Limit x-death growth to one entry per queue

Otherwise the list can grow forever in some cases.

Fixes #78.

src/rabbit_dead_letter.erl

@@ -34,6 +34,8 @@
 
 %%----------------------------------------------------------------------------
 
+-define(X_DEATH_HEADER, <<"x-death">>).
+
 publish(Msg, Reason, X, RK, QName) ->
     DLMsg = make_msg(Msg, Reason, X#exchange.name, RK, QName),
     Delivery = rabbit_basic:delivery(false, false, DLMsg, undefined),
@@ -66,8 +68,7 @@ make_msg(Msg = #basic_message{content       = Content,
                         {<<"time">>,         timestamp, TimeSec},
                         {<<"exchange">>,     longstr,   Exchange#resource.name},
                         {<<"routing-keys">>, array,     RKs1}] ++ PerMsgTTL,
-                HeadersFun1(rabbit_basic:prepend_table_header(<<"x-death">>,
-                                                              Info, Headers))
+                HeadersFun1(update_x_death_header(Info, Headers))
         end,
     Content1 = #content{properties = Props} =
         rabbit_basic:map_headers(HeadersFun2, Content),
@@ -78,6 +79,41 @@ make_msg(Msg = #basic_message{content       = Content,
                       routing_keys  = DeathRoutingKeys,
                       content       = Content2}.
 
+x_death_header(undefined) ->
+    undefined;
+x_death_header([]) ->
+    undefined;
+x_death_header(Headers) ->
+    case lists:keysearch(?X_DEATH_HEADER, 1, Headers) of
+        false        -> undefined;
+        {value, Val} -> Val
+    end.
+
+x_death_event_queue(Info) ->
+    case lists:keysearch(<<"queue">>, 1, Info) of
+        false                                -> undefined;
+        {value, {<<"queue">>, longstr, Val}} -> Val
+    end.
+
+x_death_not_for_queue({table, Info}, Queue) ->
+    x_death_event_queue(Info) =/= Queue.
+
+x_deaths_from_header({?X_DEATH_HEADER, array, Table}) ->
+    Table.
+
+update_x_death_header(Info, Headers) ->
+    Q = x_death_event_queue(Info),
+    case x_death_header(Headers) of
+        undefined ->
+            rabbit_basic:prepend_table_header(?X_DEATH_HEADER,
+                                              Info, Headers);
+        Array ->
+            XDeaths  = rabbit_misc:sort_field_table([{table, Info} |
+                                                     [XD || XD <- x_deaths_from_header(Array),
+                                                            x_death_not_for_queue(XD, Q)]]),
+            rabbit_misc:set_table_value(Headers, ?X_DEATH_HEADER, array, XDeaths)
+    end.
+
 per_msg_ttl_header(#'P_basic'{expiration = undefined}) ->
     [];
 per_msg_ttl_header(#'P_basic'{expiration = Expiration}) ->
@@ -96,7 +132,7 @@ detect_cycles(_Reason, #basic_message{content = Content}, Queues) ->
         undefined ->
             NoCycles;
         _ ->
-            case rabbit_misc:table_lookup(Headers, <<"x-death">>) of
+            case rabbit_misc:table_lookup(Headers, ?X_DEATH_HEADER) of
                 {array, Deaths} ->
                     {Cycling, NotCycling} =
                         lists:partition(fun (#resource{name = Queue}) ->