broke out fairly generic ssh stuff to Assistant.Ssh so pairing can use it too

I'd rather Utility.Ssh, but the SshData type is not sufficiently clean and
generic for Utility.

Assistant/Ssh.hs

@@ -0,0 +1,145 @@
+{- git-annex assistant ssh utilities
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Assistant.Ssh where
+
+import Common
+import Utility.TempFile
+
+import Data.Text (Text)
+import qualified Data.Text as T
+import qualified Control.Exception as E
+import System.Process (CreateProcess(..))
+import Control.Concurrent
+
+data SshData = SshData
+	{ sshHostName :: Text
+	, sshUserName :: Maybe Text
+	, sshDirectory :: Text
+	, sshRepoName :: String
+	, needsPubKey :: Bool
+	, rsyncOnly :: Bool
+	}
+	deriving (Read, Show, Eq)
+
+data SshKeyPair = SshKeyPair
+	{ sshPubKey :: String
+	, sshPrivKey :: String
+	}
+
+{- ssh -ofoo=bar command-line option -}
+sshOpt :: String -> String -> String
+sshOpt k v = concat ["-o", k, "=", v]
+
+sshDir :: IO FilePath
+sshDir = do
+	home <- myHomeDir
+	return $ home </> ".ssh"
+
+{- The output of ssh, including both stdout and stderr. -}
+sshTranscript :: [String] -> String -> IO (String, Bool)
+sshTranscript opts input = do
+	(readf, writef) <- createPipe
+	readh <- fdToHandle readf
+	writeh <- fdToHandle writef
+	(Just inh, _, _, pid) <- createProcess $
+		(proc "ssh" opts)
+			{ std_in = CreatePipe
+			, std_out = UseHandle writeh
+			, std_err = UseHandle writeh
+			}
+	hClose writeh
+
+	-- fork off a thread to start consuming the output
+	transcript <- hGetContents readh
+	outMVar <- newEmptyMVar
+	_ <- forkIO $ E.evaluate (length transcript) >> putMVar outMVar ()
+
+	-- now write and flush any input
+	when (not (null input)) $ do hPutStr inh input; hFlush inh
+	hClose inh -- done with stdin
+
+	-- wait on the output
+	takeMVar outMVar
+	hClose readh
+
+	ok <- checkSuccessProcess pid
+	return ()
+	return (transcript, ok)
+
+{- Implemented as a shell command, so it can be run on remote servers over
+ - ssh. -}
+makeAuthorizedKeys :: SshData -> SshKeyPair -> Maybe String
+makeAuthorizedKeys sshdata keypair
+	| needsPubKey sshdata = Just $ join "&&" $
+		[ "mkdir -p ~/.ssh"
+		, "touch ~/.ssh/authorized_keys"
+		, "chmod 600 ~/.ssh/authorized_keys"
+		, unwords
+			[ "echo"
+			, shellEscape $ authorizedKeysLine sshdata keypair
+			, ">>~/.ssh/authorized_keys"
+			]
+		]
+	| otherwise = Nothing
+		
+authorizedKeysLine :: SshData -> SshKeyPair -> String
+authorizedKeysLine sshdata (SshKeyPair { sshPubKey = pubkey })
+	{- TODO: Locking down rsync is difficult, requiring a rather
+	 - long perl script. -}
+	| rsyncOnly sshdata = pubkey
+	| otherwise = limitcommand "git-annex-shell -c" ++ pubkey
+	where
+		limitcommand c = "command=\"perl -e 'exec qw(" ++ c ++ "), $ENV{SSH_ORIGINAL_COMMAND}'\",no-agent-forwarding,no-port-forwarding,no-X11-forwarding "
+
+{- Generates a ssh key pair. -}
+genSshKeyPair :: IO SshKeyPair
+genSshKeyPair = withTempDir "git-annex-keygen" $ \dir -> do
+	ok <- boolSystem "ssh-keygen"
+		[ Param "-P", Param "" -- no password
+		, Param "-f", File $ dir </> "key"
+		]
+	unless ok $
+		error "ssh-keygen failed"
+	SshKeyPair
+		<$> readFile (dir </> "key.pub")
+		<*> readFile (dir </> "key")
+
+{- Installs a ssh key pair, and sets up ssh config with a mangled hostname
+ - that will enable use of the key. This way we avoid changing the user's
+ - regular ssh experience at all. Returns a modified SshData containing the
+ - mangled hostname. -}
+setupSshKeyPair :: SshKeyPair -> SshData -> IO SshData
+setupSshKeyPair sshkeypair sshdata = do
+	sshdir <- sshDir
+	let configfile = sshdir </> "config"
+	createDirectoryIfMissing True sshdir
+
+	unlessM (doesFileExist $ sshdir </> sshprivkeyfile) $ do
+		h <- fdToHandle =<<
+			createFile (sshdir </> sshprivkeyfile)
+				(unionFileModes ownerWriteMode ownerReadMode)
+		hPutStr h (sshPrivKey sshkeypair)
+		hClose h
+	unlessM (doesFileExist $ sshdir </> sshpubkeyfile) $ do
+		writeFile (sshdir </> sshpubkeyfile) (sshPubKey sshkeypair)
+
+	unlessM (catchBoolIO $ isInfixOf mangledhost <$> readFile configfile) $
+		appendFile configfile $ unlines
+			[ ""
+			, "# Added automatically by git-annex"
+			, "Host " ++ mangledhost
+			, "\tHostname " ++ T.unpack (sshHostName sshdata)
+			, "\tIdentityFile ~/.ssh/" ++ sshprivkeyfile
+			]
+
+	return $ sshdata { sshHostName = T.pack mangledhost }
+	where
+		sshprivkeyfile = "key." ++ mangledhost
+		sshpubkeyfile = sshprivkeyfile ++ ".pub"
+		mangledhost = "git-annex-" ++ T.unpack (sshHostName sshdata) ++ user
+		user = maybe "" (\u -> "-" ++ T.unpack u) (sshUserName sshdata)