Khepri: Fix topic routing for empty routing keys

An empty routing key in a binding matched routes incorrectly with
Khepri enabled: it would not match the empty routing key and would
mistakenly match some keys containing `*` patterns.

The first change avoids `split_topic_key_binary/1` since that function
counts the empty routing key as a word: `[<<>>]`. This mistakenly lets
the `*` pattern match against the component.

The second change adds a special case for the empty routing key that
connects the bindings for the empty routing key to the root node. This
matches the structure of the graph in mnesia.

The final change helps debugging failures in that test case: the
error message when a mismatch occurs now shows the expected and
actual destinations and the routing key which mismatched.

Author: the-mikedavis

deps/rabbit/src/rabbit_db_topic_exchange.erl

@@ -190,7 +190,7 @@ match_in_mnesia(XName, RoutingKey) ->
     mnesia:async_dirty(fun trie_match/2, [XName, Words]).
 
 match_in_khepri(XName, RoutingKey) ->
-    Words = split_topic_key_binary(RoutingKey),
+    Words = [list_to_binary(W) || W <- split_topic_key(RoutingKey)],
     trie_match_in_khepri(XName, Words).
 
 %% --------------------------------------------------------------

deps/rabbit/src/rabbit_khepri.erl

@@ -753,6 +753,13 @@ edges_for_path(
     Exchange = rabbit_misc:r(VHost, exchange, ExchangeName),
     edges_for_path([root | Components], Bindings, Exchange, []).
 
+edges_for_path([root, <<>>], Bindings, Exchange, Edges) ->
+    ToNodeId = {bindings, Bindings},
+    Edge = #topic_trie_edge{trie_edge = #trie_edge{exchange_name = Exchange,
+                                                   node_id =       root,
+                                                   word =          bindings},
+                            node_id = ToNodeId},
+    [Edge | Edges];
 edges_for_path([FromNodeId, To | Rest], Bindings, Exchange, Edges) ->
     ToNodeId = [To | FromNodeId],
     Edge = #topic_trie_edge{trie_edge = #trie_edge{exchange_name = Exchange,

deps/rabbit/test/unit_access_control_SUITE.erl

@@ -436,5 +436,7 @@ test_topic_expect_match(X, List) ->
                                                    kind = queue,
                                                    name = list_to_binary(Q)}
                               end, Expected),
-              true = (lists:usort(ExpectedRes) =:= lists:usort(Res))
+              ?assertEqual(
+                lists:usort(ExpectedRes), lists:usort(Res),
+                lists:flatten(io_lib:format("Routing key: ~w", [BinKey])))
       end, List).