Added a preliminary "gf -server" mode.

The command "gf -server" now starts a simple HTTP server on port 41295,
providing a simple web API to the GF compiler. It currently support the
follwing operations:

  * creating new temporary directories for grammar uploads,
  * uploading grammars files for use in the GF shell,
  * executing GF shell commands, and
  * accessing static files.

This means that GF now depends on some additional networking related packages,
but they should be available and easy to install on all platforms. There is
also a new configuration flag "server" in gf.cabal, so GF will be compiled
without support for server mode if the extra packages are unavailable.

Note that running gf -server while connected to the internet can be a security
risk. To prevent unauthorized access to the rest of the system, it is
advisable to run the server in GF_RESTRICTED mode and as a user with suitably
restricted file permissions.

src/compiler/GFI.hs

@@ -1,5 +1,5 @@
 {-# LANGUAGE ScopedTypeVariables, CPP #-}
-module GFI (mainGFI,mainRunGFI) where
+module GFI (mainGFI,mainRunGFI,mainServerGFI) where
 
 import GF.Command.Interpreter
 import GF.Command.Importing
@@ -44,6 +44,9 @@ import Control.Monad
 import Data.Version
 import Text.PrettyPrint (render)
 import GF.System.Signal
+#ifdef SERVER_MODE
+import GFServer(server)
+#endif
 --import System.IO.Error (try)
 #ifdef mingw32_HOST_OS
 import System.Win32.Console
@@ -53,9 +56,9 @@ import System.Win32.NLS
 import Paths_gf
 
 mainRunGFI :: Options -> [FilePath] -> IO ()
-mainRunGFI opts files = do
-  let opts1 = addOptions (modifyFlags (\f -> f{optVerbosity=Quiet})) opts
-  shell opts1 files
+mainRunGFI opts files = shell (beQuiet opts) files
+
+beQuiet = addOptions (modifyFlags (\f -> f{optVerbosity=Quiet}))
 
 mainGFI :: Options -> [FilePath] -> IO ()
 mainGFI opts files = do
@@ -64,6 +67,15 @@ mainGFI opts files = do
 
 shell opts files = loop opts =<< importInEnv emptyGFEnv opts files
 
+#ifdef SERVER_MODE
+mainServerGFI opts0 files =
+    server (execute1 opts) =<< importInEnv emptyGFEnv opts files
+  where opts = beQuiet opts0
+#else
+mainServerGFI opts files =
+  error "GF has not been compiled with server mode support"
+#endif
+
 -- | Read end execute commands until it is time to quit
 loop :: Options -> GFEnv -> IO ()
 loop opts gfenv = maybe (return ()) (loop opts) =<< readAndExecute1 opts gfenv