fix: move environment variables extraction to supervisor

This will make connection variables persistent between process restarts.

src/systemd_socket.erl

@@ -5,14 +5,12 @@
 -behaviour(gen_server).
 
 -define(NAME, ?MODULE).
--define(NOTIFY_SOCKET, "NOTIFY_SOCKET").
 
 -include_lib("kernel/include/logger.hrl").
--include_lib("kernel/include/file.hrl").
 
 -export([send/1]).
 
--export([start_link/0,
+-export([start_link/1,
          init/1,
          handle_call/3,
          handle_cast/2,
@@ -25,30 +23,13 @@ send(Message) ->
 
 % # Behaviour implementation
 
-start_link() ->
-    gen_server:start_link({local, ?NAME}, ?MODULE, [], []).
+start_link(Address) ->
+    gen_server:start_link({local, ?NAME}, ?MODULE, Address, []).
 
-init(_Arg) ->
-    State = case has_env(?NOTIFY_SOCKET) of
-                false ->
-                    [];
-                [$@ | AbstractPath] ->
-                    Address = {local, [0 | AbstractPath]},
-                    {ok, Socket} = gen_udp:open(0, [local]),
-                    {Socket, Address};
-                Path ->
-                    case file:read_file_info(Path) of
-                        {error, _Error} ->
-                            [];
-                        {ok, #file_info{access=Access}}
-                          when Access =:= write; Access =:= read_write ->
-                            Address = {local, Path},
-                            {ok, Socket} = gen_udp:open(0, [local]),
-                            {Socket, Address}
-                    end
-            end,
-    os:unsetenv(?NOTIFY_SOCKET),
-    {ok, State}.
+init([]) -> {ok, []};
+init(Address) ->
+    {ok, Socket} = gen_udp:open(0, [local]),
+    {ok, {Socket, Address}}.
 
 handle_call({send, Message}, _Ref, {Socket, Address}=State) ->
     ok = gen_udp:send(Socket, Address, 0, [Message, $\n]),
@@ -61,10 +42,3 @@ handle_cast(_Msg, State) ->
 
 handle_info(_Msg, State) ->
     {noreply, State}.
-
-has_env(Name) ->
-    case os:getenv(Name) of
-        false -> false;
-        "" -> false;
-        Value -> Value
-    end.

src/systemd_sup.erl

@@ -6,18 +6,74 @@
 
 -export([start_link/1, init/1]).
 
+-define(PID, "WATCHDOG_PID").
+-define(TIMEOUT, "WATCHDOG_USEC").
+-define(NOTIFY_SOCKET, "NOTIFY_SOCKET").
+
+-include_lib("kernel/include/file.hrl").
+
 start_link(Opts) ->
     supervisor:start_link(?MODULE, Opts).
 
 init(_Opts) ->
     SupFlags = #{
       strategy => one_for_one
      },
+    Pid = os:getpid(),
+
     SocketServer = #{id => socket,
-                     start => {systemd_socket, start_link, []}
+                     start => {systemd_socket, start_link, [notify_socket()]}
                     },
-    Watchdog = #{id => watchdog,
-                 start => {systemd_watchdog, start_link, []}
-                },
+    Watchdog = case {watchdog_pid(), watchdog_timeout()} of
+                   {Pid, TimeoutUS} when TimeoutUS > 0 ->
+                       Timeout = erlang:convert_time_unit(TimeoutUS,
+                                                          microsecond,
+                                                          millisecond),
+                       #{id => watchdog,
+                         start => {systemd_watchdog, start_link, [Timeout]}
+                        };
+                   _ ->
+                       #{id => watchdog,
+                         start => {systemd_watchdog, start_link, [infinity]}
+                        }
+               end,
 
     {ok, {SupFlags, [SocketServer, Watchdog]}}.
+
+watchdog_pid() ->
+    Return = case os:getenv(?PID) of
+                 false -> os:getpid();
+                 Env -> Env
+             end,
+    os:unsetenv(?PID),
+    Return.
+
+watchdog_timeout() ->
+    Return = case os:getenv(?TIMEOUT) of
+                 false -> -1;
+                 Env ->
+                     case string:to_integer(Env) of
+                         {Timeout, ""} -> Timeout;
+                         _ -> -1
+                     end
+             end,
+    os:unsetenv(?TIMEOUT),
+    Return.
+
+notify_socket() ->
+    State = case os:getenv(?NOTIFY_SOCKET) of
+                false ->
+                    [];
+                [$@ | AbstractPath] ->
+                    {local, [0 | AbstractPath]};
+                Path ->
+                    case file:read_file_info(Path) of
+                        {error, _Error} ->
+                            [];
+                        {ok, #file_info{access=Access}}
+                          when Access =:= write; Access =:= read_write ->
+                            {local, Path}
+                    end
+            end,
+    os:unsetenv(?NOTIFY_SOCKET),
+    State.

src/systemd_watchdog.erl

@@ -7,28 +7,16 @@
 -include_lib("kernel/include/logger.hrl").
 -include("systemd.hrl").
 
