Support Jitsi information from client .well-known

It can be useful for the homeserver to support a dedicated Jitsi instance instead of requiring that all their users change/update their configs manually.

src/widgets/Jitsi.ts

@@ -0,0 +1,73 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import SdkConfig from "../SdkConfig";
+import {MatrixClientPeg} from "../MatrixClientPeg";
+import {AutoDiscovery} from "matrix-js-sdk/src/autodiscovery";
+
+const JITSI_WK_PROPERTY = "im.vector.riot.jitsi";
+const JITSI_WK_CHECK_INTERVAL = 2 * 60 * 60 * 1000; // 2 hours, arbitrarily selected
+
+export class Jitsi {
+    private static instance: Jitsi;
+
+    private domain: string;
+
+    public get preferredDomain(): string {
+        return this.domain || 'jitsi.riot.im';
+    }
+
+    constructor() {
+        // We rely on the first call to be an .update() instead of doing one here. Doing one
+        // here could result in duplicate calls to the homeserver.
+
+        // Start a timer to update the server info regularly
+        setInterval(() => this.update(), JITSI_WK_CHECK_INTERVAL);
+    }
+
+    public async update(): Promise<any> {
+        // Start with a default of the config's domain
+        let domain = (SdkConfig.get()['jitsi'] || {})['preferredDomain'] || 'jitsi.riot.im';
+
+        // Now request the .well-known config to see if it changed
+        if (MatrixClientPeg.get()) {
+            try {
+                console.log("Attempting to get Jitsi conference information from homeserver");
+
+                const homeserverDomain = MatrixClientPeg.getHomeserverName();
+                const discoveryResponse = await AutoDiscovery.getRawClientConfig(homeserverDomain);
+                if (discoveryResponse && discoveryResponse[JITSI_WK_PROPERTY]) {
+                    const wkPreferredDomain = discoveryResponse[JITSI_WK_PROPERTY]['preferredDomain'];
+                    if (wkPreferredDomain) domain = wkPreferredDomain;
+                }
+            } catch (e) {
+                // These are non-fatal errors
+                console.error(e);
+            }
+        }
+
+        // Put the result into memory for us to use later
+        this.domain = domain;
+        console.log("Jitsi conference domain:", this.preferredDomain);
+    }
+
+    public static getInstance(): Jitsi {
+        if (!Jitsi.instance) {
+            Jitsi.instance = new Jitsi();
+        }
+        return Jitsi.instance;
+    }
+}