webapp: support adding existing gcrypt special remotes from removable drives

When adding a removable drive, it's now detected if the drive contains
a gcrypt special remote, and that's all handled nicely. This includes
fetching the git-annex branch from the gcrypt repo in order to find
out how to set up the special remote.

Note that gcrypt repos that are not git-annex special remotes are not
supported. It will attempt to detect such a gcrypt repo and refuse
to use it. (But this is hard to do any may fail; see
https://github.com/blake2-ppc/git-remote-gcrypt/issues/6)

The problem with supporting regular gcrypt repos is that we don't know
what the gcrypt.participants setting is intended to be for the repo.
So even if we can decrypt it, if we push changes to it they might not be
visible to other participants.

Anyway, encrypted sneakernet (or mailnet) is now fully possible with the
git-annex assistant! Assuming that the gpg key distribution is handled
somehow, which the assistant doesn't yet help with.

This commit was sponsored by Navishkar Rao.

Assistant/DeleteRemote.hs

@@ -17,8 +17,7 @@ import Logs.Location
 import Assistant.DaemonStatus
 import qualified Remote
 import Remote.List
-import qualified Git.Command
-import qualified Git.BuildVersion
+import qualified Git.Remote
 import Logs.Trust
 import qualified Annex
 
@@ -35,15 +34,7 @@ disableRemote uuid = do
 	remote <- fromMaybe (error "unknown remote")
 		<$> liftAnnex (Remote.remoteFromUUID uuid)
 	liftAnnex $ do
-		inRepo $ Git.Command.run
-			[ Param "remote"
-			-- name of this subcommand changed
-			, Param $
-				if Git.BuildVersion.older "1.8.0"
-					then "rm"
-					else "remove"
-			, Param (Remote.name remote)
-			]
+		inRepo $ Git.Remote.remove (Remote.name remote)
 		void $ remoteListRefresh
 	updateSyncRemotes
 	return remote

Assistant/MakeRemote.hs

@@ -27,8 +27,6 @@ import Creds
 import qualified Data.Text as T
 import qualified Data.Map as M
 
-type RemoteName = String
-
 {- Sets up and begins syncing with a new ssh or rsync remote. -}
 makeSshRemote :: Bool -> SshData -> Maybe Cost -> Assistant Remote
 makeSshRemote forcersync sshdata mcost = do

Assistant/WebApp/Configurators/Local.hs

@@ -38,6 +38,7 @@ import Config
 import Utility.Gpg
 import qualified Annex.Branch
 import qualified Remote.GCrypt as GCrypt
+import qualified Git.GCrypt
 import qualified Types.Remote
 
 import qualified Data.Text as T
@@ -247,16 +248,13 @@ postAddDriveR = page "Add a removable drive" (Just Configuration) $ do
  - If the repo does not already exist on the drive, prompt about
  - encryption. -}
 getConfirmAddDriveR :: RemovableDrive -> Handler Html
-getConfirmAddDriveR drive = ifM (liftIO $ doesDirectoryExist dir)
+getConfirmAddDriveR drive = ifM (liftIO $ probeRepoExists dir)
 	( do
-		mu <- liftIO $ catchMaybeIO $ inDir dir $ getUUID
+		mu <- liftIO $ probeUUID dir
 		case mu of
-			Nothing -> knownrepo
-			Just driveuuid -> 
-				ifM (M.member driveuuid <$> liftAnnex uuidMap)
-					( knownrepo
-					, askcombine
-					)
+			Nothing -> maybe askcombine isknownuuid
+				=<< liftIO (probeGCryptRemoteUUID dir)
+			Just driveuuid -> isknownuuid driveuuid
 	, newrepo
 	)
   where
@@ -269,6 +267,11 @@ getConfirmAddDriveR drive = ifM (liftIO $ doesDirectoryExist dir)
 	knownrepo = getFinishAddDriveR drive NoRepoKey
 	askcombine = page "Combine repositories?" (Just Configuration) $
 		$(widgetFile "configurators/adddrive/combine")
+	isknownuuid driveuuid =
+		ifM (M.member driveuuid <$> liftAnnex uuidMap)
+			( knownrepo
+			, askcombine
+			)
 
