tolerate dead relations

README.md

@@ -529,7 +529,7 @@ remote_unit_2_is_joining_event = Event('foo-relation-changed', relation=relation
 
 ### Networks
 
-Each relation a charm has will 
+Each relation a charm has is associated with  
 A charm can define some `extra-bindings`
 
 

pyproject.toml

@@ -8,7 +8,7 @@ build-backend = "setuptools.build_meta"
 [project]
 name = "ops-scenario"
 
-version = "5.7.1"
+version = "6.0"
 
 authors = [
     { name = "Pietro Pasotti", email = "[email protected]" }

scenario/mocking.py

@@ -5,6 +5,7 @@
 import random
 import shutil
 from io import StringIO
+from itertools import chain
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, Dict, List, Mapping, Optional, Set, Tuple, Union
 
@@ -240,9 +241,30 @@ def config_get(self):
     def network_get(self, binding_name: str, relation_id: Optional[int] = None):
         # is this an extra-binding-provided network?
         if binding_name in self._charm_spec.meta.get("extra-bindings", ()):
+            if relation_id is not None:
+                # this should not happen
+                raise RuntimeError(
+                    "cannot pass relation_id to network_get if the binding name is "
+                    "that of an extra-binding. Extra-bindings are not mapped to relation IDs.",
+                )
             network = self._state.extra_bindings.get(binding_name, Network.default())
             return network.hook_tool_output_fmt()
 
+        # is binding_name a valid relation binding name?
+        meta = self._charm_spec.meta
+        if binding_name not in set(
+            chain(
+                meta.get("peers", ()),
+                meta.get("requires", ()),
+                meta.get("provides", ()),
+            ),
+        ):
+            logger.error(
+                f"cannot get network binding for {binding_name}: is not a valid relation "
+                f"endpoint name nor an extra-binding.",
+            )
+            raise RelationNotFoundError()
+
         # Is this a network attached to a relation?
         relations = self._state.get_relations(binding_name)
         if relation_id:
@@ -260,8 +282,23 @@ def network_get(self, binding_name: str, relation_id: Optional[int] = None):
                 )
                 raise RelationNotFoundError() from e
         else:
-            # TODO: is this accurate?
+            if not relations:
+                logger.warning(
+                    "Requesting the network for an endpoint with no active relations "
+                    "will return a defaulted network.",
+                )
+                return Network.default().hook_tool_output_fmt()
+
+            # TODO: is this accurate? Any relation in particular?
             relation = relations[0]
+
+        from scenario.state import SubordinateRelation  # avoid cyclic imports
+
+        if isinstance(relation, SubordinateRelation):
+            raise RuntimeError(
+                "Subordinate relation has no associated network binding.",
+            )
+
         return relation.network.hook_tool_output_fmt()
 
     # setter methods: these can mutate the state.

scenario/state.py

@@ -325,7 +325,8 @@ class RelationBase(_DCBase):
     #  relation have a different network?
     network: Network = dataclasses.field(default=None)
     """Network associated with this relation.
-    If left empty, a default network will be assigned automatically."""
+    If left empty, a default network will be assigned automatically
+    (except for subordinate relations)."""
 
     @property
     def _databags(self):
@@ -355,7 +356,7 @@ def __post_init__(self):
         for databag in self._databags:
             self._validate_databag(databag)
 
-        if self.network is None:
+        if type(self) is not SubordinateRelation and self.network is None:
             object.__setattr__(self, "network", Network.default())
 
     def _validate_databag(self, databag: dict):

tests/test_consistency_checker.py

@@ -8,14 +8,14 @@
     Action,
     Container,
     Event,
+    Network,
     PeerRelation,
     Relation,
     Secret,
     State,
     Storage,
     SubordinateRelation,
     _CharmSpec,
-    Network,
 )
 
 

tests/test_e2e/test_network.py

@@ -4,7 +4,7 @@
 from ops.framework import Framework
 
 from scenario import Context
-from scenario.state import Network, Relation, State
+from scenario.state import Network, Relation, State, SubordinateRelation
 from tests.helpers import trigger
 
 
@@ -33,7 +33,10 @@ def test_ip_get(mycharm):
         mycharm,
         meta={
             "name": "foo",
-            "requires": {"metrics-endpoint": {"interface": "foo"}},
+            "requires": {
+                "metrics-endpoint": {"interface": "foo"},
+                "deadnodead": {"interface": "bar"},
+            },
             "extra-bindings": {"foo": {}},
         },
     )
@@ -56,19 +59,52 @@ def test_ip_get(mycharm):
         rel = mgr.charm.model.get_relation("metrics-endpoint")
         assert str(mgr.charm.model.get_binding(rel).network.bind_address) == "1.1.1.1"
 
+        # we have a network for a binding without relations on it
+        assert (
+            str(mgr.charm.model.get_binding("deadnodead").network.bind_address)
+            == "1.1.1.1"
+        )
+
         # and an extra binding
         assert str(mgr.charm.model.get_binding("foo").network.bind_address) == "4.4.4.4"
 
 
+def test_no_sub_binding(mycharm):
+    ctx = Context(
+        mycharm,
+        meta={
+            "name": "foo",
+            "requires": {"bar": {"interface": "foo", "scope": "container"}},
+        },
+    )
+
+    with ctx.manager(
+        "update_status",
+        State(
+            relations=[
+                SubordinateRelation("bar"),
+            ]
+        ),
+    ) as mgr:
+        with pytest.raises(RuntimeError):
+            # sub relations have no network
+            mgr.charm.model.get_binding("bar").network
+
+
 def test_no_relation_error(mycharm):
     """Attempting to call get_binding on a non-existing relation -> RelationNotFoundError"""
-    mycharm._call = lambda *_: True
 
-    def fetch_unit_address(charm: CharmBase):
-        with pytest.raises(RelationNotFoundError):
-            _ = charm.model.get_binding("foo").network
+    ctx = Context(
+        mycharm,
+        meta={
+            "name": "foo",
+            "requires": {"metrics-endpoint": {"interface": "foo"}},
+            "extra-bindings": {"bar": {}},
+        },
+    )
 
-    trigger(
+    with ctx.manager(
+        "update_status",
         State(
             relations=[
                 Relation(
@@ -78,13 +114,8 @@ def fetch_unit_address(charm: CharmBase):
                     relation_id=1,
                 ),
             ],
-            extra_bindings={"foo": Network.default()},
+            extra_bindings={"bar": Network.default()},
         ),
-        "update_status",
-        mycharm,
-        meta={
-            "name": "foo",
-            "requires": {"metrics-endpoint": {"interface": "foo"}},
-        },
-        post_event=fetch_unit_address,
-    )
+    ) as mgr:
+        with pytest.raises(RelationNotFoundError):
+            net = mgr.charm.model.get_binding("foo").network