fix JOURNAL_STREAM detection to make sure its actually a sd service

bin/main.ml

@@ -14,12 +14,11 @@ let no_timestamp = Option.is_some (Sys.getenv_opt "LOG_NO_TIMESTAMP")
 let no_namespace = Option.is_some (Sys.getenv_opt "LOG_NO_NAMESPACE")
 
 let () =
-  match Sys.getenv_opt "JOURNAL_STREAM" with
-  | Some _ ->
+  if Logging.should_upgrade_to_journald () then
     Logging.init_journald_writer ()
       ~min_level
-  | None ->
-    Logging.init_pretty_writer stderr
+  else
+    Logging.init_pretty_writer stdout
       ~min_level
       ~color:(not no_color)
       ~timestamp:(not no_timestamp)

lib/logging/journald.ml

@@ -9,6 +9,11 @@ type t = {
   buf : Buffer.t;
 }
 
+let should_upgrade () =
+  let stderr = Unix.fstat Unix.stderr in
+  let dev_ino = Printf.sprintf "%d:%d" stderr.st_dev stderr.st_ino in
+  Sys.getenv_opt "JOURNAL_STREAM" = Some dev_ino
+
 let make ?(path = default_socket_path) () = {
   mutex = Mutex.create ();
   sock_fd = Unix.socket PF_UNIX SOCK_DGRAM 0 ~cloexec:true;

lib/logging/logging.ml

@@ -107,3 +107,5 @@ let init_journald_writer
   Journald.make () ?path |>
   Journald.writer |>
   add_writer ?min_level
+
+let should_upgrade_to_journald = Journald.should_upgrade

lib/logging/logging.mli

@@ -36,3 +36,5 @@ val init_journald_writer :
   ?min_level:level ->
   ?path:string ->
   unit -> unit
+
+val should_upgrade_to_journald : unit -> bool