{-# LANGUAGE ForeignFunctionInterface #-}

module Network.Sendfile.BSD (sendfile) where

import Control.Concurrent
import Control.Exception
import Control.Monad
import Foreign.C.Error (eAGAIN, eINTR, getErrno, throwErrno)
import Foreign.C.Types (CInt, CSize)
import Foreign.Marshal (alloca)
import Foreign.Ptr (Ptr, nullPtr)
import Foreign.Storable (peek)
import Network.Sendfile.Types
import Network.Socket
import System.Posix.IO
import System.Posix.Types (Fd(..), COff)

{-|
   Simple binding for sendfile() of BSD.

   - Used system calls: open(), sendfile(), and close().

   The fourth action argument is called when a file is sent as chunks.
   Chucking is inevitable if the socket is non-blocking (this is the
   default) and the file is large. The action is called after a chunk
   is sent and bofore waiting the socket to be ready for writing.
-}
sendfile :: Socket -> FilePath -> FileRange -> IO () -> IO ()
sendfile sock path range hook = bracket
    (openFd path ReadOnly Nothing defaultFileFlags)
    closeFd
    sendfile'
  where
    dst = Fd $ fdSocket sock
    sendfile' fd = alloca $ \lenp ->
        case range of
            EntireFile -> sendEntire dst fd 0 lenp hook
            PartOfFile off len -> do
                let off' = fromInteger off
                    len' = fromInteger len
                sendPart dst fd off' len' lenp hook

sendEntire :: Fd -> Fd -> COff -> Ptr COff -> IO () -> IO ()
sendEntire dst src off lenp hook = do
    rc <- c_sendfile src dst off 0 lenp
    when (rc /= 0) $ do
        errno <- getErrno
        if errno `elem` [eAGAIN, eINTR]
            then do
              sent <- peek lenp
              hook
              threadWaitWrite dst
              sendEntire dst src (off + sent) lenp hook
            else throwErrno "Network.SendFile.BSD.sendEntire"

sendPart :: Fd -> Fd -> COff -> CSize -> Ptr COff -> IO () -> IO ()
sendPart dst src off len lenp hook = do
    rc <- c_sendfile src dst off len lenp
    when (rc /= 0) $ do
        errno <- getErrno
        if errno `elem` [eAGAIN, eINTR]
            then do
                sent <- peek lenp
                let off' = off + sent
                    len' = len - fromIntegral sent
                hook
                threadWaitWrite dst
                sendPart dst src off' len' lenp hook
            else throwErrno "Network.SendFile.BSD.sendPart"

c_sendfile :: Fd -> Fd -> COff -> CSize -> Ptr COff -> IO CInt
c_sendfile fd s offset len lenp = c_sendfile' fd s offset len nullPtr lenp 0

foreign import ccall unsafe "sys/uio.h sendfile" c_sendfile'
    :: Fd -> Fd -> COff -> CSize -> Ptr () -> Ptr COff -> CInt -> IO CInt