--define(PID, "WATCHDOG_PID").
--define(TIMEOUT, "WATCHDOG_USEC").
-
--export([start_link/0,
+-export([start_link/1,
          init/1,
          handle_call/3,
          handle_cast/2,
          handle_info/2]).
 
 -record(state, {timeout, enabled=true}).
 
-start_link() ->
-    Pid = os:getpid(),
-    case {watchdog_pid(), watchdog_timeout()} of
-        {Pid, TimeoutUS} when TimeoutUS > 0 ->
-            Timeout = erlang:convert_time_unit(TimeoutUS,
-                                               microsecond,
-                                               millisecond),
-            gen_server:start_link({local, ?WATCHDOG}, ?MODULE, Timeout, []);
-        _ ->
-            gen_server:start_link({local, ?WATCHDOG}, ?MODULE, infinity, [])
-    end.
+start_link(Timeout) ->
+    gen_server:start_link({local, ?WATCHDOG}, ?MODULE, Timeout, []).
 
 init(Timeout) ->
     State = #state{timeout=Timeout},
@@ -70,23 +58,3 @@ notify(#state{enabled=true, timeout=Timeout}) when is_integer(Timeout) andalso T
     erlang:send_after(Timeout div Scale, self(), keepalive);
 notify(_State) ->
     ok.
-
-watchdog_pid() ->
-    Return = case os:getenv(?PID) of
-                 false -> os:getpid();
-                 Env -> Env
-             end,
-    os:unsetenv(?PID),
-    Return.
-
-watchdog_timeout() ->
-    Return = case os:getenv(?TIMEOUT) of
-                 false -> -1;
-                 Env ->
-                     case string:to_integer(Env) of
-                         {Timeout, ""} -> Timeout;
-                         _ -> -1
-                     end
-             end,
-    os:unsetenv(?TIMEOUT),
-    Return.

test/systemd_SUITE.erl

@@ -35,6 +35,8 @@ notify(init, Config) ->
 notify(_, Config) -> Config.
 
 notify(Config) ->
+    Pid = ?config(mock_pid, Config),
+
     systemd:notify(ready),
     systemd:notify(stopping),
     systemd:notify(reloading),
@@ -46,16 +48,21 @@ notify(Config) ->
 
     ct:sleep(10),
 
-    Messages = mock_systemd:messages(?config(mock_pid, Config)),
-
     ?assertEqual(["READY=1\n",
                   "STOPPING=1\n",
                   "RELOADING=1\n",
                   "STATUS=example status\n",
                   "ERRNO=10\n",
                   "BUSERROR=test.example.bus.service.Error\n",
                   "CUSTOM=message\n",
-                  "FORMATTED=deadbeef\n"], Messages),
+                  "FORMATTED=deadbeef\n"], mock_systemd:messages(Pid)),
+
+    ct:log("Connection address persists between process restarts"),
+    gen_server:stop(systemd_socket, error, 100),
+    ct:sleep(10),
+    systemd:notify(ready),
+    ct:sleep(10),
+    ?assertEqual(["READY=1\n"], mock_systemd:messages(Pid)),
     ok.
 
 watchdog(init, Config) -> Config;
@@ -179,6 +186,20 @@ watchdog(Config) ->
 
     ok = stop(Config),
 
+    % -------------------------------------------------------------------------
+    ct:log("Watchdog process send messages after restart"),
+    os:putenv("WATCHDOG_PID", os:getpid()),
+    os:putenv("WATCHDOG_USEC", TimeoutList),
+    ok = start_with_socket(Socket),
+    ct:sleep(10),
+
+    ?assertEqual(["WATCHDOG=1\n"], mock_systemd:messages(Pid)),
+    gen_server:stop(systemd_watchdog, error, 100),
+    ct:sleep(10),
+    ?assertEqual(["WATCHDOG=1\n"], mock_systemd:messages(Pid)),
+
+    ok = stop(Config),
+
     ok.
 
 listen_fds(init, Config) -> Config;