Raise an error if a user tries to register with an excessively long username

Summary: Fixes T2348. We should probably do some of this more broadly, but can tackle them one at a time as they arise, since many fields have no effective length limit.

Test Plan: {F54126}

Reviewers: btrahan, asherkin

Reviewed By: asherkin

CC: aran

Maniphest Tasks: T2348

Differential Revision: https://secure.phabricator.com/D6744

src/applications/people/storage/PhabricatorUser.php

@@ -9,6 +9,7 @@ final class PhabricatorUser
 
   const SESSION_TABLE = 'phabricator_session';
   const NAMETOKEN_TABLE = 'user_nametoken';
+  const MAXIMUM_USERNAME_LENGTH = 64;
 
   protected $phid;
   protected $userName;
@@ -689,8 +690,11 @@ EOBODY;
   }
 
   public static function describeValidUsername() {
-    return 'Usernames must contain only numbers, letters, period, underscore '.
-           'and hyphen, and can not end with a period.';
+    return pht(
+      'Usernames must contain only numbers, letters, period, underscore and '.
+      'hyphen, and can not end with a period. They must have no more than %d '.
+      'characters.',
+      new PhutilNumber(self::MAXIMUM_USERNAME_LENGTH));
   }
 
   public static function validateUsername($username) {
@@ -701,6 +705,10 @@ EOBODY;
     //  - Unit tests, obviously.
     //  - describeValidUsername() method, above.
 
+    if (strlen($username) > self::MAXIMUM_USERNAME_LENGTH) {
+      return false;
+    }
+
     return (bool)preg_match('/^[a-zA-Z0-9._-]*[a-zA-Z0-9_-]$/', $username);
   }