From a215b5d527a6e7485f2d34b035999201756c9cd8 Mon Sep 17 00:00:00 2001
From: zach <zach@dylibso.com>
Date: Fri, 29 Sep 2023 11:27:30 -0700
Subject: [PATCH] refactor: better organization, cleanup (#5)

* cleanup: start reorganizing

* ci

* fix: shadowed variable name

* refactor: add more binary types, move memory code to its own file

* docs: show example with non-string input

* cleanup: hlint

* cleanup: reorganize

* fix: don't free errors

* cleanup: reorganize

* cleanup: bring back Memory.store functions, remove unused imports

* docs: add missing doc comments

* docs: add link

* cleanup: add explicit return code

* cleanup: add tryInput

* cleanup: count vowels example

* fix: http example
---
 CHANGELOG.md               |   9 +-
 Makefile                   |   3 +
 examples/CountVowels.hs    |  19 ++-
 examples/HTTPGet.hs        |  23 +++-
 examples/Hello.hs          |   8 +-
 extism-pdk.cabal           |  18 ++-
 src/Extism/PDK.hs          | 246 +++++++++++-----------------------
 src/Extism/PDK/Bindings.hs | 124 +++++++++++-------
 src/Extism/PDK/HTTP.hs     |  90 ++++++++-----
 src/Extism/PDK/JSON.hs     |   9 +-
 src/Extism/PDK/Memory.hs   | 261 +++++++++++++++++++++++++++++++++++++
 src/Extism/PDK/MsgPack.hs  | 132 +++++++++----------
 src/Extism/PDK/Util.hs     |  12 ++
 13 files changed, 610 insertions(+), 344 deletions(-)
 create mode 100644 src/Extism/PDK/Memory.hs
 create mode 100644 src/Extism/PDK/Util.hs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index bc83c9c..0ebe1b1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
-# Revision history for haskell-wasm
+# Revision history for extism-pdk
 
-## 0.1.0.0 -- YYYY-mm-dd
+## 0.2.0.0
+
+* API redesign, add automatic Haskell encoding using `ToMemory` and `FromMemory` classes
+
+## 0.1.0.0 -- 2023-09-28
 
 * First version. Released on an unsuspecting world.
+
diff --git a/Makefile b/Makefile
index df7fada..cd3df5d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,8 @@
 all: hello.example http_get.example count_vowels.example
 
+update:
+	wasm32-wasi-cabal update
+
 build:
 	wasm32-wasi-cabal build
 	
diff --git a/examples/CountVowels.hs b/examples/CountVowels.hs
index 3e1e5c5..89e552a 100644
--- a/examples/CountVowels.hs
+++ b/examples/CountVowels.hs
@@ -3,12 +3,17 @@ module CountVowels where
 import Extism.PDK
 import Extism.PDK.JSON
 
-isVowel c = 
-  c == 'a' || c == 'A' ||
-  c == 'e' || c == 'E' ||
-  c == 'i' || c == 'I' ||
-  c == 'o' || c == 'O' ||
-  c == 'u' || c == 'U'
+isVowel c =
+  c == 'a'
+    || c == 'A'
+    || c == 'e'
+    || c == 'E'
+    || c == 'i'
+    || c == 'I'
+    || c == 'o'
+    || c == 'O'
+    || c == 'u'
+    || c == 'U'
 
 countVowels = do
   -- Get input string from Extism host
@@ -18,4 +23,4 @@ countVowels = do
   -- Return a JSON object {"count": count} back to the host
   output $ JSONValue $ object ["count" .= count]
 
-foreign export ccall "count_vowels" countVowels ::  IO ()
+foreign export ccall "count_vowels" countVowels :: IO ()
diff --git a/examples/HTTPGet.hs b/examples/HTTPGet.hs
index 1076b51..15dd439 100644
--- a/examples/HTTPGet.hs
+++ b/examples/HTTPGet.hs
@@ -1,16 +1,27 @@
 module HTTPGet where
 
+import Data.Int
 import Extism.PDK
 import Extism.PDK.HTTP
+import Extism.PDK.Memory
+
+getInput = do
+  req <- tryInput
+  case req of
+    Right (JSONValue x) -> return x
+    Left e -> do
+      putStrLn e
+      url <- inputString
+      return $ newRequest url
 
 httpGet = do
-  -- Get URL from the host
-  url <- input
-  -- Create a new 'Request'
-  let req = newRequest url
+  -- Get URL or JSON encoded request from host
+  req <- getInput
   -- Send the request, get a 'Response'
-  res <- sendRequest req Nothing
+  res <- sendRequest req (Nothing :: Maybe String)
   -- Save response body to memory
   outputMemory (memory res)
+  -- Return code
+  return 0
 
-foreign export ccall "http_get" httpGet ::  IO ()
+foreign export ccall "http_get" httpGet :: IO Int32
diff --git a/examples/Hello.hs b/examples/Hello.hs
index 3f91d7b..3e720a5 100644
--- a/examples/Hello.hs
+++ b/examples/Hello.hs
@@ -1,20 +1,20 @@
 module Hello where
 
-import Extism.PDK
 import Data.Maybe
+import Extism.PDK
 import Foreign.C.Types
 
 defaultGreeting = "Hello"
 
 greet g n =
   output $ g ++ ", " ++ n
-  
+
 testing = do
   -- Get a name from the Extism runtime
-  name <- input
+  name <- inputString
   -- Get  configured greeting
   greeting <- getConfig "greeting"
   -- Greet the user, if no greeting is configured then "Hello" is used
   greet (fromMaybe defaultGreeting greeting) name
 
-foreign export ccall "testing" testing ::  IO ()
+foreign export ccall "testing" testing :: IO ()
diff --git a/extism-pdk.cabal b/extism-pdk.cabal
index 5777a97..7915524 100644
--- a/extism-pdk.cabal
+++ b/extism-pdk.cabal
@@ -1,12 +1,12 @@
 cabal-version:      3.0
 name:               extism-pdk
-version:            0.1.0.0
+version:            0.2.0.0
 
