterInfo = getSessionParameterInfoFromRequestBody(req);
   const result = await fetchViewerFromCookieData(req, sessionParameterInfo);
   return await handleFetchViewerResult(result, webPlatformDetails);
 }
 
 async function fetchViewerForSocket(
   req: $Request,
   clientMessage: InitialClientSocketMessage,
 ): Promise<?Viewer> {
   assertSecureRequest(req);
   const { sessionIdentification } = clientMessage.payload;
   const { sessionID } = sessionIdentification;
   const sessionParameterInfo = {
     isSocket: true,
     sessionID,
     sessionIdentifierType:
       sessionID !== undefined
         ? sessionIdentifierTypes.BODY_SESSION_ID
         : sessionIdentifierTypes.COOKIE_ID,
     ipAddress: getRequestIPAddress(req),
     userAgent: req.get('User-Agent'),
   };
 
   let result = await fetchViewerFromRequestBody(
     clientMessage.payload.sessionIdentification,
     sessionParameterInfo,
   );
   if (
     result.type === 'nonexistant' &&
     (result.cookieSource === null || result.cookieSource === undefined)
   ) {
     result = await fetchViewerFromCookieData(req, sessionParameterInfo);
   }
   if (result.type === 'valid') {
     return result.viewer;
   }
 
   const promises = {};
   if (result.cookieSource === cookieSources.BODY) {
     // We initialize a socket's Viewer after the WebSocket handshake, since to
     // properly initialize the Viewer we need a bunch of data, but that data
     // can't be sent until after the handshake. Consequently, by the time we
     // know that a cookie may be invalid, we are no longer communicating via
     // HTTP, and have no way to set a new cookie for HEADER (web) clients.
     const platformDetails =
       result.type === 'invalidated' ? result.platformDetails : null;
     const deviceToken =
       result.type === 'invalidated' ? result.deviceToken : null;
     promises.anonymousViewerData = createNewAnonymousCookie({
       platformDetails,
       deviceToken,
     });
   }
   if (result.type === 'invalidated') {
     promises.deleteCookie = deleteCookie(result.cookieID);
   }
   const { anonymousViewerData } = await promiseAll(promises);
 
   if (!anonymousViewerData) {
     return null;
   }
 
   return createViewerForInvalidFetchViewerResult(result, anonymousViewerData);
 }
 
 async function handleFetchViewerResult(
   result: FetchViewerResult,
   inputPlatformDetails?: PlatformDetails,
 ) {
   if (result.type === 'valid') {
     return result.viewer;
   }
 
   let platformDetails = inputPlatformDetails;
   if (!platformDetails && result.type === 'invalidated') {
     platformDetails = result.platformDetails;
   }
   const deviceToken = result.type === 'invalidated' ? result.deviceToken : null;
 
   const [anonymousViewerData] = await Promise.all([
     createNewAnonymousCookie({ platformDetails, deviceToken }),
     result.type === 'invalidated' ? deleteCookie(result.cookieID) : null,
   ]);
 
   return createViewerForInvalidFetchViewerResult(result, anonymousViewerData);
 }
 
 function createViewerForInvalidFetchViewerResult(
   result: InvalidFetchViewerResult,
   anonymousViewerData: AnonymousViewerData,
 ): Viewer {
   // If a null cookie was specified in the request body, result.cookieSource
   // will still be BODY here. The only way it would be null or undefined here
   // is if there was no cookie specified in either the body or the header, in
   // which case we default to returning the new cookie in the response header.
   const cookieSource =
     result.cookieSource !== null && result.cookieSource !== undefined
       ? result.cookieSource
       : cookieSources.HEADER;
   const viewer = new Viewer({
     ...anonymousViewerData,
     cookieSource,
     sessionIdentifierType: result.sessionParameterInfo.sessionIdentifierType,
     isSocket: result.sessionParameterInfo.isSocket,
     ipAddress: result.sessionParameterInfo.ipAddress,
     userAgent: result.sessionParameterInfo.userAgent,
   });
   viewer.sessionChanged = true;
 
   // If cookieName is falsey, that tells us that there was no cookie specified
   // in the request, which means we can't be invalidating anything.
   if (result.cookieName) {
     viewer.cookieInvalidated = true;
     viewer.initialCookieName = result.cookieName;
   }
 
   return viewer;
 }
 
 function addSessionChangeInfoToResult(
   viewer: Viewer,
   res: $Response,
   result: Object,
   appURLFacts: AppURLFacts,
 ) {
   let threadInfos = {},
     userInfos = {};
   if (result.cookieChange) {
     ({ threadInfos, userInfos } = result.cookieChange);
   }
   let sessionChange;
   if (viewer.cookieInvalidated) {
     sessionChange = ({
       cookieInvalidated: true,
       threadInfos,
       userInfos: (values(userInfos).map(a => a): UserInfo[]),
       currentUserInfo: {
         id: viewer.cookieID,
         anonymous: true,
       },
     }: ServerSessionChange);
   } else {
     sessionChange = ({
       cookieInvalidated: false,
       threadInfos,
       userInfos: (values(userInfos).map(a => a): UserInfo[]),
     }: ServerSessionChange);
   }
   if (viewer.cookieSource === cookieSources.BODY) {
     sessionChange.cookie = viewer.cookiePairString;
   } else {
     addActualHTTPCookie(viewer, res, appURLFacts);
   }
   if (viewer.sessionIdentifierType === sessionIdentifierTypes.BODY_SESSION_ID) {
     sessionChange.sessionID = viewer.sessionID ? viewer.sessionID : null;
   }
   result.cookieChange = sessionChange;
 }
 
 type AnonymousCookieCreationParams = Shape<{
   +platformDetails: ?PlatformDetails,
   +deviceToken: ?string,
 }>;
 const defaultPlatformDetails = {};
 
