Allow customizing the StateData in p1_fsm before error reporting.

A new callback is introduced on the p1_fsm behaviour:

print_error/1

If the module implements this function, it will be invoked
in case of process crash with the current state data *before*
printing the error in the log. The function must return the
desired State to print.

It is used in ejabberd_c2s to prune the presence sets that
can be large. Instead, the state is changed to include only
the # of elements on each set.

Change inspired in comming changes to gen_server on OTP, and
b01d15abc3 (diff-0)

src/ejabberd_c2s.erl

@@ -55,7 +55,9 @@
 	 handle_sync_event/4,
 	 code_change/4,
 	 handle_info/3,
-	 terminate/3]).
+	 terminate/3,
+     print_state/1
+     ]).
 
 
 -export([get_state/1]).
@@ -1289,6 +1291,19 @@ handle_info(Info, StateName, StateData) ->
     ?ERROR_MSG("Unexpected info: ~p", [Info]),
     fsm_next_state(StateName, StateData).
 
+
+%%----------------------------------------------------------------------
+%% Func: print_state/1
+%% Purpose: Prepare the state to be printed on error log
+%% Returns: State to print
+%%----------------------------------------------------------------------
+print_state(State = #state{pres_t = T, pres_f = F, pres_a = A, pres_i = I}) ->
+   State#state{pres_t = {pres_t, ?SETS:size(T)},
+               pres_f = {pres_f, ?SETS:size(F)},
+               pres_a = {pres_a, ?SETS:size(A)},
+               pres_i = {pres_i, ?SETS:size(I)}
+               }.
+    
 %%----------------------------------------------------------------------
 %% Func: terminate/3
 %% Purpose: Shutdown the fsm

src/p1_fsm.erl

@@ -25,7 +25,8 @@
 %%   - You can limit the time processing a message (TODO): If the
 %%   message processing does not return in a given period of time, the
 %%   process will be terminated.
-%% 
+%%   - You might customize the State data before sending it to error_logger
+%%   in case of a crash (just export the function print_state/1)
 %%     $Id$
 %%
 -module(p1_fsm).
@@ -146,7 +147,7 @@
 
 behaviour_info(callbacks) ->
     [{init,1},{handle_event,3},{handle_sync_event,4},{handle_info,3},
-     {terminate,3},{code_change,4}];
+     {terminate,3},{code_change,4}, {print_state,1}];
 behaviour_info(_Other) ->
     undefined.
 
@@ -376,7 +377,7 @@ loop(Parent, Name, StateName, StateData, Mod, hibernate, Debug,
 		       Debug, Limits, Queue1, QueueLen - 1, false);
 	{empty, _} ->
 	    Reason = internal_queue_error,
-	    error_info(Reason, Name, hibernate, StateName, StateData, Debug),
+	    error_info(Mod, Reason, Name, hibernate, StateName, StateData, Debug),
 	    exit(Reason)
     end;
 loop(Parent, Name, StateName, StateData, Mod, hibernate, Debug,
@@ -620,7 +621,7 @@ reply(Name, {To, Tag}, Reply, Debug, StateName) ->
 terminate(Reason, Name, Msg, Mod, StateName, StateData, Debug) ->
     case catch Mod:terminate(Reason, StateName, StateData) of
 	{'EXIT', R} ->
-	    error_info(R, Name, Msg, StateName, StateData, Debug),
+	    error_info(Mod, R, Name, Msg, StateName, StateData, Debug),
 	    exit(R);
 	_ ->
 	    case Reason of
@@ -639,12 +640,12 @@ terminate(Reason, Name, Msg, Mod, StateName, StateData, Debug) ->
 					   [self(), Limit]),
 		    exit(shutdown);
 		_ ->
-		    error_info(Reason, Name, Msg, StateName, StateData, Debug),
+		    error_info(Mod, Reason, Name, Msg, StateName, StateData, Debug),
 		    exit(Reason)
 	    end
     end.
 
-error_info(Reason, Name, Msg, StateName, StateData, Debug) ->
+error_info(Mod, Reason, Name, Msg, StateName, StateData, Debug) ->
     Reason1 = 
 	case Reason of
 	    {undef,[{M,F,A}|MFAs]} ->
@@ -662,12 +663,16 @@ error_info(Reason, Name, Msg, StateName, StateData, Debug) ->
 	    _ ->
 		Reason
 	end,
+    StateToPrint = case erlang:function_exported(Mod, print_state, 1) of
+      true -> (catch Mod:print_state(StateData));
+      false -> StateData
+    end,
     Str = "** State machine ~p terminating \n" ++
 	get_msg_str(Msg) ++
 	"** When State == ~p~n"
         "**      Data  == ~p~n"
         "** Reason for termination = ~n** ~p~n",
-    format(Str, [Name, get_msg(Msg), StateName, StateData, Reason1]),
+    format(Str, [Name, get_msg(Msg), StateName, StateToPrint, Reason1]),
     sys:print_log(Debug),
     ok.