Haskell Language Pipes Combining Pipes and Network communication
Example
Pipes supports simple binary communication between a client and a server
In this example:
- a client connects and sends a
FirstMessage - the server receives and answers
DoSomething 0 - the client receives and answers
DoNothing - step 2 and 3 are repeated indefinitely
The command data type exchanged over the network:
-- Command.hs
{-# LANGUAGE DeriveGeneric #-}
module Command where
import Data.Binary
import GHC.Generics (Generic)
data Command = FirstMessage
| DoNothing
| DoSomething Int
deriving (Show,Generic)
instance Binary Command
Here, the server waits for a client to connect:
module Server where
import Pipes
import qualified Pipes.Binary as PipesBinary
import qualified Pipes.Network.TCP as PNT
import qualified Command as C
import qualified Pipes.Parse as PP
import qualified Pipes.Prelude as PipesPrelude
pageSize :: Int
pageSize = 4096
-- pure handler, to be used with PipesPrelude.map
pureHandler :: C.Command -> C.Command
pureHandler c = c -- answers the same command that we have receveid
-- impure handler, to be used with PipesPremude.mapM
sideffectHandler :: MonadIO m => C.Command -> m C.Command
sideffectHandler c = do
liftIO $ putStrLn $ "received message = " ++ (show c)
return $ C.DoSomething 0
-- whatever incoming command `c` from the client, answer DoSomething 0
main :: IO ()
main = PNT.serve (PNT.Host "127.0.0.1") "23456" $
\(connectionSocket, remoteAddress) -> do
putStrLn $ "Remote connection from ip = " ++ (show remoteAddress)
_ <- runEffect $ do
let bytesReceiver = PNT.fromSocket connectionSocket pageSize
let commandDecoder = PP.parsed PipesBinary.decode bytesReceiver
commandDecoder >-> PipesPrelude.mapM sideffectHandler >-> for cat PipesBinary.encode >-> PNT.toSocket connectionSocket
-- if we want to use the pureHandler
--commandDecoder >-> PipesPrelude.map pureHandler >-> for cat PipesBinary.Encode >-> PNT.toSocket connectionSocket
return ()
The client connects thus:
module Client where
import Pipes
import qualified Pipes.Binary as PipesBinary
import qualified Pipes.Network.TCP as PNT
import qualified Pipes.Prelude as PipesPrelude
import qualified Pipes.Parse as PP
import qualified Command as C
pageSize :: Int
pageSize = 4096
-- pure handler, to be used with PipesPrelude.amp
pureHandler :: C.Command -> C.Command
pureHandler c = c -- answer the same command received from the server
-- inpure handler, to be used with PipesPremude.mapM
sideffectHandler :: MonadIO m => C.Command -> m C.Command
sideffectHandler c = do
liftIO $ putStrLn $ "Received: " ++ (show c)
return C.DoNothing -- whatever is received from server, answer DoNothing
main :: IO ()
main = PNT.connect ("127.0.0.1") "23456" $
\(connectionSocket, remoteAddress) -> do
putStrLn $ "Connected to distant server ip = " ++ (show remoteAddress)
sendFirstMessage connectionSocket
_ <- runEffect $ do
let bytesReceiver = PNT.fromSocket connectionSocket pageSize
let commandDecoder = PP.parsed PipesBinary.decode bytesReceiver
commandDecoder >-> PipesPrelude.mapM sideffectHandler >-> for cat PipesBinary.encode >-> PNT.toSocket connectionSocket
return ()
sendFirstMessage :: PNT.Socket -> IO ()
sendFirstMessage s = do
_ <- runEffect $ do
let encodedProducer = PipesBinary.encode C.FirstMessage
encodedProducer >-> PNT.toSocket s
return ()