 // The result of this function should not be passed directly to the Viewer
 // constructor. Instead, it should be passed to viewer.setNewCookie. There are
 // several fields on AnonymousViewerData that are not set by this function:
 // sessionIdentifierType, cookieSource, ipAddress, and userAgent. These
 // parameters all depend on the initial request. If the result of this function
 // is passed to the Viewer constructor directly, the resultant Viewer object
 // will throw whenever anybody attempts to access the relevant properties.
 async function createNewAnonymousCookie(
   params: AnonymousCookieCreationParams,
 ): Promise<AnonymousViewerData> {
   const { platformDetails, deviceToken } = params;
   const { platform, ...versions } = platformDetails || defaultPlatformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
 
   const time = Date.now();
   const cookiePassword = crypto.randomBytes(32).toString('hex');
   const cookieHash = bcrypt.hashSync(cookiePassword);
   const [[id]] = await Promise.all([
     createIDs('cookies', 1),
     deviceToken ? clearDeviceToken(deviceToken) : undefined,
   ]);
 
   const cookieRow = [
     id,
     cookieHash,
     null,
     platform,
     time,
     time,
     deviceToken,
     versionsString,
   ];
   const query = SQL`
     INSERT INTO cookies(id, hash, user, platform, creation_time, last_used,
       device_token, versions)
     VALUES ${[cookieRow]}
   `;
   await dbQuery(query);
   return {
     loggedIn: false,
     id,
     platformDetails,
     deviceToken,
     cookieID: id,
     cookiePassword,
     sessionID: undefined,
     sessionInfo: null,
     cookieInsertedThisRequest: true,
     isScriptViewer: false,
   };
 }
 
 type UserCookieCreationParams = {
   +platformDetails: PlatformDetails,
   +deviceToken?: ?string,
   +socialProof?: ?SIWESocialProof,
   +signedIdentityKeysBlob?: ?SignedIdentityKeysBlob,
 };
 
 // The result of this function should never be passed directly to the Viewer
 // constructor. Instead, it should be passed to viewer.setNewCookie. There are
 // several fields on UserViewerData that are not set by this function:
 // sessionID, sessionIdentifierType, cookieSource, and ipAddress. These
 // parameters all depend on the initial request. If the result of this function
 // is passed to the Viewer constructor directly, the resultant Viewer object
 // will throw whenever anybody attempts to access the relevant properties.
 async function createNewUserCookie(
   userID: string,
   params: UserCookieCreationParams,
 ): Promise<UserViewerData> {
   const { platformDetails, deviceToken, socialProof, signedIdentityKeysBlob } =
     params;
   const { platform, ...versions } = platformDetails || defaultPlatformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
 
   const time = Date.now();
   const cookiePassword = crypto.randomBytes(32).toString('hex');
   const cookieHash = bcrypt.hashSync(cookiePassword);
   const [[cookieID]] = await Promise.all([
     createIDs('cookies', 1),
     deviceToken ? clearDeviceToken(deviceToken) : undefined,
   ]);
 
   const cookieRow = [
     cookieID,
     cookieHash,
     userID,
     platform,
     time,
     time,
     deviceToken,
     versionsString,
     JSON.stringify(socialProof),
     signedIdentityKeysBlob ? JSON.stringify(signedIdentityKeysBlob) : null,
   ];
   const query = SQL`
     INSERT INTO cookies(id, hash, user, platform, creation_time, last_used,
       device_token, versions, social_proof, signed_identity_keys)
     VALUES ${[cookieRow]}
   `;
   await dbQuery(query);
   return {
     loggedIn: true,
     id: userID,
     platformDetails,
     deviceToken,
     userID,
     cookieID,
     sessionID: undefined,
     sessionInfo: null,
     cookiePassword,
     cookieInsertedThisRequest: true,
     isScriptViewer: false,
   };
 }
 
 // This gets called after createNewUserCookie and from websiteResponder. If the
 // Viewer's sessionIdentifierType is COOKIE_ID then the cookieID is used as the
 // session identifier; otherwise, a new ID is created for the session.
 async function setNewSession(
   viewer: Viewer,
   calendarQuery: CalendarQuery,
   initialLastUpdate: number,
 ): Promise<void> {
   if (viewer.sessionIdentifierType !== sessionIdentifierTypes.COOKIE_ID) {
     const [sessionID] = await createIDs('sessions', 1);
     viewer.setSessionID(sessionID);
   }
   await createSession(viewer, calendarQuery, initialLastUpdate);
 }
 
 async function extendCookieLifespan(cookieID: string) {
   const time = Date.now();
   const query = SQL`
     UPDATE cookies SET last_used = ${time} WHERE id = ${cookieID}
   `;
   await dbQuery(query);
 }
 
 function addCookieToJSONResponse(
   viewer: Viewer,
   res: $Response,
   result: Object,
   expectCookieInvalidation: boolean,
   appURLFacts: AppURLFacts,
 ) {
   if (expectCookieInvalidation) {
     viewer.cookieInvalidated = false;
   }
   if (!viewer.getData().cookieInsertedThisRequest) {
     handleAsyncPromise(extendCookieLifespan(viewer.cookieID));
   }
   if (viewer.sessionChanged) {
     addSessionChangeInfoToResult(viewer, res, result, appURLFacts);
   } else if (viewer.cookieSource !== cookieSources.BODY) {
     addActualHTTPCookie(viewer, res, appURLFacts);
   }
 }
 
