update UrlPreview settings to be more privacy-aware in e2ee rooms

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/structures/RoomView.js

@@ -618,10 +618,26 @@ module.exports = React.createClass({
         }
     },
 
-    _updatePreviewUrlVisibility: function(room) {
-        this.setState({
-            showUrlPreview: SettingsStore.getValue("urlPreviewsEnabled", room.roomId),
-        });
+    _updatePreviewUrlVisibility: function({roomId}) {
+        const levels = [
+            SettingLevel.ROOM_DEVICE,
+            SettingLevel.ROOM_ACCOUNT,
+        ];
+        let showUrlPreview;
+        if (MatrixClientPeg.get().isRoomEncrypted(roomId)) {
+            for (const level of levels) {
+                const value = SettingsStore.getValueAt(level, "urlPreviewsEnabled", roomId, true, true);
+                if (value === Boolean(value)) { // if is Boolean
+                    showUrlPreview = value;
+                    break;
+                }
+            }
+
+            showUrlPreview = showUrlPreview || false;
+        } else {
+            showUrlPreview = SettingsStore.getValue("urlPreviewsEnabled", roomId);
+        }
+        this.setState({showUrlPreview});
     },
 
     onRoom: function(room) {

src/components/views/room_settings/UrlPreviewSettings.js

@@ -1,6 +1,7 @@
 /*
 Copyright 2016 OpenMarket Ltd
 Copyright 2017 Travis Ralston
+Copyright 2018 New Vector Ltd
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -15,6 +16,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import {MatrixClient} from "matrix-js-sdk";
 const React = require('react');
 import PropTypes from 'prop-types';
 const sdk = require("../../../index");
@@ -29,6 +31,10 @@ module.exports = React.createClass({
         room: PropTypes.object,
     },
 
+    contextTypes: {
+        matrixClient: PropTypes.instanceOf(MatrixClient).isRequired,
+    },
+
     saveSettings: function() {
         const promises = [];
         if (this.refs.urlPreviewsRoom) promises.push(this.refs.urlPreviewsRoom.save());
@@ -39,19 +45,29 @@ module.exports = React.createClass({
     render: function() {
         const SettingsFlag = sdk.getComponent("elements.SettingsFlag");
         const roomId = this.props.room.roomId;
+        const isEncrypted = this.context.matrixClient.isRoomEncrypted(roomId);
 
         let previewsForAccount = null;
-        if (SettingsStore.getValueAt(SettingLevel.ACCOUNT, "urlPreviewsEnabled")) {
+        let previewsForRoom = null;
+
+
+        if (!isEncrypted) {
+            // Only show account setting state and room state setting state in non-e2ee rooms where they apply
+            const accountEnabled = SettingsStore.getValueAt(SettingLevel.ACCOUNT, "urlPreviewsEnabled");
+            if (accountEnabled) {
                 previewsForAccount = (
-                _t("You have <a>enabled</a> URL previews by default.", {}, { 'a': (sub)=><a href="#/settings">{ sub }</a> })
+                    _t("You have <a>enabled</a> URL previews by default.", {}, {
+                        'a': (sub)=><a href="#/settings">{ sub }</a>,
+                    })
                 );
-        } else {
+            } else if (accountEnabled) {
                 previewsForAccount = (
-                _t("You have <a>disabled</a> URL previews by default.", {}, { 'a': (sub)=><a href="#/settings">{ sub }</a> })
+                    _t("You have <a>disabled</a> URL previews by default.", {}, {
+                        'a': (sub)=><a href="#/settings">{ sub }</a>,
+                    })
                 );
             }
 
-        let previewsForRoom = null;
             if (SettingsStore.canSetValue("urlPreviewsEnabled", roomId, "room")) {
                 previewsForRoom = (
                     <label>
@@ -70,6 +86,12 @@ module.exports = React.createClass({
                 }
                 previewsForRoom = (<label>{ _t(str) }</label>);
             }
+        } else {
+            previewsForAccount = (
+                _t("URL Previews default to off in End-to-End Encrypted rooms to protect your privacy. " +
+                    "They are requested through your homeserver which could infer links which are otherwise encrypted")
+            );
+        }
 
         const previewsForRoomAccount = (
             <SettingsFlag name="urlPreviewsEnabled"