Added feature to avoid tags when selecting s_vlan

CHANGELOG.rst

@@ -8,7 +8,8 @@ UNRELEASED - Under development
 
 Added
 =====
-- Added option for links to obtained last TAG from ``interface.available_tags``
+- Added option for links to get last TAG from ``interface.available_tags``.
+- Added option for links to try to avoid a TAG value from ``interface.available_tags``.
 
 Fixed
 =====

kytos/core/link.py

@@ -145,9 +145,17 @@ def get_next_available_tag(
         controller,
         link_id: str,
         take_last: bool = False,
-        tag_type: str = 'vlan'
+        tag_type: str = 'vlan',
+        try_avoid_value: int = None,
     ) -> int:
-        """Return the next available tag if exists."""
+        """Return the next available tag if exists. By default this
+         method returns the smallest tag available. Apply options to
+         change behavior.
+         Options:
+           - take_last (bool): Choose the largest tag available.
+           - try_avoid_value (int): Avoid given tag if possible. Otherwise
+             return what is available.
+        """
         with self._get_available_vlans_lock[link_id]:
             with self.endpoint_a._tag_lock:
                 with self.endpoint_b._tag_lock:
@@ -156,8 +164,21 @@ def get_next_available_tag(
                     tags = range_intersection(ava_tags_a, ava_tags_b,
                                               take_last)
                     try:
-                        first, last = next(tags)
-                        tag = first if not take_last else last
+                        tag_range: list = next(tags)
+                        if (try_avoid_value is not None and
+                                tag_range[take_last] == try_avoid_value):
+                            if (tag_range[take_last] !=
+                                    tag_range[not take_last]):
+                                tag = tag_range[take_last]
+                                tag += (+1) if not take_last else (-1)
+                            else:
+                                try:
+                                    tag = next(tags)[take_last]
+                                except StopIteration:
+                                    tag = tag_range[take_last]
+                        else:
+                            tag = tag_range[take_last]
+
                         self.endpoint_a.use_tags(
                             controller, tag, use_lock=False, check_order=False
                         )

tests/unit/test_core/test_link.py

@@ -220,6 +220,50 @@ def test_get_next_available_tag_reverse(self, controller):
         assert tag == 4095
         assert next_tag == 4094
 
+    def test_get_next_available_tag_avoid_tag(self, controller):
+        """Test get next available tag avoiding a tag"""
+        link = Link(self.iface1, self.iface2)
+        avoid_vlan = 1
+
+        # Tag different that avoid tag is available in the same range
+        link.endpoint_a.available_tags['vlan'] = [[1, 5]]
+        tag = link.get_next_available_tag(
+            controller, "link_id", try_avoid_value=avoid_vlan
+        )
+        assert tag == 2
+
+        # The next tag is the next range
+        link.endpoint_a.available_tags['vlan'] = [[1, 1], [100, 300]]
+        tag = link.get_next_available_tag(
+            controller, "link_id", try_avoid_value=avoid_vlan
+        )
+        assert tag == 100
+
+        # No more tags available
+        link.endpoint_a.available_tags['vlan'] = [[1, 1]]
+        tag = link.get_next_available_tag(
+            controller, "link_id", try_avoid_value=avoid_vlan
+        )
+        assert tag == 1
+
+        # Same cases but with reversed
+        avoid_vlan = 50
+        link.endpoint_a.available_tags['vlan'] = [[3, 50]]
+        tag = link.get_next_available_tag(
+            controller, "link_id", True, try_avoid_value=avoid_vlan
+        )
+        assert tag == 49
+        link.endpoint_a.available_tags['vlan'] = [[1, 20], [50, 50]]
+        tag = link.get_next_available_tag(
+            controller, "link_id", True, try_avoid_value=avoid_vlan
+        )
+        assert tag == 20
+        link.endpoint_a.available_tags['vlan'] = [[50, 50]]
+        tag = link.get_next_available_tag(
+            controller, "link_id", True, try_avoid_value=avoid_vlan
+        )
+        assert tag == 50
+
     def test_tag_life_cicle(self, controller):
         """Test get next available tags returns different tags"""
         link = Link(self.iface1, self.iface2)