systemd-socket-activation-1: src/SocketActivation/GetFileDescriptors.hs

module SocketActivation.GetFileDescriptors where

import           Control.Monad             (Monad (return, (>>=)))
import           Data.Either               (Either)
import           Data.Function             ((.))
import           Data.Int                  (Int)
import           Data.List                 (take)
import           Numeric.Natural           (Natural)
import           Prelude                   (fromIntegral)
import           System.IO                 (IO)

import           SocketActivation.Concepts
import           SocketActivation.Env
import           SocketActivation.IO

-- | Get a list of file descriptors for the sockets.
getFileDescriptorList :: IO (Either Error [Fd])
getFileDescriptorList = run (getCount >>= enumerateFds)
  where
    getCount = IO' (getEnv' @Count)
    enumerateFds = return . fds

fds :: Count -> [Fd]
fds n = take (convert n) [firstFd ..]
  where
    convert = (fromIntegral :: Natural -> Int) . countNat
    firstFd = Fd 3