split out generic url stuff into a helper library from Remote.Web

Remote/Helper/Url.hs

@@ -0,0 +1,66 @@
+{- Url downloading for remotes.
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Remote.Helper.Url (
+	exists,
+	download,
+	get
+) where
+
+import Control.Monad (liftM)
+import Control.Monad.State (liftIO)
+import qualified Network.Browser as Browser
+import Network.HTTP
+import Network.URI
+
+import Types
+import Messages
+import Utility
+
+type URLString = String
+
+{- Checks that an url exists and could be successfully downloaded. -}
+exists :: URLString -> IO Bool
+exists url =
+	case parseURI url of
+		Nothing -> return False
+		Just u -> do
+			r <- request u HEAD
+			case rspCode r of
+				(2,_,_) -> return True
+				_ -> return False
+
+{- Used to download large files, such as the contents of keys.
+ - Uses curl program for its progress bar. -}
+download :: URLString -> FilePath -> Annex Bool
+download url file = do
+	showOutput -- make way for curl progress bar
+	liftIO $ boolSystem "curl" [Params "-L -C - -# -o", File file, File url]
+
+{- Downloads a small file. -}
+get :: URLString -> IO String
+get url =
+	case parseURI url of
+		Nothing -> error "url parse error"
+		Just u -> do
+			r <- request u GET
+			case rspCode r of
+				(2,_,_) -> return $ rspBody r
+				_ -> error $ rspReason r
+
+{- Makes a http request of an url. For example, HEAD can be used to
+ - check if the url exists, or GET used to get the url content (best for
+ - small urls). -}
+request :: URI -> RequestMethod -> IO (Response String)
+request url requesttype = Browser.browse $ do
+	Browser.setErrHandler ignore
+	Browser.setOutHandler ignore
+	Browser.setAllowRedirects True
+	liftM snd $ Browser.request
+		(mkRequest requesttype url :: Request_String)
+	where
+		ignore = const $ return ()