metadata: Fix encoding problem that led to mojibake when storing metadata strings that contained both unicode characters and a space (or '!') character.

The fix is to stop using w82s, which does not properly reconstitute unicode
strings. Instrad, use utf8 bytestring to get the [Word8] to base64. This
passes unicode through perfectly, including any invalid filesystem encoded
characters.

Note that toB64 / fromB64 are also used for creds and cipher
embedding. It would be unfortunate if this change broke those uses.

For cipher embedding, note that ciphers can contain arbitrary bytes (should
really be using ByteString.Char8 there). Testing indicated it's not safe to
use the new fromB64 there; I think that characters were incorrectly
combined.

For credpair embedding, the username or password could contain unicode.
Before, that unicode would fail to round-trip through the b64.
So, I guess this is not going to break any embedded creds that worked
before.

This bug may have affected some creds before, and if so,
this change will not fix old ones, but should fix new ones at least.

Utility/Base64.hs

@@ -1,24 +1,28 @@
-{- Simple Base64 access
+{- Simple Base64 encoding of Strings
  -
  - Copyright 2011 Joey Hess <id@joeyh.name>
  -
  - License: BSD-2-clause
  -}
 
-module Utility.Base64 (toB64, fromB64Maybe, fromB64) where
+module Utility.Base64 (toB64, fromB64Maybe, fromB64, prop_b64_roundtrips) where
 
-import "dataenc" Codec.Binary.Base64
-import Data.Bits.Utils
+import qualified "dataenc" Codec.Binary.Base64 as B64
 import Control.Applicative
 import Data.Maybe
+import qualified Data.ByteString.Lazy as L
+import Data.ByteString.Lazy.UTF8 (fromString, toString)
 
-toB64 :: String -> String		
-toB64 = encode . s2w8
+toB64 :: String -> String	
+toB64 = B64.encode . L.unpack . fromString
 
 fromB64Maybe :: String -> Maybe String
-fromB64Maybe s = w82s <$> decode s
+fromB64Maybe s = toString . L.pack <$> B64.decode s
 
 fromB64 :: String -> String
 fromB64 = fromMaybe bad . fromB64Maybe
   where
 	bad = error "bad base64 encoded data"
+
+prop_b64_roundtrips :: String -> Bool
+prop_b64_roundtrips s = s == fromB64 (toB64 s)