Exchange decorator routing improvements

3 files changed, 24 insertions, 10 deletions

diff --git a/src/rabbit_exchange.erl b/src/rabbit_exchange.erl
index a4a88661..a3b32c7b 100644
--- a/src/rabbit_exchange.erl
+++ b/src/rabbit_exchange.erl
@@ -335,7 +335,7 @@ route1(Delivery, Decorators,
        {[X = #exchange{type = Type} | WorkList], SeenXs, QNames}) ->
     ExchangeDests = (type_to_module(Type)):route(X, Delivery),
     AlternateDests = process_alternate(X, ExchangeDests),
-    DecorateDests = process_decorators(Delivery, Decorators, X),
+    DecorateDests = process_decorators(X, Decorators, Delivery),
     route1(Delivery, Decorators,
            lists:foldl(fun process_route/2, {WorkList, SeenXs, QNames},
                        AlternateDests ++ DecorateDests  ++ ExchangeDests)).
@@ -350,9 +350,9 @@ process_alternate(#exchange{name = XName, arguments = Args}, []) ->
 process_alternate(_X, _Results) ->
     [].
 
-process_decorators(_Delivery, [], _X) ->
+process_decorators(_, [], _) ->
     [];
-process_decorators(Delivery, Decorators, X) ->
+process_decorators(X, Decorators, Delivery) ->
     lists:append([Decorator:route(X, Delivery) || Decorator <- Decorators]).
 
 process_route(#resource{kind = exchange} = XName,
diff --git a/src/rabbit_exchange_decorator.erl b/src/rabbit_exchange_decorator.erl
index bf4add73..d8600835 100644
--- a/src/rabbit_exchange_decorator.erl
+++ b/src/rabbit_exchange_decorator.erl
@@ -57,6 +57,13 @@
 -callback remove_bindings(serial(), rabbit_types:exchange(),
                           [rabbit_types:binding()]) -> 'ok'.
 
+%% %% called after exchange routing
+%% %% return value is a list of queues to be added to the list of
+%% %% destination queues. decorators must register separately for
+%% %% this callback using exchange_decorator_route.
+%% -callback route(rabbit_types:exchange(), rabbit_types:delivery()) ->
+%%     [rabbit_amqqueue:name()].
+
 -else.
 
 -export([behaviour_info/1]).
diff --git a/src/rabbit_registry.erl b/src/rabbit_registry.erl
index 41b82ba5..22700a7c 100644
--- a/src/rabbit_registry.erl
+++ b/src/rabbit_registry.erl
@@ -95,20 +95,27 @@ internal_unregister(Class, TypeName) ->
     true = ets:delete(?ETS_NAME, UnregArg),
     ok.
 
-conditional_register({{exchange_decorator, _Type}, ModuleName} = RegArg) ->
+
+%% (un)register exchange decorator route callback only when implemented
+%% to avoid decorators being called unnecessarily on the fast publishing path
+conditional_register({{exchange_decorator, _Type}, ModuleName}) ->
     case erlang:function_exported(ModuleName, route, 2) of
-        true  -> true = ets:insert(?ETS_NAME, RegArg);
+        true  -> true = ets:insert(?ETS_NAME,
+                                   {{exchange_decorator_route, _Type},
+                                    ModuleName});
         false -> ok
     end;
 conditional_register(_) ->
     ok.
 
-conditional_unregister({exchange_decorator, Type} = UnregArg) ->
+conditional_unregister({exchange_decorator, Type}) ->
     case lookup_module(exchange_decorator, Type) of
-        {ok, ModName} -> case erlang:function_exported(ModName, route, 2) of
-                             true  -> true = ets:delete(?ETS_NAME, UnregArg);
-                             false -> ok
-                         end;
+        {ok, ModName} ->
+            case erlang:function_exported(ModName, route, 2) of
+                true  -> true = ets:delete(?ETS_NAME,
+                                           {exchange_decorator_route, Type});
+                false -> ok
+            end;
         {error, not_found} ->
             ok
     end;