Send a git-annex user-agent when downloading urls.

Overridable with --user-agent option.

Not yet done for S3 or WebDAV due to limitations of libraries used --
nether allows a user-agent header to be specified.

This commit sponsored by Michael Zehrer.

Annex/Url.hs

@@ -0,0 +1,27 @@
+{- Url downloading, with git-annex user agent.
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.Url (
+	module U,
+	withUserAgent,
+	getUserAgent,
+) where
+
+import Common.Annex
+import qualified Annex
+import Utility.Url as U
+import qualified Build.SysConfig as SysConfig
+
+defaultUserAgent :: U.UserAgent
+defaultUserAgent = "git-annex/" ++ SysConfig.packageversion
+
+getUserAgent :: Annex (Maybe U.UserAgent)
+getUserAgent = Annex.getState $ 
+	Just . fromMaybe defaultUserAgent . Annex.useragent
+
+withUserAgent :: (Maybe U.UserAgent -> IO a) -> Annex a
+withUserAgent a = liftIO . a =<< getUserAgent