Fix forward to no route targets

Delayed forwards cause another fork rank to be created.
However, it might be that the forward target isn't
reachable and has no route. In this case, the forward
should be dropped and not added as fork rank. This commit
fixes this and adds a regression test.

tests/test_ywsd_web.py

@@ -33,15 +33,15 @@ def validate_routing_tree(observed, expected):
 
     assert ("fork_ranks" in observed) == ("fork_ranks" in expected)
     if "fork_ranks" in observed:
-        for (observed_rank, expected_rank) in zip(
+        for observed_rank, expected_rank in zip(
             observed["fork_ranks"], expected["fork_ranks"]
         ):
             for key in expected_rank.keys():
                 if key == "members":
                     continue
                 assert observed_rank[key] == expected_rank[key]
         assert len(observed_rank["members"]) == len(expected_rank["members"])
-        for (observed_member, expected_member) in zip(
+        for observed_member, expected_member in zip(
             observed_rank["members"], expected_rank["members"]
         ):
             if "type" in expected_member:
@@ -307,3 +307,34 @@ async def test_webserver_immediate_forward_4748_to_2098(ywsd_engine_web):
             }
             validate_routing_tree(data["routing_tree"], expected_routing_tree)
             assert data["routing_tree"]["forwarding_extension"]["extension"] == "2005"
+
+
+@pytest.mark.asyncio
+@pytest.mark.usefixtures("ywsd_engine_web")
+async def test_webserver_delayed_forward_to_empty_group_4000(ywsd_engine_web):
+    async with aiohttp.ClientSession() as session:
+        async with session.get(
+            "http://localhost:9042/stage1?caller=4748&called=4001"
+        ) as response:
+            data = await response.json()
+            print(repr(data))
+            assert data["routing_status"] == "OK"
+            main_routing_result = data["main_routing_result"]
+            assert main_routing_result["type"] == "Type.FORK"
+            expected_fork_targets = [
+                {
+                    "target": "lateroute/4001",
+                    "parameters": {"eventphone_stage2": "1"},
+                },
+            ]
+            validate_fork_targets(
+                main_routing_result["fork_targets"], expected_fork_targets
+            )
+            expected_routing_tree = {
+                "extension": "4001",
+                "type": "Type.SIMPLE",
+                "forwarding_mode": "ForwardingMode.ENABLED",
+                "forwarding_delay": 10,
+            }
+            validate_routing_tree(data["routing_tree"], expected_routing_tree)
+            assert data["routing_tree"]["forwarding_extension"]["extension"] == "4000"

tests/testdata.py

@@ -116,6 +116,26 @@ async def write_testdata(conn):
                     "lang": "de_DE",
                     "ringback": None,
                 },
+                {
+                    "yate_id": None,
+                    "extension": "4000",
+                    "name": "Empty Group",
+                    "type": "GROUP",
+                    "forwarding_mode": "DISABLED",
+                    "forwarding_delay": None,
+                    "lang": "de_DE",
+                    "ringback": None,
+                },
+                {
+                    "yate_id": yates["sip"],
+                    "extension": "4001",
+                    "name": "I Forward to empty group",
+                    "type": "SIMPLE",
+                    "forwarding_mode": "DISABLED",
+                    "forwarding_delay": 10,
+                    "lang": "de_DE",
+                    "ringback": None,
+                },
             ]
         )
     )
@@ -134,6 +154,11 @@ async def write_testdata(conn):
         .where(Extension.table.c.extension == "2098")
         .values({"forwarding_extension_id": exts["2005"], "forwarding_mode": "ENABLED"})
     )
+    await conn.execute(
+        Extension.table.update()
+        .where(Extension.table.c.extension == "4001")
+        .values({"forwarding_extension_id": exts["4000"], "forwarding_mode": "ENABLED"})
+    )
 
     await conn.execute(
         ForkRank.table.insert().values(

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py38,py39,py310
+envlist = py38,py39,py310,py311
 skip_missing_interpreters = true
 
 
@@ -11,4 +11,4 @@ deps =
     pytest-black
     pytest-asyncio
     docker
-commands = pytest --black {posargs}
+commands = pytest --black {posargs}

ywsd/routing_tree.py

@@ -461,14 +461,17 @@ def _visit_for_route_calculation(
             ):
                 # this is non-immediate forward
                 forwarding_route = self._visit(node.forwarding_extension, local_path)
-                if node.forwarding_mode == Extension.ForwardingMode.ENABLED:
-                    fwd_delay = node.forwarding_delay - accumulated_delay
-                    fork_targets.append(CallTarget("|drop={}".format(fwd_delay)))
-                else:
-                    # Add a default rank, call will progress to next rang when all previous calls failed
-                    fork_targets.append(CallTarget("|"))
-                fork_targets.append(forwarding_route.target)
-                self._cache_intermediate_result(forwarding_route)
+                # if we obtained a valid route, we add this as new fork target here. Otherwise, we keep
+                # the current fork ranks and just move on.
+                if forwarding_route.is_valid:
+                    if node.forwarding_mode == Extension.ForwardingMode.ENABLED:
+                        fwd_delay = node.forwarding_delay - accumulated_delay
+                        fork_targets.append(CallTarget("|drop={}".format(fwd_delay)))
+                    else:
+                        # Add a default rank, call will progress to next rang when all previous calls failed
+                        fork_targets.append(CallTarget("|"))
+                    fork_targets.append(forwarding_route.target)
+                    self._cache_intermediate_result(forwarding_route)
 
             return self._make_intermediate_result(
                 fork_targets=fork_targets,