1 files changed, 18 insertions, 2 deletions
diff --git a/src/Propellor/Property.hs b/src/Propellor/Property.hs
index 2976acf1..c58cc9fe 100644
--- a/src/Propellor/Property.hs
+++ b/src/Propellor/Property.hs
@@ -28,6 +28,7 @@ module Propellor.Property (
 	, UncheckedProperty
 	, unchecked
 	, changesFile
+	, changesFileContent
 	, checkResult
 	, Checkable
 	, assume
@@ -36,10 +37,12 @@ module Propellor.Property (
 import System.Directory
 import System.FilePath
 import Control.Monad
+import Control.Applicative
 import Data.Monoid
 import Control.Monad.IfElse
 import "mtl" Control.Monad.RWS.Strict
 import System.Posix.Files
+import qualified Data.Hash.MD5 as MD5
 
 import Propellor.Types
 import Propellor.Types.ResultCheck
@@ -47,6 +50,7 @@ import Propellor.Info
 import Propellor.Exception
 import Utility.Exception
 import Utility.Monad
+import Utility.Misc
 
 -- | Constructs a Property, from a description and an action to run to
 -- ensure the Property is met.
@@ -185,11 +189,12 @@ fallback = combineWith combiner revertcombiner
 	revertcombiner = (<>)
 
 -- | Indicates that a Property may change a particular file. When the file
--- is modified, the property will return MadeChange instead of NoChange.
+-- is modified in any way (including changing its permissions or mtime),
+-- the property will return MadeChange instead of NoChange.
 changesFile :: Checkable p i => p i -> FilePath -> Property i
 changesFile p f = checkResult getstat comparestat p
   where
-	getstat = liftIO $ catchMaybeIO $ getSymbolicLinkStatus f
+	getstat = catchMaybeIO $ getSymbolicLinkStatus f
 	comparestat oldstat = do
 		newstat <- getstat
 		return $ if samestat oldstat newstat then NoChange else MadeChange
@@ -214,6 +219,17 @@ changesFile p f = checkResult getstat comparestat p
 		]
 	samestat _ _ = False
 
+-- | Like `changesFile`, but compares the content of the file.
+-- Changes to mtime etc that do not change file content are treated as
+-- NoChange.
+changesFileContent :: Checkable p i => p i -> FilePath -> Property i
+changesFileContent p f = checkResult getmd5 comparemd5 p
+  where
+	getmd5 = catchMaybeIO $ MD5.md5 . MD5.Str <$> readFileStrictAnyEncoding f
+	comparemd5 oldmd5 = do
+		newmd5 <- getmd5
+		return $ if oldmd5 == newmd5 then NoChange else MadeChange
+
 -- | Makes a property that is satisfied differently depending on the host's
 -- operating system. 
 --