 -- A short (one-line) description of the package.
 synopsis: Extism Plugin Development Kit
 
 -- A longer description of the package.
-description: Haskell bindings to the Extism runtime
+description: Haskell bindings to the Extism runtime for use with wasm32-wasi-ghc
 
 -- A URL where users can report bugs.
 bug-reports: https://github.com/extism/haskell-pdk
@@ -20,7 +20,14 @@ category: WASM, plugins
 extra-doc-files: CHANGELOG.md
 
 library
-    exposed-modules: Extism.PDK Extism.PDK.Bindings Extism.PDK.HTTP Extism.PDK.JSON Extism.PDK.MsgPack
+    exposed-modules:
+      Extism.PDK
+      Extism.PDK.Bindings
+      Extism.PDK.HTTP
+      Extism.PDK.JSON
+      Extism.PDK.MsgPack
+      Extism.PDK.Util
+      Extism.PDK.Memory
 
     -- Modules included in this executable, other than Main.
     -- other-modules:
@@ -34,7 +41,8 @@ library
       containers >= 0.6.7 && < 0.7,
       extism-manifest >= 0.3.0 && <= 1.0.0,
       json >= 0.11 && < 0.12,
-      messagepack >= 0.5.5 && < 0.6
+      messagepack >= 0.5.5 && < 0.6,
+      binary >= 0.8.9 && < 0.9.0
 
     hs-source-dirs:   src
     default-language: Haskell2010
@@ -45,7 +53,7 @@ executable hello
     build-depends: base, extism-pdk
     default-language: Haskell2010
     ghc-options:
-      -optl -Wl,--export=testing
+      -optl -Wl,--export=testing 
 
 executable http_get
     scope: private
diff --git a/src/Extism/PDK.hs b/src/Extism/PDK.hs
index c169d74..45c09e2 100644
--- a/src/Extism/PDK.hs
+++ b/src/Extism/PDK.hs
@@ -1,196 +1,95 @@
-{-# LANGUAGE TypeSynonymInstances, FlexibleInstances #-}
+{-# LANGUAGE Rank2Types #-}
+
+-- |
+-- Extism plugin development kit, used with the [wasm32-wasi-ghc](https://gitlab.haskell.org/ghc/ghc-wasm-meta) backend to make Extism plugins
+module Extism.PDK
+  ( module Extism.PDK,
+    ToBytes (..),
+    FromBytes (..),
+    JSONValue (..),
+    MsgPackValue (..),
+  )
+where
 
-module Extism.PDK (module Extism.PDK, module Extism.Manifest) where
-
-import Extism.PDK.Bindings
-import Extism.JSON(JSValue, JSON)
-import Extism.Manifest(toString)
-import Data.Word
-import Data.Int
 import Data.ByteString as B
-import Data.ByteString.Internal (c2w, w2c)
-import Data.ByteString.Unsafe (unsafeUseAsCString)
-import Text.JSON(JSON, decode, encode, resultToEither)
-import qualified Extism.PDK.MsgPack(MsgPack, decode, encode)
-
-newtype JSONValue a = JSONValue a
-newtype MsgPackValue a = MsgPackValue a
-
--- | Represents a block of memory
-data Memory = Memory MemoryOffset MemoryLength
-
--- | Helper function to convert a string to a bytestring
-toByteString :: String -> ByteString
-toByteString x = B.pack (Prelude.map c2w x)
-
--- | Helper function to convert a bytestring to a string
-fromByteString :: ByteString -> String
-fromByteString bs = Prelude.map w2c $ B.unpack bs
-
-class FromBytes a where
-  fromBytes :: ByteString -> a
-
-class ToBytes a where
-  toBytes :: a -> ByteString
-
-instance FromBytes ByteString where
-  fromBytes bs = bs
-
-instance ToBytes ByteString where
-  toBytes bs = bs
-
-instance FromBytes String where
-  fromBytes = fromByteString
-
-instance ToBytes String where
-  toBytes = toByteString
-
-instance JSON a => FromBytes (JSONValue a) where
-  fromBytes x =
-    case resultToEither $ decode (fromByteString x) of
-      Left e -> error e
-      Right y -> JSONValue y
-
-instance JSON a => ToBytes (JSONValue a) where
-  toBytes (JSONValue x) = toByteString (encode x)
-
-instance Extism.PDK.MsgPack.MsgPack a => FromBytes (MsgPackValue a) where
-  fromBytes x =
-    case Extism.PDK.MsgPack.decode x of
-      Left e -> error e
-      Right y -> MsgPackValue y
+import Extism.PDK.Bindings
+import Extism.PDK.Memory
+import qualified Extism.PDK.MsgPack (MsgPack, decode, encode)
+import Extism.PDK.Util
+import Text.JSON (JSON, decode, encode, resultToEither)
 
-instance Extism.PDK.MsgPack.MsgPack a => ToBytes (MsgPackValue a) where
-  toBytes (MsgPackValue x) = Extism.PDK.MsgPack.encode x
+-- | Get plugin input, returning an error message if the encoding is invalid
+tryInput :: (FromBytes a) => IO (Either String a)
+tryInput = fromBytes <$> inputByteString
 
--- | Get plugin input as 'ByteString'
-input :: FromBytes a => IO a
+-- | Get plugin input
+input :: forall a. (FromBytes a) => IO a
 input = do
+  i <- inputByteString
+  let x = fromBytes i
+  case x of
+    Left e -> error e
+    Right y -> return y
+
+-- | Get plugin input as a String
+inputString :: IO String
+inputString = do
   len <- extismInputLength
-  fromBytes <$> readInputBytes len
+  fromByteString <$> readInputBytes len
 
--- | Get plugin input as 'Memory' block
-inputMemory :: IO Memory
-inputMemory = do
+-- | Get plugin input as a ByteString
+inputByteString :: IO ByteString
+inputByteString = do
   len <- extismInputLength
-  offs <- extismAlloc len
-  Prelude.mapM_ (\x ->
-    extismStoreU8 (offs + x) <$> extismInputLoadU8 x) [0, 1 .. len]
-  return $ Memory offs len
+  readInputBytes len
 
