From a34b8f107b4dd370576e205b2a84804b907f5136 Mon Sep 17 00:00:00 2001
From: erichhasl <erich.hasl@gmail.com>
Date: Sun, 15 Oct 2017 22:32:53 +0200
Subject: [PATCH] add haskell server with delimiters

---
 haskell/Server.hs | 99 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 haskell/Server.hs

diff --git a/haskell/Server.hs b/haskell/Server.hs
new file mode 100644
index 0000000..405cf0d
--- /dev/null
+++ b/haskell/Server.hs
@@ -0,0 +1,99 @@
+module Socket where
+
+import qualified Network.Socket as Net
+import qualified System.IO as Sys
+import Control.Concurrent
+import Control.Concurrent.Chan
+import Control.Monad (forever)
+import Control.Monad.Reader
+import Data.List.Split
+
+data Buffering = NoBuffering
+               | LengthBuffering
+               | DelimiterBuffering String
+                 deriving (Show)
+
+data ServerEnv = ServerEnv
+    { buffering :: Buffering       -- ^ Buffermode
+    , socket :: Net.Socket         -- ^ the socket used to communicate
+    , global :: Chan String
+    , onReceive :: OnReceive
+    }
+
+type Server = ReaderT ServerEnv IO
+
+type OnReceive = Sys.Handle -> Net.SockAddr -> String -> Server ()
+
+broadcast :: String -> Server ()
+broadcast msg = do
+    bufmode <- asks buffering
+    chan <- asks global
+    case bufmode of
+        DelimiterBuffering delim -> liftIO $ writeChan chan $ msg ++ delim
+        _                        -> liftIO $ writeChan chan msg
+
+send :: Sys.Handle -> String -> Server ()
+send connhdl msg = do
+    bufmode <- asks buffering
+    case bufmode of
+        DelimiterBuffering delim -> liftIO $ Sys.hPutStr connhdl $ msg ++ delim
+        _                        -> liftIO $ Sys.hPutStr connhdl msg
+
+
+-- | Initialize a new server with the given port number and buffering mode
+initServer :: Net.PortNumber -> Buffering -> OnReceive -> IO ServerEnv
+initServer port buffermode handler = do
+    sock <- Net.socket Net.AF_INET Net.Stream 0
+    Net.setSocketOption sock Net.ReuseAddr 1
+    Net.bind sock (Net.SockAddrInet port Net.iNADDR_ANY)
+    Net.listen sock 5
+    chan <- newChan
+    forkIO $ forever $ do
+        msg <- readChan chan -- clearing the main channel
+        return ()
+    return (ServerEnv buffermode sock chan handler)
+
+-- | Looping over requests and establish connection
+procRequests :: Server ()
+procRequests = do
+    sock <- asks socket
+    (conn, clientaddr) <- liftIO $ Net.accept sock
+    env <- ask
+    liftIO $ forkIO $ runReaderT (procMessages conn clientaddr) env
+    procRequests
+
+-- | Handle one client
+procMessages :: Net.Socket -> Net.SockAddr -> Server ()
+procMessages conn clientaddr = do
+    connhdl <- liftIO $ Net.socketToHandle conn Sys.ReadWriteMode
+    liftIO $ Sys.hSetBuffering connhdl Sys.NoBuffering
+    globalChan <- asks global
+
+    commChan <- liftIO $ dupChan globalChan
+
+    reader <- liftIO $ forkIO $ forever $ do
+        msg <- readChan commChan
+        Sys.hPutStrLn connhdl msg
+
+    handler <- asks onReceive
+    messages <- liftIO $ Sys.hGetContents connhdl
+    buffermode <- asks buffering
+    case buffermode of
+        DelimiterBuffering delimiter ->
+            mapM_ (handler connhdl clientaddr) (splitOn delimiter messages)
+        LengthBuffering -> liftIO $ putStrLn (take 4 messages)
+        _ -> return ()
+
+    -- clean up
+    liftIO $ do killThread reader
+                Sys.hClose connhdl
+
+sampleHandler :: OnReceive
+sampleHandler connhdl addr query = do
+    liftIO $ putStrLn $ "new query " ++ query
+    send connhdl $ "> " ++ query
+
+main :: IO ()
+main = do
+    env <- initServer 4242 LengthBuffering sampleHandler
+    runReaderT procRequests env