Fixes #22518: trace bridged interfaces from either side

netbox/dcim/models/device_components.py

@@ -343,8 +343,30 @@ class PathEndpoint(models.Model):
         abstract = True
 
     def trace(self):
+        # Trace backward through this endpoint's own bridge relationship, if any, to pick up
+        # the other half of a bridged pair (e.g. a media converter's "copper" interface
+        # bridged to "fiber") before tracing forward from self. Without this, a trace started
+        # directly on the bridged interface only ever hops a bridge at the *destination* end
+        # of a segment, so the segment reached through the origin's own bridge is never
+        # included in the result (see #22518).
+        backward_path = []
+        visited = {self}
+        origin = getattr(self, 'bridge', None)
+        while origin is not None and origin not in visited:
+            visited.add(origin)
+            cable_path = origin.path
+            if cable_path is None:
+                break
+            backward_path.extend(cable_path.path_objects)
+            if len(backward_path) % 3 == 1:
+                backward_path.extend(([], []))
+            elif len(backward_path) % 3 == 2:
+                backward_path.insert(-1, [])
+            destinations = cable_path.destinations
+            origin = getattr(destinations[0], 'bridge', None) if len(destinations) == 1 else None
+
         origin = self
-        path = []
+        path = backward_path
 
         # Construct the complete path (including e.g. bridged interfaces)
         while origin is not None:

netbox/dcim/tests/test_models.py

@@ -2301,6 +2301,81 @@ class CableTestCase(TestCase):
         self.assertEqual(cable._abs_length, Decimal('1609343983.9066'))
 
 
+class PathEndpointTraceTestCase(TestCase):
+    """
+    Verify PathEndpoint.trace() includes the segment reached through an interface's own
+    bridge relationship, not just a bridge encountered at the destination end of a segment.
+
+    Models a media converter with bridged "copper" and "fiber" interfaces, each cabled to a
+    different switch. See #22518.
+    """
+
+    @classmethod
+    def setUpTestData(cls):
+        manufacturer = Manufacturer.objects.create(name='Generic', slug='generic')
+        device_type = DeviceType.objects.create(manufacturer=manufacturer, model='Device Type')
+        role = DeviceRole.objects.create(name='Device Role', slug='device-role')
+        site = Site.objects.create(name='Site', slug='site')
+
+        switch_a = Device.objects.create(site=site, device_type=device_type, role=role, name='Switch A')
+        switch_b = Device.objects.create(site=site, device_type=device_type, role=role, name='Switch B')
+        converter = Device.objects.create(site=site, device_type=device_type, role=role, name='Media Converter')
+
+        cls.switch_a_iface = Interface.objects.create(device=switch_a, name='eth0')
+        cls.switch_b_iface = Interface.objects.create(device=switch_b, name='eth0')
+        cls.copper = Interface.objects.create(device=converter, name='copper')
+        cls.fiber = Interface.objects.create(device=converter, name='fiber')
+        cls.copper.bridge = cls.fiber
+        cls.copper.save()
+        cls.fiber.bridge = cls.copper
+        cls.fiber.save()
+
+        Cable(a_terminations=[cls.switch_a_iface], b_terminations=[cls.copper]).save()
+        Cable(a_terminations=[cls.switch_b_iface], b_terminations=[cls.fiber]).save()
+
+    @staticmethod
+    def _terminations(segments):
+        return [node for segment in segments for group in (segment[0], segment[2]) for node in group]
+
+    def test_trace_from_bridged_interface_includes_both_segments(self):
+        """
+        Tracing from the bridged interface itself (copper) must include both the segment to
+        its own cable peer (Switch A) and the segment reached through its bridge (Switch B)
+        -- the same two segments a trace starting from Switch A already finds.
+        """
+        self.copper.refresh_from_db()
+        segments = self.copper.trace()
+
+        self.assertEqual(len(segments), 2)
+        terminations = self._terminations(segments)
+        self.assertIn(self.switch_a_iface, terminations)
+        self.assertIn(self.switch_b_iface, terminations)
+
+    def test_trace_from_bridge_partner_includes_both_segments(self):
+        """
+        The backward walk isn't one-directional: tracing from the fiber side must likewise
+        include both segments.
+        """
+        self.fiber.refresh_from_db()
+        segments = self.fiber.trace()
+
+        self.assertEqual(len(segments), 2)
+        terminations = self._terminations(segments)
+        self.assertIn(self.switch_a_iface, terminations)
+        self.assertIn(self.switch_b_iface, terminations)
+
+    def test_trace_from_connected_switch_unaffected(self):
+        """
+        The previously-working direction (#7761) must still return both segments.
+        """
+        segments = self.switch_a_iface.trace()
+
+        self.assertEqual(len(segments), 2)
+        terminations = self._terminations(segments)
+        self.assertIn(self.copper, terminations)
+        self.assertIn(self.switch_b_iface, terminations)
+
+
 class CableTerminationTestCase(TestCase):
 
     def test_cache_related_objects_requires_resolvable_termination(self):