update Readme with latest branch name and pointer to SocialHub

- relaxes some version constraints as dirty update quickfix
- removes hie integration as that project is abandoned, todo: switch to
  haskell-languageserver instead

FediChord.asn1

@@ -89,8 +89,8 @@ StabiliseResponsePayload ::= SEQUENCE {
 
 LeaveRequestPayload ::= SEQUENCE {
 	successors		SEQUENCE OF NodeState,
-	predecessors	SEQUENCE OF NodeState
-	-- ToDo: transfer of own data to newly responsible node
+	predecessors	SEQUENCE OF NodeState,
+	doMigration		BOOLEAN
 	}
 
 LeaveResponsePayload ::= NULL	-- just a confirmation

Hash2Pub.cabal

@@ -46,8 +46,8 @@ category:            Network
 extra-source-files:  CHANGELOG.md
 
 common deps
-  build-depends:       base ^>=4.12.0.0, containers ^>=0.6.0.1, bytestring, utf8-string ^>=1.0.1.1, network ^>=2.8.0.1, time ^>=1.8.0.2, cmdargs ^>= 0.10, cryptonite ^>= 0.25, memory, async, stm, asn1-encoding, asn1-types, asn1-parse, publicsuffix, network-byte-order, safe, iproute, mtl, random, servant, servant-server, servant-client, warp, text, unordered-containers
-  ghc-options:         -Wall
+  build-depends:       base >=4, containers ^>=0.6.0.1, bytestring, utf8-string ^>=1.0.1.1, network ^>=3.1, time, cmdargs ^>= 0.10, cryptonite, memory, async, stm, asn1-encoding, asn1-types, asn1-parse, publicsuffix, network-byte-order, safe, iproute, mtl, random, servant, servant-server, servant-client, warp, text, unordered-containers, hashable, unicode-transforms, http-client, http-types, unbounded-delays, dlist, formatting
+  ghc-options:         -Wall -Wpartial-fields -O2
 
 
 
@@ -55,10 +55,10 @@ library
   import: deps
 
   -- Modules exported by the library.
-  exposed-modules:     Hash2Pub.FediChord, Hash2Pub.FediChordTypes, Hash2Pub.DHTProtocol, Hash2Pub.ASN1Coding, Hash2Pub.ProtocolTypes, Hash2Pub.PostService, Hash2Pub.ServiceTypes, Hash2Pub.RingMap
+  exposed-modules:     Hash2Pub.FediChord, Hash2Pub.FediChordTypes, Hash2Pub.DHTProtocol, Hash2Pub.ASN1Coding, Hash2Pub.ProtocolTypes, Hash2Pub.PostService, Hash2Pub.RingMap
 
   -- Modules included in this library but not exported.
-  other-modules: Hash2Pub.Utils
+  other-modules: Hash2Pub.Utils, Hash2Pub.PostService.API
 
   -- LANGUAGE extensions used by modules in this package.
   other-extensions:    GeneralizedNewtypeDeriving, DataKinds, OverloadedStrings
@@ -91,6 +91,20 @@ executable Hash2Pub
   -- Base language which the package is written in.
   default-language:    Haskell2010
 
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+
+executable Experiment
+  -- experiment runner
+  import: deps
+
+  build-depends: Hash2Pub
+
+  main-is: Experiment.hs
+
+  hs-source-dirs: app
+
+  default-language: Haskell2010
+
   ghc-options: -threaded
 
 

Readme.md

@@ -1,7 +1,7 @@
 # Hash2Pub
 
 ***This is heavily WIP and does not provide any useful functionality yet***.  
-I aim for always having the master branch at a state where it builds and tests pass.
+I aim for always having the `mainline` branch in a state where it builds and tests pass.
 
 A fully-decentralised relay for global hashtag federation in [ActivityPub](https://activitypub.rocks) based on a distributed hash table.
 It allows querying and subscribing to all posts of a certain hashtag and is implemented in Haskell.
@@ -10,8 +10,13 @@ This is the practical implementation of the concept presented in the paper [Dece
 
 The ASN.1 module schema used for DHT messages can be found in `FediChord.asn1`.
 
+For further questions and discussins, please refer to the **Hash2Pub topic in [SocialHub](https://socialhub.activitypub.rocks/c/software/hash2pub/48)**.
+
 ## Building
 
 The project and its developent environment are built with [Nix](https://nixos.org/nix/).
 
