added handling of command line options;

added an option to set the TCP port to listen on;
in absence of this option, made the server automatically determine a free port (using linear search)

server/Main.hs

@@ -1,6 +1,9 @@
 module Main where
 
 import Scion
+import Scion.Server.Options
 import Scion.Server.Emacs
 
-main = runScion $ runServer
+main = do
+    opts <- readOptions
+    runScion $ runServer opts

server/Scion/Server/Emacs.hs

@@ -14,14 +14,14 @@
 module Scion.Server.Emacs where
 
 import Scion.Types
+import Scion.Server.Options
 import Scion.Server.Protocol
 import Scion.Server.Commands
 
-import Exception
+import Exception ( Exception, ghandle, throwIO )
 import MonadUtils
 import GHC
 
-import Control.Exception
 import Control.Monad ( liftM, when )
 import Data.Bits ( shiftL )
 import Data.Char ( isHexDigit, digitToInt )
@@ -41,22 +41,30 @@ import qualified Data.ByteString.Char8 as S
 data SocketClosed = SocketClosed deriving (Show, Typeable)
 instance Exception SocketClosed
 
+instance Bounded PortNumber where
+    minBound = 0
+    maxBound = 0xFFFF
+
 logLevel :: Int
 logLevel = 2
 
-runServer :: ScionM ()
-runServer =
+runServer :: ServerOptions -> ScionM ()
+runServer opts =
     reifyScionM $ \s ->
       withSocketsDo $ do
         liftIO $ do hSetBuffering stdout LineBuffering
                     hSetBuffering stderr LineBuffering
         log 1 "starting up server..."
-        sock <- liftIO $ listenOn (PortNumber 4005)
+        let ports = case optPort opts of
+                         AutoPort -> map PortNumber [4005..maxBound]
+                         FixedPort p -> [PortNumber (fromIntegral p)]
+        sock <- liftIO $ listenOnOneOf ports
         reflectScionM (loop sock) s
   where
     loop sock = do
       log 4 "accepting"
-      liftIO $ putStrLn "=== Listening on port: 4005"
+      portNr <- liftIO $ socketPort sock
+      liftIO $ putStrLn $ "=== Listening on port: " ++ show portNr
       (sock', _addr) <- liftIO $ accept sock
       log 4 "starting to serve"
       more <- eventLoop sock'
@@ -66,6 +74,11 @@ runServer =
       if more then loop sock
               else return ()
 
+listenOnOneOf :: [PortID] -> IO Socket
+listenOnOneOf (p:ps) = catch
+    (listenOn p)
+    (\ex -> if null ps then throwIO ex else listenOnOneOf ps)
+
 eventLoop :: Socket -> ScionM Bool
 eventLoop sock = 
     ghandle (\(_e :: SocketClosed) -> return True) $ do

server/Scion/Server/Options.hs

@@ -0,0 +1,38 @@
+module Scion.Server.Options where
+
+import System.Environment ( getArgs )
+import System.Exit ( exitWith, ExitCode(..) )
+import System.Console.GetOpt ( getOpt, usageInfo, ArgOrder(..), OptDescr(..), ArgDescr(..) )
+
+data ServerPort = AutoPort | FixedPort Int
+
+data ServerOptions = ServerOptions
+    { optPort     :: ServerPort
+    , optLogLevel :: Int
+    }
+
+defaultOptions = ServerOptions
+    { optPort     = AutoPort
+    , optLogLevel = 2
+    }
+
+readOptions :: IO ServerOptions
+readOptions = do
+    argv <- getArgs
+    case getOpt Permute options argv of
+        (o, n, []  ) -> return $ foldl (flip id) defaultOptions o
+        (_, _, errs) -> putStr (concat errs ++ usageInfo header options) >> exitWith (ExitFailure 1)
+    where
+        header = "Command line options:"
+
+
+options :: [OptDescr (ServerOptions -> ServerOptions)]
+options =
+    [ Option ['p'] ["port"]
+        (ReqArg (\p opts -> opts { optPort = FixedPort (read p) }) "<port-number>")
+        "port number to listen on"
+    , Option
+        ['v'] ["verbosity"]
+        (ReqArg (\v opts -> opts { optLogLevel = read v }) "<number>")
+        "log level (not yet implemented)"
+    ]

server/scion-server.cabal

@@ -29,4 +29,5 @@ executable scion_server
 
   other-modules: Scion.Server.Emacs,
                  Scion.Server.Commands,
+                 Scion.Server.Options,
                  Scion.Server.Protocol