isAppOwnDomain [nfc]: Define for reuse, and add tests.

Author: chrisbobbe

src/__tests__/isAppOwnDomain-test.js

@@ -0,0 +1,22 @@
+/* @flow strict-local */
+
+import isAppOwnDomain from '../isAppOwnDomain';
+
+describe('isAppOwnDomain', () => {
+  test.each([
+    ['https://chat.zulip.org', true],
+    ['https://zulipchat.com', true],
+    ['https://zulip.com', true],
+    ['https://example.zulipchat.com', true],
+    ['https://example.zulip.com', true],
+    ['https://example.zulip.com/api/v1/server_settings', true],
+    ['https://example.zulip.com/avatar/1234', true],
+
+    ['https://zulipchat.org', false],
+    ['https://www.google.com', false],
+    ['https://zulipchat.co.uk', false],
+    ['https://chat.zulip.io', false],
+  ])('%s should be %p', (urlStr: string, expected: boolean) => {
+    expect(isAppOwnDomain(new URL(urlStr))).toBe(expected);
+  });
+});

src/isAppOwnDomain.js

@@ -0,0 +1,11 @@
+/* @flow strict-local */
+import config from './config';
+
+/**
+ * Whether a URL is hosted by the same org that publishes the app.
+ */
+export default function isAppOwnDomain(url: URL): boolean {
+  return config.appOwnDomains.some(
+    domain => url.host === domain || url.host.endsWith(`.${domain}`),
+  );
+}

src/start/AuthScreen.js

@@ -14,7 +14,7 @@ import type {
 import type { RouteProp } from '../react-navigation';
 import type { AppNavigationProp } from '../nav/AppNavigator';
 import * as NavigationService from '../nav/NavigationService';
-import config from '../config';
+import isAppOwnDomain from '../isAppOwnDomain';
 import type { Dispatch } from '../types';
 import {
   IconApple,
@@ -295,16 +295,14 @@ class AuthScreenInner extends PureComponent<Props> {
       return false;
     }
 
-    const { host } = this.props.realm;
-
     // The native flow for Apple auth assumes that the app and the server
     // are operated by the same organization, so that for a user to
     // entrust private information to either one is the same as entrusting
     // it to the other.  Check that this realm is on such a server.
     //
     // (For other realms, we'll simply fall back to the web flow, which
     // handles things appropriately without relying on that assumption.)
-    return config.appOwnDomains.some(domain => host === domain || host.endsWith(`.${domain}`));
+    return isAppOwnDomain(this.props.realm);
   };
 
   handleAuth = async (method: AuthenticationMethodDetails) => {