flush responsibility cache and retry in post queue delivery

src/Hash2Pub/PostService.hs

@@ -301,6 +301,20 @@ clientAPI = Proxy
 relayInboxClient :<|> subscriptionDeliveryClient :<|> postFetchClient :<|> postMultiFetchClient :<|> postInboxClient :<|> tagDeliveryClient :<|> tagSubscribeClient :<|> tagUnsubscribeClient = client clientAPI
 
 
+---- | Deliver the subscriber list of all hashtags in the interval [fromTag, toTag]
+---- and their outstanding delivery queue to another instance.
+---- If the transfer succeeds, the transfered subscribers are removed from the local list.
+--clientDeliverSubscriptions :: PostService
+--                           -> Hashtag -- ^ fromTag
+--                           -> Hashtag -- ^ toTag
+--                           -> (String, Int)     -- ^ hostname and port of instance to deliver to
+--                           -> IO (Either String ())     -- Either signals success or failure
+--clientDeliverSubscriptions serv fromTag toTag (toHost, toPort) = do
+--    -- collect tag intearval
+--    intervalTags <- takeRMapSuccesorsFromTo (genKeyID $ Txt.unpack fromTag) (genKeyID $ Txt.unpack fromTag) =<< readTVarIO $ subscribers serv
+--    -- extract subscribers and posts
+--    -- send subscribers
+--    -- on failure return a Left, otherwise flush remaining queues atomically, schedule all newly arrived posts to still be relayed and delete subscription entry
 
 -- currently this is unused code
 getClients :: String -> Int -> HTTP.Manager -> Client IO PostServiceAPI
@@ -407,7 +421,7 @@ instance {-# OVERLAPPABLE #-} Read a => MimeUnrender PlainText a where
 
 -- ====== worker threads ======
 
--- | process the pending relays of incoming posts from the internal queue:
+-- | process the pending relay inbox of incoming posts from the internal queue:
 -- Look up responsible relay node for given hashtag and forward post to it
 processIncomingPosts :: DHT d => PostService d -> IO ()
 processIncomingPosts serv = forever $ do
@@ -422,5 +436,11 @@ processIncomingPosts serv = forever $ do
         httpMan <- HTTP.newManager HTTP.defaultManagerSettings
         resp <- runClientM (relayInboxClient tag $ pID <> "," <> pContent) (mkClientEnv httpMan (BaseUrl Http responsibleHost (fromIntegral responsiblePort) ""))
         case resp of
-          Left err  -> putStrLn $ "Error: " <> show err
+          Left err  -> do
+              putStrLn $ "Error: " <> show err
+              -- 410 error indicates outdated responsibility mapping
+              -- Simplification: just invalidate the mapping entry on all errors, force a re-lookup and re-queue the post
+              -- TODO: keep track of maximum retries
+              _ <- forceLookupKey (baseDHT serv) (Txt.unpack tag)
+              atomically . writeTQueue (relayInQueue serv) $ (tag, pID, pContent)
           Right yay -> putStrLn $ "Yay! " <> show yay