 function addCookieToHomeResponse(
   viewer: Viewer,
   res: $Response,
   appURLFacts: AppURLFacts,
 ) {
   if (!viewer.getData().cookieInsertedThisRequest) {
     handleAsyncPromise(extendCookieLifespan(viewer.cookieID));
   }
   addActualHTTPCookie(viewer, res, appURLFacts);
 }
 
 function getCookieOptions(appURLFacts: AppURLFacts) {
   const { baseDomain, basePath, https } = appURLFacts;
   const domainAsURL = new url.URL(baseDomain);
   return {
     domain: domainAsURL.hostname,
     path: basePath,
     httpOnly: true,
     secure: https,
     maxAge: cookieLifetime,
     sameSite: 'Strict',
   };
 }
 
 function addActualHTTPCookie(
   viewer: Viewer,
   res: $Response,
   appURLFacts: AppURLFacts,
 ) {
   res.cookie(
     viewer.cookieName,
     viewer.cookieString,
     getCookieOptions(appURLFacts),
   );
   if (viewer.cookieName !== viewer.initialCookieName) {
     res.clearCookie(viewer.initialCookieName, getCookieOptions(appURLFacts));
   }
 }
 
 async function setCookieSignedIdentityKeysBlob(
   cookieID: string,
   signedIdentityKeysBlob: SignedIdentityKeysBlob,
 ) {
   const signedIdentityKeysStr = JSON.stringify(signedIdentityKeysBlob);
   const query = SQL`
     UPDATE cookies 
     SET signed_identity_keys = ${signedIdentityKeysStr}
     WHERE id = ${cookieID}
   `;
   await dbQuery(query);
 }
 
 // Returns `true` if row with `id = cookieID` exists AND
 // `signed_identity_keys` is `NULL`. Otherwise, returns `false`.
 async function isCookieMissingSignedIdentityKeysBlob(
   cookieID: string,
 ): Promise<boolean> {
   const query = SQL`
     SELECT signed_identity_keys
     FROM cookies 
     WHERE id = ${cookieID}
   `;
   const [queryResult] = await dbQuery(query);
   return (
     queryResult.length === 1 && queryResult[0].signed_identity_keys === null
   );
 }
 
+async function isCookieMissingOlmNotificationsSession(
+  viewer: Viewer,
+): Promise<boolean> {
+  if (
+    !viewer.platformDetails ||
+    viewer.platformDetails.platform !== 'ios' ||
+    !viewer.platformDetails.codeVersion ||
+    viewer.platformDetails.codeVersion < 222
+  ) {
+    return false;
+  }
+  const query = SQL`
+    SELECT COUNT(*) AS count
+    FROM olm_sessions
+    WHERE cookie_id = ${viewer.cookieID} AND is_content = FALSE
+  `;
+  const [queryResult] = await dbQuery(query);
+  return queryResult[0].count === 0;
+}
+
 async function setCookiePlatform(
   viewer: Viewer,
   platform: Platform,
 ): Promise<void> {
   const newPlatformDetails = { ...viewer.platformDetails, platform };
   viewer.setPlatformDetails(newPlatformDetails);
   const query = SQL`
     UPDATE cookies
     SET platform = ${platform}
     WHERE id = ${viewer.cookieID}
   `;
   await dbQuery(query);
 }
 
 async function setCookiePlatformDetails(
   viewer: Viewer,
   platformDetails: PlatformDetails,
 ): Promise<void> {
   if (
     hasMinCodeVersion(platformDetails, { native: 70 }) &&
     !hasMinCodeVersion(viewer.platformDetails, { native: 70 })
   ) {
     await updateThreadMembers(viewer);
   }
 
   viewer.setPlatformDetails(platformDetails);
   const { platform, ...versions } = platformDetails;
   const versionsString =
     Object.keys(versions).length > 0 ? JSON.stringify(versions) : null;
   const query = SQL`
     UPDATE cookies
     SET platform = ${platform}, versions = ${versionsString}
     WHERE id = ${viewer.cookieID}
   `;
   await dbQuery(query);
 }
 
 export {
   fetchViewerForJSONRequest,
   fetchViewerForHomeRequest,
   fetchViewerForSocket,
   createNewAnonymousCookie,
   createNewUserCookie,
   setNewSession,
   extendCookieLifespan,
   addCookieToJSONResponse,
   addCookieToHomeResponse,
   setCookieSignedIdentityKeysBlob,
   isCookieMissingSignedIdentityKeysBlob,
   setCookiePlatform,
   setCookiePlatformDetails,
+  isCookieMissingOlmNotificationsSession,
 };
diff --git a/keyserver/src/socket/socket.js b/keyserver/src/socket/socket.js
index 93479ea25..ed1d8ed18 100644
--- a/keyserver/src/socket/socket.js
+++ b/keyserver/src/socket/socket.js
@@ -1,834 +1,847 @@
 // @flow
 
 import type { $Request } from 'express';
 import invariant from 'invariant';
 import _debounce from 'lodash/debounce.js';
 import t from 'tcomb';
 import type { TUnion } from 'tcomb';
 import WebSocket from 'ws';
 
