Don't just fail if hGetBufSome is used on a non-FD: fall back on the slow path instead

1 files changed, 5 insertions, 8 deletions

diff --git a/libraries/base/GHC/IO/Handle/Text.hs b/libraries/base/GHC/IO/Handle/Text.hs
index 3eedae65de..14587729c5 100644
--- a/libraries/base/GHC/IO/Handle/Text.hs
+++ b/libraries/base/GHC/IO/Handle/Text.hs
@@ -878,9 +878,9 @@ hGetBufSome h ptr count
          flushCharReadBuffer h_
          buf@Buffer{ bufSize=sz } <- readIORef haByteBuffer
          if isEmptyBuffer buf
-            then if count > sz  -- large read?
-                    then do RawIO.read (haFD h_) (castPtr ptr) count
-                    else do (r,buf') <- Buffered.fillReadBuffer haDevice buf
+            then case count > sz of  -- large read? optimize it with a little special case:
+                    True | Just fd <- haFD h_ -> do RawIO.read fd (castPtr ptr) count
+                    _ -> do (r,buf') <- Buffered.fillReadBuffer haDevice buf
                             if r == 0
                                then return 0
                                else do writeIORef haByteBuffer buf'
@@ -892,11 +892,8 @@ hGetBufSome h ptr count
               let count' = min count (bufferElems buf)
               in bufReadNBNonEmpty h_ buf (castPtr ptr) 0 count'
 
-haFD :: Handle__ -> FD
-haFD h_@Handle__{..} =
-   case cast haDevice of
-             Nothing -> error "not an FD"
-             Just fd -> fd
+haFD :: Handle__ -> Maybe FD
+haFD h_@Handle__{..} = cast haDevice
 
 -- | 'hGetBufNonBlocking' @hdl buf count@ reads data from the handle @hdl@
 -- into the buffer @buf@ until either EOF is reached, or