implemented unescapeString

gemserv.cabal

@@ -30,7 +30,9 @@ library
   ghc-options: -Wall
   build-depends:
       base >=4.7 && <5
+    , bytestring >=0.10.12.0 && <0.11
     , tcp-streams >=1.0.1.1 && <1.1
+    , text >=1.2.4.1 && <1.3
     , tls
     , x509
   default-language: Haskell2010
@@ -46,9 +48,11 @@ test-suite gemserv-test
   ghc-options: -Wall -threaded -rtsopts -with-rtsopts=-N
   build-depends:
       base >=4.7 && <5
+    , bytestring >=0.10.12.0 && <0.11
     , gemserv
     , hspec >=2.7.10 && <2.8
     , tcp-streams >=1.0.1.1 && <1.1
+    , text >=1.2.4.1 && <1.3
     , tls
     , x509
   default-language: Haskell2010

package.yaml

@@ -23,7 +23,9 @@ ghc-options:
 
 dependencies:
 - base >= 4.7 && < 5
+- bytestring >= 0.10.12.0 && < 0.11
 - tcp-streams >= 1.0.1.1 && < 1.1
+- text >= 1.2.4.1 && < 1.3
 - tls
 - x509
 

src/Network/GemServ.hs

@@ -24,13 +24,22 @@ License along with this program.  If not, see
 
 -}
 
+{-# LANGUAGE LambdaCase #-}
+
 module Network.GemServ (
   encodeRequest,
-  escapeString
+  escapeString,
+  unescapeString
 ) where
 
-import Data.Char (ord)
+import qualified Data.ByteString as BS
-import Data.List (intercalate)
+import Data.ByteString.Builder (charUtf8, toLazyByteString)
+import qualified Data.ByteString.Lazy as BSL
+import Data.Char (ord, toLower)
+import Data.List (find, intercalate)
+import Data.Maybe (fromJust)
+import qualified Data.Text as T
+import Data.Text.Encoding (decodeUtf8')
 
 import Network.GemServ.Types
 
@@ -61,6 +70,26 @@ escapeString = concatMap $ \ch ->
       low  = n `mod` 16
       in [hexDigits !! high, hexDigits !! low]
 
+-- | decode an escaped string back to its original value
+unescapeString :: String -> Maybe String
+unescapeString str = case decodeUtf8' $ BS.pack $ toBytes str of
+    Right t -> Just $ T.unpack t
+    _       -> Nothing
+  where
+    toBytes = \case
+      "" -> []
+      '%':h:l:sub -> let
+        h' = toLower h
+        l' = toLower l
+        in if h' `elem` hexDigits && l' `elem` hexDigits
+        then toByte h' l' : toBytes sub
+        else fromIntegral (ord '%') : toBytes (h : l : sub)
+      ch:sub ->
+        BSL.unpack (toLazyByteString $ charUtf8 ch) ++ toBytes sub
+    toByte h l = toNum h * 16 + toNum l
+    toNum ch = fst $ fromJust $
+      find (\x -> snd x == ch) $ zip [0..] hexDigits
+
 hexDigits :: String
 hexDigits = ['0'..'9'] ++ ['a'..'f']
 

test/Network/GemServSpec.hs

@@ -31,6 +31,7 @@ spec :: Spec
 spec = describe "Network.GemServ" $ do
   encodeRequestSpec
   escapeStringSpec
+  unescapeStringSpec
 
 encodeRequestSpec :: Spec
 encodeRequestSpec = describe "encodeRequest" $ mapM_
@@ -76,4 +77,21 @@ escapeStringSpec = describe "escapeString" $ mapM_
   , ( "foo:/?=&#%",        "foo%3a%2f%3f%3d%26%23%25" )
   ]
 
+unescapeStringSpec :: Spec
+unescapeStringSpec = describe "unescapeString" $ mapM_
+  ( \(input, expected) -> context (show input) $
+    it ("should be " ++ show expected) $
+      unescapeString input `shouldBe` expected
+  )
+
+  --  input,       expected
+  [ ( "foo",       Just "foo"     )
+  , ( "foo%20bar", Just "foo bar" )
+  , ( "foo%7x",    Just "foo%7x"  )
+  , ( "foo%a",     Just "foo%a"   )
+  , ( "foo%",      Just "foo%"    )
+  , ( "foo%c3%a9", Just "foo\xe9" )
+  , ( "foo%ff",    Nothing        )
+  ]
+
 --jl