ping potential neighbours before adding to list

for #44

app/Main.hs

@@ -55,4 +55,5 @@ readConfig = do
       , confIP = toHostAddress6 . read $ ipString
       , confDhtPort = read portString
       , confBootstrapNodes = [(bootstrapHost, read bootstrapPortString)]
+      --, confStabiliseInterval = 60
                            }

src/Hash2Pub/FediChord.hs

@@ -61,12 +61,13 @@ import           Crypto.Hash
 import qualified Data.ByteArray                as BA
 import qualified Data.ByteString               as BS
 import qualified Data.ByteString.UTF8          as BSU
+import           Data.Either                   (rights)
 import           Data.Foldable                 (foldr')
 import           Data.IP                       (IPv6, fromHostAddress6,
                                                 toHostAddress6)
 import qualified Data.Map.Strict               as Map
-import           Data.Maybe                    (fromJust, fromMaybe, isJust,
+import           Data.Maybe                    (catMaybes, fromJust, fromMaybe,
-                                                mapMaybe)
+                                                isJust, mapMaybe)
 import qualified Data.Set                      as Set
 import           Data.Time.Clock.POSIX
 import           Data.Typeable                 (Typeable (..), typeOf)
@@ -181,11 +182,16 @@ cacheWriter nsSTM =
         modifyTVar' (nodeCacheSTM ns) cacheModifier
 
 stabiliseThread :: LocalNodeStateSTM -> IO ()
-stabiliseThread nsSTM = do
+stabiliseThread nsSTM = forever $ do
+    ns <- readTVarIO nsSTM
     -- TODO: update successfully stabilised nodes in cache
-    -- placeholder
+    -- first stabilise immediate neihbours, then the next ones
-    stabiliseNeighbour nsSTM successors 1
+    forM_ [1..(kNeighbours ns)] (\num -> do
-    pure ()
+        stabiliseNeighbour nsSTM predecessors num
+        stabiliseNeighbour nsSTM successors num
+                               )
+    -- TODO: make delay configurable
+    threadDelay (60 * 1000)
   where
     stabiliseNeighbour :: LocalNodeStateSTM
                        -> (LocalNodeState -> [RemoteNodeState])
@@ -207,10 +213,25 @@ stabiliseThread nsSTM = do
                            -> m ()
     parseNeighbourResponse (Left err) = throwError err
     parseNeighbourResponse (Right (succs, preds)) = liftIO $ do
+        -- ping each returned node before actually inserting them
+        -- send pings in parallel, check whether ID is part of the returned IDs
+        nsSnap <- readTVarIO nsSTM
+        pingThreads <- mapM (async . checkReachability nsSnap) $ preds <> succs
+        -- ToDo: exception handling, maybe log them
+        -- filter out own node
+        checkedNeighbours <- filter (/= toRemoteNodeState nsSnap) . catMaybes . rights <$> mapM waitCatch pingThreads
+
         atomically $ do
             newerNsSnap <- readTVar nsSTM
-            writeTVar nsSTM $ addPredecessors preds . addSuccessors succs $ newerNsSnap
+            writeTVar nsSTM $ addPredecessors checkedNeighbours . addSuccessors checkedNeighbours $ newerNsSnap
         pure ()
+    checkReachability :: LocalNodeState -> RemoteNodeState -> IO (Maybe RemoteNodeState)
+    checkReachability ns toCheck = do
+        resp <- requestPing ns toCheck
+        pure $ either (const Nothing) (\vss ->
+            if toCheck `elem` vss then Just toCheck else Nothing
+                       ) resp
+
 
 -- periodically contact immediate successor and predecessor
 -- If they respond, see whether there is a closer neighbour in between

src/Hash2Pub/FediChordTypes.hs

@@ -613,6 +613,7 @@ data FediChordConf = FediChordConf
     , confIP             :: HostAddress6
     , confDhtPort        :: Int
     , confBootstrapNodes :: [(String, PortNumber)]
+    --, confStabiliseInterval :: Int
     }
     deriving (Show, Eq)
 

test/FediChordSpec.hs

@@ -154,7 +154,7 @@ spec = do
     describe "successors and predecessors do not disturb the ring characteristics of EpiChord operations (see #48)" $ do
         let
             emptyCache = initCache
-            -- implicitly relies on kNieghbours to be <= 3
+            -- implicitly relies on kNeighbours to be <= 3
             thisNid = toNodeID 1000
             thisNode = setNid thisNid <$> exampleLocalNode
             nid2 = toNodeID 1003