-The development environment can be entered with `nix-shell`. Then the project can be built with `cabal build` from within the environment, or using `nix-shell --command "cabal build"` to do both steps at once.
+The development environment can be entered with `nix-shell shell-minimal.nix`. Then the project can be built with `cabal build` from within the environment, or using `nix-shell --command "cabal build" shell-minimal.nix` to do both steps at once.
+
+While the `shell-minimal.nix` environment contains everything necessary for building and testing this project, the `shell.nix` additionally contains the Haskell IDE engine *hie* and the documentation for all used Haskell packages for more convenient development.  
+Be aware that these need to be build from source and can take a very long time to build.

app/Experiment.hs

@@ -0,0 +1,51 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Main where
+
+import           Control.Concurrent
+import           Control.Monad        (forM_)
+import qualified Data.Text.Lazy       as Txt
+import qualified Data.Text.Lazy.IO    as TxtI
+import qualified Network.HTTP.Client  as HTTP
+import           System.Environment   (getArgs)
+
+import           Hash2Pub.PostService (Hashtag, clientPublishPost)
+
+-- configuration constants
+timelineFile = "../simulationData/inputs/generated/timeline_sample.csv"
+
+main :: IO ()
+main = do
+    -- read CLI parameters
+    speedupStr : _ <- getArgs
+    -- read and parse timeline schedule
+    -- relying on lazyness of HaskellIO, hoping it does not introduce too strong delays
+    postEvents <- parseSchedule <$> TxtI.readFile timelineFile
+    -- actually schedule and send the post events
+    executeSchedule (read speedupStr) postEvents
+    pure ()
+
+
+
+parseSchedule :: Txt.Text
+              -> [(Int, Hashtag, (String, Int))] -- ^ [(delay in microseconds, hashtag, (hostname, port))]
+parseSchedule = fmap (parseEntry . Txt.split (== ';')) . Txt.lines
+  where
+      parseEntry [delayT, contactT, tag] =
+          (read $ Txt.unpack delayT, tag, read $ Txt.unpack contactT)
+      parseEntry entry = error $ "invalid schedule input format: " <> show entry
+
+executeSchedule :: Int  -- ^ speedup factor
+                -> [(Int, Hashtag, (String, Int))] -- ^ [(delay in microseconds, hashtag, (hostname, port))]
+                -> IO ()
+executeSchedule speedup events = do
+    -- initialise HTTP manager
+    httpMan <- HTTP.newManager $ HTTP.defaultManagerSettings { HTTP.managerResponseTimeout = HTTP.responseTimeoutMicro 60000000 }
+    forM_ events $ \(delay, tag, (pubHost, pubPort)) -> do
+        _ <- forkIO $
+            clientPublishPost httpMan pubHost pubPort ("foobar #" <> tag)
+            >>= either putStrLn (const $ pure ())
+        -- while threadDelay gives only minimum delay guarantees, let's hope the
+        -- additional delays are negligible
+        -- otherwise: evaluate usage of https://hackage.haskell.org/package/schedule-0.3.0.0/docs/Data-Schedule.html
+        threadDelay $ delay `div` speedup

app/Main.hs

@@ -10,15 +10,17 @@ import           Data.IP                     (IPv6, toHostAddress6)
 import           System.Environment
 
 import           Hash2Pub.FediChord
+import           Hash2Pub.FediChordTypes
+import           Hash2Pub.PostService        (PostService (..))
 
 main :: IO ()
 main = do
     -- ToDo: parse and pass config
     -- probably use `tomland` for that
-    conf <- readConfig
+    (fConf, sConf) <- readConfig
     -- TODO: first initialise 'RealNode', then the vservers
     -- ToDo: load persisted caches, bootstrapping nodes …
-    (serverSock, thisNode) <- fediChordInit conf
+    (serverSock, thisNode) <- fediChordInit fConf (runService sConf :: DHT d => d -> IO (PostService d))
     -- currently no masking is necessary, as there is nothing to clean up
     nodeCacheWriterThread <- forkIO $ nodeCacheWriter thisNode
     -- try joining the DHT using one of the provided bootstrapping nodes
@@ -41,15 +43,38 @@ main = do
     pure ()
 
 
-readConfig :: IO FediChordConf
+readConfig :: IO (FediChordConf, ServiceConf)
 readConfig = do
-    confDomainString : ipString : portString : bootstrapHost : bootstrapPortString : _ <- getArgs
-    pure $ FediChordConf {
-        confDomain = confDomainString
+    confDomainString : ipString : portString : servicePortString : speedupString : remainingArgs <- getArgs
+    -- allow starting the initial node without bootstrapping info to avoid
+    -- waiting for timeout
+    let
+        speedup = read speedupString
+        confBootstrapNodes' = case remainingArgs of
+            bootstrapHost : bootstrapPortString : _ ->
+                [(bootstrapHost, read bootstrapPortString)]
+            _ -> []
+        fConf = FediChordConf
+          { confDomain = confDomainString
           , confIP = toHostAddress6 . read $ ipString
           , confDhtPort = read portString
-      , confBootstrapNodes = [(bootstrapHost, read bootstrapPortString)]
-      --, confStabiliseInterval = 60
-      , confBootstrapSamplingInterval = 180
-      , confMaxLookupCacheAge = 300
+          , confBootstrapNodes = confBootstrapNodes'
+          , confStabiliseInterval = 80 * 10^6
+          , confBootstrapSamplingInterval = 180 * 10^6 `div` speedup
+          , confMaxLookupCacheAge = 300 / fromIntegral speedup
+          , confJoinAttemptsInterval = 60 * 10^6 `div` speedup
+          , confMaxNodeCacheAge = 600 / fromIntegral speedup
+          , confResponsePurgeAge = 60 / fromIntegral speedup
+          , confRequestTimeout = 5 * 10^6 `div` speedup
+          , confRequestRetries = 3
           }
+        sConf = ServiceConf
+          { confSubscriptionExpiryTime = 24*3600 / fromIntegral speedup
+          , confServicePort = read servicePortString
+          , confServiceHost = confDomainString
+          , confLogfilePath = "../simulationData/logs/" <> confDomainString <> ".log"
+          , confSpeedupFactor = speedup
+          , confStatsEvalDelay = 120 * 10^6 `div` speedup
+          }
+    pure (fConf, sConf)
+

