Add stub for "inert" exchange to be used when exchange types are missing.

Right now it just emits warnings on startup and when a message is routed
through the exchange.

I need to handle the "add_binding" and "remove_bindings" better, probably
emitting a protocol error.

Also, I'm not sure the log warning are visible enough.

2 files changed, 55 insertions, 3 deletions

diff --git a/src/rabbit_exchange.erl b/src/rabbit_exchange.erl
index a15b9be490..8b2015967a 100644
--- a/src/rabbit_exchange.erl
+++ b/src/rabbit_exchange.erl
@@ -355,11 +355,20 @@ peek_serial(XName) ->
         _                                  -> undefined
     end.
 
+inert_module(T) ->
+    rabbit_log:warning(
+      "Could not find exchange type ~p, using inert exchange instead~n", [T]),
+    put({xtype_to_module, T}, rabbit_exchange_type_inert),
+    rabbit_exchange_type_inert.
+
 %% Used with atoms from records; e.g., the type is expected to exist.
 type_to_module(T) ->
     case get({xtype_to_module, T}) of
-        undefined -> {ok, Module} = rabbit_registry:lookup_module(exchange, T),
-                     put({xtype_to_module, T}, Module),
-                     Module;
+         undefined ->
+            case rabbit_registry:lookup_module(exchange, T) of
+                {ok, Module}       -> put({xtype_to_module, T}, Module),
+                                      Module;
+                {error, not_found} -> inert_module(T)
+            end;
         Module    -> Module
     end.
diff --git a/src/rabbit_exchange_type_inert.erl b/src/rabbit_exchange_type_inert.erl
new file mode 100644
index 0000000000..9e2424e9b3
--- /dev/null
+++ b/src/rabbit_exchange_type_inert.erl
@@ -0,0 +1,43 @@
+%% The contents of this file are subject to the Mozilla Public License
+%% Version 1.1 (the "License"); you may not use this file except in
+%% compliance with the License. You may obtain a copy of the License
+%% at http://www.mozilla.org/MPL/
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and
+%% limitations under the License.
+%%
+%% The Original Code is RabbitMQ.
+%%
+%% The Initial Developer of the Original Code is VMware, Inc.
+%% Copyright (c) 2007-2012 VMware, Inc.  All rights reserved.
+%%
+
+-module(rabbit_exchange_type_inert).
+-include("rabbit.hrl").
+
+-behaviour(rabbit_exchange_type).
+
+-export([description/0, serialise_events/0, route/2]).
+-export([validate/1, create/2, delete/3,
+         add_binding/3, remove_bindings/3, assert_args_equivalence/2]).
+-include("rabbit_exchange_type_spec.hrl").
+
+description() ->
+    D = <<"Dummy exchange type, to be used when the intended one is not found">>,
+    [{name, <<"inert">>}, {description, D}].
+
+serialise_events() -> false.
+
+route(#exchange{name = Name}, _) ->
+    rabbit_log:warning("Received message at inert exchange ~p, dropping~n",
+                       [Name]).
+
+validate(_X) -> ok.
+create(_Tx, _X) -> ok.
+delete(_Tx, _X, _Bs) -> ok.
+add_binding(_Tx, _X, _B) -> ok.
+remove_bindings(_Tx, _X, _Bs) -> ok.
+assert_args_equivalence(X, Args) ->
+    rabbit_exchange:assert_args_equivalence(X, Args).