 import { baseLegalPolicies } from 'lib/facts/policies.js';
 import { mostRecentMessageTimestamp } from 'lib/shared/message-utils.js';
 import {
   serverRequestSocketTimeout,
   serverResponseTimeout,
 } from 'lib/shared/timeouts.js';
 import { mostRecentUpdateTimestamp } from 'lib/shared/update-utils.js';
 import type { Shape } from 'lib/types/core.js';
 import { endpointIsSocketSafe } from 'lib/types/endpoints.js';
 import { defaultNumberPerThread } from 'lib/types/message-types.js';
 import { redisMessageTypes, type RedisMessage } from 'lib/types/redis-types.js';
 import { serverRequestTypes } from 'lib/types/request-types.js';
 import {
   cookieSources,
   sessionCheckFrequency,
   stateCheckInactivityActivationInterval,
 } from 'lib/types/session-types.js';
 import {
   type ClientSocketMessage,
   type InitialClientSocketMessage,
   type ResponsesClientSocketMessage,
   type ServerStateSyncFullSocketPayload,
   type ServerServerSocketMessage,
   type ErrorServerSocketMessage,
   type AuthErrorServerSocketMessage,
   type PingClientSocketMessage,
   type AckUpdatesClientSocketMessage,
   type APIRequestClientSocketMessage,
   clientSocketMessageTypes,
   stateSyncPayloadTypes,
   serverSocketMessageTypes,
   serverServerSocketMessageValidator,
 } from 'lib/types/socket-types.js';
 import { ServerError } from 'lib/utils/errors.js';
 import { values } from 'lib/utils/objects.js';
 import { promiseAll } from 'lib/utils/promises.js';
 import SequentialPromiseResolver from 'lib/utils/sequential-promise-resolver.js';
 import sleep from 'lib/utils/sleep.js';
 import { tShape, tCookie } from 'lib/utils/validation-utils.js';
 
 import { RedisSubscriber } from './redis.js';
 import {
   clientResponseInputValidator,
   processClientResponses,
   initializeSession,
   checkState,
 } from './session-utils.js';
 import { fetchUpdateInfosWithRawUpdateInfos } from '../creators/update-creator.js';
 import { deleteActivityForViewerSession } from '../deleters/activity-deleters.js';
 import { deleteCookie } from '../deleters/cookie-deleters.js';
 import { deleteUpdatesBeforeTimeTargetingSession } from '../deleters/update-deleters.js';
 import { jsonEndpoints } from '../endpoints.js';
 import { fetchEntryInfos } from '../fetchers/entry-fetchers.js';
 import {
   fetchMessageInfosSince,
   getMessageFetchResultFromRedisMessages,
 } from '../fetchers/message-fetchers.js';
 import { fetchThreadInfos } from '../fetchers/thread-fetchers.js';
 import { fetchUpdateInfos } from '../fetchers/update-fetchers.js';
 import {
   fetchCurrentUserInfo,
   fetchKnownUserInfos,
 } from '../fetchers/user-fetchers.js';
 import {
   newEntryQueryInputValidator,
   verifyCalendarQueryThreadIDs,
 } from '../responders/entry-responders.js';
 import { handleAsyncPromise } from '../responders/handlers.js';
 import {
   fetchViewerForSocket,
   extendCookieLifespan,
   createNewAnonymousCookie,
   isCookieMissingSignedIdentityKeysBlob,
+  isCookieMissingOlmNotificationsSession,
 } from '../session/cookies.js';
 import { Viewer } from '../session/viewer.js';
 import { commitSessionUpdate } from '../updaters/session-updaters.js';
 import { assertSecureRequest } from '../utils/security-utils.js';
 import {
   checkInputValidator,
   checkClientSupported,
   policiesValidator,
   validateOutput,
 } from '../utils/validation-utils.js';
 
 const clientSocketMessageInputValidator: TUnion<ClientSocketMessage> = t.union([
   tShape({
     type: t.irreducible(
       'clientSocketMessageTypes.INITIAL',
       x => x === clientSocketMessageTypes.INITIAL,
     ),
     id: t.Number,
     payload: tShape({
       sessionIdentification: tShape({
         cookie: t.maybe(tCookie),
         sessionID: t.maybe(t.String),
       }),
       sessionState: tShape({
         calendarQuery: newEntryQueryInputValidator,
         messagesCurrentAsOf: t.Number,
         updatesCurrentAsOf: t.Number,
         watchedIDs: t.list(t.String),
       }),
       clientResponses: t.list(clientResponseInputValidator),
     }),
   }),
   tShape({
     type: t.irreducible(
       'clientSocketMessageTypes.RESPONSES',
       x => x === clientSocketMessageTypes.RESPONSES,
     ),
     id: t.Number,
     payload: tShape({
       clientResponses: t.list(clientResponseInputValidator),
     }),
   }),
   tShape({
     type: t.irreducible(
       'clientSocketMessageTypes.PING',
       x => x === clientSocketMessageTypes.PING,
     ),
     id: t.Number,
   }),
   tShape({
     type: t.irreducible(
       'clientSocketMessageTypes.ACK_UPDATES',
       x => x === clientSocketMessageTypes.ACK_UPDATES,
     ),
     id: t.Number,
     payload: tShape({
       currentAsOf: t.Number,
     }),
   }),
   tShape({
     type: t.irreducible(
       'clientSocketMessageTypes.API_REQUEST',
       x => x === clientSocketMessageTypes.API_REQUEST,
     ),
     id: t.Number,
     payload: tShape({
       endpoint: t.String,
       input: t.maybe(t.Object),
     }),
   }),
 ]);
 
 function onConnection(ws: WebSocket, req: $Request) {
   assertSecureRequest(req);
   new Socket(ws, req);
 }
 
 type StateCheckConditions = {
   activityRecentlyOccurred: boolean,
   stateCheckOngoing: boolean,
 };
 
 class Socket {
   ws: WebSocket;
   httpRequest: $Request;
   viewer: ?Viewer;
   redis: ?RedisSubscriber;
   redisPromiseResolver: SequentialPromiseResolver<ServerServerSocketMessage>;
 
