Switch to c2hs

Let the computer figure out its own types for most foreign imports.
Continue using the vanilla FFI for finalizers, though, as that’s the
easiest way to deal with function pointers.

Reuse the build hook from gtk2hs-buildtools to work around Cabal’s
inability to topologically sort .chs dependencies
(https://github.com/haskell/cabal/issues/1906).

1 files changed, 151 insertions, 0 deletions

diff --git a/src/Data/Digest/Internal.chs b/src/Data/Digest/Internal.chs
new file mode 100644
index 0000000..ed4e09e
--- /dev/null
+++ b/src/Data/Digest/Internal.chs
@@ -0,0 +1,151 @@
+-- Copyright 2017 Google LLC
+--
+-- Licensed under the Apache License, Version 2.0 (the "License"); you may not
+-- use this file except in compliance with the License. You may obtain a copy of
+-- the License at
+--
+--     https://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+-- License for the specific language governing permissions and limitations under
+-- the License.
+
+{-# OPTIONS_GHC -Wno-missing-methods #-}
+
+module Data.Digest.Internal where
+
+import Control.Exception (assert)
+import Data.Bits (Bits((.&.)), shiftR)
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as ByteString
+import qualified Data.ByteString.Lazy as ByteString.Lazy
+import qualified Data.ByteString.Unsafe as ByteString
+import Data.Char (intToDigit)
+import Data.Word (Word8)
+import Foreign
+       (FinalizerPtr, ForeignPtr, Ptr, Storable(alignment, peek, sizeOf),
+        addForeignPtrFinalizer, alloca, allocaArray, mallocForeignPtr,
+        nullPtr, throwIf_, withForeignPtr)
+import Foreign.C.Types
+import Foreign.Marshal.Unsafe (unsafeLocalState)
+import Unsafe.Coerce (unsafeCoerce)
+
+import Foreign.Ptr.Cast (asVoidPtr)
+
+type LazyByteString = ByteString.Lazy.ByteString
+
+#include <openssl/digest.h>
+
+-- First, we build basic bindings to the BoringSSL EVP interface.
+
+-- | The BoringSSL @ENGINE@ type.
+data Engine
+{#pointer *ENGINE as 'Ptr Engine' -> Engine nocode#}
+
+noEngine :: Ptr Engine
+noEngine = nullPtr
+
+-- | The BoringSSL @EVP_MD@ type, representing a hash algorithm.
+data EvpMd
+{#pointer *EVP_MD as 'Ptr EvpMd' -> EvpMd nocode#}
+
+-- | The BoringSSL @EVP_MD_CTX@ type, representing the state of a pending
+-- hashing operation.
+data EvpMdCtx
+{#pointer *EVP_MD_CTX as 'Ptr EvpMdCtx' -> EvpMdCtx nocode#}
+
+instance Storable EvpMdCtx where
+  sizeOf _ = {#sizeof EVP_MD_CTX#}
+  alignment _ = {#alignof EVP_MD_CTX#}
+
+-- Imported functions from BoringSSL. See
+-- https://commondatastorage.googleapis.com/chromium-boringssl-docs/digest.h.html
+-- for documentation.
+
+evpMaxMdSize :: Int
+evpMaxMdSize = {#const EVP_MAX_MD_SIZE#}
+
+-- Some of these functions return 'CInt' even though they can never fail. Wrap
+-- them to prevent warnings.
+
+alwaysSucceeds :: IO CInt -> IO ()
+alwaysSucceeds f = do
+  r <- f
+  assert (r == 1) (return ())
+
+evpDigestUpdate :: Ptr EvpMdCtx -> Ptr a -> CULong -> IO ()
+evpDigestUpdate ctx md bytes =
+  alwaysSucceeds $ {#call EVP_DigestUpdate as ^#} ctx (asVoidPtr md) bytes
+
+evpDigestFinalEx :: Ptr EvpMdCtx -> Ptr CUChar -> Ptr CUInt -> IO ()
+evpDigestFinalEx ctx mdOut outSize =
+  alwaysSucceeds $ {#call EVP_DigestFinal_ex as ^#} ctx mdOut outSize
+
+-- Convert functions that can in fact fail to throw exceptions instead.
+
+requireSuccess :: IO CInt -> IO ()
+requireSuccess f = throwIf_ (/= 1) (const "BoringSSL failure") f
+
+evpDigestInitEx :: Ptr EvpMdCtx -> Ptr EvpMd -> Ptr Engine -> IO ()
+evpDigestInitEx ctx md engine =
+  requireSuccess $ {#call EVP_DigestInit_ex as ^#} ctx md engine
+
+-- Now we can build a memory-safe allocator.
+
+-- | Memory-safe allocator for 'EvpMdCtx'.
+mallocEvpMdCtx :: IO (ForeignPtr EvpMdCtx)
+mallocEvpMdCtx = do
+  fp <- mallocForeignPtr
+  withForeignPtr fp {#call EVP_MD_CTX_init as ^#}
+  addForeignPtrFinalizer btlsFinalizeEvpMdCtxPtr fp
+  return fp
+
+foreign import ccall "&btlsFinalizeEvpMdCtx"
+  btlsFinalizeEvpMdCtxPtr :: FinalizerPtr EvpMdCtx
+
+-- Finally, we're ready to actually implement the hashing interface.
+
+-- | A cryptographic hash function.
+newtype Algorithm = Algorithm (Ptr EvpMd)
+
+-- | The result of a hash operation.
+newtype Digest =
+  Digest ByteString
+  deriving (Eq, Ord)
+
+instance Show Digest where
+  show (Digest d) = ByteString.foldr showHexPadded [] d
+    where
+      showHexPadded b xs =
+        hexit (b `shiftR` 4 .&. 0x0f) : hexit (b .&. 0x0f) : xs
+      hexit = intToDigit . fromIntegral :: Word8 -> Char
+
+-- | Hashes according to the given 'Algorithm'.
+hash :: Algorithm -> LazyByteString -> Digest
+hash (Algorithm md) bytes =
+  unsafeLocalState $ do
+    ctxFP <- mallocEvpMdCtx
+    withForeignPtr ctxFP $ \ctx -> do
+      evpDigestInitEx ctx md noEngine
+      mapM_ (updateBytes ctx) (ByteString.Lazy.toChunks bytes)
+      d <-
+        allocaArray evpMaxMdSize $ \mdOut ->
+          alloca $ \pOutSize -> do
+            evpDigestFinalEx ctx mdOut pOutSize
+            outSize <- fromIntegral <$> peek pOutSize
+            -- 'mdOut' is a 'Ptr CUChar'. However, to make life more
+            -- interesting, 'CString' is a 'Ptr CChar', and 'CChar' is signed.
+            -- This is especially unfortunate given that all we really want to
+            -- do is convert to a 'ByteString', which is unsigned. To work
+            -- around it, we're going to cheat and let Haskell reinterpret-cast
+            -- 'mdOut' to 'Ptr CChar' before it does its 'ByteString' ingestion.
+            ByteString.packCStringLen (unsafeCoerce mdOut, outSize)
+      return (Digest d)
+  where
+    updateBytes ctx chunk =
+      -- 'mdUpdate' treats its @buf@ argument as @const@, so the sharing
+      -- inherent in 'ByteString.unsafeUseAsCStringLen' is fine.
+      ByteString.unsafeUseAsCStringLen chunk $ \(buf, len) ->
+        evpDigestUpdate ctx buf (fromIntegral len)