Adds types and a basic server.

.gitignore

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+.cabal-sandbox/
+.stack-work/
+cabal.sandbox.config
+dist/

LICENSE

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+Copyright Author name here (c) 2015
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Author name here nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Setup.hs

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+import Distribution.Simple
+main = defaultMain

app/Main.hs

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+module Main where
+
+import Link.Server
+import System.Environment (getArgs)
+
+main :: IO ()
+main = do
+  port <- fmap (read . (!! 0)) getArgs
+  runServer port
+

link.cabal

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+name:                link
+version:             0.1.0.0
+synopsis:            A simple multithreded chat server
+description:         Please see README.md
+homepage:            http://github.com/abhin4v/link#readme
+license:             BSD3
+license-file:        LICENSE
+author:              Abhinav Sarkar
+maintainer:          abhinav@abhinavsarkar.net
+copyright:           2010 Abhinav Sarkar
+category:            Network
+build-type:          Simple
+-- extra-source-files:
+cabal-version:       >=1.10
+
+library
+  hs-source-dirs:      src
+  exposed-modules:     Link.Server,
+                       Link.Types
+  default-extensions:  OverloadedStrings, RecordWildCards, ScopedTypeVariables,
+                       BangPatterns, TupleSections, NamedFieldPuns
+  build-depends:       base >= 4.7 && < 5,
+                       network >= 2.6 && < 2.7,
+                       containers >= 0.5 && < 0.6
+  default-language:    Haskell2010
+
+executable link-exe
+  hs-source-dirs:      app
+  main-is:             Main.hs
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  build-depends:       base
+                     , link
+  default-language:    Haskell2010
+
+test-suite link-test
+  type:                exitcode-stdio-1.0
+  hs-source-dirs:      test
+  main-is:             Spec.hs
+  build-depends:       base
+                     , link
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  default-language:    Haskell2010
+
+source-repository head
+  type:     git
+  location: https://github.com/abhin4v/link

src/Link/Server.hs

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+module Link.Server where
+
+import Control.Exception  (finally)
+import Control.Concurrent (forkFinally, newMVar, modifyMVar, modifyMVar_)
+import Control.Monad      (forever)
+import Network            (withSocketsDo, listenOn, accept, PortID(..))
+import System.IO          (hClose, hSetNewlineMode, hSetBuffering, BufferMode(..),
+                           universalNewlineMode, hGetLine, Handle)
+import Text.Printf        (printf, hPrintf)
+
+import qualified Data.Map as Map
+
+import Link.Types
+
+runServer :: Int -> IO ()
+runServer port = withSocketsDo $ do
+  serverUsers <- newMVar Map.empty
+  let server = Server serverUsers
+  sock <- listenOn . PortNumber . fromIntegral $ port
+  printf "Listening on port %d\n" port
+  forever $ do
+     (handle, host, port') <- accept sock
+     printf "Accepted connection from %s: %s\n" host (show port')
+     forkFinally (talk server handle) (\_ -> hClose handle)
+
+talk :: Server -> Handle -> IO ()
+talk server handle = do
+  hSetNewlineMode handle universalNewlineMode
+  hSetBuffering handle LineBuffering
+  readName
+  where
+    readName = do
+      name <- hGetLine handle
+      if null name
+      then readName
+      else do
+        let user = User name
+        ok <- checkAddClient server user handle
+        case ok of
+          Nothing -> do
+             hPrintf handle
+                "The name %s is in use, please choose another\n" name
+             readName
+          Just client ->
+             runClient server client
+                 `finally` removeClient server user
+
+checkAddClient :: Server -> User -> Handle -> IO (Maybe Client)
+checkAddClient Server {..} user@User {..} handle = do
+  modifyMVar serverUsers $ \clientMap ->
+    if Map.member user clientMap
+      then return (clientMap, Nothing)
+      else do
+        let client = Client user handle
+        printf "New user connected: %s" userName
+        return (Map.insert user client clientMap, Just client)
+
+runClient :: Server -> Client -> IO ()
+runClient server Client {..} = forever $ do
+  command <- hGetLine clientHandle
+  print command
+
+removeClient :: Server -> User -> IO ()
+removeClient Server {..} user =
+  modifyMVar_ serverUsers $ \clientMap ->
+    return $ Map.delete user clientMap

src/Link/Types.hs

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+module Link.Types where
+
+import System.IO (Handle)
+import Control.Concurrent (MVar)
+import qualified Data.Map as Map
+
+data User = User { userName :: String }
+            deriving (Show, Eq, Ord)
+
+data Client = Client {
+                clientUser :: User
+              , clientHandle :: Handle
+              } deriving (Show, Eq)
+
+data Server = Server {
+                serverUsers :: MVar (Map.Map User Client)
+              }

stack.yaml

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+flags: {}
+packages:
+- '.'
+extra-deps: []
+resolver: lts-3.4

test/Spec.hs

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+main :: IO ()
+main = putStrLn "Test suite not yet implemented"