Transport.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE TypeApplications #-}

-- |
-- Module: Capnp.Rpc.Transport
-- Description: Support for exchanging messages with remote vats.
--
-- This module provides a 'Transport' type, which provides operations
-- used to transmit messages between vats in the RPC protocol.
module Capnp.Rpc.Transport
  ( Transport (..),
    handleTransport,
    socketTransport,
    tracingTransport,
    TraceConfig (..),
  )
where

import Capnp.Bits (WordCount)
import Capnp.Classes (Parsed)
import Capnp.Convert (msgToParsed)
import qualified Capnp.Gen.Capnp.Rpc as R
import Capnp.IO (hGetMsg, hPutMsg, sGetMsg, sPutMsg)
import Capnp.Message (Message, Mutability (Const))
import Capnp.TraversalLimit (evalLimitT)
import Data.Default (def)
import Network.Socket (Socket)
import System.IO (Handle)
import Text.Show.Pretty (ppShow)
import Prelude hiding (log)

-- | A @'Transport'@ handles transmitting RPC messages.
data Transport = Transport
  { -- | Send a message
    sendMsg :: Message 'Const -> IO (),
    -- | Receive a message
    recvMsg :: IO (Message 'Const)
  }

-- | @'handleTransport' handle limit@ is a transport which reads and writes
-- messages from/to @handle@. It uses @limit@ as the traversal limit when
-- reading messages and decoding.
handleTransport :: Handle -> WordCount -> Transport
handleTransport handle limit =
  Transport
    { sendMsg = hPutMsg handle,
      recvMsg = hGetMsg handle limit
    }

-- | @'socketTransport' socket limit@ is a transport which reads and writes
-- messages to/from a socket. It uses @limit@ as the traversal limit when
-- reading messages and decoing.
socketTransport :: Socket -> WordCount -> Transport
socketTransport socket limit =
  Transport
    { sendMsg = sPutMsg socket,
      recvMsg = sGetMsg socket limit
    }

data TraceConfig = TraceConfig
  { log :: String -> IO (),
    showPayloads :: !Bool
  }

-- | @'tracingTransport' log trans@ wraps another transport @trans@, loging
-- messages when they are sent or received (using the @log@ function). This
-- can be useful for debugging.
tracingTransport :: TraceConfig -> Transport -> Transport
tracingTransport tcfg trans =
  Transport
    { sendMsg = \msg -> do
        rpcMsg <- evalLimitT maxBound $ msgToParsed @R.Message msg
        log tcfg $ "sending message: " ++ ppShow (editForTrace tcfg rpcMsg)
        sendMsg trans msg,
      recvMsg = do
        msg <- recvMsg trans
        rpcMsg <- evalLimitT maxBound $ msgToParsed @R.Message msg
        log tcfg $ "received message: " ++ ppShow (editForTrace tcfg rpcMsg)
        pure msg
    }

editForTrace :: TraceConfig -> Parsed R.Message -> Parsed R.Message
editForTrace tcfg rpcMsg =
  if showPayloads tcfg
    then rpcMsg
    else
      ( case rpcMsg of
          R.Message (R.Message'call call) ->
            R.Message $
              R.Message'call $
                call {R.params = def}
          R.Message (R.Message'return R.Return {union' = R.Return'results _, ..}) ->
            R.Message $
              R.Message'return $
                R.Return {R.union' = R.Return'results def, ..}
          _ ->
            rpcMsg
      )