   stateCheckConditions: StateCheckConditions = {
     activityRecentlyOccurred: true,
     stateCheckOngoing: false,
   };
   stateCheckTimeoutID: ?TimeoutID;
 
   constructor(ws: WebSocket, httpRequest: $Request) {
     this.ws = ws;
     this.httpRequest = httpRequest;
     ws.on('message', this.onMessage);
     ws.on('close', this.onClose);
     this.resetTimeout();
     this.redisPromiseResolver = new SequentialPromiseResolver(this.sendMessage);
   }
 
   onMessage = async (
     messageString: string | Buffer | ArrayBuffer | Array<Buffer>,
   ) => {
     invariant(typeof messageString === 'string', 'message should be string');
     let clientSocketMessage: ?ClientSocketMessage;
     try {
       this.resetTimeout();
       const messageObject = JSON.parse(messageString);
       clientSocketMessage = checkInputValidator(
         clientSocketMessageInputValidator,
         messageObject,
       );
       if (clientSocketMessage.type === clientSocketMessageTypes.INITIAL) {
         if (this.viewer) {
           // This indicates that the user sent multiple INITIAL messages.
           throw new ServerError('socket_already_initialized');
         }
         this.viewer = await fetchViewerForSocket(
           this.httpRequest,
           clientSocketMessage,
         );
         if (!this.viewer) {
           // This indicates that the cookie was invalid, but the client is using
           // cookieSources.HEADER and thus can't accept a new cookie over
           // WebSockets. See comment under catch block for socket_deauthorized.
           throw new ServerError('socket_deauthorized');
         }
       }
       const { viewer } = this;
       if (!viewer) {
         // This indicates a non-INITIAL message was sent by the client before
         // the INITIAL message.
         throw new ServerError('socket_uninitialized');
       }
       if (viewer.sessionChanged) {
         // This indicates that the cookie was invalid, and we've assigned a new
         // anonymous one.
         throw new ServerError('socket_deauthorized');
       }
       if (!viewer.loggedIn) {
         // This indicates that the specified cookie was an anonymous one.
         throw new ServerError('not_logged_in');
       }
       await checkClientSupported(
         viewer,
         clientSocketMessageInputValidator,
         clientSocketMessage,
       );
       await policiesValidator(viewer, baseLegalPolicies);
 
       const serverResponses = await this.handleClientSocketMessage(
         clientSocketMessage,
       );
       if (!this.redis) {
         this.redis = new RedisSubscriber(
           { userID: viewer.userID, sessionID: viewer.session },
           this.onRedisMessage,
         );
       }
       if (viewer.sessionChanged) {
         // This indicates that something has caused the session to change, which
         // shouldn't happen from inside a WebSocket since we can't handle cookie
         // invalidation.
         throw new ServerError('session_mutated_from_socket');
       }
       if (clientSocketMessage.type !== clientSocketMessageTypes.PING) {
         handleAsyncPromise(extendCookieLifespan(viewer.cookieID));
       }
       for (const response of serverResponses) {
         this.sendMessage(response);
       }
       if (clientSocketMessage.type === clientSocketMessageTypes.INITIAL) {
         this.onSuccessfulConnection();
       }
     } catch (error) {
       console.warn(error);
       if (!(error instanceof ServerError)) {
         const errorMessage: ErrorServerSocketMessage = {
           type: serverSocketMessageTypes.ERROR,
           message: error.message,
         };
         const responseTo = clientSocketMessage ? clientSocketMessage.id : null;
         if (responseTo !== null) {
           errorMessage.responseTo = responseTo;
         }
         this.markActivityOccurred();
         this.sendMessage(errorMessage);
         return;
       }
       invariant(clientSocketMessage, 'should be set');
       const responseTo = clientSocketMessage.id;
       if (error.message === 'socket_deauthorized') {
         const authErrorMessage: AuthErrorServerSocketMessage = {
           type: serverSocketMessageTypes.AUTH_ERROR,
           responseTo,
           message: error.message,
         };
         if (this.viewer) {
           // viewer should only be falsey for cookieSources.HEADER (web)
           // clients. Usually if the cookie is invalid we construct a new
           // anonymous Viewer with a new cookie, and then pass the cookie down
           // in the error. But we can't pass HTTP cookies in WebSocket messages.
           authErrorMessage.sessionChange = {
             cookie: this.viewer.cookiePairString,
             currentUserInfo: {
               id: this.viewer.cookieID,
               anonymous: true,
             },
           };
         }
         this.sendMessage(authErrorMessage);
         this.ws.close(4100, error.message);
         return;
       } else if (error.message === 'client_version_unsupported') {
         const { viewer } = this;
         invariant(viewer, 'should be set');
         const promises = {};
         promises.deleteCookie = deleteCookie(viewer.cookieID);
         if (viewer.cookieSource !== cookieSources.BODY) {
           promises.anonymousViewerData = createNewAnonymousCookie({
             platformDetails: error.platformDetails,
             deviceToken: viewer.deviceToken,
           });
         }
         const { anonymousViewerData } = await promiseAll(promises);
         const authErrorMessage: AuthErrorServerSocketMessage = {
           type: serverSocketMessageTypes.AUTH_ERROR,
           responseTo,
           message: error.message,
         };
         if (anonymousViewerData) {
           // It is normally not safe to pass the result of
           // createNewAnonymousCookie to the Viewer constructor. That is because
           // createNewAnonymousCookie leaves several fields of
           // AnonymousViewerData unset, and consequently Viewer will throw when
           // access is attempted. It is only safe here because we can guarantee
           // that only cookiePairString and cookieID are accessed on anonViewer
           // below.
           const anonViewer = new Viewer(anonymousViewerData);
           authErrorMessage.sessionChange = {
             cookie: anonViewer.cookiePairString,
             currentUserInfo: {
               id: anonViewer.cookieID,
               anonymous: true,
             },
           };
         }
         this.sendMessage(authErrorMessage);
         this.ws.close(4101, error.message);
         return;
       }
       if (error.payload) {
         this.sendMessage({
           type: serverSocketMessageTypes.ERROR,
           responseTo,
           message: error.message,
           payload: error.payload,
         });
       } else {
         this.sendMessage({
           type: serverSocketMessageTypes.ERROR,
           responseTo,
           message: error.message,
         });
       }
       if (error.message === 'not_logged_in') {
         this.ws.close(4102, error.message);
       } else if (error.message === 'session_mutated_from_socket') {
         this.ws.close(4103, error.message);
       } else {
         this.markActivityOccurred();
       }
     }
   };
 
