When possible, build with the haskell torrent library for parsing torrent files.

BuildFlags.hs

@@ -86,6 +86,11 @@ buildFlags = filter (not . null)
 #else
 #warning Building without CryptoHash.
 #endif
+#ifdef WITH_TORRENTParser
+	, "TorrentParser"
+#else
+#warning Building without haskell torrent library; will instead use btshowmetainfo to parse torrent files.
+#endif
 #ifdef WITH_EKG
 	, "EKG"
 #endif

Remote/BitTorrent.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
+{-# LANGUAGE CPP #-}
+
 module Remote.BitTorrent (remote) where
 
 import Common.Annex
@@ -14,8 +16,6 @@ import qualified Git
 import qualified Git.Construct
 import Config.Cost
 import Logs.Web
-import Logs.Trust.Basic
-import Types.TrustLevel
 import Types.UrlContents
 import Types.CleanupActions
 import Types.Key
@@ -26,9 +26,13 @@ import Annex.Perms
 import Annex.UUID
 import qualified Annex.Url as Url
 
-import qualified Data.Map as M
 import Network.URI
 
+#ifdef WITH_TORRENTPARSER
+import Data.Torrent
+import qualified Data.ByteString.Lazy as B
+#endif
+
 remote :: RemoteType
 remote = RemoteType {
 	typename = "bittorrent",
@@ -106,7 +110,7 @@ dropKey k = do
  - implemented, it tells us nothing about the later state of the torrent.
  -}
 checkKey :: Key -> Annex Bool
-checkKey key = error "cannot reliably check torrent status"
+checkKey = error "cannot reliably check torrent status"
 
 getBitTorrentUrls :: Key -> Annex [URLString]
 getBitTorrentUrls key = filter supported <$> getUrls key
@@ -266,9 +270,16 @@ downloadTorrentContent k u dest filenum p = do
 
 checkDependencies :: Annex ()
 checkDependencies = do
-	missing <- liftIO $ filterM (not <$$> inPath) ["aria2c", "btshowmetainfo"]
+	missing <- liftIO $ filterM (not <$$> inPath) deps
 	unless (null missing) $
 		error $ "need to install additional software in order to download from bittorrent: " ++ unwords missing
+  where
+	deps =
+		[ "aria2c"
+#ifndef TORRENT
+		, "btshowmetainfo"
+#endif
+		]
 
 ariaParams :: [CommandParam] -> Annex [CommandParam]
 ariaParams ps = do
@@ -299,9 +310,8 @@ parseAriaProgress totalsize = go [] . reverse . split ['\r']
 
 	frompercent p = toBytesProcessed $ totalsize * p `div` 100
 
-{- It would be better to use http://hackage.haskell.org/package/torrent,
+{- Used only if the haskell torrent library is not available. -}
- - but that package won't currently build. I sent a patch fixing it
+#ifndef WITH_TORRENTPARSER
- - to its author and plan to upload in Jan 2015 if I don't hear back. -}
 btshowmetainfo :: FilePath -> String -> IO [String]
 btshowmetainfo torrent field = 
 	findfield [] . lines <$> readProcess "btshowmetainfo" [torrent]
@@ -319,12 +329,25 @@ btshowmetainfo torrent field =
 	multiline c [] = findfield c []
 
 	fieldkey = field ++ take (14 - length field) (repeat '.') ++ ": "
+#endif
 
 {- Examines the torrent file and gets the list of files in it,
  - and their sizes.
  -}
 torrentFileSizes :: FilePath -> IO [(FilePath, Integer)]
 torrentFileSizes torrent = do
+#ifdef WITH_TORRENTPARSER
+	let mkfile = joinPath . map (scrub . decodeBS)
+	b <- B.readFile torrent
+	return $ case readTorrent b of
+		Left e -> error $ "failed to parse torrent: " ++ e
+		Right t -> case tInfo t of
+			SingleFile { tLength = l, tName = f } ->
+				[ (mkfile [f], l) ]
+			MultiFile { tFiles = fs, tName = dir } ->
+				map (\tf -> (mkfile $ dir:filePath tf, fileLength tf)) fs
+  where
+#else
 	files <- getfield "files"
 	if null files
 		then do
@@ -334,13 +357,12 @@ torrentFileSizes torrent = do
 				((fn:[]), (Just sz:[])) -> return [(scrub fn, sz)]
 		 		_ -> parsefailed (show (fnl, szl))
 		else do
-			v <- btshowmetainfo torrent "directory name"
+			v <- getfield "directory name"
 			case v of
 				(d:[]) -> return $ map (splitsize d) files
 				_ -> parsefailed (show v)
   where
 	getfield = btshowmetainfo torrent
-
 	parsefailed s = error $ "failed to parse btshowmetainfo output for torrent file: " ++ show s
 
 	-- btshowmetainfo outputs a list of "filename (size)"
@@ -351,7 +373,7 @@ torrentFileSizes torrent = do
 				reverse l
 		fn = reverse $ drop 2 $
 			dropWhile (/= '(') $ dropWhile (== ')') $ reverse l
-
+#endif
 	-- a malicious torrent file might try to do directory traversal
 	scrub f = if isAbsolute f || any (== "..") (splitPath f)
 		then error "found unsafe filename in torrent!"

debian/changelog

@@ -13,7 +13,10 @@ git-annex (5.20141204) UNRELEASED; urgency=medium
   * addurl behavior change: When downloading an url ending in .torrent,
     it will download files from bittorrent, instead of the old behavior
     of adding the torrent file to the repository.
-  * Added Recommends on aria2 and bittornado | bittorrent.
+  * Added Recommends on aria2.
+  * When possible, build with the haskell torrent library for parsing
+    torrent files. As a fallback, can instead use btshowmetainfo from
+    bittornado | bittorrent.
 
  -- Joey Hess <id@joeyh.name>  Fri, 05 Dec 2014 13:42:08 -0400
 

doc/special_remotes/bittorrent.mdwn

@@ -8,8 +8,10 @@ torrent and add it to the git annex repository.
 See [[tips/using_the_web_as_a_special_remote]] for usage examples.
 
 git-annex uses [aria2](http://aria2.sourceforge.net/) to download torrents.
-It also needs the `btshowmetainfo` program, from either
+
-bittornado or the original BitTorrent client.
+If git-annex is not built using the haskell torrent library to parse
+torrents, it also needs the needs the `btshowmetainfo` program, from
+either bittornado or the original BitTorrent client.
 
 ## notes
 

git-annex.cabal

@@ -93,6 +93,9 @@ Flag CryptoHash
 Flag DesktopNotify
   Description: Enable desktop environment notifications
 
+Flag TorrentParser
+  Description: Use haskell torrent library to parse torrent files
+
 Flag EKG
   Description: Enable use of EKG to monitor git-annex as it runs (at http://localhost:4242/)
   Default: False
@@ -234,6 +237,10 @@ Executable git-annex
     Build-Depends: aeson
     CPP-Options: -DWITH_TAHOE
 
+  if flag(TorrentParser)
+    Build-Depends: torrent (>= 10000.0.0)
+    CPP-Options: -DWITH_TORRENTPARSER
+
   if flag(EKG)
     Build-Depends: ekg
     GHC-Options: -with-rtsopts=-T