stdlib: Make gen_fsm callbacks optional

5 files changed, 244 insertions, 23 deletions

diff --git a/lib/stdlib/doc/src/gen_fsm.xml b/lib/stdlib/doc/src/gen_fsm.xml
index 719ab2b558..691a039e34 100644
--- a/lib/stdlib/doc/src/gen_fsm.xml
+++ b/lib/stdlib/doc/src/gen_fsm.xml
@@ -562,6 +562,13 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
         <v>Extra = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not export it.
+            If a release upgrade/downgrade with <c>Change={advanced,Extra}</c>
+            specified in the <c>appup</c> file is made when <c>code_change/4</c>
+            isn't implemented the process will crash with an <c>undef</c> exit
+            reason.</p>
+        </note>
         <p>This function is called by a <c>gen_fsm</c> process when it is to
           update its internal state data during a release upgrade/downgrade,
           that is, when instruction <c>{update,Module,Change,...}</c>,
@@ -686,6 +693,13 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
         <v>&nbsp;Reason = normal | term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_fsm</c> module provides a default
+            implementation of this function that logs about the unexpected
+            <c>Info</c> message, drops it and returns
+            <c>{next_state, StateName, StateData}</c>.</p>
+        </note>
         <p>This function is called by a <c>gen_fsm</c> process when it receives
           any other message than a synchronous or asynchronous event (or a
           system message).</p>
@@ -899,6 +913,11 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
         <v>StateData = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_fsm</c> module provides a default
+            implementation without cleanup.</p>
+        </note>
         <p>This function is called by a <c>gen_fsm</c> process when it is about
           to terminate. It is to be the opposite of
           <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
diff --git a/lib/stdlib/src/gen_fsm.erl b/lib/stdlib/src/gen_fsm.erl
index e925a75fe8..39a8fd42fe 100644
--- a/lib/stdlib/src/gen_fsm.erl
+++ b/lib/stdlib/src/gen_fsm.erl
@@ -169,7 +169,8 @@
       State :: term(),
       Status :: term().
 
--optional_callbacks([format_status/2]).
+-optional_callbacks(
+    [handle_info/3, terminate/3, code_change/4, format_status/2]).
 
 %%% ---------------------------------------------------
 %%% Starts a generic state machine.
@@ -466,6 +467,10 @@ handle_msg(Msg, Parent, Name, StateName, StateData, Mod, _Time) -> %No debug her
 					   StateName, NStateData, [])),
 	    reply(From, Reply),
 	    exit(R);
+        {'EXIT', {undef, [{Mod, handle_info, [_,_,_], _}|_]}} ->
+            error_logger:warning_msg("** Undefined handle_info in ~p~n"
+                                     "** Unhandled message: ~p~n", [Mod, Msg]),
+            loop(Parent, Name, StateName, StateData, Mod, infinity, []);
 	{'EXIT', What} ->
 	    terminate(What, Name, Msg, Mod, StateName, StateData, []);
 	Reply ->
@@ -540,24 +545,30 @@ reply(Name, {To, Tag}, Reply, Debug, StateName) ->
 -spec terminate(term(), _, _, atom(), _, _, _) -> no_return().
 
 terminate(Reason, Name, Msg, Mod, StateName, StateData, Debug) ->
-    case catch Mod:terminate(Reason, StateName, StateData) of
-	{'EXIT', R} ->
-	    FmtStateData = format_status(terminate, Mod, get(), StateData),
-	    error_info(R, Name, Msg, StateName, FmtStateData, Debug),
-	    exit(R);
-	_ ->
-	    case Reason of
-		normal ->
-		    exit(normal);
-		shutdown ->
-		    exit(shutdown);
- 		{shutdown,_}=Shutdown ->
- 		    exit(Shutdown);
+    case erlang:function_exported(Mod, terminate, 3) of
+	true ->
+	    case catch Mod:terminate(Reason, StateName, StateData) of
+		{'EXIT', R} ->
+		    FmtStateData = format_status(terminate, Mod, get(), StateData),
+		    error_info(R, Name, Msg, StateName, FmtStateData, Debug),
+		    exit(R);
 		_ ->
-                    FmtStateData = format_status(terminate, Mod, get(), StateData),
-		    error_info(Reason,Name,Msg,StateName,FmtStateData,Debug),
-		    exit(Reason)
-	    end
+		    ok
+	    end;
+	false ->
+	    ok
+    end,
+    case Reason of
+	normal ->
+	    exit(normal);
+	shutdown ->
+	    exit(shutdown);
+ 	{shutdown,_}=Shutdown ->
+ 	    exit(Shutdown);
+	_ ->
+	    FmtStateData1 = format_status(terminate, Mod, get(), StateData),
+	    error_info(Reason,Name,Msg,StateName,FmtStateData1,Debug),
+	    exit(Reason)
     end.
 