   onClose = async () => {
     this.clearStateCheckTimeout();
     this.resetTimeout.cancel();
     this.debouncedAfterActivity.cancel();
     if (this.viewer && this.viewer.hasSessionInfo) {
       await deleteActivityForViewerSession(this.viewer);
     }
     if (this.redis) {
       this.redis.quit();
       this.redis = null;
     }
   };
 
   sendMessage = (message: ServerServerSocketMessage) => {
     invariant(
       this.ws.readyState > 0,
       "shouldn't send message until connection established",
     );
     if (this.ws.readyState === 1) {
       const { viewer } = this;
       const validatedMessage = validateOutput(
         viewer?.platformDetails,
         serverServerSocketMessageValidator,
         message,
       );
       this.ws.send(JSON.stringify(validatedMessage));
     }
   };
 
   async handleClientSocketMessage(
     message: ClientSocketMessage,
   ): Promise<ServerServerSocketMessage[]> {
     const resultPromise = (async () => {
       if (message.type === clientSocketMessageTypes.INITIAL) {
         this.markActivityOccurred();
         return await this.handleInitialClientSocketMessage(message);
       } else if (message.type === clientSocketMessageTypes.RESPONSES) {
         this.markActivityOccurred();
         return await this.handleResponsesClientSocketMessage(message);
       } else if (message.type === clientSocketMessageTypes.PING) {
         return this.handlePingClientSocketMessage(message);
       } else if (message.type === clientSocketMessageTypes.ACK_UPDATES) {
         this.markActivityOccurred();
         return await this.handleAckUpdatesClientSocketMessage(message);
       } else if (message.type === clientSocketMessageTypes.API_REQUEST) {
         this.markActivityOccurred();
         return await this.handleAPIRequestClientSocketMessage(message);
       }
       return [];
     })();
     const timeoutPromise = (async () => {
       await sleep(serverResponseTimeout);
       throw new ServerError('socket_response_timeout');
     })();
     return await Promise.race([resultPromise, timeoutPromise]);
   }
 
   async handleInitialClientSocketMessage(
     message: InitialClientSocketMessage,
   ): Promise<ServerServerSocketMessage[]> {
     const { viewer } = this;
     invariant(viewer, 'should be set');
 
     const responses = [];
 
     const { sessionState, clientResponses } = message.payload;
     const {
       calendarQuery,
       updatesCurrentAsOf: oldUpdatesCurrentAsOf,
       messagesCurrentAsOf: oldMessagesCurrentAsOf,
       watchedIDs,
     } = sessionState;
     await verifyCalendarQueryThreadIDs(calendarQuery);
 
     const sessionInitializationResult = await initializeSession(
       viewer,
       calendarQuery,
       oldUpdatesCurrentAsOf,
     );
 
     const threadCursors = {};
     for (const watchedThreadID of watchedIDs) {
       threadCursors[watchedThreadID] = null;
     }
     const messageSelectionCriteria = {
       threadCursors,
       joinedThreads: true,
       newerThan: oldMessagesCurrentAsOf,
     };
     const [fetchMessagesResult, { serverRequests, activityUpdateResult }] =
       await Promise.all([
         fetchMessageInfosSince(
           viewer,
           messageSelectionCriteria,
           defaultNumberPerThread,
         ),
         processClientResponses(viewer, clientResponses),
       ]);
     const messagesResult = {
       rawMessageInfos: fetchMessagesResult.rawMessageInfos,
       truncationStatuses: fetchMessagesResult.truncationStatuses,
       currentAsOf: mostRecentMessageTimestamp(
         fetchMessagesResult.rawMessageInfos,
         oldMessagesCurrentAsOf,
       ),
     };
 
     const isCookieMissingSignedIdentityKeysBlobPromise =
       isCookieMissingSignedIdentityKeysBlob(viewer.cookieID);
 
