added git-annex remotedaemon

So far, handling connecting to git-annex-shell notifychanges, and
pulling immediately when a change is pushed to a remote.

A little bit buggy (crashes after the first pull), but it already works!

This commit was sponsored by Mark Sheppard.

RemoteDaemon/Transport/Ssh.hs

@@ -0,0 +1,75 @@
+{- git-remote-daemon, git-annex-shell over ssh transport
+ -
+ - Copyright 2014 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module RemoteDaemon.Transport.Ssh (transport) where
+
+import Common.Annex
+import qualified Annex
+import RemoteDaemon.Types
+import qualified RemoteDaemon.Transport.Ssh.Types as SshRemote
+import Remote.Helper.Ssh
+import Utility.SimpleProtocol
+import qualified Git
+import Annex.CatFile
+import Git.Command
+
+import Control.Concurrent.Chan
+import Control.Concurrent.Async
+import System.Process (std_in, std_out)
+
+transport :: Transport
+transport r remotename annexstate ichan ochan = Annex.eval annexstate $ do
+	v <- git_annex_shell r "notifychanges" [] []
+	case v of
+		Nothing -> noop
+		Just (cmd, params) -> liftIO $ go cmd (toCommand params)
+  where
+	send msg = writeChan ochan (msg remotename)
+	go cmd params = do
+		(Just toh, Just fromh, _, pid) <- createProcess (proc cmd params)
+			{ std_in = CreatePipe
+			, std_out = CreatePipe
+			}
+		
+		let shutdown = do
+			hClose toh
+			hClose fromh
+			void $ waitForProcess pid
+			send DISCONNECTED
+
+		let fromshell = forever $ do
+			l <- hGetLine fromh
+			case parseMessage l of
+				Just SshRemote.READY -> send CONNECTED
+				Just (SshRemote.CHANGED refs) ->
+					Annex.eval annexstate $
+						fetchNew remotename refs
+				Nothing -> shutdown
+
+		-- The only control message that matters is STOP.
+		--
+		-- Note that a CHANGED control message is not handled;
+		-- we don't push to the ssh remote. The assistant
+		-- and git-annex sync both handle pushes, so there's no
+		-- need to do it here.
+		let handlecontrol = forever $ do
+			msg <- readChan ichan
+			case msg of
+				STOP -> ioError (userError "done")
+				_ -> noop
+
+		-- Run both threads until one finishes.
+		void $ tryIO $ concurrently fromshell handlecontrol
+		shutdown
+
+-- Check if any of the shas are actally new, to avoid unnecessary fetching.
+fetchNew :: RemoteName -> [Git.Sha] -> Annex ()
+fetchNew remotename = check
+  where
+	check [] = void $ inRepo $ runBool [Param "fetch", Param remotename]
+	check (r:rs) = maybe (check rs) (const noop)
+		=<< catObjectDetails r