fromkey, registerurl: Allow urls to be specified instead of keys, and generate URL keys.

This is especially useful because the caller doesn't need to generate valid
url keys, which involves some escaping of characters, and may involve
taking a md5sum of the url if it's too long.

Command/FromKey.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010 Joey Hess <id@joeyh.name>
+ - Copyright 2010, 2015 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -15,6 +15,9 @@ import qualified Annex.Queue
 import Annex.Content
 import Types.Key
 import qualified Annex
+import qualified Backend.URL
+
+import Network.URI
 
 cmd :: [Command]
 cmd = [notDirect $ notBareRepo $
@@ -28,7 +31,7 @@ seek ps = do
 
 start :: Bool -> [String] -> CommandStart
 start force (keyname:file:[]) = do
-	let key = fromMaybe (error "bad key") $ file2key keyname
+	let key = mkKey keyname
 	unless force $ do
 		inbackend <- inAnnex key
 		unless inbackend $ error $
@@ -45,12 +48,19 @@ massAdd = go True =<< map (separate (== ' ')) . lines <$> liftIO getContents
   where
 	go status [] = next $ return status
 	go status ((keyname,f):rest) | not (null keyname) && not (null f) = do
-		let key = fromMaybe (error $ "bad key " ++ keyname) $ file2key keyname
+		let key = mkKey keyname
 		ok <- perform' key f
 		let !status' = status && ok
 		go status' rest
 	go _ _ = error "Expected pairs of key and file on stdin, but got something else."
 
+mkKey :: String -> Key
+mkKey s = case file2key s of
+	Just k -> k
+	Nothing -> case parseURI s of
+		Just _u -> Backend.URL.fromUrl s Nothing
+		Nothing -> error $ "bad key " ++ s
+
 perform :: Key -> FilePath -> CommandPerform
 perform key file = do
 	ok <- perform' key file