git-annex enable-tor command

Tor unfortunately does not come out of the box configured to let hidden
services register themselves on the fly via the ControlPort.

And, changing the config to enable the ControlPort and a particular type
of auth for it may break something already using the ControlPort, or
lessen the security of the system.

So, this leaves only one option to us: Add a hidden service to the
torrc. git-annex enable-tor does so, and picks an unused high port for
tor to listen on for connections to the hidden service.

It's up to the caller to somehow pick a local port to listen on
that won't be used by something else. That may be difficult to do..

This commit was sponsored by Jochen Bartl on Patreon.

Command/EnableTor.hs

@@ -0,0 +1,28 @@
+{- git-annex command
+ -
+ - Copyright 2016 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Command.EnableTor where
+
+import Command
+import Utility.Tor
+
+cmd :: Command
+cmd = noCommit $ dontCheck repoExists $
+	command "enable-tor" SectionPlumbing ""
+		paramNumber (withParams seek)
+
+seek :: CmdParams -> CommandSeek
+seek = withWords start
+
+start :: CmdParams -> CommandStart
+start (localport:[]) = case readish localport of
+	Nothing -> error "Bad localport"
+	Just lp -> do
+		(onionaddr, onionport) <- liftIO $ addHiddenService lp
+		liftIO $ putStrLn (onionaddr ++ ":" ++ show onionport)
+		stop
+start _ = error "Need 1 localport parameter"