add equivilant key log for VURL keys

When downloading a VURL from the web, make sure that the equivilant key
log is populated.

Unfortunately, this does not hash the content while it's being
downloaded from the web. There is not an interface in Backend currently
for incrementally hash generation, only for incremental verification of an
existing hash. So this might add a noticiable delay, and it has to show
a "(checksum...") message. This could stand to be improved.

But, that separate hashing step only has to happen on the first download
of new content from the web. Once the hash is known, the VURL key can have
its hash verified incrementally while downloading except when the
content in the web has changed. (Doesn't happen yet because
verifyKeyContentIncrementally is not implemented yet for VURL keys.)

Note that the equivilant key log file is formatted as a presence log.
This adds a tiny bit of overhead (eg "1 ") per line over just listing the
urls. The reason I chose to use that format is it seems possible that
there will need to be a way to remove an equivilant key at some point in
the future. I don't know why that would be necessary, but it seemed wise
to allow for the possibility.

Downloads of VURL keys from other special remotes that claim urls,
like bittorrent for example, does not popilate the equivilant key log.
So for now, no checksum verification will be done for those.

Sponsored-by: Nicholas Golder-Manning on Patreon

Backend.hs

@@ -1,6 +1,6 @@
 {- git-annex key/value backends
  -
- - Copyright 2010-2021 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2024 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -10,6 +10,7 @@
 module Backend (
 	builtinList,
 	defaultBackend,
+	defaultHashBackend,
 	genKey,
 	getBackend,
 	chooseBackend,
@@ -18,6 +19,7 @@ module Backend (
 	maybeLookupBackendVariety,
 	isStableKey,
 	isCryptographicallySecure,
+	isCryptographicallySecure',
 ) where
 
 import Annex.Common
@@ -40,7 +42,13 @@ import qualified Data.Map as M
 builtinList :: [Backend]
 builtinList = Backend.Hash.backends ++ Backend.WORM.backends ++ Backend.URL.backends
 
-{- Backend to use by default when generating a new key. -}
+{- The default hashing backend. This must use a cryptographically secure
+ - hash. -}
+defaultHashBackend :: Backend
+defaultHashBackend = Prelude.head builtinList
+
+{- Backend to use by default when generating a new key. Takes git config
+ - and --backend option into account. -}
 defaultBackend :: Annex Backend
 defaultBackend = maybe cache return =<< Annex.getState Annex.backend
   where
@@ -49,7 +57,7 @@ defaultBackend = maybe cache return =<< Annex.getState Annex.backend
 			=<< Annex.getRead Annex.forcebackend
 		b <- case n of
 			Just name | valid name -> lookupname name
-			_ -> pure (Prelude.head builtinList)
+			_ -> pure defaultHashBackend
 		Annex.changeState $ \s -> s { Annex.backend = Just b }
 		return b
 	valid name = not (null name)
@@ -116,5 +124,8 @@ isStableKey k = maybe False (`B.isStableKey` k)
 	<$> maybeLookupBackendVariety (fromKey keyVariety k)
 
 isCryptographicallySecure :: Key -> Annex Bool
-isCryptographicallySecure k = maybe False B.isCryptographicallySecure
+isCryptographicallySecure k = maybe False isCryptographicallySecure'
 	<$> maybeLookupBackendVariety (fromKey keyVariety k)
+
+isCryptographicallySecure' :: Backend -> Bool
+isCryptographicallySecure' = B.isCryptographicallySecure

Backend/Hash.hs

@@ -11,6 +11,7 @@ module Backend.Hash (
 	backends,
 	testKeyBackend,
 	keyHash,
+	descChecksum,
 ) where
 
 import Annex.Common

Backend/URL.hs

@@ -15,6 +15,7 @@ import Annex.Common
 import Types.Key
 import Types.Backend
 import Backend.Utilities
+import Logs.EquivilantKeys
 
 backends :: [Backend]
 backends = [backendURL, backendVURL]

