[keyserver][lib] Block users from creating reserved invite links

Summary:
A user should not be able to create a link which is included in a list of reserved usernames. The copy is similar to a message that is shown when a user tries to create an account with reserved username: `/native/account/registration/registration-server-call.js`, but I'm not sure if we should mention support email (the user is already registered and can contact us on Comm).

Depends on D8527

Test Plan: Try to create `/comm` invite link - a message should be displayed.

Reviewers: kamil, inka, ashoat

Reviewed By: inka

Differential Revision: https://phab.comm.dev/D8615

keyserver/src/creators/invite-link-creator.js

@@ -8,6 +8,7 @@ import type {
 } from 'lib/types/link-types.js';
 import { threadPermissions } from 'lib/types/thread-permission-types.js';
 import { ServerError } from 'lib/utils/errors.js';
+import { reservedUsernamesSet } from 'lib/utils/reserved-users.js';
 
 import createIDs from './id-creator.js';
 import {
@@ -33,6 +34,9 @@ async function createOrUpdatePublicLink(
   if (badWordsFilter.isProfane(request.name)) {
     throw new ServerError('offensive_words');
   }
+  if (reservedUsernamesSet.has(request.name)) {
+    throw new ServerError('link_reserved');
+  }
 
   const permissionPromise = checkThreadPermission(
     viewer,

lib/shared/invite-links.js

@@ -1,9 +1,12 @@
 // @flow
 
-const inviteLinkErrorMessages = {
+const inviteLinkErrorMessages: { +[string]: string } = {
   invalid_characters: 'Link cannot contain any spaces or special characters.',
   offensive_words: 'No offensive or abusive words allowed.',
   already_in_use: 'Public link URL already in use.',
+  link_reserved:
+    'This public link is currently reserved. Please contact support@' +
+    'comm.app if you would like to claim this link.',
 };
 
 const defaultErrorMessage = 'Unknown error.';