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-rw-r--r--tests/storage/test_event_federation.py241
1 files changed, 193 insertions, 48 deletions
diff --git a/tests/storage/test_event_federation.py b/tests/storage/test_event_federation.py
index 9c151a5e62..7a4ecab2d5 100644
--- a/tests/storage/test_event_federation.py
+++ b/tests/storage/test_event_federation.py
@@ -13,7 +13,19 @@
 # limitations under the License.
 
 import datetime
-from typing import Dict, List, Tuple, Union, cast
+from typing import (
+    Collection,
+    Dict,
+    FrozenSet,
+    Iterable,
+    List,
+    Mapping,
+    Set,
+    Tuple,
+    TypeVar,
+    Union,
+    cast,
+)
 
 import attr
 from parameterized import parameterized
@@ -38,6 +50,138 @@ from synapse.util import Clock, json_encoder
 import tests.unittest
 import tests.utils
 
+# The silly auth graph we use to test the auth difference algorithm,
+# where the top are the most recent events.
+#
+#   A   B
+#    \ /
+#  D  E
+#  \  |
+#   ` F   C
+#     |  /|
+#     G ´ |
+#     | \ |
+#     H   I
+#     |   |
+#     K   J
+
+AUTH_GRAPH: Dict[str, List[str]] = {
+    "a": ["e"],
+    "b": ["e"],
+    "c": ["g", "i"],
+    "d": ["f"],
+    "e": ["f"],
+    "f": ["g"],
+    "g": ["h", "i"],
+    "h": ["k"],
+    "i": ["j"],
+    "k": [],
+    "j": [],
+}
+
+DEPTH_GRAPH = {
+    "a": 7,
+    "b": 7,
+    "c": 4,
+    "d": 6,
+    "e": 6,
+    "f": 5,
+    "g": 3,
+    "h": 2,
+    "i": 2,
+    "k": 1,
+    "j": 1,
+}
+
+T = TypeVar("T")
+
+
+def get_all_topologically_sorted_orders(
+    nodes: Iterable[T],
+    graph: Mapping[T, Collection[T]],
+) -> List[List[T]]:
+    """Given a set of nodes and a graph, return all possible topological
+    orderings.
+    """
+
+    # This is implemented by Kahn's algorithm, and forking execution each time
+    # we have a choice over which node to consider next.
+
+    degree_map = {node: 0 for node in nodes}
+    reverse_graph: Dict[T, Set[T]] = {}
+
+    for node, edges in graph.items():
+        if node not in degree_map:
+            continue
+
+        for edge in set(edges):
+            if edge in degree_map:
+                degree_map[node] += 1
+
+            reverse_graph.setdefault(edge, set()).add(node)
+        reverse_graph.setdefault(node, set())
+
+    zero_degree = [node for node, degree in degree_map.items() if degree == 0]
+
+    return _get_all_topologically_sorted_orders_inner(
+        reverse_graph, zero_degree, degree_map
+    )
+
+
+def _get_all_topologically_sorted_orders_inner(
+    reverse_graph: Dict[T, Set[T]],
+    zero_degree: List[T],
+    degree_map: Dict[T, int],
+) -> List[List[T]]:
+    new_paths = []
+
+    # Rather than only choosing *one* item from the list of nodes with zero
+    # degree, we "fork" execution and run the algorithm for each node in the
+    # zero degree.
+    for node in zero_degree:
+        new_degree_map = degree_map.copy()
+        new_zero_degree = zero_degree.copy()
+        new_zero_degree.remove(node)
+
+        for edge in reverse_graph.get(node, []):
+            if edge in new_degree_map:
+                new_degree_map[edge] -= 1
+                if new_degree_map[edge] == 0:
+                    new_zero_degree.append(edge)
+
+        paths = _get_all_topologically_sorted_orders_inner(
+            reverse_graph, new_zero_degree, new_degree_map
+        )
+        for path in paths:
+            path.insert(0, node)
+
+        new_paths.extend(paths)
+
+    if not new_paths:
+        return [[]]
+
+    return new_paths
+
+
+def get_all_topologically_consistent_subsets(
+    nodes: Iterable[T],
+    graph: Mapping[T, Collection[T]],
+) -> Set[FrozenSet[T]]:
+    """Get all subsets of the graph where if node N is in the subgraph, then all
+    nodes that can reach that node (i.e. for all X there exists a path X -> N)
+    are in the subgraph.
+    """
+    all_topological_orderings = get_all_topologically_sorted_orders(nodes, graph)
+
+    graph_subsets = set()
+    for ordering in all_topological_orderings:
+        ordering.reverse()
+
+        for idx in range(len(ordering)):
+            graph_subsets.add(frozenset(ordering[:idx]))
+
+    return graph_subsets
+
 