--- | Get input as 'JSON'
-inputJSON :: JSON a => IO (Maybe a)
+-- | Get input as 'JSON', this is similar to calling `input (JsonValue ...)`
+inputJSON :: (JSON a) => IO (Either String a)
 inputJSON = do
-  s <- input :: IO String
-  case resultToEither $ decode s of
-    Left _ -> return Nothing
-    Right x -> return (Just x)
-
--- | Load data from 'Memory' block
-load :: FromBytes a => Memory -> IO a
-load (Memory offs len) =
-  fromBytes <$> readBytes offs len
-
--- | Store data into a 'Memory' block
-store :: ToBytes a => Memory -> a -> IO ()
-store (Memory offs len) a =
-  let bs = toBytes a in
-  writeBytes offs len bs
-
--- | Set plugin output to the provided 'Memory' block
-outputMemory :: Memory -> IO ()
-outputMemory (Memory offs len) =
+  s <- tryInput :: IO (Either String String)
+  case s of
+    Left e -> return (Left e)
+    Right x ->
+      case resultToEither $ decode x of
+        Left e -> return (Left e)
+        Right y -> return (Right y)
+
+-- | Set plugin output
+output :: (ToBytes a) => a -> IO ()
+output x = do
+  Memory offs len <- alloc x
   extismSetOutput offs len
 
--- | Set plugin output to the provided 'ByteString'
-output :: ToBytes a => a -> IO ()
-output x =
-  let bs = toBytes x in
-  let len = fromIntegral $ B.length bs in
-  do
-    offs <- extismAlloc len
-    b <- store (Memory offs len) bs
-    extismSetOutput offs len
-
 -- | Set plugin output to a JSON encoded version of the provided value
-outputJSON :: JSON a => a -> IO ()
+outputJSON :: (JSON a) => a -> IO ()
 outputJSON x =
-  output (toString x)
-
--- | Load string from 'Memory' block
-loadString :: Memory -> IO String
-loadString mem = do
-  bs <- load mem
-  return $ fromByteString bs
-
--- | Store string in 'Memory' block
-storeString :: Memory -> String -> IO ()
-storeString mem s =
-  let bs = toByteString s in
-  store mem bs
-
--- | Allocate a new 'Memory' block
-alloc :: Int -> IO Memory
-alloc n =
-  let len = fromIntegral n in
-  do
-    offs <- extismAlloc len
-    return $ Memory offs len
-
--- | Free a 'Memory' block
-free :: Memory -> IO ()
-free (Memory 0 _) = return ()
-free (Memory _ 0) = return ()
-free (Memory offs _) =
-  extismFree offs
-
--- | Allocate a new 'Memory' block and copy the contents of the provided 'ByteString'
-allocByteString :: ByteString -> IO Memory
-allocByteString bs = do
-  mem <- alloc (B.length bs)
-  store mem bs
-  return mem
-
--- | Allocate a new 'Memory' block and copy the contents of the provided 'String'
-allocString :: String -> IO Memory
-allocString s =
-  let bs = toByteString s in
-  allocByteString bs
-
--- | Get the offset of a 'Memory' block
-memoryOffset (Memory offs _) = offs
-
--- | Get the length of a 'Memory' block
-memoryLength (Memory _ len) = len
-
--- | Find 'Memory' block by offset
-findMemory offs = do
-  len <- extismLength offs
-  return $ Memory offs len
+  output (encode x)
 
 -- | Get a variable from the Extism runtime
-getVar :: String -> IO (Maybe ByteString)
+getVar :: (FromBytes a) => String -> IO (Maybe a)
 getVar key = do
   k <- allocString key
   v <- extismGetVar (memoryOffset k)
   free k
-  if v == 0 then
-    return Nothing
-  else do
-    mem <- findMemory v
-    bs <- load mem
-    free mem
-    return (Just bs)
+  if v == 0
+    then return Nothing
+    else do
+      mem <- findMemory v
+      bs <- load mem
+      free k
+      case bs of
+        Left _ -> return Nothing
+        Right x -> return (Just x)
 
 -- | Set a variable
-setVar :: ToBytes a => String -> Maybe a -> IO ()
+setVar :: (ToBytes a) => String -> Maybe a -> IO ()
 setVar key Nothing = do
   k <- allocString key
   extismSetVar (memoryOffset k) 0
   free k
 setVar key (Just v) = do
   k <- allocString key
-  x <- allocByteString (toBytes v)
+  x <- alloc v
   extismSetVar (memoryOffset k) (memoryOffset x)
   free k
   free x
@@ -201,23 +100,24 @@ getConfig key = do
   k <- allocString key
   v <- extismGetConfig (memoryOffset k)
   free k
-  if v == 0 then
-    return Nothing
-  else do
-    mem <- findMemory v
-    s <- loadString mem
-    free mem
-    return $ Just s
+  if v == 0
+    then return Nothing
+    else do
+      mem <- findMemory v
+      s <- loadString mem
+      free mem
+      return $ Just s
 
 -- | Set the current error message
 setError :: String -> IO ()
 setError msg = do
   s <- allocString msg
   extismSetError $ memoryOffset s
-  free s
 
+-- | Log level
 data LogLevel = Info | Debug | Warn | Error
 
+-- | Log to configured log file
 log :: LogLevel -> String -> IO ()
 log Info msg = do
   s <- allocString msg
diff --git a/src/Extism/PDK/Bindings.hs b/src/Extism/PDK/Bindings.hs
index 6d40ece..45fd831 100644
--- a/src/Extism/PDK/Bindings.hs
+++ b/src/Extism/PDK/Bindings.hs
@@ -2,75 +2,109 @@
 
 module Extism.PDK.Bindings where
 
+import Control.Monad
+import Data.ByteString as B
 import Data.ByteString.Internal
+import Data.Int
+import Data.Word
+import Foreign.C.Types
 import Foreign.ForeignPtr
 import Foreign.Ptr
 import Foreign.Storable
-import Control.Monad
-
 import System.Exit
-import Data.Word
-import Data.Int
-import Foreign.C.Types
-
-import Data.ByteString as B
-
 
