Demonstration of Pipes for Web Programming

gistfile1.hs

module Main where

import Prelude hiding (take)
import Control.Pipe
import Control.Pipe.Combinators hiding (take)
import Control.Pipe.Binary
import Data.ByteString hiding (take,cons)
import Data.ByteString.Char8 hiding (take,cons)

type Header = Int

requestSize :: Header -> Int
requestSize = id

main = runPipe (fileReader "input.txt" >+> webserver echoApp >+> fileWriter "output.txt")

echoApp :: Pipe ByteString ByteString IO ()
echoApp = idP

webserver :: Pipe ByteString ByteString IO a -> Pipe ByteString ByteString IO ()
webserver app = do
    (header,rest) <- getHeader
    cons rest >+> (take (requestSize header) >> return ()) >+> (app >> discard)

cons :: (Monad m) => a -> Pipe a a m r
cons x = yield x >> idP

getHeader :: Pipe ByteString ByteString IO (Header,ByteString)
getHeader = await >>= return . maybe (error "couldn't parse header") id . readInt

{- input.txt
13 hello this
is a
test
-}