Specify which content types we provide. Closes #24.

The lack of this information was causing webmachine to assume we provided
text/html (even though that's not at all true) and reject HTTP requests
which only accept application/json.

src/rabbit_mgmt_wm_exchange_publish.erl

@@ -17,7 +17,7 @@
 -module(rabbit_mgmt_wm_exchange_publish).
 
 -export([init/1, resource_exists/2, post_is_create/2, is_authorized/2,
-         allowed_methods/2, process_post/2]).
+         allowed_methods/2,  content_types_provided/2, process_post/2]).
 
 -include("rabbit_mgmt.hrl").
 -include_lib("webmachine/include/webmachine.hrl").
@@ -29,6 +29,9 @@ init(_Config) -> {ok, #context{}}.
 allowed_methods(ReqData, Context) ->
     {['POST'], ReqData, Context}.
 
+content_types_provided(ReqData, Context) ->
+   {[{"application/json", to_json}], ReqData, Context}.
+
 resource_exists(ReqData, Context) ->
     {case rabbit_mgmt_wm_exchange:exchange(ReqData) of
          not_found -> false;