 setupDriveModal :: Widget
 setupDriveModal = $(widgetFile "configurators/adddrive/setupmodal")
@@ -290,9 +293,7 @@ getGenKeyForDriveR drive = withNewSecretKey $ \key -> do
 getFinishAddDriveR :: RemovableDrive -> RepoKey -> Handler Html
 getFinishAddDriveR drive = go
   where
-	go NoRepoKey = makewith $ \isnew -> (,)
-		<$> liftIO (initRepo isnew False dir $ Just remotename)
-		<*> combineRepos dir remotename
+  	{- Set up new gcrypt special remote. -}
 	go (RepoKey keyid) = ifM (liftIO $ inPath "git-remote-gcrypt")
 		( makewith $ \_ -> do
 			r <- liftAnnex $ addRemote $ 
@@ -306,6 +307,33 @@ getFinishAddDriveR drive = go
 		, page "Encrypt repository" (Just Configuration) $
 			$(widgetFile "configurators/needgcrypt")
 		)
+	{- Either making a new unencrypted repo, or combining with
+	 - an existing unencrypted repo, or combining with an existing
+	 - gcrypt special remot, or some other existing gcrypt repo. -}
+	go NoRepoKey = do
+		mu <- liftIO $ probeGCryptRemoteUUID dir
+		case mu of
+			Just u -> enablegcryptremote u
+			Nothing ->
+				ifM (liftAnnex $ inRepo $ Git.GCrypt.probeGCryptRepo dir)
+					( error "The drive contains a gcrypt repository that is not a git-annex special remote. This is not supported."
+					, makeunencrypted
+					)
+	{- Sync the git-annex branch from the gcrypt repo, in order to
+	 - make sure we know how the special remote should be set up. -}
+	enablegcryptremote u = do
+		mname <- liftAnnex $ getGCryptRemoteName u dir
+		case mname of
+			Nothing -> error $ "Unable to use the gcrypt remote at " ++ dir ++ ". Perhaps it is encrypted using a GnuPG key that you do not have?"
+			Just name -> makewith $ const $ do
+				r <- liftAnnex $ addRemote $
+					enableSpecialRemote name GCrypt.remote $ M.fromList
+						[("gitrepo", dir)]
+				return (u, r)
+	{- Making a new unencrypted repo, or combining with an existing one. -}
+	makeunencrypted = makewith $ \isnew -> (,)
+		<$> liftIO (initRepo isnew False dir $ Just remotename)
+		<*> combineRepos dir remotename
 	makewith a = do
 		liftIO $ createDirectoryIfMissing True dir
 		isnew <- liftIO $ makeRepo dir True
@@ -385,7 +413,7 @@ startFullAssistant path repogroup setup = do
 {- Makes a new git repository. Or, if a git repository already
  - exists, returns False. -}
 makeRepo :: FilePath -> Bool -> IO Bool
-makeRepo path bare = ifM alreadyexists
+makeRepo path bare = ifM (probeRepoExists path)
 	( return False
 	, do
 		(transcript, ok) <-
@@ -395,8 +423,6 @@ makeRepo path bare = ifM alreadyexists
 		return True
 	)
   where
-  	alreadyexists = isJust <$> 
-		catchDefaultIO Nothing (Git.Construct.checkForRepo path)
 	baseparams = [Param "init", Param "--quiet"]
 	params
 		| bare = baseparams ++ [Param "--bare", File path]
@@ -455,3 +481,23 @@ canWrite dir = do
 	tocheck <- ifM (doesDirectoryExist dir)
 		(return dir, return $ parentDir dir)
 	catchBoolIO $ fileAccess tocheck False True False
+
+{- Checks if a git repo exists at a location. -}
+probeRepoExists :: FilePath -> IO Bool
+probeRepoExists dir = isJust <$>
+	catchDefaultIO Nothing (Git.Construct.checkForRepo dir)
+
+{- Gets the UUID of the git repo at a location, which may not exist, or
+ - not be a git-annex repo. -}
+probeUUID :: FilePath -> IO (Maybe UUID)
+probeUUID dir = catchDefaultIO Nothing $ inDir dir $ do
+	u <- getUUID
+	return $ if u == NoUUID then Nothing else Just u
+
+{- Gets the UUID of the gcrypt repo at a location, which may not exist.
+ - Only works if the gcrypt repo was created as a git-annex remote. -}
+probeGCryptRemoteUUID :: FilePath -> IO (Maybe UUID)
+probeGCryptRemoteUUID dir = catchDefaultIO Nothing $ do
+	r <- Git.Construct.fromAbsPath dir
+	(genUUIDInNameSpace gCryptNameSpace <$>) . fst
+		<$> GCrypt.getGCryptId r

