Move the Report, Logging, and Terminal modules into their own namespace.

[dead/htsn.git] / src / Unix.hs

diff --git a/src/Unix.hs b/src/Unix.hs
index 893132624165566232ae1da28bd698faea2f6465..b6990d2a663e3ef31df3d70ad5efa4e503b127c1 100644 (file)
--- a/src/Unix.hs
+++ b/src/Unix.hs
@@ -1,15 +1,19 @@
+-- | Non-portable code for daemonizing on unix.
+--
 module Unix
 where
 
 import Control.Concurrent ( ThreadId, myThreadId )
 import Control.Exception ( throwTo )
 import System.Exit ( ExitCode( ExitSuccess ) )
+import System.IO.Error ( catchIOError )
 import System.Posix (
   GroupEntry ( groupID ),
   GroupID,
   Handler ( Catch ),
   UserEntry ( userID ),
   UserID,
+  exitImmediately,
   getGroupEntryForName,
   getProcessID,
   getRealGroupID,
@@ -17,6 +21,7 @@ import System.Posix (
   getUserEntryForName,
   installHandler,
   removeLink,
+  setFileCreationMask,
   setGroupID,
   setUserID,
   sigTERM )
@@ -26,41 +31,88 @@ import Configuration (
   Configuration( pidfile,
                  run_as_group,
                  run_as_user ))
-import Logging ( log_info )
+import Network.Services.TSN.Logging ( log_info, log_error )
+import Network.Services.TSN.Terminal ( display_error )
 
+-- | Retrieve the uid associated with the given system user name. We
+--   take a Maybe String as an argument so the user name can be passed
+--   in directly from the config.
+--
 get_user_id :: Maybe String -> IO UserID
 get_user_id Nothing  = getRealUserID
 get_user_id (Just s) = fmap userID (getUserEntryForName s)
 
+
+-- | Retrieve the gid associated with the given system group name. We
+--   take a Maybe String as an argument so the group name can be
+--   passed in directly from the config.
+--
 get_group_id :: Maybe String -> IO GroupID
 get_group_id Nothing  = getRealGroupID
 get_group_id (Just s) = fmap groupID (getGroupEntryForName s)
 
+
+-- | This function will be called in response to a SIGTERM; i.e. when
+--   someone tries to kill our process. We simply delete the PID file
+--   and signal our parent thread to quit (successfully).
+--
+--   If that doesn't work, report the error and quit rudely.
+--
 graceful_shutdown :: Configuration -> ThreadId -> IO ()
 graceful_shutdown cfg main_thread_id = do
   log_info "SIGTERM received, removing PID file and shutting down."
-  removeLink (pidfile cfg)
-  throwTo main_thread_id ExitSuccess
+  catchIOError try_nicely (\e -> do
+                             display_error (show e)
+                             log_error (show e)
+                             exitImmediately ExitSuccess )
+  where
+    try_nicely = do
+      removeLink (pidfile cfg)
+      throwTo main_thread_id ExitSuccess
 
+
+-- | Write a PID file, install a SIGTERM handler, drop privileges, and
+--   finally do the daemonization dance.
+--
 full_daemonize :: Configuration -> IO () -> IO ()
 full_daemonize cfg program = do
-  -- This is the 'daemonize' from System.Posix.Daemonize.
-  daemonize program'
+  -- The call to 'daemonize' will set the umask to zero, but we want
+  -- to retain it. So, we set the umask to zero before 'daemonize'
+  -- can, so that we can record the previous umask value (returned by
+  -- setFileCreationMask).
+  orig_umask <- setFileCreationMask 0
+  -- This is the 'daemonize' from System.Posix.Daemonize. If it
+  -- doesn't work, we report the error and do not much else.
+  catchIOError (daemonize (program' orig_umask))
+                 (\e -> do
+                    display_error (show e)
+                    log_error (show e))
   where
     -- We need to do all this stuff *after* we daemonize.
-    program' = do
-      -- First write the PID file which probably requires root.
-      pid <- getProcessID
-      writeFile (pidfile cfg) (show pid)
-
-      -- We need to pass the thread ID to the signal handler so it
-      -- knows which process to "exit."
+    program' orig_umask = do
+      -- First we install a signal handler for sigTERM. We need to
+      -- pass the thread ID to the signal handler so it knows which
+      -- process to "exit."
       tid <- myThreadId
       _ <- installHandler sigTERM (Catch (graceful_shutdown cfg tid)) Nothing
 
-      -- Then drop privileges.
-      get_user_id  (run_as_user cfg)  >>= setUserID
+      -- Next we drop privileges. Group ID has to go first, otherwise
+      -- you ain't root to change groups.
       get_group_id (run_as_group cfg) >>= setGroupID
+      get_user_id  (run_as_user cfg) >>= setUserID
+
+      -- Now we create the PID file.
+      pid <- getProcessID
+
+      -- The PID file needs to be read-only for anyone but its
+      -- owner. Hopefully the umask accomplishes this!
+      _ <- setFileCreationMask orig_umask
+
+      -- When we later attempt to delete the PID file, it requires
+      -- write permission to the parent directory and not to the PID
+      -- file itself. Therefore, if that's going to work, this has to
+      -- work, even as a limited user.
+      writeFile (pidfile cfg) (show pid)
 
       -- Finally run the program we were asked to.
       program