Correct decoding of uncompressed frames

Author: andrewthad

src/Lz4/Frame.hs

@@ -21,13 +21,11 @@ import Lz4.Internal (requiredBufferSize,c_hs_compress_HC,c_hs_decompress_safe)
 
 import Control.Monad (when)
 import Control.Monad.ST (runST)
-import Control.Monad.ST.Run (runByteArrayST)
 import Data.Bits ((.&.))
 import Data.Bytes.Types (Bytes (Bytes))
 import Data.Int (Int32)
 import Data.Primitive (ByteArray (..), MutableByteArray (..))
 import Data.Word (Word8, Word32)
-import GHC.Exts (ByteArray#,MutableByteArray#)
 import GHC.IO (unsafeIOToST)
 
 import qualified Data.Primitive as PM
@@ -45,7 +43,7 @@ decompressU ::
      Int -- ^ The exact size of the decompressed bytes
   -> Bytes -- ^ Compressed bytes
   -> Maybe ByteArray
-decompressU !decompressedSize bytes@(Bytes arr@(ByteArray arr# ) off len) = do
+decompressU !decompressedSize (Bytes arr@(ByteArray arr# ) off len) = do
   when (len < 11) Nothing
   when (indexWord8 arr off /= 0x04) Nothing
   when (indexWord8 arr (off + 1) /= 0x22) Nothing
@@ -88,7 +86,8 @@ decompressU !decompressedSize bytes@(Bytes arr@(ByteArray arr# ) off len) = do
       -- suite, and I cannot find examples of this feature used in the wild.
       -- If anyone knows of an example, open a PR.
       when (decompressedSize /= compressedSizeI) Nothing
-      Just $! Bytes.toByteArray bytes
+      when (decompressedSize + 15 /= len) Nothing
+      Just $! Bytes.toByteArrayClone (Bytes arr (off + 11) decompressedSize)
 
 {- | Use HC compression to produce a frame with a single block.
 All optional fields (checksums, content sizes, and dictionary IDs)

test/Main.hs

@@ -6,7 +6,7 @@ import Data.Primitive (ByteArray,sizeofByteArray)
 import Data.Word (Word8)
 import Lz4.Block (compress, compressHighly, decompress)
 import Test.Tasty (TestTree, defaultMain, testGroup)
-import Test.Tasty.HUnit (testCase)
+import Test.Tasty.HUnit (testCase,(@=?))
 import Test.Tasty.QuickCheck (Gen, choose, forAll, testProperty, vectorOf, (===))
 
 import qualified Data.Bytes as Bytes
@@ -39,6 +39,9 @@ tests = testGroup "lz4"
     , testCase "example-a" $ case Frame.decompressU 20 (Bytes.fromByteArray exampleA) of
         Nothing -> fail "decompression failed"
         Just _ -> pure ()
+    , testCase "example-b" $ case Frame.decompressU 10 (Bytes.fromByteArray exampleB) of
+        Nothing -> fail "decompression failed"
+        Just x -> x @=? Exts.fromList [0xbb :: Word8, 0x01, 0xbb, 0x01, 0xbb, 0x01, 0xbb, 0x01, 0xbb, 0x01 ]
     ]
   ]
 
@@ -62,3 +65,17 @@ exampleA = Exts.fromList
   , 0x47, 0x15, 0x08, 0x01, 0x0a, 0x04 , 0x00, 0x50, 0x0a, 0x15, 0x08, 0x01, 0x0a
   , 0x00, 0x00, 0x00, 0x00
   ]
+
+-- Example that tests a frame that does not use compression
+exampleB :: ByteArray
+exampleB = Exts.fromList
+  [ 0x04, 0x22, 0x4d, (0x18 :: Word8)
+  , 0x60, 0x40, 0x82
+  , 0x0a, 0x00, 0x00, 0x80 -- little-endian encoding of 10 but with the high bit set to disable compression
+  , 0xbb, 0x01
+  , 0xbb, 0x01
+  , 0xbb, 0x01
+  , 0xbb, 0x01
+  , 0xbb, 0x01
+  , 0x00, 0x00, 0x00, 0x00
+  ]