{-# LANGUAGE GeneralizedNewtypeDeriving #-}
-- |
--
-- A socket could be used indirectly via a 'System.IO.Handle' or a conduit from
-- Michael Snoyman's conduit package.  But doing so presents an encapsulation
-- problem.  Do we allow access to the underlying socket and trust that it wont
-- be used in an unsafe way?  Or do we protect it at the higher level and deny
-- access to various state information?
--
-- The 'SocketLike' class enables the approach that provides a safe wrapper to
-- the underlying socket and gives access to various state information without
-- enabling direct reads or writes.
module Network.SocketLike
    ( SocketLike(..)
    , RestrictedSocket
    , restrictSocket
    , restrictHandleSocket
    -- * Re-exports
    --
    -- | To make the 'SocketLike' methods less awkward to use, the types
    -- 'CUInt', 'SockAddr', and 'PortNumber' are re-exported.
    , CUInt
    , PortNumber
    , SockAddr(..)
    ) where

import Network.Socket
    ( PortNumber
    , SockAddr
    )
import Foreign.C.Types ( CUInt )

import qualified Network.Socket as NS
import System.IO (Handle,hClose,hIsOpen)

-- | A safe (mostly read-only) interface to a 'NS.Socket'.  Note that despite
-- how this class is named, it provides no access to typical 'NS.Socket' uses
-- like sending or receiving network packets.
class SocketLike sock where
    -- | See 'NS.getSocketName'
    getSocketName :: sock -> IO SockAddr
    -- | See 'NS.getPeerName'
    getPeerName   :: sock -> IO SockAddr
    -- | See 'NS.getPeerCred'
    getPeerCred   :: sock -> IO (CUInt, CUInt, CUInt)
    -- | See 'NS.socketPort'
    socketPort    :: sock -> IO PortNumber
    -- | See 'NS.sIsConnected'
    --
    -- __Warning__: Don't rely on this method if it's possible the socket was
    -- converted into a 'Handle'.
    sIsConnected  :: sock -> IO Bool
    -- | See 'NS.sIsBound'
    sIsBound      :: sock -> IO Bool
    -- | See 'NS.sIsListening'
    sIsListening  :: sock -> IO Bool
    -- | See 'NS.sIsReadable'
    sIsReadable   :: sock -> IO Bool
    -- | See 'NS.sIsWritable'
    sIsWritable   :: sock -> IO Bool

    -- | This is the only exposed write-access method to the
    -- underlying state.  Usually implemented by 'NS.close'
    sClose        :: sock -> IO ()

instance SocketLike NS.Socket where
    getSocketName = NS.getSocketName
    getPeerName   = NS.getPeerName
    getPeerCred   = NS.getPeerCred
    socketPort    = NS.socketPort
    sIsConnected  = NS.sIsConnected -- warning: this is always False if the socket
                                    --          was converted to a Handle
    sIsBound      = NS.sIsBound
    sIsListening  = NS.sIsListening
    sIsReadable   = NS.sIsReadable
    sIsWritable   = NS.sIsWritable

    sClose        = NS.sClose

-- | An encapsulated socket.  Data reads and writes are not possible.
data RestrictedSocket = Restricted (Maybe Handle) NS.Socket deriving Show

instance SocketLike RestrictedSocket where
    getSocketName (Restricted mb sock) = NS.getSocketName sock
    getPeerName   (Restricted mb sock) = NS.getPeerName sock
    getPeerCred   (Restricted mb sock) = NS.getPeerCred sock
    socketPort    (Restricted mb sock) = NS.socketPort sock
    sIsConnected  (Restricted mb sock) = maybe (NS.sIsConnected sock) (hIsOpen) mb
    sIsBound      (Restricted mb sock) = NS.sIsBound sock
    sIsListening  (Restricted mb sock) = NS.sIsListening sock
    sIsReadable   (Restricted mb sock) = NS.sIsReadable sock
    sIsWritable   (Restricted mb sock) = NS.sIsWritable sock
    sClose        (Restricted mb sock) = maybe (NS.sClose sock) (\h -> hClose h >> NS.sClose sock) mb

-- | Create a 'RestrictedSocket' that explicitly disallows sending or
-- receiving data.
restrictSocket :: NS.Socket -> RestrictedSocket
restrictSocket socket = Restricted Nothing socket

-- | Build a 'RestrictedSocket' for which 'sClose' will close the given
-- 'Handle'.  It is intended that this 'Handle' was obtained via
-- 'NS.socketToHandle'.
restrictHandleSocket :: Handle ->  NS.Socket -> RestrictedSocket
restrictHandleSocket h socket = Restricted (Just h) socket