Assistant/WebApp/Gpg.hs

@@ -12,6 +12,12 @@ module Assistant.WebApp.Gpg where
 import Assistant.WebApp.Common
 import Utility.Gpg
 import Utility.UserInfo
+import qualified Git.Command
+import qualified Git.Remote
+import qualified Annex.Branch
+import qualified Git.GCrypt
+import Assistant.MakeRemote
+import Logs.Remote
 
 import qualified Data.Map as M
 
@@ -45,3 +51,25 @@ withNewSecretKey use = do
 	case results of
 		[] -> error "Failed to generate gpg key!"
 		(key:_) -> use key
+
+{- Tries to find the name used in remote.log for a gcrypt repository
+ - with a given uuid.
+ -
+ - The gcrypt remote may not be on that is listed in the local remote.log
+ - (or the info may be out of date), so this actually fetches the git-annex
+ - branch from the gcrypt remote and merges it in, and then looks up
+ - the name.
+ -}
+getGCryptRemoteName :: UUID -> String -> Annex (Maybe Git.Remote.RemoteName)
+getGCryptRemoteName u repoloc = do
+	tmpremote <- uniqueRemoteName "tmpgcryptremote" 0 <$> gitRepo
+	void $ inRepo $ Git.Command.runBool
+		[Params "remote add", Param tmpremote, Param $ Git.GCrypt.urlPrefix ++ repoloc]
+	mname <- ifM (inRepo $ Git.Command.runBool [Param "fetch", Param tmpremote])
+		( do
+			void $ Annex.Branch.forceUpdate
+			(M.lookup "name" <=< M.lookup u) <$> readRemoteLog
+		, return Nothing
+		)
+	void $ inRepo $ Git.Remote.remove tmpremote
+	return mname

Git/GCrypt.hs

@@ -13,6 +13,7 @@ import Common
 import Git.Types
 import Git.Construct
 import qualified Git.Config as Config
+import qualified Git.Command as Command
 import Utility.Gpg
 
 urlPrefix :: String
@@ -44,12 +45,28 @@ encryptedRepo baserepo = go
 	go _ = notencrypted
 	notencrypted = error "not a gcrypt encrypted repository"
 
+{- Checks if the git repo at a location is a gcrypt repo that
+ - we can decrypt. This works by trying to fetch from the repo
+ - at the location, into the baserepo.
+ -
+ - Returns false if the git repo is not using gcrypt, or if it is using
+ - gcrypt but cannot be decrypted. We do not try to detect gcrypt
+ - repos that cannot be decrypted, because gcrypt may change in the future
+ - to avoid easy fingerprinting of gcrypt repos.
+ -}
+probeGCryptRepo :: FilePath -> Repo -> IO Bool
+probeGCryptRepo dir baserepo = catchBoolIO $ Command.runBool
+	[ Param "fetch"
+	, Param $ urlPrefix ++ dir
+	] baserepo
+
 type RemoteName = String
+type GCryptId = String
 
