Enable encryption in DMs with device keys

When the cross-signing lab is enabled, this changes DMs to use encryption as
long as all invited users have uploaded device keys (which we're using as a
proxy for "has some client that understands E2E").

Fixes https://github.com/vector-im/riot-web/issues/12005

src/components/views/dialogs/InviteDialog.js

@@ -33,6 +33,7 @@ import Modal from "../../../Modal";
 import {humanizeTime} from "../../../utils/humanize";
 import createRoom from "../../../createRoom";
 import {inviteMultipleToRoom} from "../../../RoomInvite";
+import SettingsStore from '../../../settings/SettingsStore';
 
 export const KIND_DM = "dm";
 export const KIND_INVITE = "invite";
@@ -493,7 +494,7 @@ export default class InviteDialog extends React.PureComponent {
         return false;
     }
 
-    _startDm = () => {
+    _startDm = async () => {
         this.setState({busy: true});
         const targetIds = this.state.targets.map(t => t.userId);
 
@@ -510,14 +511,31 @@ export default class InviteDialog extends React.PureComponent {
             return;
         }
 
+        const createRoomOptions = {};
+
+        if (SettingsStore.isFeatureEnabled("feature_cross_signing")) {
+            // Check whether all users have uploaded device keys before.
+            // If so, enable encryption in the new room.
+            const client = MatrixClientPeg.get();
+            const usersToDevicesMap = await client.downloadKeys(targetIds);
+            const allHaveDeviceKeys = Object.values(usersToDevicesMap).every(devices => {
+                // `devices` is an object of the form { deviceId: deviceInfo, ... }.
+                return Object.keys(devices).length > 0;
+            });
+            if (allHaveDeviceKeys) {
+                createRoomOptions.encryption = true;
+            }
+        }
+
         // Check if it's a traditional DM and create the room if required.
         // TODO: [Canonical DMs] Remove this check and instead just create the multi-person DM
         let createRoomPromise = Promise.resolve();
         if (targetIds.length === 1) {
-            createRoomPromise = createRoom({dmUserId: targetIds[0]});
+            createRoomOptions.dmUserId = targetIds[0];
+            createRoomPromise = createRoom(createRoomOptions);
         } else {
             // Create a boring room and try to invite the targets manually.
-            createRoomPromise = createRoom().then(roomId => {
+            createRoomPromise = createRoom(createRoomOptions).then(roomId => {
                 return inviteMultipleToRoom(roomId, targetIds);
             }).then(result => {
                 if (this._shouldAbortAfterInviteError(result)) {

src/components/views/right_panel/UserInfo.js

@@ -82,7 +82,7 @@ const _getE2EStatus = (cli, userId, devices) => {
     return "warning";
 };
 
-function openDMForUser(matrixClient, userId) {
+async function openDMForUser(matrixClient, userId) {
     const dmRooms = DMRoomMap.shared().getDMRoomsForUserId(userId);
     const lastActiveRoom = dmRooms.reduce((lastActiveRoom, roomId) => {
         const room = matrixClient.getRoom(roomId);
@@ -100,9 +100,27 @@ function openDMForUser(matrixClient, userId) {
             action: 'view_room',
             room_id: lastActiveRoom.roomId,
         });
-    } else {
-        createRoom({dmUserId: userId});
+        return;
     }
+
+    const createRoomOptions = {
+        dmUserId: userId,
+    };
+
+    if (SettingsStore.isFeatureEnabled("feature_cross_signing")) {
+        // Check whether all users have uploaded device keys before.
+        // If so, enable encryption in the new room.
+        const usersToDevicesMap = await matrixClient.downloadKeys([userId]);
+        const allHaveDeviceKeys = Object.values(usersToDevicesMap).every(devices => {
+            // `devices` is an object of the form { deviceId: deviceInfo, ... }.
+            return Object.keys(devices).length > 0;
+        });
+        if (allHaveDeviceKeys) {
+            createRoomOptions.encryption = true;
+        }
+    }
+
+    createRoom(createRoomOptions);
 }
 
 function useIsEncrypted(cli, room) {