+-- | Offset in Extism memory
 type MemoryOffset = Word64
+
+-- | Offset of input from 0 to 'InputLength'
 type InputOffset = Word64
+
+-- | Length of allocated block of memory
 type MemoryLength = Word64
+
+-- | Total length of the input
 type InputLength = Word64
 
 foreign import ccall "extism_output_set" extismSetOutput :: MemoryOffset -> MemoryLength -> IO ()
+
 foreign import ccall "extism_error_set" extismSetError :: MemoryOffset -> IO ()
+
 foreign import ccall "extism_log_info" extismLogInfo :: MemoryOffset -> IO ()
+
 foreign import ccall "extism_log_warn" extismLogWarn :: MemoryOffset -> IO ()
+
 foreign import ccall "extism_log_debug" extismLogDebug :: MemoryOffset -> IO ()
+
 foreign import ccall "extism_log_error" extismLogError :: MemoryOffset -> IO ()
+
 foreign import ccall "extism_store_u8" extismStoreU8 :: MemoryOffset -> Word8 -> IO ()
+
 foreign import ccall "extism_store_u64" extismStoreU64 :: MemoryOffset -> Word64 -> IO ()
+
 foreign import ccall "extism_load_u8" extismLoadU8 :: MemoryOffset -> IO Word8
+
 foreign import ccall "extism_load_u64" extismLoadU64 :: MemoryOffset -> IO Word64
+
 foreign import ccall "extism_alloc" extismAlloc :: MemoryLength -> IO MemoryOffset
+
 foreign import ccall "extism_length" extismLength :: MemoryOffset -> IO MemoryLength
+
 foreign import ccall "extism_free" extismFree :: MemoryOffset -> IO ()
+
 foreign import ccall "extism_input_length" extismInputLength :: IO InputLength
+
 foreign import ccall "extism_input_load_u8" extismInputLoadU8 :: InputOffset -> IO Word8
+
 foreign import ccall "extism_input_load_u64" extismInputLoadU64 :: InputOffset -> IO Word64
+
 foreign import ccall "extism_config_get" extismGetConfig :: MemoryOffset -> IO MemoryOffset
+
 foreign import ccall "extism_var_get" extismGetVar :: MemoryOffset -> IO MemoryOffset
+
 foreign import ccall "extism_var_set" extismSetVar :: MemoryOffset -> MemoryOffset -> IO ()
+
 foreign import ccall "extism_http_request" extismHTTPRequest :: MemoryOffset -> MemoryOffset -> IO MemoryOffset
+
 foreign import ccall "extism_http_status_code" extismHTTPStatusCode :: IO Int32
+
 foreign import ccall "__wasm_call_ctors" wasmConstructor :: IO ()
-foreign import ccall "__wasm_call_dtors" wasmDestructor :: IO ()
 
+foreign import ccall "__wasm_call_dtors" wasmDestructor :: IO ()
 
 bsToWord64 :: ByteString -> IO Word64
 bsToWord64 (BS fp len) =
-  if len /= 8 then error "invalid bytestring"
-  else
-    withForeignPtr fp (\p ->
-      peek $ castPtr @Word8 @Word64 p)
+  if len /= 8
+    then error "invalid bytestring"
+    else
+      withForeignPtr
+        fp
+        ( peek . castPtr @Word8 @Word64
+        )
 
 word64ToBS :: Word64 -> ByteString
-word64ToBS word = unsafeCreate 8 (\p ->
-  poke (castPtr @Word8 @Word64 p) word)
+word64ToBS word =
+  unsafeCreate
+    8
+    ( \p ->
+        poke (castPtr @Word8 @Word64 p) word
+    )
 
 readLoop :: (Word64 -> IO Word8) -> (Word64 -> IO Word64) -> Word64 -> Word64 -> [ByteString] -> IO ByteString
 readLoop f1 f8 total index acc =
-  if index >= total then
-    return $ B.concat . Prelude.reverse $ acc
-  else
-    let diff = total - index in
-    do
-      (n, x) <- if diff >= 8 then do
-                    u <- f8 index
-                    return (8, word64ToBS u)
-                  else do
-                    b <- f1 index
-                    return (1, B.singleton b)
-      readLoop f1 f8 total (index + n) (x : acc)
+  if index >= total
+    then return $ B.concat . Prelude.reverse $ acc
+    else
+      let diff = total - index
+       in do
+            (n, x) <-
+              if diff >= 8
+                then do
+                  u <- f8 index
+                  return (8, word64ToBS u)
+                else do
+                  b <- f1 index
+                  return (1, B.singleton b)
+            readLoop f1 f8 total (index + n) (x : acc)
 
 readInputBytes :: InputLength -> IO ByteString
 readInputBytes len =
@@ -82,22 +116,24 @@ readBytes offs len =
 
 writeBytesLoop :: MemoryOffset -> MemoryOffset -> ByteString -> IO ()
 writeBytesLoop index total src =
-  if index >= total then
-    return ()
-  else
-    let diff = total - index in
-    do
-      (n, sub) <- if diff >= 8 then do
-                    let (curr, next) = B.splitAt 8 src
-                    u <- bsToWord64 curr
-                    extismStoreU64 index u
-                    return (8, next)
-                  else do
-                    let u = B.head src
-                    extismStoreU8 index u
-                    return (1, B.tail src)
-      writeBytesLoop (index + n) total sub
+  if index >= total
+    then return ()
+    else
+      let diff = total - index
+       in do
+            (n, sub) <-
+              if diff >= 8
+                then do
+                  let (curr, next) = B.splitAt 8 src
+                  u <- bsToWord64 curr
+                  extismStoreU64 index u
+                  return (8, next)
+                else do
+                  let u = B.head src
+                  extismStoreU8 index u
+                  return (1, B.tail src)
+            writeBytesLoop (index + n) total sub
 
 writeBytes :: MemoryOffset -> MemoryLength -> ByteString -> IO ()
-writeBytes offs len src =
-  writeBytesLoop offs (offs + len) src
+writeBytes offs len =
+  writeBytesLoop offs (offs + len)
diff --git a/src/Extism/PDK/HTTP.hs b/src/Extism/PDK/HTTP.hs
index 5468f91..d88f031 100644
--- a/src/Extism/PDK/HTTP.hs
+++ b/src/Extism/PDK/HTTP.hs
@@ -1,40 +1,42 @@
+-- |
+-- Contains bindings to the Extism PDK HTTP interface
 module Extism.PDK.HTTP where
 
