extract and build subscriber payload for sending

src/Hash2Pub/PostService.hs

@@ -301,20 +301,47 @@ 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
+-- | 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 d
+                           -> 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 <- takeRMapSuccessorsFromTo (genKeyID $ Txt.unpack fromTag) (genKeyID $ Txt.unpack fromTag) <$> readTVarIO (subscribers serv)
+    -- returns a [ (TagSubscribersSTM, TChan PostID, Hashtag) ]
+    -- extract subscribers and posts
+    -- no need for extracting as a single atomic operation, as newly incoming posts are supposed to be rejected because of already having re-positioned on the DHT
+    subscriberData <- foldM (\response (subSTM, _, tag) -> do
+        subMap <- readTVarIO subSTM
+        thisTagsData <- foldM (\tagResponse (subscriber, (subChan, lease)) -> do
+            -- duplicate the pending queue to work on a copy, in case of a delivery error
+            pending <- atomically $ do
+                queueCopy <- cloneTChan subChan
+                channelGetAll queueCopy
+            if null pending
+               then pure tagResponse
+               else pure $ tag <> "," <> Txt.pack (show subscriber) <> "," <> Txt.pack (show lease) <> "," <> Txt.unwords pending <> "\n"
+              )
+            ""
+            (HMap.toList subMap)
+        pure $ thisTagsData <> response
+            )
+        ""
+        intervalTags
+    -- 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
+    pure . Right $ ()
+  where
+      channelGetAll :: TChan a -> STM [a]
+      channelGetAll chan = channelGetAll' chan []
+      channelGetAll' :: TChan a -> [a] -> STM [a]
+      channelGetAll' chan acc = do
+          haveRead <- tryReadTChan chan
+          maybe (pure acc) (\x -> channelGetAll' chan (x:acc)) haveRead
 
 -- currently this is unused code
 getClients :: String -> Int -> HTTP.Manager -> Client IO PostServiceAPI