Fixes #35: fd{Read,Write} with ByteString payload

System/Posix/IO.hsc

@@ -63,6 +63,13 @@ module System.Posix.IO (
 
   ) where
 
+import Foreign ( allocaBytes, castPtr )
+import Foreign.C ( peekCStringLen, withCStringLen )
+
+import GHC.IO.Exception ( IOErrorType(EOF) )
+
+import System.IO.Error ( ioeSetErrorString, mkIOError )
+
 import System.Posix.Types
 import System.Posix.Error
 import System.Posix.IO.Common
@@ -88,9 +95,9 @@ openFdAt :: Maybe Fd -- ^ Optional directory file descriptor
          -> OpenFileFlags -- ^ Append, exclusive, truncate, etc.
          -> IO Fd
 openFdAt fdMay name how flags =
-   withFilePath name $ \str ->
-     throwErrnoPathIfMinus1Retry "openFdAt" name $
-       openat_ fdMay str how flags
+  withFilePath name $ \str ->
+    throwErrnoPathIfMinus1Retry "openFdAt" name $
+      openat_ fdMay str how flags
 
 -- |Create and open this file in WriteOnly mode.  A special case of
 -- 'openFd'.  See 'System.Posix.Files' for information on how to use
@@ -111,3 +118,25 @@ createFileAt :: Maybe Fd -- ^ Optional directory file descriptor
              -> IO Fd
 createFileAt fdMay name mode
   = openFdAt fdMay name WriteOnly defaultFileFlags{ trunc=True, creat=(Just mode) }
+
+-- | Read data from an 'Fd' and convert it to a 'String' using the locale encoding.
+-- Throws an exception if this is an invalid descriptor, or EOF has been
+-- reached.
+fdRead :: Fd
+       -> ByteCount -- ^How many bytes to read
+       -> IO (String, ByteCount) -- ^The bytes read, how many bytes were read.
+fdRead _fd 0 = return ("", 0)
+fdRead fd nbytes =
+  allocaBytes (fromIntegral nbytes) $ \ buf -> do
+  rc <- fdReadBuf fd buf nbytes
+  case rc of
+    0 -> ioError (ioeSetErrorString (mkIOError EOF "fdRead" Nothing Nothing) "EOF")
+    n -> do
+      s <- peekCStringLen (castPtr buf, fromIntegral n)
+      return (s, n)
+
+-- | Write a 'String' to an 'Fd' using the locale encoding.
+fdWrite :: Fd -> String -> IO ByteCount
+fdWrite fd str =
+  withCStringLen str $ \ (buf,len) ->
+    fdWriteBuf fd (castPtr buf) (fromIntegral len)

System/Posix/IO/ByteString.hsc

@@ -1,4 +1,4 @@
-{-# LANGUAGE Safe #-}
+{-# LANGUAGE Trustworthy #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  System.Posix.IO.ByteString
@@ -63,6 +63,16 @@ module System.Posix.IO.ByteString (
 
   ) where
 
+import Data.ByteString ( ByteString, empty )
+import qualified Data.ByteString.Internal as BI
+import qualified Data.ByteString.Unsafe as BU
+
+import Foreign ( castPtr )
+
+import GHC.IO.Exception ( IOErrorType(EOF) )
+
+import System.IO.Error ( ioeSetErrorString, mkIOError )
+
 import System.Posix.Types
 import System.Posix.IO.Common
 
@@ -88,9 +98,9 @@ openFdAt :: Maybe Fd -- ^ Optional directory file descriptor
          -> OpenFileFlags -- ^ Append, exclusive, truncate, etc.
          -> IO Fd
 openFdAt fdMay name how flags =
-   withFilePath name $ \str ->
-     throwErrnoPathIfMinus1Retry "openFdAt" name $
-       openat_ fdMay str how flags
+  withFilePath name $ \str ->
+    throwErrnoPathIfMinus1Retry "openFdAt" name $
+      openat_ fdMay str how flags
 
 -- |Create and open this file in WriteOnly mode.  A special case of
 -- 'openFd'.  See 'System.Posix.Files' for information on how to use
@@ -111,3 +121,23 @@ createFileAt :: Maybe Fd -- ^ Optional directory file descriptor
              -> IO Fd
 createFileAt fdMay name mode
   = openFdAt fdMay name WriteOnly defaultFileFlags{ trunc=True, creat=(Just mode) }
+
+-- | Read data from an 'Fd' and return it as a 'ByteString'.
+-- Throws an exception if this is an invalid descriptor, or EOF has been
+-- reached.
+fdRead :: Fd
+       -> ByteCount -- ^How many bytes to read
+       -> IO ByteString -- ^The bytes read
+fdRead _fd 0 = return empty
+fdRead fd nbytes =
+  BI.createUptoN (fromIntegral nbytes) $ \ buf -> do
+  rc <- fdReadBuf fd buf nbytes
+  case rc of
+    0 -> ioError (ioeSetErrorString (mkIOError EOF "fdRead" Nothing Nothing) "EOF")
+    n -> return (fromIntegral n)
+
+-- | Write a 'ByteString' to an 'Fd'.
+fdWrite :: Fd -> ByteString -> IO ByteCount
+fdWrite fd bs =
+  BU.unsafeUseAsCStringLen bs $ \ (buf,len) ->
+    fdWriteBuf fd (castPtr buf) (fromIntegral len)

System/Posix/IO/Common.hsc

@@ -31,7 +31,6 @@ module System.Posix.IO.Common (
     -- |Programmers using the 'fdRead' and 'fdWrite' API should be aware that
     -- EAGAIN exceptions may occur for non-blocking IO!
 
-    fdRead, fdWrite,
     fdReadBuf, fdWriteBuf,
 
     -- ** Seeking
@@ -447,23 +446,7 @@ waitToSetLock (Fd fd) lock = do
 #endif // HAVE_F_GETLK
 
 -- -----------------------------------------------------------------------------
--- fd{Read,Write}
-
--- | Read data from an 'Fd' and convert it to a 'String' using the locale encoding.
--- Throws an exception if this is an invalid descriptor, or EOF has been
--- reached.
-fdRead :: Fd
-       -> ByteCount -- ^How many bytes to read
-       -> IO (String, ByteCount) -- ^The bytes read, how many bytes were read.
-fdRead _fd 0 = return ("", 0)
-fdRead fd nbytes = do
-    allocaBytes (fromIntegral nbytes) $ \ buf -> do
-    rc <- fdReadBuf fd buf nbytes
-    case rc of
-      0 -> ioError (ioeSetErrorString (mkIOError EOF "fdRead" Nothing Nothing) "EOF")
-      n -> do
-       s <- peekCStringLen (castPtr buf, fromIntegral n)
-       return (s, n)
+-- fd{Read,Write}Buf
 
 -- | Read data from an 'Fd' into memory.  This is exactly equivalent
 -- to the POSIX @read@ function.
@@ -480,12 +463,6 @@ fdReadBuf fd buf nbytes =
 foreign import ccall safe "read"
    c_safe_read :: CInt -> Ptr CChar -> CSize -> IO CSsize
 
--- | Write a 'String' to an 'Fd' using the locale encoding.
-fdWrite :: Fd -> String -> IO ByteCount
-fdWrite fd str =
-  withCStringLen str $ \ (buf,len) ->
-    fdWriteBuf fd (castPtr buf) (fromIntegral len)
-
 -- | Write data from memory to an 'Fd'.  This is exactly equivalent
 -- to the POSIX @write@ function.
 fdWriteBuf :: Fd