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/GFServer.hs

@@ -0,0 +1,148 @@
+module GFServer(server) where
+import Data.List(partition)
+import qualified Data.Map as M
+import Control.Monad(when)
+import System.Random(randomRIO)
+import System.IO(stdout,stderr)
+import System.IO.Error(try,ioError)
+import System.Directory(doesDirectoryExist,doesFileExist,createDirectory,
+                        setCurrentDirectory,getCurrentDirectory)
+import System.FilePath(takeExtension,(</>))
+import Control.Concurrent.MVar(newMVar,modifyMVar)
+import Network.URI(URI(..))
+import Network.Shed.Httpd(initServer,Request(..),Response(..),queryToArguments,
+                          noCache)
+import System.IO.Silently(hCapture)
+import Codec.Binary.UTF8.String(encodeString)
+import GF.Infra.UseIO(readBinaryFile)
+
+-- * Configuraiton
+port = 41295
+documentRoot = "."
+
+-- * HTTP server
+server execute1 state0 = 
+  do state <- newMVar M.empty
+     putStrLn $ "Starting server on port "++show port
+     initServer port (modifyMVar state . handle state0 execute1)
+
+-- * HTTP request handler
+handle state0 execute1 (Request method URI{uriPath=path,uriQuery=q} hdrs body) state =
+    do let qs = decodeQ $ 
+                case method of
+                  "GET" -> queryToArguments q
+                  "POST" -> queryToArguments body
+
+       logPutStrLn $ method++" "++path++" "++show qs
+       case path of
+         "/new" -> new
+--       "/stop" ->
+--       "/start" ->
+         "/gfshell" -> inDir qs $ look "command" . command
+         "/upload" -> inDir qs upload
+         '/':rpath -> do resp <- serveStaticFile (translatePath rpath)
+                         return (state,resp)
+         _ -> return (state,resp400 path)
+  where
+    look field ok qs =
+        case partition ((==field).fst) qs of
+          ((_,value):qs1,qs2) -> ok value (qs1++qs2)
+          _ -> bad
+      where
+        bad = return (state,resp400 $ "no "++field++" in request")
+    
+    inDir qs ok = look "dir" cd qs
+      where
+        cd ('/':dir@('t':'m':'p':_)) qs' =
+          do cwd <- getCurrentDirectory
+             b <- try $ setCurrentDirectory dir
+             case b of
+               Left _ -> return (state,resp404 dir)
+               Right _ -> do logPutStrLn $ "cd "++dir
+                             r <- try (ok dir qs')
+                             setCurrentDirectory cwd
+                             either ioError return r
+        cd dir _ = return (state,resp400 $ "unacceptable directory "++dir)
+
+    new =
+      do dir <- newDirectory
+         return (state,ok200 dir)
+
+    command dir cmd _ =
+      do let st = maybe state0 id $ M.lookup dir state
+         (output,st') <- hCapture [stdout,stderr] (execute1 st cmd)
+         let state' = maybe state (flip (M.insert dir) state) st'
+         return (state',ok200 output)
+
+    upload dir files=
+      do let update (name,contents)= updateFile (name++".gf") contents
+         mapM_ update files
+         return (state,resp204)
+
+-- * Static content
+
+translatePath path = documentRoot</>path -- hmm, check for ".."
+
+serveStaticFile path =
+  do b <- doesDirectoryExist path
+     let path' = if b then path </> "index.html" else path
+     serveStaticFile' path'
+
+serveStaticFile' path =
+  do b <- doesFileExist path
+     let (t,rdFile,encode) = contentTypeFromExt (takeExtension path)
+     if b then fmap (ok200' (ct t) . encode) $ rdFile path
+          else return (resp404 path)
+
+-- * Logging
+logPutStrLn = putStrLn
+
+-- * Standard HTTP responses
+ok200 body   = Response 200 [plainUTF8,noCache] (encodeString body)
+ok200' t body = Response 200 [t] body
+resp204      = Response 204 [] "" -- no content
+resp400 msg  = Response 400 [plain] $ "Bad request: "++msg++"\n"
+resp404 path = Response 404 [plain] $ "Not found: "++path++"\n"
+
+-- * Content types
+plain = ct "text/plain"
+plainUTF8 = ct "text/plain; charset=UTF-8"
+ct t = ("Content-Type",t)
+
+contentTypeFromExt ext =
+  case ext of
+    ".html" -> text "html"
+    ".htm" -> text "html"
+    ".xml" -> text "xml"
+    ".txt" -> text "plain"
+    ".css" -> text "css"
+    ".js" -> text "javascript"
+    ".png" -> bin "image/png"
+    ".jpg" -> bin "image/jpg"
+    _ -> bin "application/octet-stream"
+  where
+     text subtype = ("text/"++subtype++"; charset=UTF-8",readFile,encodeString)
+     bin t = (t,readBinaryFile,id)
+
+-- * IO utilities
+updateFile path new =
+  do old <- try $ readFile path
+     when (Right new/=old) $ do logPutStrLn $ "Updating "++path
+                                seq (either (const 0) length old) $
+                                    writeFile path new
+
+
+newDirectory =
+  do k <- randomRIO (1,maxBound::Int)
+     let path = "tmp/gfse."++show k
+     b <- try $ createDirectory path
+     case b of
+       Left _ -> newDirectory
+       Right _ -> return ('/':path)
+
+-- * misc utils
+
+decodeQ qs = [(decode n,decode v)|(n,v)<-qs]
+decode = map decode1
+decode1 '+' = ' ' -- httpd-shed bug workaround
+decode1 c   = c