app.hs

--cabal install Network-- 

import Network.Socket
import Control.Exception
    
main :: IO()
main = do
    hole <- socket AF_INET Stream defaultProtocol
    bind hole (SockAddrInet 3000 0)
    listen hole 5
    handle_request hole
    sClose hole

-- server
handle_request hole = do
    (conn, _) <- accept hole
    req <- (recv conn 4096) `catch` (\(SomeException e) -> return "eof")
          
    let url = getUrl req
    let resp = router url
    putStrLn (url ++ " " ++  resp)
    send conn resp

    sClose conn
    handle_request hole


-- framework utils
getUrl msg = (words ((lines msg) !! 0)) !! 1

-- application define             
hello = "hello,world"

-- routing config
router :: String -> String
router "/hello" = hello
router "/hello/" = hello
router _ = "404 not found"