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diff --git a/Annex/Multicast.hs b/Annex/Multicast.hs
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+{- git-annex multicast receive callback
+ -
+ - Copyright 2017 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.Multicast where
+
+import Config.Files
+import Utility.Env
+import Utility.PartialPrelude
+
+import System.Process
+import System.IO
+import GHC.IO.Handle.FD
+
+multicastReceiveEnv :: String
+multicastReceiveEnv = "GIT_ANNEX_MULTICAST_RECEIVE"
+
+multicastCallbackEnv :: IO (FilePath, [(String, String)], Handle)
+multicastCallbackEnv = do
+	gitannex <- readProgramFile
+	(rfd, wfd) <- createPipeFd
+	rh <- fdToHandle rfd
+	environ <- addEntry multicastReceiveEnv (show wfd) <$> getEnvironment
+	return (gitannex, environ, rh)
+
+-- This is run when uftpd has received a file. Rather than move
+-- the file into the annex here, which would require starting up the
+-- Annex monad, parsing git config, and verifying the content, simply
+-- output to the specified FD the filename. This keeps the time
+-- that uftpd is not receiving the next file as short as possible.
+runMulticastReceive :: [String] -> String -> IO ()
+runMulticastReceive ("-I":_sessionid:fs) hs = case readish hs of
+	Just fd -> do
+		h <- fdToHandle fd
+		mapM_ (hPutStrLn h) fs
+		hClose h
+	Nothing -> return ()
+runMulticastReceive _ _ = return ()