fix port subrange from subclass (#13001)

cloutierMat · web-flow · commit 5a920cb0876b · 2025-08-13T12:23:10.000-06:00
diff --git a/localstack-core/localstack/utils/net.py b/localstack-core/localstack/utils/net.py
@@ -342,7 +342,8 @@ def subrange(self, start: int = None, end: int = None) -> "PortRange":
         if end > self.end:
             raise ValueError(f"end not in range ({end} < {self.end})")
 
-        port_range = PortRange(start, end)
+        # ensures that we return an instance of a subclass
+        port_range = type(self)(start, end)
         port_range._ports_cache = self._ports_cache
         port_range._ports_lock = self._ports_lock
         return port_range
diff --git a/tests/unit/utils/test_net_utils.py b/tests/unit/utils/test_net_utils.py
@@ -23,6 +23,10 @@
 )
 
 
+class TestPortRange(PortRange):
+    pass
+
+
 @markers.skip_offline
 def test_resolve_hostname():
     assert "127." in resolve_hostname(LOCALHOST)
@@ -117,6 +121,14 @@ def test_subrange():
     assert r.is_port_reserved(50005)
 
 
+def test_subrange_from_subclass():
+    r = TestPortRange(1000, 5000)
+    sr = r.subrange(1000, 2000)
+
+    assert isinstance(sr, TestPortRange)
+    assert sr.as_range() == range(1000, 2001)
+
+
 def test_get_free_tcp_port_range_fails_if_reserved(monkeypatch):
     mock = MagicMock()
     mock.return_value = True
