Change default response to QueryID for unjoined nodes

reason: allow unjoined nodes to find bootstrap node in local cache,
while always advertising itself to incoming requests for bootstrapping.

src/Hash2Pub/DHTProtocol.hs

@@ -32,6 +32,7 @@ module Hash2Pub.DHTProtocol
     , ackRequest
     , isPossibleSuccessor
     , isPossiblePredecessor
+    , isJoined
     , closestCachePredecessors
     )
         where
@@ -89,7 +90,9 @@ import           Debug.Trace                    (trace)
 queryLocalCache :: LocalNodeState -> NodeCache -> Int -> NodeID -> QueryResponse
 queryLocalCache ownState nCache lBestNodes targetID
     -- as target ID falls between own ID and first predecessor, it is handled by this node
-      | targetID `isInOwnResponsibilitySlice` ownState = FOUND . toRemoteNodeState $ ownState
+    -- This only makes sense if the node is part of the DHT by having joined.
+    -- A default answer to nodes querying an unjoined node is provided by 'respondQueryID'.
+      | isJoined ownState && targetID `isInOwnResponsibilitySlice` ownState = FOUND . toRemoteNodeState $ ownState
     -- my interpretation: the "l best next hops" are the l-1 closest preceding nodes and
     -- the closest succeeding node (like with the p initiated parallel queries
       | otherwise = FORWARD $ closestSuccessor `Set.union` closestCachePredecessors (lBestNodes-1) targetID nCache
@@ -213,8 +216,8 @@ markCacheEntryAsVerified timestamp nid = RingMap . Map.adjust adjustFunc nid . g
 
 -- | uses the successor and predecessor list of a node as an indicator for whether a
 -- node has properly joined the DHT
-isJoined_ :: LocalNodeState -> Bool
-isJoined_ ns = not . all null $ [successors ns, predecessors ns]
+isJoined :: LocalNodeState -> Bool
+isJoined ns = not . all null $ [successors ns, predecessors ns]
 
 -- | the size limit to be used when serialising messages for sending
 sendMessageSize :: Num i => i
@@ -260,8 +263,8 @@ handleIncomingRequest nsSTM sendQ msgSet sourceAddr = do
                 -- ToDo: figure out what happens if not joined
                 QueryID -> Just <$> respondQueryID nsSTM msgSet
                 -- only when joined
-                Leave -> if isJoined_ ns then Just <$> respondLeave nsSTM msgSet else pure Nothing
-                Stabilise -> if isJoined_ ns then Just <$> respondStabilise nsSTM msgSet else pure Nothing
+                Leave -> if isJoined ns then Just <$> respondLeave nsSTM msgSet else pure Nothing
+                Stabilise -> if isJoined ns then Just <$> respondStabilise nsSTM msgSet else pure Nothing
             )
       -- for single part request, response starts with part number 1. For multipart requests, response starts with part number n+1.
 
@@ -295,7 +298,11 @@ respondQueryID nsSTM msgSet = do
             cache <- readTVar $ nodeCacheSTM nsSnap
             let
                 responsePayload = QueryIDResponsePayload {
-                    queryResult = queryLocalCache nsSnap cache (fromIntegral $ queryLBestNodes senderPayload') (queryTargetID senderPayload')
+                    queryResult = if isJoined nsSnap
+                                     then queryLocalCache nsSnap cache (fromIntegral $ queryLBestNodes senderPayload') (queryTargetID senderPayload')
+                                     -- if not joined yet, attract responsibility for
+                                     -- all keys to make bootstrapping possible
+                                     else FOUND (toRemoteNodeState nsSnap)
                                                         }
                 queryResponseMsg = Response {
                     requestID = requestID aRequestPart

src/Hash2Pub/FediChord.hs

@@ -253,7 +253,9 @@ checkCacheSliceInvariants :: LocalNodeState
                           -> NodeCache
                           -> [NodeID]   -- ^ list of middle IDs of slices not
                                         -- ^ fulfilling the invariant
-checkCacheSliceInvariants ns = checkPredecessorSlice jEntries (getNid ns) startBound lastPred <> checkSuccessorSlice jEntries (getNid ns) startBound lastSucc
+checkCacheSliceInvariants ns 
+  | isJoined ns = checkPredecessorSlice jEntries (getNid ns) startBound lastPred <> checkSuccessorSlice jEntries (getNid ns) startBound lastSucc
+  | otherwise = const []
   where
     jEntries = jEntriesPerSlice ns
     lastPred = getNid <$> lastMay (predecessors ns)
@@ -340,7 +342,7 @@ stabiliseThread nsSTM = forever $ do
     -- try looking up additional neighbours if list too short
     forM_ [(length $ predecessors updatedNs)..(kNeighbours updatedNs)] (\_ -> do
         ns' <- readTVarIO nsSTM
-        nextEntry <- requestQueryID ns' $ pred . getNid $ atDef (toRemoteNodeState ns') (predecessors ns') (-1)
+        nextEntry <- requestQueryID ns' $ pred . getNid $ lastDef (toRemoteNodeState ns') (predecessors ns')
         atomically $ do
             latestNs <- readTVar nsSTM
             writeTVar nsSTM $ addPredecessors [nextEntry] latestNs
@@ -348,7 +350,7 @@ stabiliseThread nsSTM = forever $ do
 