-import Extism.Manifest(toString, HTTPRequest(..), method, headers, url)
-import Extism.JSON(Nullable(..), decode, JSON, Result(..))
-import Extism.PDK.Bindings
-import Extism.PDK
-import Data.Word
 import Data.ByteString as B
+import Data.Word
+import Extism.JSON (JSON, Nullable (..), Result (..), decode)
+import Extism.Manifest (HTTPRequest (..), headers, method, toString, url)
+import Extism.PDK
+import Extism.PDK.Bindings
+import Extism.PDK.Memory
 
 -- | HTTP Request
 type Request = HTTPRequest
 
 -- | HTTP Response
 data Response = Response
-  {
-    statusCode :: Int
-  , memory :: Memory
+  { statusCode :: Int,
+    memory :: Memory
   }
 
 -- | Creates a new 'Request'
 newRequest :: String -> Request
 newRequest url =
-  HTTPRequest {
-    url = url
-  , headers = Null
-  , method = Null
-  }
+  HTTPRequest
+    { url = url,
+      headers = Null,
+      method = Null
+    }
 
 -- | Update a 'Request' with the provided HTTP request method (GET, POST, PUT, DELETE, ...)
 withMethod :: String -> Request -> Request
 withMethod meth req =
-  req { method = NotNull meth }
+  req {method = NotNull meth}
 
 -- | Update a 'Request' with the provided HTTP request headers
 withHeaders :: [(String, String)] -> Request -> Request
 withHeaders h req =
-  req { headers = NotNull h }
+  req {headers = NotNull h}
 
 -- | Access the Memory block associated with a 'Response'
 responseMemory :: Response -> Memory
@@ -42,38 +44,60 @@ responseMemory (Response _ mem) = mem
 
 -- | Get the 'Response' body as a 'ByteString'
 responseByteString :: Response -> IO ByteString
-responseByteString (Response _ mem) = load mem
+responseByteString (Response _ mem) = do
+  a <- load mem
+  case a of
+    Left e -> error e
+    Right x -> return x
 
 -- | Get the 'Response' body as a 'String'
 responseString :: Response -> IO String
 responseString (Response _ mem) = loadString mem
 
 -- | Get the 'Response' body as JSON
-responseJSON :: JSON a => Response -> IO (Either String a)
+responseJSON :: (JSON a) => Response -> IO (Either String a)
 responseJSON (Response _ mem) = do
   json <- decode <$> loadString mem
   case json of
     Ok json -> return $ Right json
     Extism.JSON.Error msg -> return (Left msg)
 
+-- | Get the 'Response' body and decode it
+response :: (FromBytes a) => Response -> IO (Either String a)
+response (Response _ mem) = load mem
 
 -- | Send HTTP request with an optional request body
-sendRequest :: Request -> Maybe ByteString -> IO Response
-sendRequest req b =
-  let json = Extism.Manifest.toString req in
-  let bodyMem = case b of
-               Nothing -> return $ Memory 0 0
-               Just b -> allocByteString b
-  in
-  do
-    body <- bodyMem
-    j <- allocString json
-    res <- extismHTTPRequest (memoryOffset j) (memoryOffset body)
-    free j
-    free body
-    code <- extismHTTPStatusCode
-    if res == 0 then
-      return (Response (fromIntegral code) (Memory 0 0))
+sendRequestWithBody :: (ToBytes a) => Request -> a -> IO Response
+sendRequestWithBody req b = do
+  body <- alloc b
+  let json = Extism.Manifest.toString req
+  j <- allocString json
+  res <- extismHTTPRequest (memoryOffset j) (memoryOffset body)
+  free j
+  free body
+  code <- extismHTTPStatusCode
+  if res == 0
+    then return (Response (fromIntegral code) (Memory 0 0))
     else do
       mem <- findMemory res
       return (Response (fromIntegral code) mem)
+
+-- | Send HTTP request with an optional request body
+sendRequest :: (ToBytes a) => Request -> Maybe a -> IO Response
+sendRequest req b =
+  let json = Extism.Manifest.toString req
+   in let bodyMem = case b of
+            Nothing -> return $ Memory 0 0
+            Just b -> alloc b
+       in do
+            body <- bodyMem
+            j <- allocString json
+            res <- extismHTTPRequest (memoryOffset j) (memoryOffset body)
+            free j
+            free body
+            code <- extismHTTPStatusCode
+            if res == 0
+              then return (Response (fromIntegral code) (Memory 0 0))
+              else do
+                mem <- findMemory res
+                return (Response (fromIntegral code) mem)
diff --git a/src/Extism/PDK/JSON.hs b/src/Extism/PDK/JSON.hs
index fe85133..e6fcdb3 100644
--- a/src/Extism/PDK/JSON.hs
+++ b/src/Extism/PDK/JSON.hs
@@ -1,6 +1,7 @@
-module Extism.PDK.JSON (
-  module Extism.PDK.JSON,
-  module Extism.JSON
-) where
+module Extism.PDK.JSON
+  ( module Extism.PDK.JSON,
+    module Extism.JSON,
+  )
+where
 
