%% @doc Watchdog process, publishes the will if a session process fails.
%% @author Marc Worrell <marc@worrell.nl>
%% @copyright 2018 Marc Worrell
%% Copyright 2018 Marc Worrell
%%
%% 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.
-module(mqtt_sessions_will).
-behaviour(gen_server).
-export([
start_link/2,
connected/4,
reconnected/1,
disconnected/3,
disconnected/1,
set_user_context/2,
stop/1
]).
-export([
init/1,
handle_call/3,
handle_cast/2,
handle_info/2,
code_change/3,
terminate/2
]).
-record(state, {
pool :: atom(),
session_pid :: pid(),
will :: map(),
user_context :: term(),
session_expiry_interval :: non_neg_integer(),
expiry_ref = undefined :: reference() | undefined,
timer_ref = undefined,
is_stopping :: boolean()
}).
%% The connect handshake must complete in 20 seconds.
-define(CONNECT_EXPIRY_INTERVAL, 20).
-spec start_link( atom(), pid() ) -> {ok, pid()}.
start_link(Pool, SessionPid) ->
gen_server:start_link(?MODULE, [Pool, SessionPid], []).
%% @todo Race condition: the will process might have stopped (and sent the will)
%% In the time the new connect is handled. If so the will process is now
%% killing the session, which will force the client to re-connect.
-spec connected(pid(), map() | undefined, non_neg_integer(), term()) -> ok.
connected(Pid, Will, SessionExpiry, UserContext) ->
gen_server:cast(Pid, {connected, Will, SessionExpiry, UserContext}).
-spec reconnected(pid()) -> ok.
reconnected(Pid) ->
gen_server:cast(Pid, reconnected).
%% @doc Signal the will process that the session got disconnected from the client.
-spec disconnected(pid() | undefined, boolean(), non_neg_integer()) -> ok.
disconnected(Pid, IsWill, ExpiryInterval) ->
gen_server:cast(Pid, {disconnected, IsWill, ExpiryInterval}).
-spec disconnected(pid()) -> ok.
disconnected(Pid) ->
gen_server:cast(Pid, disconnected).
%% @doc Set a new user context, needed after reauthentication
-spec set_user_context(pid(), term()) -> ok.
set_user_context(Pid, UserContext) ->
gen_server:cast(Pid, {user_context, UserContext}).
%% @doc Sync request to stop the will process
-spec stop( pid() | undefined ) -> ok.
stop(undefined) ->
ok;
stop(Pid) ->
gen_server:call(Pid, stop, infinity).
% ---------------------------------------------------------------------------------------
% --------------------------- gen_server functions --------------------------------------
% ---------------------------------------------------------------------------------------
init([ Pool, SessionPid ]) ->
erlang:monitor(process, SessionPid),
State = #state{
pool = Pool,
session_pid = SessionPid,
will = #{},
is_stopping = false,
session_expiry_interval = 0
},
State1 = do_disconnected(State, ?CONNECT_EXPIRY_INTERVAL),
{ok, State1}.
handle_call(stop, _From, State) ->
self() ! stop,
{reply, ok, stop_timer(State#state{ is_stopping = true })};
handle_call(Msg, _From, State) ->
{stop, {unknown_message, Msg}, State}.
handle_cast({connected, undefined, SessionExpiry, UserContext}, State) ->
State1 = State#state{
user_context = UserContext,
session_expiry_interval = case SessionExpiry of
undefined -> 0;
_ -> SessionExpiry
end
},
{noreply, stop_timer(State1)};
handle_cast({connected, Will, SessionExpiry, UserContext}, State) ->
State1 = State#state{
will = Will,
user_context = UserContext,
session_expiry_interval = SessionExpiry
},
{noreply, stop_timer(State1)};
handle_cast(reconnected, State) ->
{noreply, stop_timer(State)};
handle_cast({disconnected, IsWill, ExpiryInterval}, State) ->
{noreply, do_disconnected(State, IsWill, ExpiryInterval)};
handle_cast(disconnected, State) ->
{noreply, do_disconnected(State, true, undefined)};
handle_cast({user_context, UserContext}, State) ->
{noreply, State#state{ user_context = UserContext }};
handle_cast(stop, State) ->
{stop, shutdown, State};
handle_cast(Msg, State) ->
{stop, {unknown_message, Msg}, State}.
handle_info({'DOWN', _Mref, process, Pid, _Reason}, #state{ session_pid = Pid } = State) ->
% Session unexpectedly stopped, publish the will immediately
do_publish_will(State),
{stop, shutdown, State};
handle_info(stop, State) ->
{stop, shutdown, State};
handle_info({expired, Ref}, #state{ expiry_ref = Ref } = State) ->
mqtt_sessions_process:kill(State#state.session_pid),
do_publish_will(State),
{stop, shutdown, State};
handle_info({expired, Ref}, #state{ expiry_ref = Ref } = State) ->
do_publish_will(State),
{stop, shutdown, State};
handle_info({expired, _Ref}, State) ->
% old timer - ignore
{noreply, State}.
code_change(_Vsn, State, _Extra) ->
{ok, State}.
terminate(_Reason, _State) ->
ok.
% ---------------------------------------------------------------------------------------
% ----------------------------- support functions ---------------------------------------
% ---------------------------------------------------------------------------------------
%% @doc Handle a disconnect of the MQTT connection, if not reconnected within the delay interval
%% then we kill the connection process and the will is published.
do_disconnected(State, IsWill, undefined) ->
do_disconnected(State, IsWill, State#state.session_expiry_interval);
do_disconnected(State, false, DelayInterval) ->
State1 = State#state{ will = #{} },
do_disconnected(State1, DelayInterval);
do_disconnected(State, true, DelayInterval) ->
Delay = erlang:min(
DelayInterval,
maps:get(delay_interval, State#state.will, DelayInterval)),
do_disconnected(State, Delay).
do_disconnected(State, DelayInterval) ->
Ref = erlang:make_ref(),
Timer = erlang:send_after(DelayInterval * 1000, self(), {expired, Ref}),
State#state{ timer_ref = Timer, expiry_ref = Ref }.
stop_timer(#state{ timer_ref = undefined } = State) ->
State;
stop_timer(#state{ timer_ref = TRef } = State) ->
erlang:cancel_timer(TRef),
State#state{ timer_ref = undefined, expiry_ref = undefined }.
%% @doc Publish the will message. A will is published if the connection process crashes or if
%% it is has been disconnected for a too long time.
do_publish_will(#state{ is_stopping = true }) ->
ok;
do_publish_will(#state{ pool = Pool, will = #{ topic := Topic, payload := Payload } = Will, user_context = UserContext }) ->
Options = #{
qos => maps:get(qos, Will, 0),
retain => maps:get(retain, Will, false),
properties => maps:get(properties, Will, #{})
},
mqtt_sessions:publish(Pool, Topic, Payload, Options, UserContext);
do_publish_will(#state{}) ->
ok.