Logs.hs

@@ -1,6 +1,6 @@
 {- git-annex log file names
  -
- - Copyright 2013-2023 Joey Hess <id@joeyh.name>
+ - Copyright 2013-2024 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -35,7 +35,9 @@ getLogVariety config f
 	| isRemoteStateLog f = Just NewUUIDBasedLog
 	| isRemoteContentIdentifierLog f = Just NewUUIDBasedLog
 	| isRemoteMetaDataLog f = Just RemoteMetaDataLog
-	| isMetaDataLog f || f `elem` otherTopLevelLogs = Just OtherLog
+	| isMetaDataLog f
+		|| f `elem` otherTopLevelLogs
+		|| isEquivilantKeyLog f = Just OtherLog
 	| otherwise = (LocationLog <$> locationLogFileKey config f)
 		<|> (ChunkLog <$> extLogFileKey chunkLogExt f)
 		<|> (UrlLog  <$> urlLogFileKey f)
@@ -70,6 +72,7 @@ keyLogFiles config k =
 	, remoteMetaDataLogFile config k
 	, remoteContentIdentifierLogFile config k
 	, chunkLogFile config k
+	, equivilantKeysLogFile config k
 	] ++ oldurlLogs config k
 
 {- All uuid-based logs stored in the top of the git-annex branch. -}
@@ -208,6 +211,18 @@ chunkLogFile config key =
 chunkLogExt :: S.ByteString
 chunkLogExt = ".log.cnk"
 
+{- The filename of the equivilant keys log for a given key. -}
+equivilantKeysLogFile :: GitConfig -> Key -> RawFilePath
+equivilantKeysLogFile config key = 
+	(branchHashDir config key P.</> keyFile key)
+		<> equivilantKeyLogExt
+
+equivilantKeyLogExt :: S.ByteString
+equivilantKeyLogExt = ".log.ek"
+
+isEquivilantKeyLog :: RawFilePath -> Bool
+isEquivilantKeyLog path = equivilantKeyLogExt `S.isSuffixOf` path
+
 {- The filename of the metadata log for a given key. -}
 metaDataLogFile :: GitConfig -> Key -> RawFilePath
 metaDataLogFile config key =

Logs/EquivilantKeys.hs

@@ -0,0 +1,31 @@
+{- Logs listing keys that are equivilant to a key.
+ -
+ - Copyright 2024 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+{-# LANGUAGE BangPatterns #-}
+
+module Logs.EquivilantKeys (
+	getEquivilantKeys,
+	setEquivilantKey,
+) where
+
+import Annex.Common
+import qualified Annex
+import Logs
+import Logs.Presence
+import qualified Annex.Branch
+
+getEquivilantKeys :: Key -> Annex [Key]
+getEquivilantKeys key = do
+	config <- Annex.getGitConfig
+	mapMaybe (deserializeKey' . fromLogInfo)
+		<$> presentLogInfo (equivilantKeysLogFile config key)
+
+setEquivilantKey :: Key -> Key -> Annex ()
+setEquivilantKey key equivkey = do
+	config <- Annex.getGitConfig
+	addLog (Annex.Branch.RegardingUUID []) (equivilantKeysLogFile config key)
+		InfoPresent (LogInfo (serializeKey' equivkey))

Remote/Web.hs

@@ -1,6 +1,6 @@
 {- Web remote.
  -
- - Copyright 2011-2023 Joey Hess <id@joeyh.name>
+ - Copyright 2011-2024 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -11,6 +11,8 @@ import Annex.Common
 import Types.Remote
 import Types.ProposedAccepted
 import Types.Creds
+import Types.Key
+import Types.KeySource
 import Remote.Helper.Special
 import Remote.Helper.ExportImport
 import qualified Git
@@ -27,6 +29,9 @@ import qualified Annex.Url as Url
 import Annex.YoutubeDl
 import Annex.SpecialRemote.Config
 import Logs.Remote
+import Logs.EquivilantKeys
+import Backend
+import Backend.Hash (descChecksum)
 
 import qualified Data.Map as M
 
@@ -124,22 +129,61 @@ downloadKey urlincludeexclude key _af dest p vc =
 			, "known url(s) failed"
 			]
 	
