Cron.hs

module Propellor.Property.Cron (
	Times(..),
	job,
	niceJob,
	jobDropped,
	Propellor.Property.Cron.runPropellor
) where

import Propellor.Base
import qualified Propellor.Property.File as File
import qualified Propellor.Property.Apt as Apt
import Propellor.Bootstrap

import Data.Char

-- | When to run a cron job.
--
-- The Daily, Monthly, and Weekly options allow the cron job to be run
-- by anacron, which is useful for non-servers.
data Times
	= Times String -- ^ formatted as in crontab(5)
	| Daily
	| Weekly
	| Monthly

-- | Installs a cron job, that will run as a specified user in a particular
-- directory. Note that the Desc must be unique, as it is used for the
-- cron job filename.
--
-- Only one instance of the cron job is allowed to run at a time, no matter
-- how long it runs. This is accomplished using flock locking of the cron
-- job file.
--
-- The cron job's output will only be emailed if it exits nonzero.
job :: Desc -> Times -> User -> FilePath -> String -> Property DebianLike
job desc times (User u) cddir command = combineProperties ("cronned " ++ desc) $ props
	& Apt.serviceInstalledRunning "cron"
	& Apt.installed ["util-linux", "moreutils"]
	& cronjobfile desc times `File.hasContent`
		[ case times of
			Times _ -> ""
			_ -> "#!/bin/sh\nset -e"
		, "# Generated by propellor"
		, ""
		, "SHELL=/bin/sh"
		, "PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin"
		, ""
		, case times of
			Times t -> t ++ "\t" ++ u ++ "\tchronic "
				++ shellEscape (scriptfile desc)
			_ -> case u of
				"root" -> "chronic " ++ shellEscape (scriptfile desc)
				_ -> "chronic su " ++ u ++ " -c "
					++ shellEscape (scriptfile desc)
		]
	& case times of
		Times _ -> doNothing
		_ -> (cronjobfile desc times)
			`File.mode` combineModes (readModes ++ executeModes)
	-- Use a separate script because it makes the cron job name
	-- prettier in emails, and also allows running the job manually.
	& scriptfile desc `File.hasContent`
		[ "#!/bin/sh"
		, "# Generated by propellor"
		, "set -e"
		, "flock -n " ++ shellEscape (cronjobfile desc times)
			++ " sh -c " ++ shellEscape cmdline
		]
	& scriptfile desc `File.mode` combineModes (readModes ++ executeModes)
  where
	cmdline = "cd " ++ cddir ++ " && ( " ++ command ++ " )"

-- | Removes a cron job created by 'job' or 'niceJob', as identified by the
-- 'Desc' passed to those properties when the cronjob was set up
--
-- Those properties are not revertable because simply removing a cronjob does
-- not undo the changes it might have made to the system, i.e., 'jobDropped' is
-- not in the general case a reversion of 'job' or 'niceJob'
jobDropped :: Desc -> Times -> Property UnixLike
jobDropped desc times = combineProperties ("uncronned " ++ desc) $ props
	& File.notPresent (scriptfile desc)
	& File.notPresent (cronjobfile desc times)

-- | Installs a cron job, and runs it niced and ioniced.
niceJob :: Desc -> Times -> User -> FilePath -> String -> Property DebianLike
niceJob desc times user cddir command = job desc times user cddir
	("nice ionice -c 3 sh -c " ++ shellEscape command)

-- | Installs a cron job to run propellor.
runPropellor :: Times -> RevertableProperty DebianLike UnixLike
runPropellor times = cronned <!> uncronned
  where
	cronned = withOS "propellor cron job" $ \w o -> do
		bootstrapper <- getBootstrapper
		ensureProperty w $
			niceJob "propellor" times (User "root") localdir
				(bootstrapPropellorCommand bootstrapper o ++ "; ./propellor")
	uncronned = jobDropped "propellor" times

-- Utility functions

cronjobname :: Desc -> String
cronjobname d = map sanitize d
  where
	sanitize c
		| isAlphaNum c = c
		| otherwise = '_'

scriptfile :: Desc -> FilePath
scriptfile d = "/usr/local/bin/" ++ (cronjobname d) ++ "_cronjob"

cronjobfile :: Desc -> Times -> FilePath
cronjobfile d times = "/etc" </> cronjobdir </> (cronjobname d)
  where
	cronjobdir = case times of
		Times _ -> "cron.d"
		Daily -> "cron.daily"
		Weekly -> "cron.weekly"
		Monthly -> "cron.monthly"