+    const isCookieMissingOlmNotificationsSessionPromise =
+      isCookieMissingOlmNotificationsSession(viewer);
+
     if (!sessionInitializationResult.sessionContinued) {
       const [threadsResult, entriesResult, currentUserInfo, knownUserInfos] =
         await Promise.all([
           fetchThreadInfos(viewer),
           fetchEntryInfos(viewer, [calendarQuery]),
           fetchCurrentUserInfo(viewer),
           fetchKnownUserInfos(viewer),
         ]);
       const payload: ServerStateSyncFullSocketPayload = {
         type: stateSyncPayloadTypes.FULL,
         messagesResult,
         threadInfos: threadsResult.threadInfos,
         currentUserInfo,
         rawEntryInfos: entriesResult.rawEntryInfos,
         userInfos: values(knownUserInfos),
         updatesCurrentAsOf: oldUpdatesCurrentAsOf,
       };
       if (viewer.sessionChanged) {
         // If initializeSession encounters,
         // sessionIdentifierTypes.BODY_SESSION_ID but the session
         // is unspecified or expired,
         // it will set a new sessionID and specify viewer.sessionChanged
         const { sessionID } = viewer;
         invariant(
           sessionID !== null && sessionID !== undefined,
           'should be set',
         );
         payload.sessionID = sessionID;
         viewer.sessionChanged = false;
       }
       responses.push({
         type: serverSocketMessageTypes.STATE_SYNC,
         responseTo: message.id,
         payload,
       });
     } else {
       const { sessionUpdate, deltaEntryInfoResult } =
         sessionInitializationResult;
 
       const promises = {};
       promises.deleteExpiredUpdates = deleteUpdatesBeforeTimeTargetingSession(
         viewer,
         oldUpdatesCurrentAsOf,
       );
       promises.fetchUpdateResult = fetchUpdateInfos(
         viewer,
         oldUpdatesCurrentAsOf,
         calendarQuery,
       );
       promises.sessionUpdate = commitSessionUpdate(viewer, sessionUpdate);
       const { fetchUpdateResult } = await promiseAll(promises);
 
       const { updateInfos, userInfos } = fetchUpdateResult;
       const newUpdatesCurrentAsOf = mostRecentUpdateTimestamp(
         [...updateInfos],
         oldUpdatesCurrentAsOf,
       );
       const updatesResult = {
         newUpdates: updateInfos,
         currentAsOf: newUpdatesCurrentAsOf,
       };
 
       responses.push({
         type: serverSocketMessageTypes.STATE_SYNC,
         responseTo: message.id,
         payload: {
           type: stateSyncPayloadTypes.INCREMENTAL,
           messagesResult,
           updatesResult,
           deltaEntryInfos: deltaEntryInfoResult.rawEntryInfos,
           deletedEntryIDs: deltaEntryInfoResult.deletedEntryIDs,
           userInfos: values(userInfos),
         },
       });
     }
 
-    const signedIdentityKeysBlobMissing =
-      await isCookieMissingSignedIdentityKeysBlobPromise;
+    const [signedIdentityKeysBlobMissing, olmNotificationsSessionMissing] =
+      await Promise.all([
+        isCookieMissingSignedIdentityKeysBlobPromise,
+        isCookieMissingOlmNotificationsSessionPromise,
+      ]);
 
     if (signedIdentityKeysBlobMissing) {
       serverRequests.push({
         type: serverRequestTypes.SIGNED_IDENTITY_KEYS_BLOB,
       });
     }
 
+    if (olmNotificationsSessionMissing) {
+      serverRequests.push({
+        type: serverRequestTypes.INITIAL_NOTIFICATIONS_ENCRYPTED_MESSAGE,
+      });
+    }
+
     if (serverRequests.length > 0 || clientResponses.length > 0) {
       // We send this message first since the STATE_SYNC triggers the client's
       // connection status to shift to "connected", and we want to make sure the
       // client responses are cleared from Redux before that happens
       responses.unshift({
         type: serverSocketMessageTypes.REQUESTS,
         responseTo: message.id,
         payload: { serverRequests },
       });
     }
 
     if (activityUpdateResult) {
       // Same reason for unshifting as above
       responses.unshift({
         type: serverSocketMessageTypes.ACTIVITY_UPDATE_RESPONSE,
         responseTo: message.id,
         payload: activityUpdateResult,
       });
     }
 
     return responses;
   }
 
   async handleResponsesClientSocketMessage(
     message: ResponsesClientSocketMessage,
   ): Promise<ServerServerSocketMessage[]> {
     const { viewer } = this;
     invariant(viewer, 'should be set');
 
     const { clientResponses } = message.payload;
     const { stateCheckStatus } = await processClientResponses(
       viewer,
       clientResponses,
     );
 
     const serverRequests = [];
     if (stateCheckStatus && stateCheckStatus.status !== 'state_check') {
       const { sessionUpdate, checkStateRequest } = await checkState(
         viewer,
         stateCheckStatus,
         viewer.calendarQuery,
       );
       if (sessionUpdate) {
         await commitSessionUpdate(viewer, sessionUpdate);
         this.setStateCheckConditions({ stateCheckOngoing: false });
       }
       if (checkStateRequest) {
         serverRequests.push(checkStateRequest);
       }
     }
 
     // We send a response message regardless of whether we have any requests,
     // since we need to ack the client's responses
     return [
       {
         type: serverSocketMessageTypes.REQUESTS,
         responseTo: message.id,
         payload: { serverRequests },
       },
     ];
   }
 
   handlePingClientSocketMessage(
     message: PingClientSocketMessage,
   ): ServerServerSocketMessage[] {
     return [
       {
         type: serverSocketMessageTypes.PONG,
         responseTo: message.id,
       },
     ];
   }
 
   async handleAckUpdatesClientSocketMessage(
     message: AckUpdatesClientSocketMessage,
   ): Promise<ServerServerSocketMessage[]> {
     const { viewer } = this;
     invariant(viewer, 'should be set');
     const { currentAsOf } = message.payload;
     await Promise.all([
       deleteUpdatesBeforeTimeTargetingSession(viewer, currentAsOf),
       commitSessionUpdate(viewer, { lastUpdate: currentAsOf }),
     ]);
     return [];
   }
 