 import Extism.JSON
diff --git a/src/Extism/PDK/Memory.hs b/src/Extism/PDK/Memory.hs
new file mode 100644
index 0000000..104684e
--- /dev/null
+++ b/src/Extism/PDK/Memory.hs
@@ -0,0 +1,261 @@
+{-# LANGUAGE FlexibleInstances #-}
+
+-- |
+-- Extism.PDK.Memory implements a low-level interface for interacting with Extism memory
+module Extism.PDK.Memory
+  ( Memory (..),
+    MemoryOffset,
+    MemoryLength,
+    FromBytes (..),
+    ToBytes (..),
+    JSONValue (..),
+    MsgPackValue (..),
+    load,
+    loadString,
+    loadByteString,
+    outputMemory,
+    memAlloc,
+    free,
+    alloc,
+    allocString,
+    allocByteString,
+    memoryOffset,
+    memoryLength,
+    findMemory,
+  )
+where
+
+import Data.Binary.Get
+import Data.Binary.Put
+import qualified Data.ByteString as B
+import Data.ByteString.Internal (c2w, w2c)
+import Data.Int
+import Data.Word
+import Extism.PDK.Bindings
+import qualified Extism.PDK.MsgPack (MsgPack, decode, encode)
+import Extism.PDK.Util
+import Text.JSON (JSON, decode, encode, resultToEither)
+
+-- | Represents a block of memory by offset and length
+data Memory = Memory MemoryOffset MemoryLength
+
+-- | Load data from 'Memory' block
+load :: (FromBytes a) => Memory -> IO (Either String a)
+load (Memory offs len) = do
+  x <- readBytes offs len
+  return $ fromBytes x
+
+-- | Store data into a 'Memory' block
+store :: (ToBytes a) => Memory -> a -> IO ()
+store (Memory offs len) a =
+  let bs = toBytes a
+   in writeBytes offs len bs
+
+-- | Set plugin output to the provided 'Memory' block
+outputMemory :: Memory -> IO ()
+outputMemory (Memory offs len) =
+  extismSetOutput offs len
+
+-- | Load ByteString from 'Memory' block
+loadByteString :: Memory -> IO B.ByteString
+loadByteString (Memory offs len) = do
+  readBytes offs len
+
+-- | Load string from 'Memory' block
+loadString :: Memory -> IO String
+loadString (Memory offs len) =
+  fromByteString <$> readBytes offs len
+
+-- | Store string in 'Memory' block
+storeString :: Memory -> String -> IO ()
+storeString mem s =
+  let bs = toByteString s
+   in storeByteString mem bs
+
+-- | Store byte string in 'Memory' block
+storeByteString :: Memory -> B.ByteString -> IO ()
+storeByteString (Memory offs len) =
+  writeBytes offs len
+
+-- | Encode a value and copy it into Extism memory, returning the Memory block
+alloc :: (ToBytes a) => a -> IO Memory
+alloc x =
+  let bs = toBytes x
+   in do
+        Memory offs len <- memAlloc (B.length bs)
+        writeBytes offs len bs
+        return $ Memory offs len
+
+-- | Allocate a new 'Memory' block
+memAlloc :: Int -> IO Memory
+memAlloc n =
+  let len = fromIntegral n
+   in do
+        offs <- extismAlloc len
+        return $ Memory offs len
+
+-- | Free a 'Memory' block
+free :: Memory -> IO ()
+free (Memory 0 _) = return ()
+free (Memory _ 0) = return ()
+free (Memory offs _) =
+  extismFree offs
+
+-- | Allocate a new 'Memory' block and copy the encoded value
+allocByteString :: B.ByteString -> IO Memory
+allocByteString bs = do
+  Memory offs len <- memAlloc (B.length bs)
+  writeBytes offs len bs
+  return (Memory offs len)
+
+-- | Allocate a new 'Memory' block and copy the contents of the provided 'String'
+allocString :: String -> IO Memory
+allocString = allocByteString . toByteString
+
+-- | Get the offset of a 'Memory' block
+memoryOffset :: Memory -> MemoryOffset
+memoryOffset (Memory offs _) = offs
+
+-- | Get the length of a 'Memory' block
+memoryLength :: Memory -> MemoryLength
+memoryLength (Memory _ len) = len
+
+-- | Find 'Memory' block by offset
+findMemory :: MemoryOffset -> IO Memory
+findMemory offs = do
+  len <- extismLength offs
+  return $ Memory offs len
+
+-- | A class used to convert values from bytes read from linear memory
+class FromBytes a where
+  fromBytes :: B.ByteString -> Either String a
+
+-- | A class used to convert values to bytes to be written into linear memory
+class ToBytes a where
+  toBytes :: a -> B.ByteString
+
+-- | A wrapper type for JSON encoded values
+newtype JSONValue a = JSONValue a
+
+-- | A wrapper type for MsgPack encoded values
+newtype MsgPackValue a = MsgPackValue a
+
+instance FromBytes B.ByteString where
+  fromBytes = Right
+
+instance ToBytes B.ByteString where
+  toBytes = id
+
+instance FromBytes String where
+  fromBytes mem =
+    let s = fromBytes mem
+     in case s of
+          Left e -> Left e
+          Right x -> Right $ fromByteString x
+
+instance ToBytes String where
+  toBytes = toByteString
+
+instance (JSON a) => FromBytes (JSONValue a) where
+  fromBytes mem =
+    let a = fromBytes mem
+     in case a of
+          Left e -> Left e
+          Right x ->
+            case resultToEither $ decode x of
+              Left e -> Left e
+              Right y -> Right (JSONValue y)
+
+instance (JSON a) => ToBytes (JSONValue a) where
+  toBytes (JSONValue x) = toBytes (encode x)
+
+instance (Extism.PDK.MsgPack.MsgPack a) => FromBytes (MsgPackValue a) where
+  fromBytes mem =
+    let a = fromBytes mem
+     in case a of
+          Left e -> Left e
+          Right x ->
+            case Extism.PDK.MsgPack.decode x of
+              Left e -> Left e
+              Right y -> Right (MsgPackValue y)
+
+instance (Extism.PDK.MsgPack.MsgPack a) => ToBytes (MsgPackValue a) where
+  toBytes (MsgPackValue x) = toBytes $ Extism.PDK.MsgPack.encode x
+
+instance ToBytes Int32 where
+  toBytes i = toBytes $ B.toStrict (runPut (putInt32le i))
+
+instance FromBytes Int32 where
+  fromBytes mem =
+    let bs = fromBytes mem
+     in case bs of
+          Left e -> Left e
+          Right x ->
+            case runGetOrFail getInt32le (B.fromStrict x) of
+              Left (_, _, e) -> Left e
+              Right (_, _, x) -> Right x
+
+instance ToBytes Int64 where
+  toBytes i = toBytes $ B.toStrict (runPut (putInt64le i))
+
+instance FromBytes Int64 where
+  fromBytes mem =
+    let bs = fromBytes mem
+     in case bs of
+          Left e -> Left e
+          Right x ->
+            case runGetOrFail getInt64le (B.fromStrict x) of
+              Left (_, _, e) -> Left e
+              Right (_, _, x) -> Right x
+
+instance ToBytes Word32 where
+  toBytes i = toBytes $ B.toStrict (runPut (putWord32le i))
+
+instance FromBytes Word32 where
+  fromBytes mem =
+    let bs = fromBytes mem
+     in case bs of
+          Left e -> Left e
+          Right x ->
+            case runGetOrFail getWord32le (B.fromStrict x) of
+              Left (_, _, e) -> Left e
+              Right (_, _, x) -> Right x
+
+instance ToBytes Word64 where
+  toBytes i = toBytes $ B.toStrict (runPut (putWord64le i))
+
+instance FromBytes Word64 where
+  fromBytes mem =
+    let bs = fromBytes mem
+     in case bs of
+          Left e -> Left e
+          Right x ->
+            case runGetOrFail getWord64le (B.fromStrict x) of
+              Left (_, _, e) -> Left e
+              Right (_, _, x) -> Right x
+
+instance ToBytes Float where
+  toBytes i = toBytes $ B.toStrict (runPut (putFloatle i))
+
+instance FromBytes Float where
+  fromBytes mem =
+    let bs = fromBytes mem
+     in case bs of
+          Left e -> Left e
+          Right x ->
+            case runGetOrFail getFloatle (B.fromStrict x) of
+              Left (_, _, e) -> Left e
+              Right (_, _, x) -> Right x
+
+instance ToBytes Double where
+  toBytes i = toBytes $ B.toStrict (runPut (putDoublele i))
+
+instance FromBytes Double where
+  fromBytes mem =
+    let bs = fromBytes mem
+     in case bs of
+          Left e -> Left e
+          Right x ->
+            case runGetOrFail getDoublele (B.fromStrict x) of
+              Left (_, _, e) -> Left e
+              Right (_, _, x) -> Right x
diff --git a/src/Extism/PDK/MsgPack.hs b/src/Extism/PDK/MsgPack.hs
index 62176a3..5cc3376 100644
--- a/src/Extism/PDK/MsgPack.hs
+++ b/src/Extism/PDK/MsgPack.hs
@@ -1,93 +1,97 @@
-{-# LANGUAGE TypeSynonymInstances, FlexibleInstances, TypeOperators #-}
-
-module Extism.PDK.MsgPack (
-  module Extism.PDK.MsgPack, 
-  module Data.MessagePack,
-  module Map,
-) where
-
-import GHC.Generics
-import Data.MessagePack
-import Data.Int
-import Data.Word
-import qualified Data.Map.Strict as Map
-
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE TypeOperators #-}
+
+-- |
+-- Provides the ability to use MessagePack for plugin input/output
+module Extism.PDK.MsgPack
+  ( module Extism.PDK.MsgPack,
+    module Data.MessagePack,
+    module Map,
+  )
+where
+
+import Data.Bifunctor (bimap)
 import qualified Data.ByteString as B
 import Data.ByteString.Internal (c2w, w2c)
+import Data.Int
+import qualified Data.Map.Strict as Map
+import Data.MessagePack
 import qualified Data.Serialize as S
+import Data.Word
+import GHC.Generics
 
