fix: not logging termination unix signals

Under container environments like ECS, it's hard to know when PostgREST
is being terminated.

src/PostgREST/Unix.hs

@@ -11,26 +11,27 @@ import qualified System.Posix.Signals as Signals
 import System.Posix.Types       (FileMode)
 import System.PosixCompat.Files (setFileMode)
 
-import           Data.String      (String)
-import qualified Network.Socket   as NS
+import           Data.String           (String)
+import qualified Network.Socket        as NS
+import qualified PostgREST.Observation as Observation
 import           Protolude
-import           System.Directory (removeFile)
-import           System.IO.Error  (isDoesNotExistError)
+import           System.Directory      (removeFile)
+import           System.IO.Error       (isDoesNotExistError)
 
 -- | Set signal handlers, only for systems with signals
-installSignalHandlers :: ThreadId -> IO () -> IO () -> IO ()
+installSignalHandlers :: Observation.ObservationHandler -> ThreadId -> IO () -> IO () -> IO ()
 #ifndef mingw32_HOST_OS
-installSignalHandlers tid usr1 usr2 = do
+installSignalHandlers observer tid usr1 usr2 = do
   let interrupt = throwTo tid UserInterrupt
-  install Signals.sigINT interrupt
-  install Signals.sigTERM interrupt
+  install Signals.sigINT  $ observer (Observation.TerminationUnixSignalObs "SIGINT") >> interrupt
+  install Signals.sigTERM $ observer (Observation.TerminationUnixSignalObs "SIGTERM") >> interrupt
   install Signals.sigUSR1 usr1
   install Signals.sigUSR2 usr2
   where
     install signal handler =
       void $ Signals.installHandler signal (Signals.Catch handler) Nothing
 #else
-installSignalHandlers _ _ _ = pass
+installSignalHandlers _ _ _ _ = pass
 #endif
 
 -- | Create a unix domain socket and bind it to the given path.