6 files changed, 38 insertions, 6 deletions
diff --git a/debian/changelog b/debian/changelog
index 9ac8c3f8..db9ffbd9 100644
--- a/debian/changelog
+++ b/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
diff --git a/doc/usage.mdwn b/doc/usage.mdwn
index 8cd9af21..4030628f 100644
--- a/doc/usage.mdwn
+++ b/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
diff --git a/src/Propellor/Bootstrap.hs b/src/Propellor/Bootstrap.hs
index 214f65d5..b0b4e58a 100644
--- a/src/Propellor/Bootstrap.hs
+++ b/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 " && "
+	  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"
diff --git a/src/Propellor/CmdLine.hs b/src/Propellor/CmdLine.hs
index 9d7d0d95..1298daf2 100644
--- a/src/Propellor/CmdLine.hs
+++ b/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
diff --git a/src/Propellor/Property/Cron.hs b/src/Propellor/Property/Cron.hs
index 2a28a157..222f3849 100644
--- a/src/Propellor/Property/Cron.hs
+++ b/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")
diff --git a/src/Propellor/Types/CmdLine.hs b/src/Propellor/Types/CmdLine.hs
index b8f488a4..bd0cbdfd 100644
--- a/src/Propellor/Types/CmdLine.hs
+++ b/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)