module Network.Socket.Free (openFreePort) where
import qualified Network.Socket as N
import qualified Control.Concurrent as C
import qualified Control.Exception as E
import qualified System.IO.Error as Error

-- | Open a TCP socket on a random free port. This is like 'warp''s
--   openFreePort.
openFreePort :: IO (Int, N.Socket)
openFreePort =
  E.bracketOnError (N.socket N.AF_INET N.Stream N.defaultProtocol) N.close
    $ \sock -> do
      N.bind sock $ N.SockAddrInet 0 $ N.tupleToHostAddress (127,0,0,1)
      N.getSocketName sock >>= \case
        N.SockAddrInet port _ -> pure (fromIntegral port, sock)
        addr -> E.throwIO
          $ Error.mkIOError Error.userErrorType
            (  "openFreePort was unable to create socket with a SockAddrInet. "
            <> "Got " <> show addr
            )
            Nothing
            Nothing