 @attr.s(auto_attribs=True, frozen=True, slots=True)
 class _BackfillSetupInfo:
@@ -172,49 +316,6 @@ class EventFederationWorkerStoreTestCase(tests.unittest.HomeserverTestCase):
     def _setup_auth_chain(self, use_chain_cover_index: bool) -> str:
         room_id = "@ROOM:local"
 
-        # The silly auth graph we use to test the auth difference algorithm,
-        # where the top are the most recent events.
-        #
-        #   A   B
-        #    \ /
-        #  D  E
-        #  \  |
-        #   ` F   C
-        #     |  /|
-        #     G ´ |
-        #     | \ |
-        #     H   I
-        #     |   |
-        #     K   J
-
-        auth_graph: Dict[str, List[str]] = {
-            "a": ["e"],
-            "b": ["e"],
-            "c": ["g", "i"],
-            "d": ["f"],
-            "e": ["f"],
-            "f": ["g"],
-            "g": ["h", "i"],
-            "h": ["k"],
-            "i": ["j"],
-            "k": [],
-            "j": [],
-        }
-
-        depth_map = {
-            "a": 7,
-            "b": 7,
-            "c": 4,
-            "d": 6,
-            "e": 6,
-            "f": 5,
-            "g": 3,
-            "h": 2,
-            "i": 2,
-            "k": 1,
-            "j": 1,
-        }
-
         # Mark the room as maybe having a cover index.
 
         def store_room(txn: LoggingTransaction) -> None:
@@ -238,9 +339,9 @@ class EventFederationWorkerStoreTestCase(tests.unittest.HomeserverTestCase):
         def insert_event(txn: LoggingTransaction) -> None:
             stream_ordering = 0
 
-            for event_id in auth_graph:
+            for event_id in AUTH_GRAPH:
                 stream_ordering += 1
-                depth = depth_map[event_id]
+                depth = DEPTH_GRAPH[event_id]
 
                 self.store.db_pool.simple_insert_txn(
                     txn,
@@ -260,8 +361,8 @@ class EventFederationWorkerStoreTestCase(tests.unittest.HomeserverTestCase):
             self.persist_events._persist_event_auth_chain_txn(
                 txn,
                 [
-                    cast(EventBase, FakeEvent(event_id, room_id, auth_graph[event_id]))
-                    for event_id in auth_graph
+                    cast(EventBase, FakeEvent(event_id, room_id, AUTH_GRAPH[event_id]))
+                    for event_id in AUTH_GRAPH
                 ],
             )
 
@@ -344,7 +445,51 @@ class EventFederationWorkerStoreTestCase(tests.unittest.HomeserverTestCase):
         room_id = self._setup_auth_chain(use_chain_cover_index)
 
         # Now actually test that various combinations give the right result:
+        self.assert_auth_diff_is_expected(room_id)
+
+    @parameterized.expand(
+        [
+            [graph_subset]
+            for graph_subset in get_all_topologically_consistent_subsets(
+                AUTH_GRAPH, AUTH_GRAPH
+            )
+        ]
+    )
+    def test_auth_difference_partial(self, graph_subset: Collection[str]) -> None:
+        """Test that if we only have a chain cover index on a partial subset of
+        the room we still get the correct auth chain difference.
+
+        We do this by removing the chain cover index for every valid subset of the
+        graph.
+        """
+        room_id = self._setup_auth_chain(True)
+
+        for event_id in graph_subset:
+            # Remove chain cover from that event.
+            self.get_success(
+                self.store.db_pool.simple_delete(
+                    table="event_auth_chains",
+                    keyvalues={"event_id": event_id},
+                    desc="test_auth_difference_partial_remove",
+                )
+            )
+            self.get_success(
+                self.store.db_pool.simple_insert(
+                    table="event_auth_chain_to_calculate",
+                    values={
+                        "event_id": event_id,
+                        "room_id": room_id,
+                        "type": "",
+                        "state_key": "",
+                    },
+                    desc="test_auth_difference_partial_remove",
+                )
+            )
+
+        self.assert_auth_diff_is_expected(room_id)
 
+    def assert_auth_diff_is_expected(self, room_id: str) -> None:
+        """Assert the auth chain difference returns the correct answers."""
         difference = self.get_success(
             self.store.get_auth_chain_difference(room_id, [{"a"}, {"b"}])
         )