 error_info(Reason, Name, Msg, StateName, StateData, Debug) ->
diff --git a/lib/stdlib/test/erl_internal_SUITE.erl b/lib/stdlib/test/erl_internal_SUITE.erl
index c4c4a0408b..099f21f905 100644
--- a/lib/stdlib/test/erl_internal_SUITE.erl
+++ b/lib/stdlib/test/erl_internal_SUITE.erl
@@ -99,7 +99,7 @@ optional_callbacks(application) ->
 optional_callbacks(gen_server) ->
     [{handle_info, 2}, {terminate, 2}, {code_change, 3}, {format_status, 2}];
 optional_callbacks(gen_fsm) ->
-    [{format_status,2}];
+    [{handle_info, 3}, {terminate, 3}, {code_change, 4}, {format_status, 2}];
 optional_callbacks(gen_event) ->
     [{handle_info, 2}, {terminate, 2}, {code_change, 3}, {format_status, 2}];
 optional_callbacks(supervisor_bridge) ->
diff --git a/lib/stdlib/test/gen_fsm_SUITE.erl b/lib/stdlib/test/gen_fsm_SUITE.erl
index d6bb002b5f..361680a9b2 100644
--- a/lib/stdlib/test/gen_fsm_SUITE.erl
+++ b/lib/stdlib/test/gen_fsm_SUITE.erl
@@ -39,6 +39,11 @@
 	  call_format_status/1, error_format_status/1, terminate_crash_format/1,
 	  get_state/1, replace_state/1]).
 
+-export([undef_handle_event/1, undef_handle_sync_event/1, undef_handle_info/1,
+         undef_init/1, undef_code_change/1, undef_terminate1/1, undef_terminate2/1]).
+
+-export([undef_in_handle_info/1, undef_in_terminate/1]).
+
 -export([hibernate/1,hiber_idle/3,hiber_wakeup/3,hiber_idle/2,hiber_wakeup/2]).
 
 -export([enter_loop/1]).
@@ -48,7 +53,7 @@
 
 %% The gen_fsm behaviour
 -export([init/1, handle_event/3, handle_sync_event/4, terminate/3,
-	 handle_info/3, format_status/2]).
+	 handle_info/3, format_status/2, code_change/4]).
 -export([idle/2,	idle/3,
 	 timeout/2,
 	 wfor_conf/2,	wfor_conf/3,
@@ -63,7 +68,8 @@ suite() -> [{ct_hooks,[ts_install_cth]}].
 
 all() ->
     [{group, start}, {group, abnormal}, shutdown,
-     {group, sys}, hibernate, enter_loop].
+     {group, sys}, hibernate, enter_loop, {group, undef_callbacks},
+     undef_in_handle_info, undef_in_terminate].
 
 groups() ->
     [{start, [],
@@ -74,7 +80,10 @@ groups() ->
      {abnormal, [], [abnormal1, abnormal2]},
      {sys, [],
       [sys1, call_format_status, error_format_status, terminate_crash_format,
-       get_state, replace_state]}].
+       get_state, replace_state]},
+     {undef_callbacks, [],
+      [undef_handle_event, undef_handle_sync_event, undef_handle_info,
+       undef_init, undef_code_change, undef_terminate1, undef_terminate2]}].
 
 init_per_suite(Config) ->
     Config.
@@ -82,6 +91,11 @@ init_per_suite(Config) ->
 end_per_suite(_Config) ->
     ok.
 
