queryCheck.hs

{-# LANGUAGE OverloadedStrings #-}

import Data.String (fromString)
import System.Environment (getArgs)
import qualified Network.Wai.Handler.Warp as Warp
import qualified Network.Wai as Wai
import qualified Network.HTTP.Types as H

import qualified Data.ByteString as BS -- use for input 
import qualified Data.ByteString.Lazy as LBS -- use for out
import qualified Data.Text as T
import Data.Text.Encoding (decodeLatin1,encodeUtf8)


  
main :: IO ()
main = do
  mainHost:mainPort:_ <- getArgs
  Warp.runSettings (
    Warp.setHost (fromString mainHost) $
    Warp.setPort (read mainPort) $
    Warp.defaultSettings
    ) httpApp



httpApp :: Wai.Application
httpApp req respond = do
  let reqQuery = Wai.queryString req

  let eitherParams = do
        p1 <- case lookupQuery "param1" reqQuery of
          Nothing -> Left "param1 not specified"
          Just p  -> Right p
        p2 <- case lookupQuery "param2" reqQuery of
          Nothing -> Left "param2 not specified"
          Just p  -> Right p
        return (p1,p2)

  case eitherParams of
    Left err ->
      respond $ Wai.responseLBS H.status404 [("Content-Type","text/plain")] $
      LBS.fromStrict $ encodeUtf8 $ T.pack err
    Right (param1,param2) ->
      respond $ Wai.responseLBS H.status200 [("Content-Type","text/plain")] $
      LBS.fromStrict $ encodeUtf8 $ T.pack $ mconcat [param1,",",param2]
    


lookupQuery :: BS.ByteString -> [(BS.ByteString, Maybe BS.ByteString)] -> Maybe String
lookupQuery key query = do
  val <- lookup key query
  val' <- val -- strip Maybe
  return $ T.unpack $ decodeLatin1 val'