Make s2s connection table cleanup more robust

Using monitors instead of doint that from terminate() makes us immune to
s2s handler processes being forcefully killed.

src/ejabberd_s2s.erl

@@ -33,8 +33,8 @@
 
 %% API
 -export([start_link/0, stop/0, route/1, have_connection/1,
-	 get_connections_pids/1, try_register/1,
-	 remove_connection/2, start_connection/2, start_connection/3,
+	 get_connections_pids/1,
+	 start_connection/2, start_connection/3,
 	 dirty_get_connections/0, allow_host/2,
 	 incoming_s2s_number/0, outgoing_s2s_number/0,
 	 stop_s2s_connections/0,
@@ -112,24 +112,6 @@ is_temporarly_blocked(Host) ->
 	    end
     end.
 
--spec remove_connection({binary(), binary()}, pid()) -> ok.
-remove_connection({From, To} = FromTo, Pid) ->
-    case mnesia:dirty_match_object(s2s, #s2s{fromto = FromTo, pid = Pid}) of
-	[#s2s{pid = Pid}] ->
-	    F = fun() ->
-			mnesia:delete_object(#s2s{fromto = FromTo, pid = Pid})
-		end,
-	    case mnesia:transaction(F) of
-		{atomic, _} -> ok;
-		{aborted, Reason} ->
-		    ?ERROR_MSG("Failed to unregister s2s connection ~ts -> ~ts: "
-			       "Mnesia failure: ~p",
-			       [From, To, Reason])
-	    end;
-	_ ->
-	    ok
-    end.
-
 -spec have_connection({binary(), binary()}) -> boolean().
 have_connection(FromTo) ->
     case catch mnesia:dirty_read(s2s, FromTo) of
@@ -148,31 +130,6 @@ get_connections_pids(FromTo) ->
 	    []
     end.
 
--spec try_register({binary(), binary()}) -> boolean().
-try_register({From, To} = FromTo) ->
-    MaxS2SConnectionsNumber = max_s2s_connections_number(FromTo),
-    MaxS2SConnectionsNumberPerNode =
-	max_s2s_connections_number_per_node(FromTo),
-    F = fun () ->
-		L = mnesia:read({s2s, FromTo}),
-		NeededConnections = needed_connections_number(L,
-							      MaxS2SConnectionsNumber,
-							      MaxS2SConnectionsNumberPerNode),
-		if NeededConnections > 0 ->
-			mnesia:write(#s2s{fromto = FromTo, pid = self()}),
-			true;
-		   true -> false
-		end
-	end,
-    case mnesia:transaction(F) of
-	{atomic, Res} -> Res;
-	{aborted, Reason} ->
-	    ?ERROR_MSG("Failed to register s2s connection ~ts -> ~ts: "
-		       "Mnesia failure: ~p",
-		       [From, To, Reason]),
-	    false
-    end.
-
 -spec dirty_get_connections() -> [{binary(), binary()}].
 dirty_get_connections() ->
     mnesia:dirty_all_keys(s2s).
@@ -269,6 +226,8 @@ init([]) ->
 	    {stop, Reason}
     end.
 
+handle_call({new_connection, Args}, _From, State) ->
+    {reply, erlang:apply(fun new_connection_int/7, Args), State};
 handle_call(Request, From, State) ->
     ?WARNING_MSG("Unexpected call from ~p: ~p", [From, Request]),
     {noreply, State}.
@@ -289,6 +248,21 @@ handle_info({route, Packet}, State) ->
 			misc:format_exception(2, Class, Reason, StackTrace)])
     end,
     {noreply, State};
+handle_info({'DOWN', _Ref, process, Pid, _Reason}, State) ->
+    case mnesia:dirty_match_object(s2s, #s2s{pid = Pid, fromto = '_'}) of
+	[#s2s{pid = Pid, fromto = {From, To}} = Obj] ->
+	    F = fun() -> mnesia:delete_object(Obj) end,
+	    case mnesia:transaction(F) of
+		{atomic, _} -> ok;
+		{aborted, Reason} ->
+		    ?ERROR_MSG("Failed to unregister s2s connection for pid ~p (~ts -> ~ts):"
+			       "Mnesia failure: ~p",
+			       [Pid, From, To, Reason])
+	    end,
+	    {noreply, State};
+	_ ->
+	    {noreply, State}
+    end;
 handle_info(Info, State) ->
     ?WARNING_MSG("Unexpected info: ~p", [Info]),
     {noreply, State}.
@@ -458,6 +432,18 @@ open_several_connections(N, MyServer, Server, From,
 		     integer(), integer(), [proplists:property()]) -> [pid()].
 new_connection(MyServer, Server, From, FromTo,
 	       MaxS2SConnectionsNumber, MaxS2SConnectionsNumberPerNode, Opts) ->
+    case whereis(ejabberd_s2s) == self() of
+	true ->
+	    new_connection_int(MyServer, Server, From, FromTo,
+			       MaxS2SConnectionsNumber, MaxS2SConnectionsNumberPerNode, Opts);
+	false ->
+	    gen_server:call(ejabberd_s2s, {new_connection, [MyServer, Server, From, FromTo,
+							    MaxS2SConnectionsNumber,
+							    MaxS2SConnectionsNumberPerNode, Opts]})
+    end.
+
+new_connection_int(MyServer, Server, From, FromTo,
+	       MaxS2SConnectionsNumber, MaxS2SConnectionsNumberPerNode, Opts) ->
     {ok, Pid} = ejabberd_s2s_out:start(MyServer, Server, Opts),
     F = fun() ->
 		L = mnesia:read({s2s, FromTo}),
@@ -474,6 +460,7 @@ new_connection(MyServer, Server, From, FromTo,
     case TRes of
 	{atomic, Pid1} ->
 	    if Pid1 == Pid ->
+		    erlang:monitor(process, Pid),
 		    ejabberd_s2s_out:connect(Pid);
 	       true ->
 		    ejabberd_s2s_out:stop_async(Pid)

src/ejabberd_s2s_out.erl

@@ -318,7 +318,6 @@ handle_info(Info, #{server_host := ServerHost} = State) ->
 
 terminate(Reason, #{server := LServer,
 		    remote_server := RServer} = State) ->
-    ejabberd_s2s:remove_connection({LServer, RServer}, self()),
     State1 = case Reason of
 		 normal -> State;
 		 _ -> State#{stop_reason => internal_failure}
@@ -351,21 +350,12 @@ bounce_queue(State) ->
       end, State).
 
 -spec bounce_message_queue({binary(), binary()}, state()) -> state().
-bounce_message_queue({LServer, RServer} = FromTo, State) ->
-    Pids = ejabberd_s2s:get_connections_pids(FromTo),
-    case lists:member(self(), Pids) of
-	true ->
-	    ?WARNING_MSG("Outgoing s2s connection ~ts -> ~ts is supposed "
-			 "to be unregistered, but pid ~p still presents "
-			 "in 's2s' table", [LServer, RServer, self()]),
-	    State;
-	false ->
-	    receive {route, Pkt} ->
-		    State1 = bounce_packet(Pkt, State),
-		    bounce_message_queue(FromTo, State1)
-	    after 0 ->
-		    State
-	    end
+bounce_message_queue(FromTo, State) ->
+    receive {route, Pkt} ->
+	    State1 = bounce_packet(Pkt, State),
+	    bounce_message_queue(FromTo, State1)
+    after 0 ->
+	    State
     end.
 
 -spec bounce_packet(xmpp_element(), state()) -> state().