Added Propellor.Property.File.configFileName and related functions to generate good filenames for config directories.

spwhitton has a branch that could use this, and there are several places
in propellor that do something ad-hoc that would have been better
implemented using this. I was not able to switch any of the existing
ad-hoc stuff, but this can be used going forward for new stuff.

This commit was sponsored by Anthony DeRobertis on Patreon.

1 files changed, 40 insertions, 0 deletions

diff --git a/src/Propellor/Property/File.hs b/src/Propellor/Property/File.hs
index 95fc6f81..fe2b1057 100644
--- a/src/Propellor/Property/File.hs
+++ b/src/Propellor/Property/File.hs
@@ -8,6 +8,7 @@ import Utility.FileMode
 import qualified Data.ByteString.Lazy as L
 import System.Posix.Files
 import System.Exit
+import Data.Char
 
 type Line = String
 
@@ -221,3 +222,42 @@ viaStableTmp a f = bracketIO setup cleanup go
 	go tmpfile = do
 		a tmpfile
 		liftIO $ rename tmpfile f
+
+-- | Generates a base configuration file name from a String, which
+-- can be put in a configuration directory, such as
+-- /etc/apt/sources.list.d/
+--
+-- The generated file name is limited to using ASCII alphanumerics,
+-- '_' and '.', so that programs that only accept a limited set of
+-- characters will accept it. Any other characters will be encoded
+-- in escaped form.
+--
+-- Some file extensions, such as ".dpkg-new" may be filtered out by
+-- programs that use configuration directories. To avoid such problems,
+-- it's a good idea to add an static prefix and extension to the 
+-- result of this function. For example:
+--
+-- > aptSource foo = "/etc/apt/sources.list.d" </> "propellor_" ++ configFileName foo <.> ".conf"
+configFileName :: String -> FilePath
+configFileName = concatMap escape
+  where
+	escape c
+		| isAscii c && isAlphaNum c = [c]
+		| c == '.' = [c]
+		| otherwise = '_' : show (ord c)
+
+-- | Applies configFileName to any value that can be shown.
+showConfigFileName :: Show v => v -> FilePath
+showConfigFileName = configFileName . show
+
+-- | Inverse of showConfigFileName.
+readConfigFileName :: Read v => FilePath -> Maybe v
+readConfigFileName = readish . unescape
+  where
+	unescape [] = []
+	unescape ('_':cs) = case break (not . isDigit) cs of
+		([], _) -> '_' : unescape cs
+		(ns, cs') -> case readish ns of
+			Nothing -> '_' : ns ++ unescape cs'
+			Just n -> chr n : unescape cs'
+	unescape (c:cs) = c : unescape cs