+init_per_group(undef_callbacks, Config) ->
+    DataDir = ?config(data_dir, Config),
+    Server = filename:join(DataDir, "oc_fsm.erl"),
+    {ok, oc_fsm} = compile:file(Server),
+    Config;
 init_per_group(_GroupName, Config) ->
     Config.
 
@@ -868,6 +882,99 @@ enter_loop(Reg1, Reg2) ->
 	    gen_fsm:enter_loop(?MODULE, [], state0, [])
     end.
 
+%% Start should return an undef error if init isn't implemented
+undef_init(Config) when is_list(Config) ->
+    {error, {undef, [{oc_init_fsm, init, [[]], []}|_]}}
+        =  gen_fsm:start(oc_init_fsm, [], []),
+    ok.
+
+%% Test that the server crashes correctly if the handle_event callback is
+%% not exported in the callback module
+undef_handle_event(Config) when is_list(Config) ->
+    {ok, FSM} = gen_fsm:start(oc_fsm, [], []),
+    MRef = monitor(process, FSM),
+    gen_fsm:send_all_state_event(FSM, state_name),
+    ok = verify_undef_down(MRef, FSM, oc_fsm, handle_event).
+
+%% Test that the server crashes correctly if the handle_sync_event callback is
+%% not exported in the callback module
+undef_handle_sync_event(Config) when is_list(Config) ->
+    {ok, FSM} = gen_fsm:start(oc_fsm, [], []),
+    try
+        gen_fsm:sync_send_all_state_event(FSM, state_name),
+        ct:fail(should_crash)
+    catch exit:{{undef, [{oc_fsm, handle_sync_event, _, _}|_]},_} ->
+        ok
+    end.
+
+%% The fsm should log but not crash if the handle_info callback is
+%% calling an undefined function
+undef_handle_info(Config) when is_list(Config) ->
+    error_logger_forwarder:register(),
+    {ok, FSM} = gen_fsm:start(oc_fsm, [], []),
+    MRef = monitor(process, FSM),
+    FSM ! hej,
+    receive
+        {'DOWN', MRef, process, FSM, _} ->
+            ct:fail(should_not_crash)
+    after 500 ->
+        ok
+    end,
+    receive
+        {warning_msg, _GroupLeader,
+         {FSM, "** Undefined handle_info in " ++ _, [oc_fsm, hej]}} ->
+            ok;
+        Other ->
+            io:format("Unexpected: ~p", [Other]),
+            ct:fail(failed)
+    end.
+
+%% The upgrade should fail if code_change is expected in the callback module
+%% but not exported, but the fsm should continue with the old code
+undef_code_change(Config) when is_list(Config) ->
+    {ok, FSM} = gen_fsm:start(oc_fsm, [], []),
+    {error, {'EXIT', {undef, [{oc_fsm, code_change, [_, _, _, _], _}|_]}}}
+        = fake_upgrade(FSM, oc_fsm),
+    ok.
+
+%% Test the default implementation of terminate with normal reason if the
+%% callback module does not export it
+undef_terminate1(Config) when is_list(Config) ->
+    {ok, FSM} = gen_fsm:start(oc_fsm, [], []),
+    MRef = monitor(process, FSM),
+    ok = gen_fsm:stop(FSM),
+    ok = verify_down_reason(MRef, FSM, normal).
+
+%% Test the default implementation of terminate with error reason if the
+%% callback module does not export it
+undef_terminate2(Config) when is_list(Config) ->
+    {ok, FSM} = gen_fsm:start(oc_fsm, [], []),
+    MRef = monitor(process, FSM),
+    ok = gen_fsm:stop(FSM, {error, test}, infinity),
+    ok = verify_down_reason(MRef, FSM, {error, test}).
+
+%% Test that the server crashes correctly if the handle_info callback is
+%% calling an undefined function
+undef_in_handle_info(Config) when is_list(Config) ->
+    {ok, FSM} = gen_fsm:start(?MODULE, [], []),
+    MRef = monitor(process, FSM),
+    FSM ! {call_undef_fun, {?MODULE, handle_info}},
+    verify_undef_down(MRef, FSM, ?MODULE, handle_info),
+    ok.
+
+%% Test that the server crashes correctly if the terminate callback is
+%% calling an undefined function
+undef_in_terminate(Config) when is_list(Config) ->
+    State = {undef_in_terminate, {?MODULE, terminate}},
+    {ok, FSM} = gen_fsm:start(?MODULE, {state_data, State}, []),
+    try
+        gen_fsm:stop(FSM),
+        ct:fail(failed)
+    catch
+        exit:{undef, [{?MODULE, terminate, _, _}|_]} ->
+            ok
+    end.
+
 %%
 %% Functionality check
 %%
@@ -962,7 +1069,31 @@ do_sync_disconnect(FSM) ->
     yes = gen_fsm:sync_send_event(FSM, disconnect),
     check_state(FSM, idle).
 
