Support backend modules defining their own gen_event handler ID

src/lager_app.erl

@@ -79,17 +79,21 @@ stop(Handlers) ->
 expand_handlers([]) ->
     [];
 expand_handlers([{lager_file_backend, Configs}|T]) ->
-    [ to_config(Config) || Config <- Configs] ++
+    [ {lager_file_backend:config_to_id(Config), Config} || Config <- Configs] ++
       expand_handlers(T);
+expand_handlers([{Mod, Config}|T]) when is_atom(Mod) ->
+    %% allow the backend to generate a gen_event handler id, if it wants to
+    code:load_file(Mod),
+    Res = case erlang:function_exported(Mod, config_to_id, 1) of
+        true ->
+            {Mod:config_to_id(Config), Config};
+        false ->
+            {Mod, Config}
+    end,
+    [Res | expand_handlers(T)];
 expand_handlers([H|T]) ->
     [H | expand_handlers(T)].
 
-to_config({Name,Severity}) ->
-    {{lager_file_backend, Name}, {Name, Severity}};
-to_config({Name,_Severity,_Size,_Rotation,_Count}=Config) ->
-    {{lager_file_backend, Name}, Config};
-to_config([{Name,_Severity,_Size,_Rotation,_Count}, _Format] = Config) ->
-    {{lager_file_backend, Name}, Config}.
 
 
 

src/lager_file_backend.erl

@@ -41,6 +41,8 @@
 -export([init/1, handle_call/2, handle_event/2, handle_info/2, terminate/2,
         code_change/3]).
 
+-export([config_to_id/1]).
+
 -record(state, {
         name :: string(),
         level :: integer(),
@@ -121,6 +123,15 @@ terminate(_Reason, #state{fd=FD}) ->
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
 
+%% convert the config into a gen_event handler ID
+config_to_id({Name,_Severity}) ->
+    {?MODULE, Name};
+config_to_id({Name,_Severity,_Size,_Rotation,_Count}) ->
+    {?MODULE, Name};
+config_to_id([{Name,_Severity,_Size,_Rotation,_Count}, _Format]) ->
+    {?MODULE, Name}.
+
+
 write(#state{name=Name, fd=FD, inode=Inode, flap=Flap, size=RotSize,
         count=Count} = State, Level, Msg) ->
     case lager_util:ensure_logfile(Name, FD, Inode, true) of