[Haskell-cafe] IO in HApps handler ?

19 Aug 2007

      Subject: IO in HApps handler ?
I am trying to add a handler that would run an external command in
HApps 0.8.8, and I got a type issue I do not know how to get around..

can we have IO in a handler ?

testcmdpost.hs:52:8:
    Couldn't match expected type `Ev st Request'
           against inferred type `IO'
      Expected type: ServerPart (Ev st Request) Request IO Result
      Inferred type: ServerPart IO Request im Result
    In the expression:
          (h ["xxx"] GET)
        $ (ok
         $ (\ () ()
                -> do (MySt val) <- get
                      runCommand "ls" ["."]
                      respond (show "dfdf")))

here is the handler iI am adding :

  ,h ["xxx"] GET $ ok $ \() () -> do   (MySt val) <- get; runCommand
"ls" ["."]; respond (show  "dfdf" )

in there :
import HAppS.Util.Common...
...
main :: IO ()
main = stdHTTP
       [debugFilter -- we want to see debug messages in the console
       ,h [""] GET $ ok $ val "GETting root hello"
  --     ,h (Prefix ["s"]) GET $ respIO $ fileServe staticPath
        , hs (Prefix ["s"]) GET $ basicFileServe staticPath -- 0.8.8
       -- /val shows us the current value
       ,h ["val"] GET $ ok $ \() () -> do (MySt val) <- get; respond (show val)
       -- /set with the POST data "val"=56 would set the value to 56
       ,h ["xxx"] GET $ ok $ \() () -> do   (MySt val) <- get;
runCommand "ls" ["."]; respond (show  "dfdf" )
       ,h ["set"] POST $ ok $ \() newVal -> do put newVal; respond
("New value is " ++ show newVal)
       -- The first one is FromReqURI and the second one is FromMessage
       -- The cryptic comment about is referring to the arguments () and newVal
       -- to the method. The type of newVal being MyState is what
       -- invokes our custom FromMessage instance above.
       ]

this is the runcommand from
HAppS.Util.Common , not from

defined as
-- | Run an external command. Upon failure print status
--   to stderr.
runCommand :: String -> [String] -> IO ()
runCommand cmd args = do
    (_, outP, errP, pid) <- runInteractiveProcess cmd args Nothing Nothing
    let pGetContents h = do mv <- newEmptyMVar
                            let put [] = putMVar mv []
                                put xs = last xs `seq` putMVar mv xs
                            forkIO (hGetContents h >>= put)
                            takeMVar mv
    os <- pGetContents outP
    es <- pGetContents errP
    ec <- waitForProcess pid
    case ec of
      ExitSuccess   -> return ()
      ExitFailure e ->
          do hPutStrLn stderr ("Running process "++unwords
(cmd:args)++" FAILED ("++show e++")")
             hPutStrLn stderr os
             hPutStrLn stderr es
             hPutStrLn stderr ("Raising error...")
             fail "Running external command failed"

[Haskell-cafe] IO in HApps handler ?

Luc TAESCH