 class MsgPack a where
   toMsgPack :: a -> Object
   fromMsgPack :: Object -> Maybe a
 
-class GMsgPack f  where
+class GMsgPack f where
   toGMsgPack :: f a -> Object
   fromGMsgPack :: Object -> Maybe (f a)
   fromGMsgPack _ = Nothing
-  
+
 instance GMsgPack U1 where
   toGMsgPack U1 = ObjectNil
   fromGMsgPack ObjectNil = Just U1
-  
-instance (GMsgPack a, GMsgPack b) => GMsgPack ( a :*: b) where
+
+instance (GMsgPack a, GMsgPack b) => GMsgPack (a :*: b) where
   toGMsgPack (x :*: y) = array [toGMsgPack x, toGMsgPack y]
-  -- fromGMsgPack (ObjectArray [a, b]) = Just (a :*: b)
-  
-instance (GMsgPack a, GMsgPack b) => GMsgPack ( a :+: b) where
+
+-- fromGMsgPack (ObjectArray [a, b]) = Just (a :*: b)
+
+instance (GMsgPack a, GMsgPack b) => GMsgPack (a :+: b) where
   toGMsgPack (L1 x) = toGMsgPack x
   toGMsgPack (R1 x) = toGMsgPack x
-  
-instance GMsgPack a => GMsgPack (M1 i c a) where
+
+instance (GMsgPack a) => GMsgPack (M1 i c a) where
   toGMsgPack (M1 x) = toGMsgPack x
-  
+
 instance (MsgPack a) => GMsgPack (K1 i a) where
   toGMsgPack (K1 x) = toMsgPack x
 
 toByteString x = B.pack (Prelude.map c2w x)
+
 fromByteString bs = Prelude.map w2c $ B.unpack bs
 
