> {-# LANGUAGE OverloadedStrings #-}
> module Main where
In this example we will take a look at 'IOWorker' and how to use it in
your programs. We will create a simple worker that would echo back to
us whatever we sent it.
Let's start by importing some libraries
> import qualified Data.ByteString as BS
> import Data.Default (def)
> import Data.Monoid ((<>))
> import System.IO (BufferMode (..), Handle, hClose,
> hSetBuffering, stdin)
>
> import System.Restricted.Worker
Let's take a look at 'startIOWorker' function:
```haskell
startIOWorker :: String -- ^ Name
-> LimitSettings -- ^ Restrictions
-> FilePath -- ^ UNIX socket
-> (Handle -> IO ()) -- ^ Callback
-> IO (Worker IOWorker, RestartWorker IO IOWorker)
```
it takes a worker name, a UNIX socket filepath, callback. It returns
the worker itself together with the restarting function.
Firstly, let's implement our callback:
> echoHandler :: Handle -> IO ()
> echoHandler h = do
> hSetBuffering h LineBuffering
> s <- BS.hGetLine h
> BS.putStr $ "Got: " <> s <> "\n"
> BS.hPutStrLn h s
> hClose h
we are not doing anything fancy here, just getting one line of text,
printing it to stdout and sending it back.
Now we are going to write the main loop function that would take care
of restarting the worker:
> loop :: (Worker IOWorker, RestartWorker IO IOWorker) -> IO ()
> loop (w, restart) = do
> putStrLn "Press <ENTER> to restart the worker"
> _ <- getChar
> w' <- restart w
> loop (w', restart)
and a main function:
> main :: IO ()
> main = do
> hSetBuffering stdin NoBuffering
> loop =<< startIOWorker "Testworker" def "/tmp/1.sock" echoHandler
> return ()
We can test it:
```
(In one shell)
$ ./EchoWorker
tarting worker "Testworker"
Press <ENTER> to restart the worker
(In another shell)
$ echo -n whatsup | nc -U /tmp/1.sock
whatsup
$ echo -n test | nc -U /tmp/1.sock
test
```
Now in the first window we can see the following:
```
Starting worker "Testworker"
Press <ENTER> to restart the worker
Got: whatsup
Got: test
```
We can press enter to restart the worker:
```
Starting worker "Testworker"
Press <ENTER> to restart the worker
Got: whatsup
Got: test
Starting worker "Testworker"
Press <ENTER> to restart the worker
```