preserve handle buffering

silently.cabal

@@ -56,6 +56,7 @@ test-suite spec-specific
     , silently
     , directory
     , nanospec
+    , temporary
 
 -- This tests the generic implementation, that should work on all platforms.
 test-suite spec-generic
@@ -76,3 +77,4 @@ test-suite spec-generic
     , deepseq
     , directory
     , nanospec
+    , temporary

src/System/IO/Silently.hs

@@ -104,8 +104,14 @@ hCapture handles action = do
       go hs = goBracket go tmpHandle hs
 
 goBracket :: ([Handle] -> IO a) -> Handle -> [Handle] -> IO a
-goBracket go tmpHandle (h:hs) = E.bracket (do old <- hDuplicate h
-                                              hDuplicateTo tmpHandle h
-                                              return old)
-                                        (\old -> hDuplicateTo old h >> hClose old)
-                                        (\_   -> go hs)
+goBracket go tmpHandle (h:hs) = do
+  buffering <- hGetBuffering h
+  let redirect = do
+        old <- hDuplicate h
+        hDuplicateTo tmpHandle h
+        return old
+      restore old = do
+        hDuplicateTo old h
+        hSetBuffering h buffering
+        hClose old
+  E.bracket redirect restore (\_ -> go hs)

test/Spec.hs

@@ -4,8 +4,10 @@ import           Test.Hspec
 import           System.IO
 import           System.IO.Silently
 import           System.Directory
+import           System.IO.Temp
 
 import           Control.Exception
+import           Control.Monad
 
 main :: IO ()
 main = hspec spec
@@ -26,3 +28,11 @@ spec = do
   describe "capture" $ do
     it "captures stdout" $ do
       capture (putStr "foo" >> return 23) `shouldReturn` ("foo", 23 :: Int)
+
+  describe "hCapture" $ do
+    forM_ [NoBuffering, LineBuffering, BlockBuffering Nothing] $ \buffering -> do
+      it ("preserves " ++ show buffering) $ do
+        withSystemTempFile "silently" $ \_file h -> do
+          hSetBuffering h buffering
+          _ <- hCapture [h] (return ())
+          hGetBuffering h `shouldReturn` buffering