+verify_down_reason(MRef, Pid, Reason) ->
+    receive
+        {'DOWN', MRef, process, Pid, Reason} ->
+            ok;
+        {'DOWN', MRef, process, Pid, Other}->
+            ct:fail({wrong_down_reason, Other})
+    after 5000 ->
+        ct:fail(should_shutdown)
+    end.
 
+verify_undef_down(MRef, Pid, Mod, Fun) ->
+    ok = receive
+        {'DOWN', MRef, process, Pid,
+         {undef, [{Mod, Fun, _, _}|_]}} ->
+            ok
+    after 5000 ->
+        ct:fail(should_crash)
+    end.
+
+fake_upgrade(Pid, Mod) ->
+    sys:suspend(Pid),
+    sys:replace_state(Pid, fun(State) -> {new, State} end),
+    Ret = sys:change_code(Pid, Mod, old_vsn, []),
+    ok = sys:resume(Pid),
+    Ret.
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%
@@ -992,6 +1123,9 @@ init(_) ->
 
 terminate(_, _State, crash_terminate) ->
     exit({crash, terminate});
+terminate(_, _, {undef_in_terminate, {Mod, Fun}}) ->
+    Mod:Fun(),
+    ok;
 terminate({From, stopped}, State, _Data) ->
     From ! {self(), {stopped, State}},
     ok;
@@ -1089,7 +1223,9 @@ handle_info(hibernate_now, _SName, _State) ->
     {next_state, hiber_idle, [], hibernate};
 handle_info(hibernate_later, _SName, _State) ->
     {next_state, hiber_idle, hibernate_me, 1000};
-
+handle_info({call_undef_fun, {Mod, Fun}}, State, Data) ->
+    Mod:Fun(),
+    {next_state, State, Data};
 handle_info(Info, _State, Data) ->
     {stop, {unexpected,Info}, Data}.
 
@@ -1134,6 +1270,13 @@ format_status(terminate, [_Pdict, StateData]) ->
 format_status(normal, [_Pdict, _StateData]) ->
     [format_status_called].
 
+code_change(_OldVsn, State,
+            {idle, {undef_in_code_change, {Mod, Fun}}} = Data, _Extra) ->
+    Mod:Fun(),
+    {ok, State, Data};
+code_change(_OldVsn, State, Data, _Extra) ->
+    {ok, State, Data}.
+
 get_messages() ->
     receive
 	Msg -> [Msg|get_messages()]
diff --git a/lib/stdlib/test/gen_fsm_SUITE_data/oc_fsm.erl b/lib/stdlib/test/gen_fsm_SUITE_data/oc_fsm.erl
new file mode 100644
index 0000000000..27fb1bc3b6
--- /dev/null
+++ b/lib/stdlib/test/gen_fsm_SUITE_data/oc_fsm.erl
@@ -0,0 +1,48 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2017. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+-module(oc_fsm).
+
+-behaviour(gen_fsm).
+
+%% API
+-export([start/0]).
+
+%% gen_fsm callbacks
+-export([init/1,
+         state_name/2,
+         state_name/3]).
+
+-define(SERVER, ?MODULE).
+
+-record(state, {}).
+
+start() ->
+    gen_fsm:start({local, ?SERVER}, ?MODULE, [], []).
+
+init([]) ->
+    {ok, state_name, #state{}}.
+
+state_name(_Event, State) ->
+    {next_state, state_name, State}.
+
+state_name(_Event, _From, State) ->
+    Reply = ok,
+    {reply, Reply, state_name, State}.
+