   async handleAPIRequestClientSocketMessage(
     message: APIRequestClientSocketMessage,
   ): Promise<ServerServerSocketMessage[]> {
     if (!endpointIsSocketSafe(message.payload.endpoint)) {
       throw new ServerError('endpoint_unsafe_for_socket');
     }
     const { viewer } = this;
     invariant(viewer, 'should be set');
     const responder = jsonEndpoints[message.payload.endpoint];
     await policiesValidator(viewer, responder.requiredPolicies);
     const response = await responder.responder(viewer, message.payload.input);
     return [
       {
         type: serverSocketMessageTypes.API_RESPONSE,
         responseTo: message.id,
         payload: response,
       },
     ];
   }
 
   onRedisMessage = async (message: RedisMessage) => {
     try {
       await this.processRedisMessage(message);
     } catch (e) {
       console.warn(e);
     }
   };
 
   async processRedisMessage(message: RedisMessage) {
     if (message.type === redisMessageTypes.START_SUBSCRIPTION) {
       this.ws.terminate();
     } else if (message.type === redisMessageTypes.NEW_UPDATES) {
       const { viewer } = this;
       invariant(viewer, 'should be set');
       if (message.ignoreSession && message.ignoreSession === viewer.session) {
         return;
       }
       const rawUpdateInfos = message.updates;
       this.redisPromiseResolver.add(
         (async () => {
           const { updateInfos, userInfos } =
             await fetchUpdateInfosWithRawUpdateInfos(rawUpdateInfos, {
               viewer,
             });
           if (updateInfos.length === 0) {
             console.warn(
               'could not get any UpdateInfos from redisMessageTypes.NEW_UPDATES',
             );
             return null;
           }
           this.markActivityOccurred();
           return {
             type: serverSocketMessageTypes.UPDATES,
             payload: {
               updatesResult: {
                 currentAsOf: mostRecentUpdateTimestamp([...updateInfos], 0),
                 newUpdates: updateInfos,
               },
               userInfos: values(userInfos),
             },
           };
         })(),
       );
     } else if (message.type === redisMessageTypes.NEW_MESSAGES) {
       const { viewer } = this;
       invariant(viewer, 'should be set');
       const rawMessageInfos = message.messages;
       const messageFetchResult = getMessageFetchResultFromRedisMessages(
         viewer,
         rawMessageInfos,
       );
       if (messageFetchResult.rawMessageInfos.length === 0) {
         console.warn(
           'could not get any rawMessageInfos from ' +
             'redisMessageTypes.NEW_MESSAGES',
         );
         return;
       }
       this.redisPromiseResolver.add(
         (async () => {
           this.markActivityOccurred();
           return {
             type: serverSocketMessageTypes.MESSAGES,
             payload: {
               messagesResult: {
                 rawMessageInfos: messageFetchResult.rawMessageInfos,
                 truncationStatuses: messageFetchResult.truncationStatuses,
                 currentAsOf: mostRecentMessageTimestamp(
                   messageFetchResult.rawMessageInfos,
                   0,
                 ),
               },
             },
           };
         })(),
       );
     }
   }
 
   onSuccessfulConnection() {
     if (this.ws.readyState !== 1) {
       return;
     }
     this.handleStateCheckConditionsUpdate();
   }
 
   // The Socket will timeout by calling this.ws.terminate()
   // serverRequestSocketTimeout milliseconds after the last
   // time resetTimeout is called
   resetTimeout = _debounce(
     () => this.ws.terminate(),
     serverRequestSocketTimeout,
   );
 
   debouncedAfterActivity = _debounce(
     () => this.setStateCheckConditions({ activityRecentlyOccurred: false }),
     stateCheckInactivityActivationInterval,
   );
 
   markActivityOccurred = () => {
     if (this.ws.readyState !== 1) {
       return;
     }
     this.setStateCheckConditions({ activityRecentlyOccurred: true });
     this.debouncedAfterActivity();
   };
 
   clearStateCheckTimeout() {
     const { stateCheckTimeoutID } = this;
     if (stateCheckTimeoutID) {
       clearTimeout(stateCheckTimeoutID);
       this.stateCheckTimeoutID = null;
     }
   }
 
   setStateCheckConditions(newConditions: Shape<StateCheckConditions>) {
     this.stateCheckConditions = {
       ...this.stateCheckConditions,
       ...newConditions,
     };
     this.handleStateCheckConditionsUpdate();
   }
 
   get stateCheckCanStart() {
     return Object.values(this.stateCheckConditions).every(cond => !cond);
   }
 
   handleStateCheckConditionsUpdate() {
     if (!this.stateCheckCanStart) {
       this.clearStateCheckTimeout();
       return;
     }
     if (this.stateCheckTimeoutID) {
       return;
     }
     const { viewer } = this;
     if (!viewer) {
       return;
     }
     const timeUntilStateCheck =
       viewer.sessionLastValidated + sessionCheckFrequency - Date.now();
     if (timeUntilStateCheck <= 0) {
       this.initiateStateCheck();
     } else {
       this.stateCheckTimeoutID = setTimeout(
         this.initiateStateCheck,
         timeUntilStateCheck,
       );
     }
   }
 
   initiateStateCheck = async () => {
     this.setStateCheckConditions({ stateCheckOngoing: true });
 
     const { viewer } = this;
     invariant(viewer, 'should be set');
 
     const { checkStateRequest } = await checkState(
       viewer,
       { status: 'state_check' },
       viewer.calendarQuery,
     );
     invariant(checkStateRequest, 'should be set');
 
     this.sendMessage({
       type: serverSocketMessageTypes.REQUESTS,
       payload: { serverRequests: [checkStateRequest] },
     });
   };
 }
 
 export { onConnection };