smp agent: use static RNG function to avoid dynamic C stub created by Haskell FFI wrapper (#1556)

Author: epoberezkin

src/Simplex/Messaging/Crypto/SNTRUP761/Bindings.hs

@@ -10,11 +10,10 @@ import Data.Bifunctor (bimap)
 import Data.ByteArray (ScrubbedBytes)
 import qualified Data.ByteArray as BA
 import Data.ByteString (ByteString)
-import Foreign (nullPtr)
 import Simplex.Messaging.Agent.Store.DB (FromField (..), ToField (..))
 import Simplex.Messaging.Crypto.SNTRUP761.Bindings.Defines
 import Simplex.Messaging.Crypto.SNTRUP761.Bindings.FFI
-import Simplex.Messaging.Crypto.SNTRUP761.Bindings.RNG (withDRG)
+import Simplex.Messaging.Crypto.SNTRUP761.Bindings.RNG (rngFuncPtr, withDRG)
 import Simplex.Messaging.Encoding
 import Simplex.Messaging.Encoding.String
 
@@ -43,7 +42,7 @@ sntrup761Keypair drg =
       c_SNTRUP761_SECRETKEY_SIZE
       ( \skPtr ->
           BA.alloc c_SNTRUP761_PUBLICKEY_SIZE $ \pkPtr ->
-            withDRG drg $ c_sntrup761_keypair pkPtr skPtr nullPtr
+            withDRG drg $ \cxtPtr -> c_sntrup761_keypair pkPtr skPtr cxtPtr rngFuncPtr
       )
 
 sntrup761Enc :: TVar ChaChaDRG -> KEMPublicKey -> IO (KEMCiphertext, KEMSharedKey)
@@ -54,7 +53,7 @@ sntrup761Enc drg (KEMPublicKey pk) =
         c_SNTRUP761_SIZE
         ( \kPtr ->
             BA.alloc c_SNTRUP761_CIPHERTEXT_SIZE $ \cPtr ->
-              withDRG drg $ c_sntrup761_enc cPtr kPtr pkPtr nullPtr
+              withDRG drg $ \cxtPtr -> c_sntrup761_enc cPtr kPtr pkPtr cxtPtr rngFuncPtr
         )
 
 sntrup761Dec :: KEMCiphertext -> KEMSecretKey -> IO KEMSharedKey

src/Simplex/Messaging/Crypto/SNTRUP761/Bindings/RNG.hs

@@ -1,5 +1,6 @@
 module Simplex.Messaging.Crypto.SNTRUP761.Bindings.RNG
   ( withDRG,
+    rngFuncPtr,
     RNGContext,
     RNGFunc,
   ) where
@@ -12,19 +13,20 @@ import Foreign
 import Foreign.C
 import qualified Simplex.Messaging.Crypto as C
 
-withDRG :: TVar ChaChaDRG -> (FunPtr RNGFunc -> IO a) -> IO a
-withDRG drg = bracket (createRNGFunc drg) freeHaskellFunPtr
+withDRG :: TVar ChaChaDRG -> (Ptr RNGContext -> IO a) -> IO a
+withDRG drg = bracket (castStablePtrToPtr <$> newStablePtr drg) (freeStablePtr . castPtrToStablePtr)
 
-createRNGFunc :: TVar ChaChaDRG -> IO (FunPtr RNGFunc)
-createRNGFunc drg =
-  mkRNGFunc $ \_ctx sz buf -> do
-    bs <- atomically $ C.randomBytes (fromIntegral sz) drg
-    copyByteArrayToPtr bs buf
+rngFunc :: RNGFunc
+rngFunc cxt sz buf = do
+  drg <- deRefStablePtr $ castPtrToStablePtr cxt
+  bs <- atomically $ C.randomBytes (fromIntegral sz) drg
+  copyByteArrayToPtr bs buf
 
 type RNGContext = ()
 
 -- typedef void random_func (void *ctx, size_t length, uint8_t *dst);
 type RNGFunc = Ptr RNGContext -> CSize -> Ptr Word8 -> IO ()
 
-foreign import ccall "wrapper"
-  mkRNGFunc :: RNGFunc -> IO (FunPtr RNGFunc)
+foreign export ccall "haskell_rng_func" rngFunc :: RNGFunc
+
+foreign import ccall "&haskell_rng_func" rngFuncPtr :: FunPtr RNGFunc