Behave sensibly if a full room alias is entered

Check explicitly to see if the room name that's enetered into the box
looks like a room alias and if so, do the sensible thing.

Fixes https://github.com/vector-im/element-call/issues/852

src/home/RegisteredView.tsx

@@ -24,7 +24,11 @@ import { useHistory } from "react-router-dom";
 import { MatrixClient } from "matrix-js-sdk/src/client";
 import { useTranslation } from "react-i18next";
 
-import { createRoom, roomAliasLocalpartFromRoomName } from "../matrix-utils";
+import {
+  createRoom,
+  roomAliasLocalpartFromRoomName,
+  sanitiseRoomNameInput,
+} from "../matrix-utils";
 import { useGroupCallRooms } from "./useGroupCallRooms";
 import { Header, HeaderLogo, LeftNav, RightNav } from "../Header";
 import commonStyles from "./common.module.css";
@@ -57,7 +61,10 @@ export function RegisteredView({ client, isPasswordlessUser }: Props) {
       e.preventDefault();
       const data = new FormData(e.target as HTMLFormElement);
       const roomNameData = data.get("callName");
-      const roomName = typeof roomNameData === "string" ? roomNameData : "";
+      const roomName =
+        typeof roomNameData === "string"
+          ? sanitiseRoomNameInput(roomNameData)
+          : "";
       const ptt = callType === CallType.Radio;
 
       async function submit() {

src/home/UnauthenticatedView.tsx

@@ -24,7 +24,11 @@ import { Header, HeaderLogo, LeftNav, RightNav } from "../Header";
 import { UserMenuContainer } from "../UserMenuContainer";
 import { FieldRow, InputField, ErrorMessage } from "../input/Input";
 import { Button } from "../button";
-import { createRoom, roomAliasLocalpartFromRoomName } from "../matrix-utils";
+import {
+  createRoom,
+  roomAliasLocalpartFromRoomName,
+  sanitiseRoomNameInput,
+} from "../matrix-utils";
 import { useInteractiveRegistration } from "../auth/useInteractiveRegistration";
 import { useModalTriggerState } from "../Modal";
 import { JoinExistingCallModal } from "./JoinExistingCallModal";
@@ -54,7 +58,7 @@ export const UnauthenticatedView: FC = () => {
     (e) => {
       e.preventDefault();
       const data = new FormData(e.target as HTMLFormElement);
-      const roomName = data.get("callName") as string;
+      const roomName = sanitiseRoomNameInput(data.get("callName") as string);
       const displayName = data.get("displayName") as string;
       const ptt = callType === CallType.Radio;
 

src/matrix-utils.ts

@@ -211,6 +211,31 @@ export function fullAliasFromRoomName(
   return `#${roomAliasLocalpartFromRoomName(roomName)}:${client.getDomain()}`;
 }
 
+/**
+ * Applies some basic sanitisation to an room name that the user
+ * has given us
+ * @param input The room name from the user
+ * @param client A matrix client object
+ */
+export function sanitiseRoomNameInput(input: string): string {
+  // check to see if the user has enetered a fully qualified room
+  // alias. If so, turn it into just the localpart because that's what
+  // we use
+  const parts = input.split(":", 2);
+  if (parts.length === 2 && parts[0][0] === "#") {
+    // looks like a room alias
+    if (parts[1] === Config.defaultServerName()) {
+      // it's local to our own homeserver
+      return parts[0];
+    } else {
+      throw new Error("Unsupported remote room alias");
+    }
+  }
+
+  // that's all we do here right now
+  return input;
+}
+
 /**
  * XXX: What is this trying to do? It looks like it's getting the localpart from
  * a room alias, but why is it splitting on hyphens and then putting spaces in??