instantiate remotes that are behind a proxy remote

Untested, but this should be close to working. The proxied remotes have
the same url but a different uuid. When talking to current
git-annex-shell, it will fail due to a uuid mismatch. Once it supports
proxies, it will know that the presented uuid is for a remote that it
proxies for.

The check for any git config settings for a remote with the same name as
the proxied remote is there for several reasons. One is security:
Writing a name to the proxy log should not cause changes to
how an existing, configured git remote operates in a different clone of
the repo.

It's possible that the user has been using a proxied remote, and decides
to set a git config for it. We can't tell the difference between that
scenario and an evil remote trying to eg, intercept a file upload
by replacing their remote with a proxied remote.

Also, if the user sets some git config, does it override the config
inherited from the proxy remote? Seems a difficult question. Luckily,
the above means we don't need to think through it.

This does mean though, that in order for a user to change the config of
a proxy remote, they have to manually set its annex-uuid and url, as
well as the config they want to change. They may also have to set any of
the inherited configs that they were relying on.

Annex/UUID.hs

@@ -6,7 +6,7 @@
  - UUIDs of remotes are cached in git config, using keys named
  - remote.<name>.annex-uuid
  -
- - Copyright 2010-2016 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2024 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -15,6 +15,7 @@
 
 module Annex.UUID (
 	configkeyUUID,
+	configRepoUUID,
 	getUUID,
 	getRepoUUID,
 	getUncachedUUID,
@@ -47,6 +48,9 @@ import Data.String
 configkeyUUID :: ConfigKey
 configkeyUUID = annexConfig "uuid"
 
+configRepoUUID :: Git.Repo -> ConfigKey
+configRepoUUID r = remoteAnnexConfig r "uuid"
+
 {- Generates a random UUID, that does not include the MAC address. -}
 genUUID :: IO UUID
 genUUID = toUUID <$> U4.nextRandom
@@ -82,7 +86,7 @@ getRepoUUID r = do
 	updatecache u = do
 		g <- gitRepo
 		when (g /= r) $ storeUUIDIn cachekey u
-	cachekey = remoteAnnexConfig r "uuid"
+	cachekey = configRepoUUID r
 
 removeRepoUUID :: Annex ()
 removeRepoUUID = do

Logs/Proxy.hs

@@ -36,7 +36,6 @@ data Proxy = Proxy
 	, proxyRemoteName :: RemoteName
 	} deriving (Show, Eq, Ord)
 
--- TODO caching
 getProxies :: Annex (M.Map UUID (S.Set Proxy))
 getProxies = M.map (validateProxies . value) . fromMapLog . parseProxyLog
 	<$> Annex.Branch.get proxyLog

Remote/Git.hs

@@ -45,6 +45,7 @@ import Annex.Init
 import Types.CleanupActions
 import qualified CmdLine.GitAnnexShell.Fields as Fields
 import Logs.Location
+import Logs.Proxy
 import Utility.Metered
 import Utility.Env
 import Utility.Batch
@@ -66,7 +67,8 @@ import Messages.Progress
 
 import Control.Concurrent
 import qualified Data.Map as M
-import qualified Data.ByteString as S
+import qualified Data.Set as S
+import qualified Data.ByteString as B
 import qualified Utility.RawFilePath as R
 import Network.URI
 
@@ -92,7 +94,13 @@ list :: Bool -> Annex [Git.Repo]
 list autoinit = do
 	c <- fromRepo Git.config
 	rs <- mapM (tweakurl c) =<< Annex.getGitRemotes
-	mapM (configRead autoinit) (filter (not . isGitRemoteAnnex) rs)
+	rs' <- mapM (configRead autoinit) (filter (not . isGitRemoteAnnex) rs)
+	proxies <- getProxies
+	if proxies == mempty
+		then return rs'
+		else do
+			proxied <- listProxied proxies rs'
+			return (proxied++rs')
   where
 	annexurl r = remoteConfig r "annexurl"
 	tweakurl c r = do
@@ -265,7 +273,7 @@ tryGitConfigRead autoinit r hasuuid
 		v <- liftIO $ Git.Config.fromPipe r cmd params st
 		case v of
 			Right (r', val, _err) -> do
-				unless (isUUIDConfigured r' || S.null val || not mustincludeuuuid) $ do
+				unless (isUUIDConfigured r' || val == mempty || not mustincludeuuuid) $ do
 					warning $ UnquotedString $ "Failed to get annex.uuid configuration of repository " ++ Git.repoDescribe r
 					warning $ UnquotedString $ "Instead, got: " ++ show val
 					warning "This is unexpected; please check the network transport!"
@@ -772,3 +780,65 @@ mkState r u gc = do
 				)
 
 			return (duc, getrepo)
+
+listProxied :: M.Map UUID (S.Set Proxy) -> [Git.Repo] -> Annex [Git.Repo]
+listProxied proxies rs = concat <$> mapM go rs
+  where
+	go r = do
+		g <- Annex.gitRepo
+		u <- getRepoUUID r
+		gc <- Annex.getRemoteGitConfig r
+		let cu = fromMaybe u $ remoteAnnexConfigUUID gc
+		pure $ if not (canproxy gc r) || cu ==NoUUID
+			then []
+			else case M.lookup cu proxies of
+				Nothing -> []
+				Just s -> mapMaybe (mkproxied g r) (S.toList s)
+	
+	proxyremotename r p = do
+		n <- Git.remoteName r
+		pure $ n ++ "-" ++ proxyRemoteName p
+
+	mkproxied g r p = mkproxied' g r p =<< proxyremotename r p
+	
+	mkproxied' g r p proxyname
+		| any isconfig (M.keys (Git.config g)) = Nothing
+		-- The proxied remote is constructed by renaming the
+		-- proxy remote, changing its uuid, and inheriting some
+		-- of its config. The url in particular stays the same.
+		| otherwise = Just $ renamedr
+			{ Git.config = M.map Prelude.head c
+			, Git.fullconfig = c
+			}
+	  where
+		renamedr = r { Git.remoteName = Just proxyname }
+		
+		c = M.insert
+			(configRepoUUID renamedr)
+			[Git.ConfigValue $ fromUUID $ proxyRemoteUUID p]
+			inheritedconfig
+
+		inheritedconfig = M.fromList $
+			mapMaybe inheritconfig proxyInheritedFields
+		
+		inheritconfig k = do
+			let rk = remoteAnnexConfig r k
+			v <- M.lookup rk (Git.fullconfig r)
+			pure $ (rk, v)
+		
+		-- When the git config has anything set for a remote,
+		-- avoid making a proxied remote with the same name.
+		-- It is possible to set git configs of proxies, but it
+		-- needs both the url and uuid config to be manually set.
+		isconfig (Git.ConfigKey configkey) = 
+			configprefix `B.isPrefixOf` configkey
+		  where
+			Git.ConfigKey configprefix = remoteConfig proxyname mempty
+
+	-- Git remotes that are gcrypt or git-lfs special remotes cannot
+	-- proxy. Proxing is also not yet supported for remotes using P2P
+	-- addresses.
+	canproxy gc r
+		| remoteAnnexGitLFS gc = False
+		| Git.GCrypt.isEncrypted r = False
+		| otherwise = isNothing (repoP2PAddress r)