use binary search when finding new uid (#39)

closes #36

Co-authored-by: Daniel Liu <mr.picklepinosaur@gmail.com>
Reviewed-on: #39
Co-authored-by: d278liu <d278liu@localhost>
Co-committed-by: d278liu <d278liu@localhost>

ceod/model/LDAPService.py

@@ -1,6 +1,4 @@
 import contextlib
-import grp
-import pwd
 from typing import Union, Dict, List
 
 from flask import g
@@ -119,19 +117,6 @@ class LDAPService:
 
     def _get_next_uid(self, conn: ldap3.Connection, min_id: int, max_id: int) -> int:
         """Gets the next available UID number between min_id and max_id, inclusive."""
-        def uid_exists(uid: int) -> bool:
-            try:
-                pwd.getpwuid(uid)
-                return True
-            except KeyError:
-                return False
-
-        def gid_exists(gid: int) -> bool:
-            try:
-                grp.getgrgid(gid)
-                return True
-            except KeyError:
-                return False
 
         def ldap_uid_or_gid_exists(uid: int) -> bool:
             return conn.search(
@@ -139,12 +124,17 @@ class LDAPService:
                 f'(|(uidNumber={uid})(gidNumber={uid}))',
                 size_limit=1)
 
-        # TODO: replace this with binary search
-        for uid in range(min_id, max_id + 1):
-            if uid_exists(uid) or gid_exists(uid) or ldap_uid_or_gid_exists(uid):
-                continue
-            return uid
+        while min_id != max_id:
+            cur_uid = (min_id + max_id) // 2
+            if ldap_uid_or_gid_exists(cur_uid):
+                min_id = cur_uid + 1
+            else:
+                max_id = cur_uid
+
+        if ldap_uid_or_gid_exists(min_id):
             raise Exception('no UIDs remaining')
+        else:
+            return min_id
 
     def add_sudo_role(self, uid: str):
         conn = self._get_ldap_conn()