Simplify Docker IP determination in middleware.py

debug_toolbar/middleware.py

@@ -36,11 +36,7 @@ def show_toolbar(request):
         # This is a hack for docker installations. It attempts to look
         # up the IP address of the docker host.
         # This is not guaranteed to work.
-        docker_ip = (
-            # Convert the last segment of the IP address to be .1
-            ".".join(socket.gethostbyname("host.docker.internal").rsplit(".")[:-1])
-            + ".1"
-        )
+        docker_ip = socket.gethostbyname("gateway.docker.internal")
         if request.META.get("REMOTE_ADDR") == docker_ip:
             return True
     except socket.gaierror:

docs/changes.rst

@@ -15,6 +15,7 @@ Pending
 * Added a Makefile target (``make help``) to get a quick overview
   of each target.
 * Avoided reinitializing the staticfiles storage during instrumentation.
+* Simplify Docker IP determination by using gateway IP.
 
 5.0.1 (2025-01-13)
 ------------------

tests/test_integration.py

@@ -67,13 +67,12 @@ def test_show_toolbar_INTERNAL_IPS(self):
         with self.settings(INTERNAL_IPS=[]):
             self.assertFalse(show_toolbar(self.request))
 
-    @patch("socket.gethostbyname", return_value="127.0.0.255")
+    @patch("socket.gethostbyname", return_value="192.168.65.1")
     def test_show_toolbar_docker(self, mocked_gethostbyname):
         with self.settings(INTERNAL_IPS=[]):
-            # Is true because REMOTE_ADDR is 127.0.0.1 and the 255
-            # is shifted to be 1.
+            self.request.META["REMOTE_ADDR"] = "192.168.65.1"
             self.assertTrue(show_toolbar(self.request))
-        mocked_gethostbyname.assert_called_once_with("host.docker.internal")
+        mocked_gethostbyname.assert_called_once_with("gateway.docker.internal")
 
     def test_not_iterating_over_INTERNAL_IPS(self):
         """Verify that the middleware does not iterate over INTERNAL_IPS in some way.

tests/test_integration_async.py

@@ -54,13 +54,12 @@ async def test_show_toolbar_INTERNAL_IPS(self):
         with self.settings(INTERNAL_IPS=[]):
             self.assertFalse(show_toolbar(self.request))
 
-    @patch("socket.gethostbyname", return_value="127.0.0.255")
+    @patch("socket.gethostbyname", return_value="192.168.65.1")
     async def test_show_toolbar_docker(self, mocked_gethostbyname):
         with self.settings(INTERNAL_IPS=[]):
-            # Is true because REMOTE_ADDR is 127.0.0.1 and the 255
-            # is shifted to be 1.
+            self.request.META["REMOTE_ADDR"] = "192.168.65.1"
             self.assertTrue(show_toolbar(self.request))
-        mocked_gethostbyname.assert_called_once_with("host.docker.internal")
+        mocked_gethostbyname.assert_called_once_with("gateway.docker.internal")
 
     async def test_not_iterating_over_INTERNAL_IPS(self):
         """