{-# language BangPatterns #-}
{-# language DuplicateRecordFields #-}
{-# language PatternSynonyms #-}
{-# language LambdaCase #-}
{-# language NamedFieldPuns #-}

module Network.Unexceptional.MutableBytes
  ( receive
  ) where

import Control.Exception (throwIO)
import Data.Bytes.Types (MutableBytes(MutableBytes))
import Data.Primitive (MutableByteArray)
import Foreign.C.Error (Errno)
import Foreign.C.Error.Pattern (pattern EWOULDBLOCK,pattern EAGAIN)
import GHC.Conc (threadWaitRead)
import GHC.Exts (RealWorld)
import Network.Socket (Socket)
import System.Posix.Types (Fd(Fd))

import qualified Network.Unexceptional.Types as Types
import qualified Data.Bytes.Types
import qualified Linux.Socket as X
import qualified Network.Socket as S
import qualified Posix.Socket as X

-- | Receive bytes from a socket. Receives at most N bytes, where N
-- is the size of the buffer. Returns the number of bytes that were
-- actually received.
receive ::
     Socket
  -> MutableBytes RealWorld -- ^ Slice of a buffer
  -> IO (Either Errno Int)
receive s MutableBytes{array,offset,length=len} =
  if len > 0
    then S.withFdSocket s $ \fd ->
      -- We attempt the first receive without testing if the socket is
      -- ready for reads.
      receiveLoop (Fd fd) array offset len
    else throwIO Types.NonpositiveReceptionSize

-- Does not wait for file descriptor to be ready. Only performs
-- a single successful recv syscall
receiveLoop :: Fd -> MutableByteArray RealWorld -> Int -> Int -> IO (Either Errno Int)
receiveLoop !fd !arr !off !len =
  X.uninterruptibleReceiveMutableByteArray fd arr off (fromIntegral len) X.dontWait >>= \case
    Left e -> if e == EAGAIN || e == EWOULDBLOCK
      then do
        threadWaitRead fd
        receiveLoop fd arr off len
      else pure (Left e)
    Right recvSzC ->
      let recvSz = fromIntegral recvSzC :: Int
       in case compare recvSz len of
            GT -> throwIO Types.ReceivedTooManyBytes
            _ -> pure (Right recvSz)