Socket.hsc

module System.Socket.Internal.Socket (
    Socket (..)
  , GetSocketOption (..)
  , unsafeGetSocketOption
  , SetSocketOption (..)
  , unsafeSetSocketOption
  , Error (..)
  , ReuseAddress (..)
  ) where

import Control.Concurrent.MVar
import Control.Exception
import Control.Monad
import Control.Applicative

import Foreign.Ptr
import Foreign.Storable
import Foreign.C.Types
import Foreign.Marshal.Alloc
import System.Posix.Types

import System.Socket.Internal.Platform
import System.Socket.Internal.Exception

#include "hs_socket.h"

-- | A generic socket type. Also see `socket` for details.
--
--   The socket is just an `Control.Concurrent.MVar.MVar`-wrapped file descriptor.
--   It is exposed in order to make this library easily extensible, but it is
--   usually not necessary nor advised to work directly on the file descriptor.
--   If you do, the following rules must be obeyed:
--
--   - Make sure not to deadlock. Use `Control.Concurrent.MVar.withMVar` or similar.
--   - The lock __must not__ be held during a blocking call. This would make it impossible
--     to send and receive simultaneously or to close the socket.
--   - The lock __must__ be held when calling operations that use the file descriptor.
--     Otherwise the socket might get closed or even reused by another
--     thread/capability which might result in reading from or writing
--     totally different connection. This is a security nightmare!
--   - The socket is non-blocking and all the code relies on that assumption.
--     You need to use GHC's eventing mechanism primitives to block until
--     something happens. The former rules forbid to use `GHC.Conc.threadWaitRead` as it
--     does not seperate between registering the file descriptor (for which
--     the lock __must__ be held) and the actual waiting (for which you must
--     __not__ hold the lock).
--     Also see [this](https://mail.haskell.org/pipermail/haskell-cafe/2014-September/115823.html)
--     thread and read the library code to see how the problem is currently circumvented.
newtype Socket f t p
      = Socket (MVar Fd)

class GetSocketOption o where
  getSocketOption :: Socket f t p -> IO o

class SetSocketOption o where
  setSocketOption :: Socket f t p -> o -> IO ()

-- | @SO_ERROR@
data Error
   = Error SocketException
   deriving (Eq, Ord, Show)

instance GetSocketOption Error where
  getSocketOption s =
    Error . SocketException <$> unsafeGetSocketOption s (#const SOL_SOCKET) (#const SO_ERROR)

-- | @SO_REUSEADDR@
data ReuseAddress
   = ReuseAddress Bool
   deriving (Eq, Ord, Show)

instance GetSocketOption ReuseAddress where
  getSocketOption s =
    ReuseAddress . ((/=0) :: CInt -> Bool) <$> unsafeGetSocketOption s (#const SOL_SOCKET) (#const SO_REUSEADDR)

instance SetSocketOption ReuseAddress where
  setSocketOption s (ReuseAddress o) =
    unsafeSetSocketOption s (#const SOL_SOCKET) (#const SO_REUSEADDR) (if o then 1 else 0 :: CInt)

-------------------------------------------------------------------------------
-- Unsafe helpers
-------------------------------------------------------------------------------

unsafeSetSocketOption :: Storable a => Socket f t p -> CInt -> CInt -> a -> IO ()
unsafeSetSocketOption (Socket mfd) level name value = do
  withMVar mfd $ \fd->
    alloca $ \vPtr-> do
        poke vPtr value
        i <- c_setsockopt fd level name 
                          vPtr
                          (fromIntegral $ sizeOf value)
        when (i < 0) $ do
          c_get_last_socket_error >>= throwIO

unsafeGetSocketOption :: Storable a => Socket f t p -> CInt -> CInt -> IO a
unsafeGetSocketOption (Socket mfd) level name = do
  u <- return undefined
  withMVar mfd $ \fd->
    alloca $ \vPtr-> do
      alloca $ \lPtr-> do
        poke lPtr (fromIntegral $ sizeOf u)
        i <- c_getsockopt fd level name vPtr (lPtr :: Ptr CInt)
        if i < 0 then do
          c_get_last_socket_error >>= throwIO
        else do
          x <- peek vPtr
          return (x `asTypeOf` u)