Network/StreamDebugger.hs

-----------------------------------------------------------------------------
-- |
-- Module : Network.StreamDebugger
-- Copyright : See LICENSE file
-- License : BSD
--
-- Maintainer : Ganesh Sittampalam <http@projects.haskell.org>
-- Stability : experimental
-- Portability : non-portable (not tested)
--
-- Implements debugging of @Stream@s. Originally part of Gray's\/Bringert's
-- HTTP module.
--
-- * Changes by Robin Bate Boerop <robin@bateboerop.name>:
-- - Created. Made minor formatting changes.
-- 
-----------------------------------------------------------------------------
module Network.StreamDebugger
 ( StreamDebugger
 , debugStream
 , debugByteStream
 ) where

import Network.Stream (Stream(..))
import System.IO
 ( Handle, hFlush, hPutStrLn, IOMode(AppendMode), hClose, openFile,
 hSetBuffering, BufferMode(NoBuffering)
 )
import Network.TCP ( HandleStream, HStream, 
 		 StreamHooks(..), setStreamHooks, getStreamHooks )

-- | Allows stream logging. Refer to 'debugStream' below.
data StreamDebugger x
 = Dbg Handle x

instance (Stream x) => Stream (StreamDebugger x) where
 readBlock (Dbg h x) n =
 do val <- readBlock x n
 hPutStrLn h ("--readBlock " ++ show n)
	 hPutStrLn h (show val)
 return val
 readLine (Dbg h x) =
 do val <- readLine x
 hPutStrLn h ("--readLine")
	 hPutStrLn h (show val)
 return val
 writeBlock (Dbg h x) str =
 do val <- writeBlock x str
 hPutStrLn h ("--writeBlock" ++ show str)
	 hPutStrLn h (show val)
 return val
 close (Dbg h x) =
 do hPutStrLn h "--closing..."
 hFlush h
 close x
 hPutStrLn h "--closed."
 hClose h
 closeOnEnd (Dbg h x) f =
 do hPutStrLn h ("--close-on-end.." ++ show f)
 hFlush h 
 closeOnEnd x f

-- | Wraps a stream with logging I\/O.
-- The first argument is a filename which is opened in @AppendMode@.
debugStream :: (Stream a) => FilePath -> a -> IO (StreamDebugger a)
debugStream file stream = 
 do h <- openFile file AppendMode
 hPutStrLn h ("File \"" ++ file ++ "\" opened for appending.")
 return (Dbg h stream)

debugByteStream :: HStream ty => FilePath -> HandleStream ty -> IO (HandleStream ty)
debugByteStream file stream = do
 sh <- getStreamHooks stream 
 case sh of
 Just h 
 | hook_name h == file -> return stream -- reuse the stream hooks.
 _ -> do
 h <- openFile file AppendMode
 hSetBuffering h NoBuffering
 hPutStrLn h ("File \"" ++ file ++ "\" opened for appending.")
 setStreamHooks stream (debugStreamHooks h file)
 return stream

debugStreamHooks :: HStream ty => Handle -> String -> StreamHooks ty
debugStreamHooks h nm = 
 StreamHooks
 { hook_readBlock = \ toStr n val -> do
 let eval = case val of { Left e -> Left e ; Right v -> Right $ toStr v}
 hPutStrLn h ("--readBlock " ++ show n)
 hPutStrLn h (either show show eval)
 , hook_readLine = \ toStr val -> do
	 let eval = case val of { Left e -> Left e ; Right v -> Right $ toStr v}
 hPutStrLn h ("--readLine")
	 hPutStrLn h (either show show eval)
 , hook_writeBlock = \ toStr str val -> do
 hPutStrLn h ("--writeBlock " ++ show val)
	 hPutStrLn h (toStr str)
 , hook_close = do
 hPutStrLn h "--closing..."
 hFlush h
 hClose h
 , hook_name = nm
 }