From 7e18d48951315caebe5056a3fbd3788cdc681e1c Mon Sep 17 00:00:00 2001
From: Edsko de Vries <edsko@well-typed.com>
Date: Wed, 22 Mar 2023 08:03:44 +0100
Subject: [PATCH] `BorshMaxSize` should work similar to _fixed_ size

(instead of similiar to variable size, as it was prior to this commit.)
---
 src/Foreign/Rust/Marshall/Fixed.hs    | 25 +++++++++++++++++++------
 src/Foreign/Rust/Marshall/Variable.hs | 25 -------------------------
 2 files changed, 19 insertions(+), 31 deletions(-)

diff --git a/src/Foreign/Rust/Marshall/Fixed.hs b/src/Foreign/Rust/Marshall/Fixed.hs
index dc7d91d..2e2fd26 100644
--- a/src/Foreign/Rust/Marshall/Fixed.hs
+++ b/src/Foreign/Rust/Marshall/Fixed.hs
@@ -9,7 +9,8 @@ module Foreign.Rust.Marshall.Fixed (
     toBorshFixed
     -- * Rust to Haskell
   , allocFixedBuffer
-  , fromBorshFixed
+  , allocMaxBuffer
+  , fromBorsh
   ) where
 
 import Codec.Borsh
@@ -33,7 +34,7 @@ toBorshFixed a k =
     Strict.useAsCStringLen (serialiseStrict a) (k . castFromSignedLen)
 
 {-------------------------------------------------------------------------------
-  Rust to Haskell
+  Rust to Haskell: exact size known
 -------------------------------------------------------------------------------}
 
 allocFixedBuffer :: forall a.
@@ -47,9 +48,21 @@ allocFixedBuffer k =
     cast :: Word32 -> Int
     cast = fromIntegral
 
-fromBorshFixed ::
-     (FromBorsh a, StaticBorshSize a ~ 'HasKnownSize, Typeable a)
-  => Ptr CUChar -> CULong -> IO a
-fromBorshFixed ptr len =
+allocMaxBuffer :: forall a.
+     ( BorshSize a
+     , StaticBorshSize a ~ 'HasVariableSize
+     , BorshMaxSize a
+     )
+  => ((Ptr CUChar, CULong) -> IO a) -> IO a
+allocMaxBuffer k =
+    let n = borshMaxSize (Proxy @a)
+    in allocaBytes (cast n) $ \ptr -> k (ptr, fromIntegral n)
+  where
+    cast :: Word32 -> Int
+    cast = fromIntegral
+
+fromBorsh :: (FromBorsh a, Typeable a) => Ptr CUChar -> CULong -> IO a
+fromBorsh ptr len =
     deserialiseStrictOrPanic <$>
       Strict.packCStringLen (castToSigned ptr, fromIntegral len)
+
diff --git a/src/Foreign/Rust/Marshall/Variable.hs b/src/Foreign/Rust/Marshall/Variable.hs
index a84b591..a141e78 100644
--- a/src/Foreign/Rust/Marshall/Variable.hs
+++ b/src/Foreign/Rust/Marshall/Variable.hs
@@ -11,11 +11,9 @@ module Foreign.Rust.Marshall.Variable (
   , Buffer -- opaque
   , getVarBuffer
   , withBorshVarBuffer
-  , withBorshMaxBuffer
   , withBorshFailure
     -- ** Pure variants
   , withPureBorshVarBuffer
-  , withPureBorshMaxBuffer
   , withPureBorshFailure
   ) where
 
@@ -73,19 +71,6 @@ withBorshVarBuffer :: forall a.
   => (Buffer a -> IO ()) -> IO a
 withBorshVarBuffer = withBorshBufferOfInitSize 1024
 
-withBorshMaxBuffer :: forall a.
-     ( FromBorsh a
-     , StaticBorshSize a ~ 'HasVariableSize
-     , BorshMaxSize a
-     , Typeable a
-     )
-  => (Buffer a -> IO ()) -> IO a
-withBorshMaxBuffer =
-   withBorshBufferOfInitSize initBufSize
-  where
-    initBufSize :: CULong
-    initBufSize = fromIntegral $ borshMaxSize (Proxy @a)
-
 -- | Wrapper around 'withBorshVarBuffer' with explicit support for failures
 withBorshFailure :: forall a.
      ( FromBorsh a
@@ -108,15 +93,6 @@ withPureBorshVarBuffer :: forall a.
   => (Buffer a -> IO ()) -> a
 withPureBorshVarBuffer = unsafePerformIO . withBorshVarBuffer
 
-withPureBorshMaxBuffer :: forall a.
-     ( FromBorsh a
-     , StaticBorshSize a ~ 'HasVariableSize
-     , BorshMaxSize a
-     , Typeable a
-     )
-  => (Buffer a -> IO ()) -> a
-withPureBorshMaxBuffer = unsafePerformIO . withBorshMaxBuffer
-
 withPureBorshFailure :: forall a.
      ( FromBorsh a
      , StaticBorshSize a ~ 'HasVariableSize
@@ -126,7 +102,6 @@ withPureBorshFailure :: forall a.
   => (Buffer (Either Text a) -> IO ()) -> Either Failure a
 withPureBorshFailure = unsafePerformIO . withBorshFailure
 
-
 {-------------------------------------------------------------------------------
   Internal auxiliary
 -------------------------------------------------------------------------------}