 instance MsgPack Bool where
-  toMsgPack b = ObjectBool b
+  toMsgPack = ObjectBool
   fromMsgPack (ObjectBool b) = Just b
   fromMsgPack _ = Nothing
-  
 
 instance MsgPack String where
   toMsgPack s = ObjectString (toByteString s)
   fromMsgPack (ObjectString s) = Just (fromByteString s)
   fromMsgPack _ = Nothing
-  
-  
+
 instance MsgPack B.ByteString where
-  toMsgPack s = ObjectBinary s
+  toMsgPack = ObjectBinary
   fromMsgPack (ObjectString s) = Just s
   fromMsgPack (ObjectBinary s) = Just s
   fromMsgPack _ = Nothing
-  
+
 instance MsgPack Int where
   toMsgPack i = ObjectInt (fromIntegral i)
   fromMsgPack (ObjectInt i) = Just (fromIntegral i)
   fromMsgPack _ = Nothing
-    
+
 instance MsgPack Int64 where
-  toMsgPack i = ObjectInt i
+  toMsgPack = ObjectInt
   fromMsgPack (ObjectInt i) = Just i
   fromMsgPack _ = Nothing
-  
+
 instance MsgPack Word where
   toMsgPack w = ObjectUInt (fromIntegral w)
   fromMsgPack (ObjectUInt x) = Just (fromIntegral x)
   fromMsgPack _ = Nothing
-  
+
 instance MsgPack Word64 where
-  toMsgPack w = ObjectUInt w
+  toMsgPack = ObjectUInt
   fromMsgPack (ObjectUInt x) = Just x
   fromMsgPack _ = Nothing
-  
-instance MsgPack a => MsgPack (Maybe a) where
+
+instance (MsgPack a) => MsgPack (Maybe a) where
   toMsgPack Nothing = ObjectNil
   toMsgPack (Just a) = toMsgPack a
-  fromMsgPack bs = fromMsgPack bs
+  fromMsgPack = fromMsgPack
 
 instance MsgPack () where
   toMsgPack () = ObjectNil
@@ -95,53 +99,49 @@ instance MsgPack () where
   fromMsgPack _ = Nothing
 
 instance MsgPack Float where
-  toMsgPack f = ObjectFloat f
+  toMsgPack = ObjectFloat
   fromMsgPack (ObjectFloat f) = Just f
   fromMsgPack _ = Nothing
-  
+
 instance MsgPack Double where
-  toMsgPack d = ObjectDouble d
+  toMsgPack = ObjectDouble
   fromMsgPack (ObjectDouble d) = Just d
   fromMsgPack _ = Nothing
-  
+
 instance MsgPack Object where
   toMsgPack x = x
-  fromMsgPack x = Just x
-  
-
-( .= ) :: MsgPack a => MsgPack b => a -> b -> (Object, Object)
-( .= ) k v = (toMsgPack k, toMsgPack v)
-
-lookup :: MsgPack a => MsgPack b => a -> Object -> Maybe b
-lookup k (ObjectMap map) = 
-  let x = Map.lookup (toMsgPack k) map in
-  case x of
-    Nothing -> Nothing
-    Just x -> fromMsgPack x
+  fromMsgPack = Just
+
+(.=) :: (MsgPack a) => (MsgPack b) => a -> b -> (Object, Object)
+(.=) k v = (toMsgPack k, toMsgPack v)
+
+lookup :: (MsgPack a) => (MsgPack b) => a -> Object -> Maybe b
+lookup k (ObjectMap map) =
+  let x = Map.lookup (toMsgPack k) map
+   in fromMsgPack =<< x
 lookup _ _ = Nothing
 
 set k v (ObjectMap map) =
   ObjectMap $ Map.insert (toMsgPack k) (toMsgPack v) map
 
-( .? ) :: MsgPack a => MsgPack b => Object -> a -> Maybe b
-( .? ) a b = Extism.PDK.MsgPack.lookup b a
+(.?) :: (MsgPack a) => (MsgPack b) => Object -> a -> Maybe b
+(.?) a b = Extism.PDK.MsgPack.lookup b a
 
-object :: MsgPack a => MsgPack b => [(a, b)] -> Object
-object l = ObjectMap (Map.fromList $ map (\(k, v) -> (toMsgPack k, toMsgPack v)) l)
+object :: (MsgPack a) => (MsgPack b) => [(a, b)] -> Object
+object l = ObjectMap (Map.fromList $ map (bimap toMsgPack toMsgPack) l)
 
-array :: MsgPack a => [a] -> Object
+array :: (MsgPack a) => [a] -> Object
 array l = ObjectArray (map toMsgPack l)
 
-encode :: MsgPack a => a -> B.ByteString
+encode :: (MsgPack a) => a -> B.ByteString
 encode x =
-  let y = toMsgPack x in
-  S.encode y
+  let y = toMsgPack x
+   in S.encode y
 
-decode :: MsgPack a => B.ByteString -> Either String a
+decode :: (MsgPack a) => B.ByteString -> Either String a
 decode bs =
   case S.decode bs of
     Right a -> case fromMsgPack a of
-                 Nothing -> Left "Invalid type conversion"
-                 Just x -> Right x
+      Nothing -> Left "Invalid type conversion"
+      Just x -> Right x
     Left s -> Left s
-    
diff --git a/src/Extism/PDK/Util.hs b/src/Extism/PDK/Util.hs
new file mode 100644
index 0000000..3a016c9
--- /dev/null
+++ b/src/Extism/PDK/Util.hs
@@ -0,0 +1,12 @@
+module Extism.PDK.Util where
+
+import qualified Data.ByteString as B
+import Data.ByteString.Internal (c2w, w2c)
+
+-- | Helper function to convert a string to a bytestring
+toByteString :: String -> B.ByteString
+toByteString x = B.pack (Prelude.map c2w x)
+
+-- | Helper function to convert a bytestring to a string
+fromByteString :: B.ByteString -> String
+fromByteString bs = Prelude.map w2c $ B.unpack bs