quicklz 1.5.0.3 → 1.5.0.4

raw patch · 3 files changed

+28/−24 lines, 3 filesPVP ok

version bump matches the API change (PVP)

API changes (from Hackage documentation)

Files

• Codec/Compression/QuickLZ.hsc +17/−14
• quicklz.cabal +3/−3
• tests/Properties.hs +8/−7

@@ -17,22 +17,22 @@ -- The library that is bundled with this version is QuickLZ v1.5.0,
 -- with the compression level set to 1.
 -- 
--- Truthfully, the only laws that hold with this library are the following:
+-- The following laws hold:
 -- 
 -- @(decompress . compress) == id@
 -- 
 -- @(decompress xs) == (decompress xs)@
 -- 
--- Note that:
--- 
 -- @(compress xs) == (compress xs)@
 -- 
--- Does not hold.
--- QuickLZ uses random data to seed part of the compression, so the lengths
--- and compressed results can differ. But they will always decompress back
--- to the same string, e.g., @compress@ is not referentially transparent, but
--- @decompress@ is (so don't go and insert compressed data as keys into any `Data.Map`s.)
+-- A word of notice: QuickLZ, for inputs of less than 5 bytes in length, will generate
+-- different compression results for the same input on identical runs.
 -- 
+-- Because this behavior is not referentially transparent, we use a hack: merely short-circuit
+-- on an empty input, and always pad the input with 4 extra null bytes otherwise. This yields
+-- identical compression results for every input, giving compress the above nice law.
+-- On decompression, after yielding the resulting string from decompression, we cut the characters off.
+-- 
 -- Arguably this is an abomination; nonetheless, this pure interface is a
 -- nice abstraction.
 -- 
@@ -45,7 +45,7 @@ import Foreign
 import Foreign.C
 
-import qualified Data.ByteString.Char8 as S
+import qualified Data.ByteString as S
 import qualified Data.ByteString.Internal as SI
 import qualified Data.ByteString.Unsafe as U
 
@@ -57,10 +57,12 @@ 
 -- | Compresses the input 'ByteString'.
 compress :: S.ByteString -> S.ByteString
-compress xs
-  | S.null xs = S.empty
+compress xs'
+  | S.null xs'    = S.empty
   | otherwise = 
-      unsafePerformIO . allocaBytes qlz_state_compress_sz $ \compress_state ->
+      -- hack: always append 4 extra bytes to ensure input len >= 5
+      let xs = xs' `S.append` (S.pack [0,0,0,0]) 
+      in unsafePerformIO . allocaBytes qlz_state_compress_sz $ \compress_state ->
         SI.createAndTrim (S.length xs + 400) $ \output -> do
           U.unsafeUseAsCStringLen xs $ \(cstr,len) -> 
             c_qlz_compress cstr output len compress_state
@@ -74,8 +76,9 @@       unsafePerformIO . allocaBytes qlz_state_decompress_sz $ \decompress_state -> do
         sz <- U.unsafeUseAsCString xs c_qlz_size_decompressed
         SI.createAndTrim sz $ \output -> do
-          U.unsafeUseAsCString xs $ \cstr -> 
-            c_qlz_decompress cstr output decompress_state
+          U.unsafeUseAsCString xs $ \cstr -> do 
+            c_ <- c_qlz_decompress cstr output decompress_state
+            return $ c_ - 4 -- hack: remove 4 ending bytes off of output string
 {-# INLINEABLE decompress #-}
 
 -- 

@@ -1,8 +1,8 @@ name:                quicklz
-version:             1.5.0.3
+version:             1.5.0.4
 synopsis:            binding to QuickLZ compression library
 description:         
-  This package provides a high level binding to the QuickLZ (<http:\\quicklz.com>) library
+  This package provides a high level binding to the QuickLZ (<http://quicklz.com>) library
   for ByteStrings, under the GPLv2 license. QuickLZ is fast and compresses very well.
   .
   This package includes the QuickLZ 1.5.0 source code, with compression level 1 and streaming
@@ -62,5 +62,5 @@     test-framework-quickcheck2 == 0.2.*,
     quicklz
 
-  ghc-options:    -Wall -fno-cse
+  ghc-options:      -fno-cse
   default-language: Haskell98

@@ -1,7 +1,7 @@ {-# LANGUAGE ViewPatterns #-}
 module Main (main) where
 
-import Data.ByteString.Char8
+import qualified Data.ByteString as S
 import Codec.Compression.QuickLZ
 
 import Test.Framework (defaultMain, testGroup)
@@ -9,17 +9,18 @@ 
 main :: IO ()
 main = defaultMain [ testGroup "simple" [
-                       testProperty "compress identity" prop_id
-                     , testProperty "decompress transparent" prop_decompress_id
+                       testProperty "compression identity" prop_compression_id
+                     , testProperty "decompress is pure" prop_decompress_pure
+                     , testProperty "compress is pure" prop_compress_pure
                      ]
                    ]
 
-prop_id :: String -> Bool
-prop_id (pack -> xs) =
+prop_compression_id (S.pack -> xs) =
   xs == (decompress . compress) xs
 
-prop_decompress_id :: String -> Bool
-prop_decompress_id (pack -> xs) =
+prop_decompress_pure (S.pack -> xs) =
   let z  = compress xs
   in (decompress z) == (decompress z)
 
+prop_compress_pure (S.pack -> xs) =
+  (compress xs) == (compress xs)