bugfix: fix join by adding join node and waiting for it

- additionally to adding neighbours of join node, add the join node
  itself as a neighbour as well
- wait for migrations from the node

src/Hash2Pub/DHTProtocol.hs

@@ -516,20 +516,19 @@ requestJoin toJoinOn ownStateSTM = do
                     ([], Set.empty, Set.empty)
                     responses
                 -- sort, slice and set the accumulated successors and predecessors
-                newState = setSuccessors (Set.elems succAccSet) . setPredecessors (Set.elems predAccSet) $ stateSnap
+                -- the contacted node itself is a successor as well and, with few 
+                -- nodes, can be a predecessor as well
+                newState = setSuccessors (toRemoteNodeState toJoinOn:Set.elems succAccSet) . setPredecessors (toRemoteNodeState toJoinOn:Set.elems predAccSet) $ stateSnap
             writeTVar ownStateSTM newState
             pure (cacheInsertQ, newState)
         -- execute the cache insertions
         mapM_ (\f -> f joinedState) cacheInsertQ
         if responses == Set.empty
                   then pure . Left $ "join error: got no response from " <> show (getNid toJoinOn)
-           else if null (predecessors joinedState) && null (successors joinedState)
-                then pure $ Left "join error: no predecessors or successors"
-                -- successful join
-                else do
-                    -- wait for migration data to be completely received
-                    waitForMigrationFrom (nodeService prn) (getNid ownState)
-                    pure $ Right ownStateSTM
+           else do
+                -- wait for migration data to be completely received
+                waitForMigrationFrom (nodeService prn) (getNid toJoinOn)
+                pure $ Right ownStateSTM
                                    )
         `catch` (\e -> pure . Left $ displayException (e :: IOException))
 

src/Hash2Pub/PostService.hs

@@ -10,16 +10,10 @@ module Hash2Pub.PostService where
 
 import           Control.Concurrent
 import           Control.Concurrent.Async
-import           Control.Concurrent.MVar
 import           Control.Concurrent.STM
-import           Control.Concurrent.STM.TChan
-import           Control.Concurrent.STM.TChan
-import           Control.Concurrent.STM.TQueue
-import           Control.Concurrent.STM.TVar
 import           Control.Exception             (Exception (..), try)
 import           Control.Monad                 (foldM, forM, forM_, forever, when, void)
 import           Control.Monad.IO.Class        (liftIO)
-import           Control.Monad.STM
 import           Data.Bifunctor
 import qualified Data.ByteString.Lazy.UTF8     as BSUL
 import qualified Data.ByteString.UTF8          as BSU
@@ -40,7 +34,6 @@ import           Text.Read                     (readEither)
 import qualified Network.Wai.Handler.Warp      as Warp
 import           Servant
 import           Servant.Client
-import           Servant.Server
 
 import           Hash2Pub.FediChordTypes
 import           Hash2Pub.RingMap
@@ -355,7 +348,7 @@ clientDeliverSubscriptions :: PostService d
                            -> (String, Int)     -- ^ hostname and port of instance to deliver to
                            -> IO (Either String ())     -- Either signals success or failure
 clientDeliverSubscriptions serv fromNode fromKey toKey (toHost, toPort) = do
-    -- collect tag intearval
+    -- collect tag interval
     intervalTags <- takeRMapSuccessorsFromTo fromKey toKey <$> readTVarIO (subscribers serv)
     -- returns a [ (TagSubscribersSTM, TChan PostID, Hashtag) ]
     -- extract subscribers and posts