+	isyoutube (_, YoutubeDownloader) = True
+	isyoutube _ = False
+
 	dl ([], ytus) = flip getM (map fst ytus) $ \u ->
 		ifM (youtubeDlTo key u dest p)
-			( return (Just UnVerified)
+			( postdl UnVerified
 			, return Nothing
 			)
 	dl (us, ytus) = do
 		iv <- startVerifyKeyContentIncrementally vc key
 		ifM (Url.withUrlOptions $ downloadUrl True key p iv (map fst us) dest)
 			( finishVerifyKeyContentIncrementally iv >>= \case
-				(True, v) -> return (Just v)
+				(True, v) -> postdl v
 				(False, _) -> dl ([], ytus)
 			, dl ([], ytus)
 			)
 
-	isyoutube (_, YoutubeDownloader) = True
+	postdl v@Verified = return (Just v)
-	isyoutube _ = False
+	postdl v = do
+		when (fromKey keyVariety key == VURLKey) $
+			recordvurlkey
+		return (Just v)
+	
+	-- For a VURL key that was not verified on download, 
+	-- need to generate a hashed key for the content downloaded
+	-- from the web, and record it for later use verifying this content.
+	--
+	-- But when the VURL key has a known size, and already has a
+	-- recorded hashed key, don't record a new key, since the content
+	-- on the web is expected to be stable for such a key.
+	recordvurlkey = case fromKey keySize key of
+		Nothing -> recordvurlkey' =<< getEquivilantKeys key
+		Just _ -> do
+			eks <- getEquivilantKeys key
+			if null eks
+				then recordvurlkey' eks
+				else return ()
+	
+	recordvurlkey' eks = do
+		-- Make sure to pick a backend that is cryptographically
+		-- secure.
+		db <- defaultBackend
+		let b = if isCryptographicallySecure' db
+			then db
+			else defaultHashBackend
+		showSideAction (UnquotedString descChecksum)
+		(hashk, _) <- genKey ks nullMeterUpdate b
+		unless (hashk `elem` eks) $
+			setEquivilantKey key hashk
+	  where
+		ks = KeySource
+			{ keyFilename = mempty -- avoid adding any extension
+			, contentLocation = toRawFilePath dest
+			, inodeCache = Nothing
+			}
 
 uploadKey :: Key -> AssociatedFile -> MeterUpdate -> Annex ()
 uploadKey _ _ _ = giveup "upload to web not supported"

Types/Key.hs

@@ -134,12 +134,12 @@ buildKeyData k = byteString (formatKeyVariety (keyVariety k))
 	c ?: (Just b) = sepbefore (char7 c <> b)
 	_ ?: Nothing = mempty
 
-{- This is a strict parser for security reasons; a key
+{- This is a strict parser for security reasons; in addition to keyName,
- - can contain only 4 fields, which all consist only of numbers.
+ - a key can contain only 4 fields, which all consist only of numbers.
  - Any key containing other fields, or non-numeric data will fail
  - to parse.
  -
- - If a key contained non-numeric fields, they could be used to
+ - If a key contained other non-numeric fields, they could be used to
  - embed data used in a SHA1 collision attack, which would be a
  - problem since the keys are committed to git.
  -}

doc/internals.mdwn

@@ -224,6 +224,13 @@ These log files record urls used by the
 Their format is similar to the location tracking files, but with urls
 rather than UUIDs.
 
+## `aaa/bbb/*.log.ek`
+
+These log files record other keys that are equivilant to the key
+used in the filename. This is currently used for the `VURL` backend.
+Their format is similar to the location tracking files, but with keys
+rather than UUIDs.
+
 ## `aaa/bbb/*.log.rmt`
 
 These log files are used by remotes that need to record their own state

git-annex.cabal

@@ -812,6 +812,7 @@ Executable git-annex
     Logs.ContentIdentifier.Pure
     Logs.Difference
     Logs.Difference.Pure
+    Logs.EquivilantKeys
     Logs.Export
     Logs.Export.Pure
     Logs.File