 {- gcrypt gives each encrypted repository a uique gcrypt-id,
  - which is stored in the repository (in encrypted form)
  - and cached in a per-remote gcrypt-id configuration setting. -}
-remoteRepoId :: Repo -> Maybe RemoteName -> Maybe String
+remoteRepoId :: Repo -> Maybe RemoteName -> Maybe GCryptId
 remoteRepoId = getRemoteConfig "gcrypt-id"
 
 getRemoteConfig :: String -> Repo -> Maybe RemoteName -> Maybe String

Git/Remote.hs

@@ -8,15 +8,21 @@
 module Git.Remote where
 
 import Common
+import Git
+import qualified Git.Command
+import qualified Git.BuildVersion
+
 import Data.Char
 
+type RemoteName = String
+
 {- Construct a legal git remote name out of an arbitrary input string.
  -
  - There seems to be no formal definition of this in the git source,
  - just some ad-hoc checks, and some other things that fail with certian
  - types of names (like ones starting with '-').
  -}
-makeLegalName :: String -> String
+makeLegalName :: String -> RemoteName
 makeLegalName s = case filter legal $ replace "/" "_" s of
 	-- it can't be empty
 	[] -> "unnamed"
@@ -31,3 +37,14 @@ makeLegalName s = case filter legal $ replace "/" "_" s of
 	legal '_' = True
 	legal '.' = True
 	legal c = isAlphaNum c
+	
+remove :: RemoteName -> Repo -> IO ()
+remove remotename = Git.Command.run
+	[ Param "remote"
+	-- name of this subcommand changed
+	, Param $
+		if Git.BuildVersion.older "1.8.0"
+			then "rm"
+			else "remove"
+	, Param remotename
+	]

Remote/GCrypt.hs

@@ -5,7 +5,7 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
-module Remote.GCrypt (remote, gen) where
+module Remote.GCrypt (remote, gen, getGCryptId) where
 
 import qualified Data.Map as M
 import qualified Data.ByteString.Lazy as L
@@ -52,13 +52,10 @@ gen gcryptr u c gc = do
 	-- get underlying git repo with real path, not gcrypt path
 	r <- liftIO $ Git.GCrypt.encryptedRepo g gcryptr
 	let r' = r { Git.remoteName = Git.remoteName gcryptr }
-	-- read config of underlying repo if it's local
-	r'' <- if Git.repoIsLocalUnknown r'
-		then liftIO $ catchDefaultIO r' $ Git.Config.read r'
-		else return r'
+	(mgcryptid, r'') <- liftIO $ getGCryptId r'
 	-- doublecheck that local cache matches underlying repo's gcrypt-id
 	-- (which might not be set)
-	case (Git.Config.getMaybe "core.gcrypt-id" r'', Git.GCrypt.remoteRepoId g (Git.remoteName gcryptr)) of
+	case (mgcryptid, Git.GCrypt.remoteRepoId g (Git.remoteName gcryptr)) of
 		(Just gcryptid, Just cachedgcryptid)
 			| gcryptid /= cachedgcryptid -> resetup gcryptid r''
 		_ -> gen' r'' u c gc
@@ -81,6 +78,17 @@ gen gcryptr u c gc = do
 				warning $ "not using unknown gcrypt repository pointed to by remote " ++ Git.repoDescribe r
 				return Nothing
 
+{- gcrypt repos set up by git-annex as special remotes have a
+ - core.gcrypt-id setting in their config, which can be mapped back to
+ - the remote's UUID. This only works for local repos.
+ - (Also returns a version of input repo with its config read.) -}
+getGCryptId :: Git.Repo -> IO (Maybe Git.GCrypt.GCryptId, Git.Repo)
+getGCryptId r
+	| Git.repoIsLocalUnknown r = do
+		r' <- catchDefaultIO r $ Git.Config.read r
+		return (Git.Config.getMaybe "core.gcrypt-id" r', r')
+	| otherwise = return (Nothing, r)
+
 gen' :: Git.Repo -> UUID -> RemoteConfig -> RemoteGitConfig -> Annex (Maybe Remote)
 gen' r u c gc = do
 	cst <- remoteCost gc $