send LEN to ACK/SUB when suspended queue has no messages

src/Simplex/Messaging/Client.hs

@@ -375,8 +375,11 @@ subscribeSMPQueue :: SMPClient -> RcvPrivateSignKey -> RecipientId -> ExceptT Pr
 subscribeSMPQueue c rpKey rId =
   sendSMPCommand c (Just rpKey) rId SUB >>= \case
     OK -> return ()
-    cmd@MSG {} -> liftIO $ writeSMPMessage c rId cmd
+    cmd@MSG {} -> deliver cmd
+    cmd@LEN {} -> deliver cmd
     r -> throwE . PCEUnexpectedResponse $ bshow r
+  where
+    deliver = liftIO . writeSMPMessage c rId
 
 -- | Subscribe to multiple SMP queues batching commands if supported.
 subscribeSMPQueues :: SMPClient -> NonEmpty (RcvPrivateSignKey, RecipientId) -> IO (NonEmpty (Either ProtocolClientError ()))
@@ -385,9 +388,12 @@ subscribeSMPQueues c qs = sendProtocolCommands c cs >>= mapM response . L.zip qs
     cs = L.map (\(rpKey, rId) -> (Just rpKey, rId, Cmd SRecipient SUB)) qs
     response ((_, rId), r) = case r of
       Right OK -> pure $ Right ()
-      Right cmd@MSG {} -> writeSMPMessage c rId cmd $> Right ()
+      Right cmd@MSG {} -> deliver cmd
+      Right cmd@LEN {} -> deliver cmd
       Right r' -> pure . Left . PCEUnexpectedResponse $ bshow r'
       Left e -> pure $ Left e
+      where
+        deliver cmd = writeSMPMessage c rId cmd $> Right ()
 
 writeSMPMessage :: SMPClient -> RecipientId -> BrokerMsg -> IO ()
 writeSMPMessage c rId msg = atomically $ mapM_ (`writeTBQueue` serverTransmission c rId msg) (msgQ c)
@@ -403,8 +409,11 @@ getSMPMessage :: SMPClient -> RcvPrivateSignKey -> RecipientId -> ExceptT Protoc
 getSMPMessage c rpKey rId =
   sendSMPCommand c (Just rpKey) rId GET >>= \case
     OK -> pure Nothing
-    cmd@(MSG msg) -> liftIO (writeSMPMessage c rId cmd) $> Just msg
+    cmd@(MSG msg) -> deliver cmd $> Just msg
+    cmd@LEN {} -> deliver cmd $> Nothing
     r -> throwE . PCEUnexpectedResponse $ bshow r
+  where
+    deliver = liftIO . writeSMPMessage c rId
 
 -- | Subscribe to the SMP queue notifications.
 --
@@ -469,8 +478,11 @@ ackSMPMessage :: SMPClient -> RcvPrivateSignKey -> QueueId -> MsgId -> ExceptT P
 ackSMPMessage c rpKey rId msgId =
   sendSMPCommand c (Just rpKey) rId (ACK msgId) >>= \case
     OK -> return ()
-    cmd@MSG {} -> liftIO $ writeSMPMessage c rId cmd
+    cmd@MSG {} -> deliver cmd
+    cmd@LEN {} -> deliver cmd
     r -> throwE . PCEUnexpectedResponse $ bshow r
+  where
+    deliver = liftIO . writeSMPMessage c rId
 
 -- | Irreversibly suspend SMP queue.
 -- The existing messages from the queue will still be delivered.

src/Simplex/Messaging/Server.hs

@@ -590,7 +590,9 @@ client clnt@Client {thVersion, subscriptions, ntfSubscriptions, rcvQ, sndQ} Serv
                 Just msg ->
                   let encMsg = encryptMsg qr msg
                    in atomically (setDelivered s msg) $> (corrId, rId, MSG encMsg)
-                _ -> forkSub $> ok
+                _
+                  | status qr == QueueActive -> forkSub $> ok
+                  | otherwise -> pure (corrId, rId, LEN 0)
             _ -> pure ok
           where
             forkSub :: m ()

tests/AgentTests/FunctionalAPITests.hs

@@ -189,8 +189,8 @@ runAgentClientTest alice bob baseId = do
     get alice =##> \case ("", c, Msg "hello too") -> c == bobId; _ -> False
     ackMessage alice bobId $ baseId + 3
     get alice =##> \case ("", c, Msg "message 1") -> c == bobId; _ -> False
-    ackMessage alice bobId $ baseId + 4
     _ <- suspendConnection alice bobId
+    ackMessage alice bobId $ baseId + 4
     5 <- msgId <$> sendMessage bob aliceId SMP.noMsgFlags "message 2"
     get bob ##> ("", aliceId, MERR (baseId + 5) (SMP AUTH))
     deleteConnection alice bobId

tests/ServerTests.hs

@@ -265,7 +265,7 @@ testCreateDelete (ATransport t) =
       Resp "bcda" _ err2 <- signSendRecv rh rKey ("bcda", sId, OFF)
       (err2, ERR AUTH) #== "rejects OFF with sender's ID"
 
-      Resp "cdab" rId2 (LEN _) <- signSendRecv rh rKey ("cdab", rId, OFF)
+      Resp "cdab" rId2 (LEN 2) <- signSendRecv rh rKey ("cdab", rId, OFF)
       (rId2, rId) #== "same queue ID in response 2"
 
       Resp "dabc" _ err3 <- signSendRecv sh sKey ("dabc", sId, _SEND "hello")
@@ -279,6 +279,11 @@ testCreateDelete (ATransport t) =
       Resp "cdab" _ (Msg mId2 msg2) <- signSendRecv rh rKey ("cdab", rId, SUB)
       (dec mId2 msg2, Right "hello") #== "accepts SUB when suspended and delivers the message again (because was not ACKed)"
 
+      Resp "abcd" _ (Msg mId3 msg3) <- signSendRecv rh rKey ("abcd", rId, ACK mId2)
+      (dec mId3 msg3, Right "hello 2") #== "deliver the next message on ACK"
+
+      Resp "bcda" _ (LEN 0) <- signSendRecv rh rKey ("bcda", rId, ACK mId3)
+
       Resp "dabc" _ err5 <- sendRecv rh (sampleSig, "dabc", rId, DEL)
       (err5, ERR AUTH) #== "rejects DEL with wrong signature"