respond to QueryLoad requests

closes #71
closes #72
contributes to #2

src/Hash2Pub/DHTProtocol.hs

@@ -77,7 +77,7 @@ import           Hash2Pub.ASN1Coding
 import           Hash2Pub.FediChordTypes        (CacheEntry (..),
                                                  CacheEntry (..),
                                                  FediChordConf (..),
-                                                 HasKeyID (..),
+                                                 HasKeyID (..), LoadStats (..),
                                                  LocalNodeState (..),
                                                  LocalNodeStateSTM, NodeCache,
                                                  NodeID, NodeState (..),
@@ -95,6 +95,7 @@ import           Hash2Pub.FediChordTypes        (CacheEntry (..),
                                                  rMapLookupSucc,
                                                  setPredecessors, setSuccessors)
 import           Hash2Pub.ProtocolTypes
+import           Hash2Pub.RingMap
 
 import           Debug.Trace                    (trace)
 
@@ -253,6 +254,15 @@ ackRequest req@Request{} = serialiseMessage sendMessageSize $ Response {
 ackRequest _ = Map.empty
 
 
+-- | extract the first payload from a received message set
+extractFirstPayload :: Set.Set FediChordMessage -> Maybe ActionPayload
+extractFirstPayload msgSet = foldr' (\msg plAcc ->
+    if isNothing plAcc && isJust (payload msg)
+       then payload msg
+       else plAcc
+                                 ) Nothing msgSet
+
+
 -- | Dispatch incoming requests to the dedicated handling and response function, and enqueue
 -- the response to be sent.
 handleIncomingRequest :: Service s (RealNodeSTM s)
@@ -282,6 +292,7 @@ handleIncomingRequest nsSTM sendQ msgSet sourceAddr = do
                 -- only when joined
                 Leave -> if isJoined ns then dropSpoofedIDs sourceIP nsSTM msgSet respondLeave else pure Nothing
                 Stabilise -> if isJoined ns then dropSpoofedIDs sourceIP nsSTM msgSet respondStabilise else pure Nothing
+                QueryLoad -> if isJoined ns then Just <$> respondLoadQuery 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.
 
@@ -321,12 +332,8 @@ respondQueryID nsSTM msgSet = do
     let
         aRequestPart = Set.elemAt 0 msgSet
         senderID = getNid . sender $ aRequestPart
-        senderPayload = foldr' (\msg plAcc ->
-            if isNothing plAcc && isJust (payload msg)
-               then payload msg
-               else plAcc
-                               ) Nothing msgSet
-    -- return only empty message serialisation if no payload was included in parts
+        senderPayload = extractFirstPayload msgSet
+        -- return only empty message serialisation if no payload was included in parts
     maybe (pure Map.empty) (\senderPayload' -> do
         responseMsg <- atomically $ do
             nsSnap <- readTVar nsSTM
@@ -426,6 +433,43 @@ respondPing nsSTM msgSet = do
                                 }
     pure $ serialiseMessage sendMessageSize pingResponse
 
+respondLoadQuery :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
+respondLoadQuery nsSTM msgSet = do
+    nsSnap <- readTVarIO nsSTM
+    -- this message cannot be split reasonably, so just
+    -- consider the first payload
+    let
+        aRequestPart = Set.elemAt 0 msgSet
+        senderPayload = extractFirstPayload msgSet
+    responsePl <- maybe (pure Nothing) (\pl ->
+        case pl of
+          LoadRequestPayload{} -> do
+            serv <- nodeService <$> readTVarIO (parentRealNode nsSnap)
+            lStats <- getServiceLoadStats serv
+            let
+                directSucc = getNid . head . predecessors $ nsSnap
+                handledTagSum = sum . takeRMapSuccessorsFromTo directSucc (loadSegmentUpperBound pl) $ loadPerTag lStats
+            pure $ Just LoadResponsePayload
+                { loadSum = handledTagSum
+                , loadRemainingTarget = remainingLoadTarget lStats
+                , loadSegmentLowerBound = directSucc
+                }
+          _ -> pure Nothing
+                           )
+                           senderPayload
+
+    pure $ maybe
+        Map.empty
+        (\pl -> serialiseMessage sendMessageSize $ Response
+            { requestID = requestID aRequestPart
+            , senderID = getNid nsSnap
+            , part = if Set.size msgSet == 1 then 1 else fromIntegral $ Set.size msgSet + 1
+            , isFinalPart = False
+            , action = QueryLoad
+            , payload = Just pl
+            }
+        ) responsePl
+
 
 respondJoin :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
 respondJoin nsSTM msgSet = do
@@ -759,14 +803,7 @@ requestQueryLoad ns upperIdBound target = do
     responseMsgSet <- liftEither responses
     -- throws an error if an exception happened
     loadResPl <- maybe (throwError "no load response payload found") pure
-        (foldr' (\msg acc -> case payload msg of
-            -- just extract the first found LoadResponsePayload
-              Just pl@LoadResponsePayload{} | isNothing acc -> Just pl
-              _                                             -> Nothing
-                )
-            Nothing
-            responseMsgSet
-        )
+        (extractFirstPayload responseMsgSet)
     pure SegmentLoadStats
         { segmentLowerKeyBound = loadSegmentLowerBound loadResPl
         , segmentUpperKeyBound = upperIdBound