assistant: XMPP git pull and push requests are cached and sent when presence of a new client is detected.

Noticed that, At startup or network reconnect, git push messages were sent,
often before presence info has been gathered, so were not sent to any
buddies.

To fix this, keep track of which buddies have seen such messages,
and when new presence is received from a buddy that has not yet seen it,
resend.

This is done only for push initiation messages, so very little data needs
to be stored.

Assistant/NetMessager.hs

@@ -15,6 +15,7 @@ import Control.Concurrent.STM
 import Control.Concurrent.MSampleVar
 import Control.Exception as E
 import qualified Data.Set as S
+import qualified Data.Map as M
 
 sendNetMessage :: NetMessage -> Assistant ()
 sendNetMessage m = 
@@ -30,6 +31,42 @@ notifyNetMessagerRestart =
 waitNetMessagerRestart :: Assistant ()
 waitNetMessagerRestart = readSV <<~ (netMessagerRestart . netMessager)
 
+{- Store an important NetMessage for a client, and if the same message was
+ - already sent, remove it from sentImportantNetMessages. -}
+storeImportantNetMessage :: NetMessage -> ClientID -> (ClientID -> Bool) -> Assistant ()
+storeImportantNetMessage m client matchingclient = go <<~ netMessager
+  where
+	go nm = atomically $ do
+		q <- takeTMVar $ importantNetMessages nm
+		sent <- takeTMVar $ sentImportantNetMessages nm
+		putTMVar (importantNetMessages nm) $
+			M.alter (Just . maybe (S.singleton m) (S.insert m)) client q
+		putTMVar (sentImportantNetMessages nm) $
+			M.mapWithKey removematching sent
+	removematching someclient s
+		| matchingclient someclient = S.delete m s
+		| otherwise = s
+
+{- Indicates that an important NetMessage has been sent to a client. -}
+sentImportantNetMessage :: NetMessage -> ClientID -> Assistant ()
+sentImportantNetMessage m client = go <<~ (sentImportantNetMessages . netMessager)
+  where
+	go v = atomically $ do
+		sent <- takeTMVar v
+		putTMVar v $
+			M.alter (Just . maybe (S.singleton m) (S.insert m)) client sent
+
+{- Checks for important NetMessages that have been stored for a client, and
+ - sent to a client. Typically the same client for both, although 
+ - a modified or more specific client may need to be used. -}
+checkImportantNetMessages :: (ClientID, ClientID) -> Assistant (S.Set NetMessage, S.Set NetMessage)
+checkImportantNetMessages (storedclient, sentclient) = go <<~ netMessager
+  where
+	go nm = atomically $ do
+		stored <- M.lookup storedclient <$> (readTMVar $ importantNetMessages nm)
+		sent <- M.lookup sentclient <$> (readTMVar $ sentImportantNetMessages nm)
+		return (fromMaybe S.empty stored, fromMaybe S.empty sent)
+
 {- Runs an action that runs either the send or receive side of a push.
  -
  - While the push is running, netMessagesPush will get messages put into it