Make propellor resistent to changes to shared libraries, such as libffi

* Make propellor resistent to changes to shared libraries, such as libffi,
  which might render the propellor binary unable to run. This is dealt with
  by checking the binary both when running propellor on a remote host,
  and by Cron.runPropellor. If the binary doesn't work, it will be rebuilt.
* Note that since a new switch had to be added to allow testing the binary,
  upgrading to this version will cause a rebuild from scratch of propellor.

debian/changelog

@@ -1,3 +1,14 @@
+propellor (2.2.2) UNRELEASED; urgency=medium
+
+  * Make propellor resistent to changes to shared libraries, such as libffi,
+    which might render the propellor binary unable to run. This is dealt with
+    by checking the binary both when running propellor on a remote host,
+    and by Cron.runPropellor. If the binary doesn't work, it will be rebuilt.
+  * Note that since a new switch had to be added to allow testing the binary,
+    upgrading to this version will cause a rebuild from scratch of propellor.
+
+ -- Joey Hess <id@joeyh.name>  Thu, 02 Apr 2015 10:09:46 -0400
+
 propellor (2.2.1) unstable; urgency=medium
 
   * userScriptProperty now passes --shell /bin/sh, so it can be used

doc/usage.mdwn

@@ -95,6 +95,10 @@ and configured in haskell.
 
   (This will result in a trapezoid pattern in gitk.)
 
+* propellor --check
+
+  If propellor is able to run, this simply exists successfully.
+
 * propellor hostname
 
   When run with a hostname and no other options, propellor will

src/Propellor/Bootstrap.hs

@@ -1,5 +1,6 @@
 module Propellor.Bootstrap (
 	bootstrapPropellorCommand,
+	checkBinaryCommand,
 	installGitCommand,
 	buildPropellor,
 ) where
@@ -12,17 +13,27 @@ import Data.List
 
 type ShellCommand = String
 
--- Shell command line to build propellor, used when bootstrapping on a new
--- host. Should be run inside the propellor config dir, and will install
--- all necessary build dependencies.
+-- Shell command line to ensure propellor is bootstrapped and ready to run.
+-- Should be run inside the propellor config dir, and will install
+-- all necessary build dependencies and build propellor.
 bootstrapPropellorCommand :: ShellCommand
-bootstrapPropellorCommand = "if ! test -x ./propellor; then " ++ go ++ "; fi"
+bootstrapPropellorCommand = "if ! test -x ./propellor; then " ++ go ++ "; fi;" ++ checkBinaryCommand
   where
 	  go = intercalate " && "
 		[ depsCommand
 		, buildCommand
 		]
 
+-- Use propellor --check to detect if the local propellor binary has
+-- stopped working (eg due to library changes), and must be rebuilt.
+checkBinaryCommand :: ShellCommand
+checkBinaryCommand = "if test -x ./propellor && ! ./propellor --check; then " ++ go ++ "; fi"
+  where
+	go = intercalate " && "
+		[ "cabal clean"
+		, buildCommand
+		]
+
 buildCommand :: ShellCommand
 buildCommand = intercalate " && "
 	[ "cabal configure"

src/Propellor/CmdLine.hs

@@ -33,6 +33,7 @@ usage h = hPutStrLn h $ unlines
 	, "  propellor --list-fields"
 	, "  propellor --merge"
 	, "  propellor --build"
+	, "  propellor --check"
 	]
 
 usageError :: [String] -> IO a
@@ -43,6 +44,7 @@ usageError ps = do
 processCmdLine :: IO CmdLine
 processCmdLine = go =<< getArgs
   where
+  	go ("--check":_) = return Check
 	go ("--spin":ps) = case reverse ps of
 		(r:"--via":hs) -> Spin 
 			<$> mapM hostname (reverse hs) 
@@ -91,6 +93,7 @@ defaultMain hostlist = do
   where
 	go _ (Serialized cmdline) = go True cmdline
 	go _ (Continue cmdline) = go False cmdline
+	go _ Check = return ()
 	go _ (Set field context) = setPrivData field context
 	go _ (Dump field context) = dumpPrivData field context
 	go _ (Edit field context) = editPrivData field context

src/Propellor/Property/Cron.hs

@@ -3,6 +3,7 @@ module Propellor.Property.Cron where
 import Propellor
 import qualified Propellor.Property.File as File
 import qualified Propellor.Property.Apt as Apt
+import Propellor.Bootstrap
 import Utility.SafeCommand
 import Utility.FileMode
 
@@ -81,4 +82,5 @@ niceJob desc times user cddir command = job desc times user cddir
 
 -- | Installs a cron job to run propellor.
 runPropellor :: Times -> Property NoInfo
-runPropellor times = niceJob "propellor" times "root" localdir "./propellor"
+runPropellor times = niceJob "propellor" times "root" localdir
+	(bootstrapPropellorCommand ++ "; ./propellor")

src/Propellor/Types/CmdLine.hs

@@ -23,5 +23,6 @@ data CmdLine
 	| DockerChain HostName String
 	| ChrootChain HostName FilePath Bool Bool
 	| GitPush Fd Fd
+	| Check
 	deriving (Read, Show, Eq)