Support x-death event proplists from before #78

We group x-death header values before processing them
to make sure there's only one per {queue, reason}.

src/rabbit_dead_letter.erl

@@ -84,36 +84,85 @@ x_death_event_key(Info, Key, KeyType) ->
         {value, {Key, KeyType, Val}} -> Val
     end.
 
+maybe_append_to_event_group(Info, _Queue, _Reason, []) ->
+    [Info];
+maybe_append_to_event_group(Info, Queue, Reason, Acc) ->
+    case lists:any(queue_and_reason_matcher(Queue, Reason), Acc) of
+        true  -> Acc;
+        false -> [Info | Acc]
+    end.
+
+group_by_queue_and_reason(Tables) ->
+    Infos = [Info || {table, Info} <- Tables],
+    Grouped =
+        lists:foldl(fun (Info, Acc) ->
+            Q = x_death_event_key(Info, <<"queue">>, longstr),
+            R = x_death_event_key(Info, <<"reason">>, longstr),
+            Matcher = queue_and_reason_matcher(Q, R),
+            {Matches, _} = lists:partition(Matcher, Infos),
+            case Matches of
+                [X] ->
+                    maybe_append_to_event_group(
+                        ensure_xdeath_event_count(X), Q, R, Acc);
+                [X|_] = Xs when is_list(Xs) ->
+                    maybe_append_to_event_group(
+                        ensure_xdeath_event_count(X, length(Xs)), Q, R, Acc)
+            end
+        end, [], Infos),
+    [{table, Info} || Info <- Grouped].
+
 update_x_death_header(Info, Headers) ->
     Q = x_death_event_key(Info, <<"queue">>, longstr),
     R = x_death_event_key(Info, <<"reason">>, longstr),
     case rabbit_basic:header(<<"x-death">>, Headers) of
         undefined ->
             rabbit_basic:prepend_table_header(<<"x-death">>,
-              [{<<"count">>, long, 1} | Info], Headers);
+                [{<<"count">>, long, 1} | Info], Headers);
         {<<"x-death">>, array, Tables} ->
+            %% group existing x-death headers in case we have some from
+            %% before rabbitmq-server#78
+            GroupedTables = group_by_queue_and_reason(Tables),
             {Matches, Others} = lists:partition(
-              fun ({table, Info0}) ->
-                  x_death_event_key(Info0, <<"queue">>, longstr) =:= Q
-                  andalso x_death_event_key(Info0, <<"reason">>, longstr) =:= R
-              end, Tables),
+                queue_and_reason_matcher(Q, R), GroupedTables),
             Info1 = case Matches of
                         [] ->
                             [{<<"count">>, long, 1} | Info];
                         [{table, M}] ->
-                            case x_death_event_key(M, <<"count">>, long) of
-                                undefined ->
-                                    [{<<"count">>, long, 1} | M];
-                                N ->
-                                    lists:keyreplace(
-                                      <<"count">>, 1, M,
-                                      {<<"count">>, long, N + 1})
-                            end
+                            increment_xdeath_event_count(M)
                     end,
             rabbit_misc:set_table_value(Headers, <<"x-death">>, array,
-              [{table, rabbit_misc:sort_field_table(Info1)} | Others])
+                [{table, rabbit_misc:sort_field_table(Info1)} | Others])
+    end.
+
+ensure_xdeath_event_count(Info) ->
+    ensure_xdeath_event_count(Info, 1).
+ensure_xdeath_event_count(Info, InitialVal) when InitialVal >= 1 ->
+    case x_death_event_key(Info, <<"count">>, long) of
+        undefined ->
+            [{<<"count">>, long, InitialVal} | Info];
+        _ ->
+            Info
+    end.
+
+increment_xdeath_event_count(Info) ->
+    case x_death_event_key(Info, <<"count">>, long) of
+        undefined ->
+            [{<<"count">>, long, 1} | Info];
+        N ->
+            lists:keyreplace(
+                <<"count">>, 1, Info,
+                {<<"count">>, long, N + 1})
     end.
 
+queue_and_reason_matcher(Q, R) ->
+  fun({table, Info}) ->
+        x_death_event_key(Info, <<"queue">>, longstr) =:= Q
+          andalso x_death_event_key(Info, <<"reason">>, longstr) =:= R;
+     (Info) when is_list(Info) ->
+        x_death_event_key(Info, <<"queue">>, longstr) =:= Q
+          andalso x_death_event_key(Info, <<"reason">>, longstr) =:= R
+  end.
+
 per_msg_ttl_header(#'P_basic'{expiration = undefined}) ->
     [];
 per_msg_ttl_header(#'P_basic'{expiration = Expiration}) ->