fix(recipe): prevent perpetual re-election if sequence node overflows

kazoo/recipe/lock.py

@@ -276,15 +276,15 @@ def _get_predecessor(self, node):
         (e.g. rlock), this and also edge cases where the lock's ephemeral node
         is gone.
         """
-        node_sequence = node[len(self.prefix) :]
+        node_sequence = int(node[len(self.prefix) :])
         children = self.client.get_children(self.path)
         found_self = False
         # Filter out the contenders using the computed regex
         contender_matches = []
         for child in children:
             match = self._contenders_re.search(child)
             if match is not None:
-                contender_sequence = match.group(1)
+                contender_sequence = int(match.group(1))
                 # Only consider contenders with a smaller sequence number.
                 # A contender with a smaller sequence number has a higher
                 # priority.

kazoo/tests/test_lock.py

@@ -799,6 +799,46 @@ def _thread(sem, event, timeout):
 
 class TestSequence(unittest.TestCase):
     def test_get_predecessor(self):
+        """Validate selection of predecessors."""
+        pyLock_prefix = "514e5a831836450cb1a56c741e990fd8__lock__"
+        pyLock_predecessor = f"{pyLock_prefix}0000000030"
+        pyLock = f"{pyLock_prefix}0000000031"
+        pyLock_successor = f"{pyLock_prefix}0000000032"
+        children = [
+            "hello",
+            pyLock_predecessor,
+            "world",
+            pyLock,
+            pyLock_successor,
+        ]
+        client = MagicMock()
+        client.get_children.return_value = children
+        lock = Lock(client, "test")
+        assert lock._get_predecessor(pyLock) == pyLock_predecessor
+
+    def test_get_predecessor_with_overflowed_sequence(self):
+        """Validate selection of predecessors with negative sequence.
+
+        This can occur in case of an integer overflow, if the sequence
+        counter is incremented beyond 2147483647.
+        """
+        pyLock_prefix = "514e5a831836450cb1a56c741e990fd8__lock__"
+        pyLock_predecessor = f"{pyLock_prefix}-0000000032"
+        pyLock = f"{pyLock_prefix}-0000000031"
+        pyLock_successor = f"{pyLock_prefix}-0000000030"
+        children = [
+            "hello",
+            pyLock_predecessor,
+            "world",
+            pyLock,
+            pyLock_successor,
+        ]
+        client = MagicMock()
+        client.get_children.return_value = children
+        lock = Lock(client, "test")
+        assert lock._get_predecessor(pyLock) == pyLock_predecessor
+
+    def test_get_predecessor_no_predecessor(self):
         """Validate selection of predecessors."""
         goLock = "_c_8eb60557ba51e0da67eefc47467d3f34-lock-0000000031"
         pyLock = "514e5a831836450cb1a56c741e990fd8__lock__0000000032"