     forM_ [(length $ successors updatedNs)..(kNeighbours updatedNs)] (\_ -> do
         ns' <- readTVarIO nsSTM
-        nextEntry <- requestQueryID ns' $ succ . getNid $ atDef (toRemoteNodeState ns') (successors ns') (-1)
+        nextEntry <- requestQueryID ns' $ succ . getNid $ lastDef (toRemoteNodeState ns') (successors ns')
         atomically $ do
             latestNs <- readTVar nsSTM
             writeTVar nsSTM $ addSuccessors [nextEntry] latestNs
@@ -460,6 +462,9 @@ fediMessageHandler :: TQueue (BS.ByteString, SockAddr)  -- ^ send queue
                    -> LocalNodeStateSTM                    -- ^ acting NodeState
                    -> IO ()
 fediMessageHandler sendQ recvQ nsSTM = do
+    -- Read node state just once, assuming that all relevant data for this function does
+    -- not change.
+    -- Other functions are passed the nsSTM reference and thus can get the latest state.
     nsSnap <- readTVarIO nsSTM
     -- handling multipart messages:
     -- Request parts can be insert into a map (key: (sender IP against spoofing, request ID), value: timestamp + set of message parts, handle all of them when size of set == parts) before being handled. This map needs to be purged periodically by a separate thread and can be protected by an MVar for fairness.

test/FediChordSpec.hs

@@ -132,10 +132,11 @@ spec = do
             cacheWith2Entries :: NodeCache
             cacheWith2Entries = addCacheEntryPure 10 (RemoteCacheEntry node5 10) (addCacheEntryPure 10 (RemoteCacheEntry node2 10) emptyCache)
             cacheWith4Entries = addCacheEntryPure 10 (RemoteCacheEntry node3 10) (addCacheEntryPure 10 (RemoteCacheEntry node4 10) cacheWith2Entries)
-        it "nodes not joined provide the default answer FOUND" $ do
+        it "unjoined nodes should never return themselfs" $ do
             exampleLocalNodeAsRemote <- toRemoteNodeState <$> exampleLocalNode
-            queryLocalCache <$> exampleLocalNode <*> pure emptyCache <*> pure 3 <*> pure (toNodeID 2^(9::Integer)+5) `shouldReturn` FOUND exampleLocalNodeAsRemote
-            queryLocalCache <$> exampleLocalNode <*> pure cacheWith4Entries <*> pure 1 <*> pure (toNodeID 2342) `shouldReturn` FOUND exampleLocalNodeAsRemote
+            queryLocalCache <$> exampleLocalNode <*> pure emptyCache <*> pure 3 <*> pure (toNodeID 2^(9::Integer)+5) `shouldReturn` FORWARD Set.empty
+            (FORWARD fwSet) <- queryLocalCache <$> exampleLocalNode <*> pure cacheWith4Entries <*> pure 1 <*> (getNid <$> exampleLocalNode)
+            remoteNode (head $ Set.elems fwSet) `shouldBe` node4
         it "joined nodes do not fall back to the default" $
             queryLocalCache <$> node1 <*> pure emptyCache <*> pure 1 <*> pure (toNodeID 3) `shouldReturn` FORWARD Set.empty
         it "works on a cache with less entries than needed" $ do
@@ -265,6 +266,17 @@ spec = do
             let startAt5 = serialiseMessage 600 (largeMessage {part = 5})
             Map.lookup 1 startAt5 `shouldBe` Nothing
             part <$> (deserialiseMessage . fromJust) (Map.lookup 5 startAt5) `shouldBe` Right 5
+    describe "join cache lookup" $
+        it "A bootstrap cache initialised with just one node returns that one." $ do
+            let
+                bootstrapNid = toNodeID 34804191837661041451755206127000721433747285589603756490902196113256157045194
+                bootstrapNode = setNid bootstrapNid exampleNodeState
+                bootstrapCache = addCacheEntryPure 10 (RemoteCacheEntry bootstrapNode 19) initCache
+                ownId = toNodeID 34804191837661041451755206127000721433707928516052624394829818586723613390165
+            ownNode <- setNid ownId <$> exampleLocalNode
+            let (FORWARD qResult) = queryLocalCache ownNode bootstrapCache 2 ownId
+            remoteNode (head $ Set.elems qResult) `shouldBe` bootstrapNode
+            
 
 
 -- some example data