Merge pull request #87 from haskell-cryptography/jdral/create-and-trim

`botan-low`: Use `createAndTrim` rather than `createUpToN`

Author: jorisdral

botan-low/CHANGELOG.md

@@ -41,7 +41,8 @@
   `blockCipherDecryptBlocks` that occasionally caused segfaults.
 * PATCH: fix an "insufficient buffer space" bug in
   `Botan.Low.PubKey.Encrypt.encrypt` and `Botan.Low.PubKey.Decrypt.decrypt`. See
-  PR [#79](https://github.com/haskell-cryptography/botan/pull/79).
+  PR [#79](https://github.com/haskell-cryptography/botan/pull/79), PR
+  [#87](https://github.com/haskell-cryptography/botan/pull/87).
 * PATCH: Fix an "insufficient buffer space" bug in
   `Botan.Low.Cipher.cipherUpdate`. See PR
   [#84](https://github.com/haskell-cryptography/botan/pull/84)

botan-low/src/Botan/Low/PubKey/Decrypt.hs

@@ -73,7 +73,7 @@ decrypt dec ctext =
     alloca $ \szPtr -> do
       sz <- decryptOutputLength dec (BS.length ctext)
       poke szPtr (fromIntegral sz)
-      BSI.createUptoN sz $ \outPtr -> do
+      BSI.createAndTrim sz $ \outPtr -> do
         throwBotanIfNegative_ $
           botan_pk_op_decrypt
             decPtr

botan-low/src/Botan/Low/PubKey/Encrypt.hs

@@ -76,7 +76,7 @@ encrypt enc rng ptext =
     alloca $ \szPtr -> do
       sz <- encryptOutputLength enc (BS.length ptext)
       poke szPtr (fromIntegral sz)
-      BSI.createUptoN sz $ \outPtr -> do
+      BSI.createAndTrim sz $ \outPtr -> do
         throwBotanIfNegative_ $
           botan_pk_op_encrypt
             encPtr

botan-low/src/Botan/Low/SRP6.hs

@@ -433,8 +433,8 @@ srp6GroupSize groupId =
   Utility
 -------------------------------------------------------------------------------}
 
--- | A version of 'BS.create' that determines the size of the byte string based
--- on an argument 'DLGroupName'.
+-- | Like 'createWithSize', but we determine the maximum size of the byte string
+-- based on an argument 'DLGroupName'.
 createWithGroupSize ::
      DLGroupName
   -> (Ptr Word8 -> Ptr CSize -> IO ())
@@ -443,21 +443,27 @@ createWithGroupSize groupId k = do
     sz <- srp6GroupSize groupId
     createWithSize sz k
 
--- | A version of 'BS.create' that also creates a pointer for the size of the
--- byte string.
+-- | Given the maximum size needed and a function to make the contents of a
+-- 'ByteString', 'createWithSize' makes the 'ByteString'.
+--
+-- The generating function is required to write the actual final size (<= the
+-- maximum size) to the 'CSize' pointer, and the resulting byte array is
+-- reallocated to this size.
+--
+-- NOTE: this is based on 'BS.createAndTrim'.
 createWithSize ::
      Int
   -> (Ptr Word8 -> Ptr CSize -> IO ())
   -> IO ByteString
 createWithSize sz k =
-    BS.createUptoN sz $ \bytesPtr ->
+    BS.createAndTrim sz $ \bytesPtr ->
     alloca $ \lenPtr -> do
       poke lenPtr (fromIntegral sz)
       k bytesPtr lenPtr
       fromIntegral <$> peek lenPtr
 
--- | A version of 'BS.createUptoN'' that determines the size of the byte string
--- based on an argument 'DLGroupName'.
+-- | Like 'createWithGroupSize', but also returns an additional value created by
+-- the action.
 createWithGroupSize' ::
      DLGroupName
   -> (Ptr Word8 -> Ptr CSize -> IO a)
@@ -466,16 +472,18 @@ createWithGroupSize' groupId k = do
     sz <- srp6GroupSize groupId
     createWithSize' sz k
 
--- | A version of 'BS.createUptoN'' that also creates a pointer for the size of
--- the byte string.
+-- | Like 'createWithSize', but also returns an additional value created by the
+-- action.
+--
+-- NOTE: this is based on 'BS.createAndTrim''.
 createWithSize' ::
      Int
   -> (Ptr Word8 -> Ptr CSize -> IO a)
   -> IO (ByteString, a)
 createWithSize' sz k =
-    BS.createUptoN' sz $ \bytesPtr ->
+    BS.createAndTrim' sz $ \bytesPtr ->
     alloca $ \lenPtr -> do
       poke lenPtr (fromIntegral sz)
       x <- k bytesPtr lenPtr
       sz' <- fromIntegral <$> peek lenPtr
-      pure (sz', x)
+      pure (0, sz', x)