endAction can be used to register an action to run once propellor has successfully run on a host.

debian/changelog

@@ -28,6 +28,8 @@ propellor (1.1.0) UNRELEASED; urgency=medium
   * propellor.debug can be set in the git config to enable more persistent
     debugging output.
   * Run apt-cache policy with LANG=C so it works on other locales.
+  * endAction can be used to register an action to run once propellor
+    has successfully run on a host.
 
  -- Joey Hess <joeyh@debian.org>  Sat, 22 Nov 2014 00:12:35 -0400
 

src/Propellor/Engine.hs

@@ -7,7 +7,7 @@ import System.IO
 import Data.Monoid
 import Control.Applicative
 import System.Console.ANSI
-import "mtl" Control.Monad.Reader
+import "mtl" Control.Monad.RWS.Strict
 import Control.Exception (bracket)
 import System.PosixCompat
 import System.Posix.IO
@@ -22,21 +22,37 @@ import Utility.Exception
 import Utility.PartialPrelude
 import Utility.Monad
 
-runPropellor :: Host -> Propellor a -> IO a
-runPropellor host a = runReaderT (runWithHost a) host
-
+-- | Gets the Properties of a Host, and ensures them all,
+-- with nice display of what's being done.
 mainProperties :: Host -> IO ()
 mainProperties host = do
-	r <- runPropellor host $
+	ret <- runPropellor host $
 		ensureProperties [Property "overall" (ensureProperties $ hostProperties host) mempty]
 	h <- mkMessageHandle
         whenConsole h $
 		setTitle "propellor: done"
 	hFlush stdout
-	case r of
+	case ret of
 		FailedChange -> exitWith (ExitFailure 1)
 		_ -> exitWith ExitSuccess
 
+-- | Runs a Propellor action with the specified host.
+--
+-- If the Result is not FailedChange, any EndActions
+-- that were accumulated while running the action
+-- are then also run.
+runPropellor :: Host -> Propellor Result -> IO Result
+runPropellor host a = do
+	(ret, _s, endactions) <- runRWST (runWithHost a) host ()
+	endrets <- mapM (runEndAction host) endactions
+	return $ mconcat (ret:endrets)
+
+runEndAction :: Host -> EndAction -> IO Result
+runEndAction host (EndAction desc a) = actionMessageOn (hostName host) desc $ do
+	(ret, _s, _) <- runRWST (runWithHost (catchPropellor a)) host ()
+	return ret
+
+-- | Ensures a list of Properties, with a display of each as it runs.
 ensureProperties :: [Property] -> Propellor Result
 ensureProperties ps = ensure ps NoChange
   where
@@ -46,6 +62,8 @@ ensureProperties ps = ensure ps NoChange
 		r <- actionMessageOn hn (propertyDesc l) (ensureProperty l)
 		ensure ls (r <> rs)
 
+-- | For when code running in the Propellor monad needs to ensure a
+-- Property.
 ensureProperty :: Property -> Propellor Result
 ensureProperty = catchPropellor . propertySatisfy
 
@@ -55,8 +73,11 @@ ensureProperty = catchPropellor . propertySatisfy
 fromHost :: [Host] -> HostName -> Propellor a -> Propellor (Maybe a)
 fromHost l hn getter = case findHost l hn of
 	Nothing -> return Nothing
-	Just h -> liftIO $ Just <$>
-		runReaderT (runWithHost getter) h
+	Just h -> do
+		(ret, _s, runlog) <- liftIO $
+			runRWST (runWithHost getter) h ()
+		tell runlog
+		return (Just ret)
 
 onlyProcess :: FilePath -> IO a -> IO a
 onlyProcess lockfile a = bracket lock unlock (const a)

src/Propellor/Property.hs

@@ -7,7 +7,7 @@ import System.FilePath
 import Control.Monad
 import Data.Monoid
 import Control.Monad.IfElse
-import "mtl" Control.Monad.Reader
+import "mtl" Control.Monad.RWS.Strict
 
 import Propellor.Types
 import Propellor.Info
@@ -131,11 +131,11 @@ boolProperty desc a = property desc $ ifM (liftIO a)
 revert :: RevertableProperty -> RevertableProperty
 revert (RevertableProperty p1 p2) = RevertableProperty p2 p1
 
--- Changes the action that is performed to satisfy a property. 
+-- | Changes the action that is performed to satisfy a property. 
 adjustProperty :: Property -> (Propellor Result -> Propellor Result) -> Property
 adjustProperty p f = p { propertySatisfy = f (propertySatisfy p) }
 
--- Combines the Info of two properties.
+-- | Combines the Info of two properties.
 combineInfo :: (IsProp p, IsProp q) => p -> q -> Info
 combineInfo p q = getInfo p <> getInfo q
 
@@ -147,3 +147,8 @@ makeChange a = liftIO a >> return MadeChange
 
 noChange :: Propellor Result
 noChange = return NoChange
+
+-- | Registers an action that should be run at the very end,
+-- and only when all configured Properties of the host succeed.
+endAction :: Desc -> Propellor Result -> Propellor ()
+endAction desc a = tell [EndAction desc a]

src/Propellor/Types.hs

@@ -23,6 +23,8 @@ module Propellor.Types
 	, SshKeyType(..)
 	, Val(..)
 	, fromVal
+	, RunLog
+	, EndAction(..)
 	, module Propellor.Types.OS
 	, module Propellor.Types.Dns
 	) where
@@ -31,7 +33,7 @@ import Data.Monoid
 import Control.Applicative
 import System.Console.ANSI
 import System.Posix.Types
-import "mtl" Control.Monad.Reader
+import "mtl" Control.Monad.RWS.Strict
 import "MonadCatchIO-transformers" Control.Monad.CatchIO
 import qualified Data.Set as S
 import qualified Propellor.Types.Dns as Dns
@@ -52,13 +54,14 @@ data Host = Host
 	deriving (Show)
 
 -- | Propellor's monad provides read-only access to info about the host
--- it's running on.
-newtype Propellor p = Propellor { runWithHost :: ReaderT Host IO p }
+-- it's running on, and a writer to accumulate logs about the run.
+newtype Propellor p = Propellor { runWithHost :: RWST Host RunLog () IO p }
 	deriving
 		( Monad
 		, Functor
 		, Applicative
 		, MonadReader Host
+		, MonadWriter RunLog
 		, MonadIO
 		, MonadCatchIO
 		)
@@ -197,3 +200,9 @@ instance Monoid (Val a) where
 fromVal :: Val a -> Maybe a
 fromVal (Val a) = Just a
 fromVal NoVal = Nothing
+
+type RunLog = [EndAction]
+
+-- | An action that Propellor runs at the end, after trying to satisfy all
+-- properties.
+data EndAction = EndAction Desc (Propellor Result)