default.nix

@@ -1,14 +1,19 @@
-{ pkgs ? import (
-  builtins.fetchGit {
-    name = "nixpkgs-pinned";
-    url = https://github.com/NixOS/nixpkgs/;
-    ref = "refs/heads/release-20.03";
-    rev = "da7ddd822e32aeebea00e97ab5aeca9758250a40";
-  }) {},
-  compiler ? "ghc865"
+{
+  compiler ? "ghc884"
 }:
 
 let
+  pkgs = import (
+    builtins.fetchGit {
+      name = "nixpkgs-pinned";
+      url = https://github.com/NixOS/nixpkgs/;
+      ref = "refs/heads/release-20.09";
+      rev = "e065200fc90175a8f6e50e76ef10a48786126e1c";
+    }) {
+      # Pass no config for purity
+          config = {};
+              overlays = [];
+    };
   hp = pkgs.haskell.packages."${compiler}";
   src = pkgs.nix-gitignore.gitignoreSource [] ./.;
   drv = hp.callCabal2nix "Hash2Pub" "${src}/Hash2Pub.cabal" {};

shell-minimal.nix

@@ -0,0 +1 @@
+(import ./default.nix {withHIE = false;}).shell

src/Hash2Pub/ASN1Coding.hs

@@ -38,6 +38,7 @@ splitPayload numParts pl@LeaveRequestPayload{} = [
     LeaveRequestPayload {
         leaveSuccessors = atDef []  (listInto numParts $ leaveSuccessors pl) (thisPart-1)
       , leavePredecessors = atDef  [] (listInto numParts $ leavePredecessors pl) (thisPart-1)
+      , leaveDoMigration = leaveDoMigration pl
                         } | thisPart <- [1..numParts] ]
 splitPayload numParts pl@StabiliseResponsePayload{} = [
     StabiliseResponsePayload {
@@ -134,9 +135,8 @@ encodePayload payload'@LeaveRequestPayload{} =
   <> [End Sequence
   , Start Sequence]
   <> concatMap encodeNodeState (leavePredecessors payload')
-  <> [End Sequence
-  , End Sequence]
--- currently StabiliseResponsePayload and LeaveRequestPayload are equal
+  <> [End Sequence]
+  <> [Boolean (leaveDoMigration payload'), End Sequence]
 encodePayload payload'@StabiliseResponsePayload{} =
     Start Sequence
   : Start Sequence
@@ -144,8 +144,7 @@ encodePayload payload'@StabiliseResponsePayload{} =
   <> [End Sequence
   , Start Sequence]
   <> concatMap encodeNodeState (stabilisePredecessors payload')
-  <> [End Sequence
-  , End Sequence]
+  <> [End Sequence, End Sequence]
 encodePayload payload'@StabiliseRequestPayload = [Null]
 encodePayload payload'@QueryIDResponsePayload{} =
   let
@@ -415,9 +414,11 @@ parseLeaveRequest :: ParseASN1 ActionPayload
 parseLeaveRequest = onNextContainer Sequence $ do
     succ' <- onNextContainer Sequence (getMany parseNodeState)
     pred' <- onNextContainer Sequence (getMany parseNodeState)
+    doMigration <- parseBool
     pure $ LeaveRequestPayload {
         leaveSuccessors = succ'
       , leavePredecessors = pred'
+      , leaveDoMigration = doMigration
                                       }
 
 parseLeaveResponse :: ParseASN1 ActionPayload

src/Hash2Pub/DHTProtocol.hs

@@ -19,6 +19,7 @@ module Hash2Pub.DHTProtocol
     , sendQueryIdMessages
     , requestQueryID
     , requestJoin
+    , requestLeave
     , requestPing
     , requestStabilise
     , lookupMessage
@@ -34,21 +35,25 @@ module Hash2Pub.DHTProtocol
     , ackRequest
     , isPossibleSuccessor
     , isPossiblePredecessor
+    , isInOwnResponsibilitySlice
     , isJoined
     , closestCachePredecessors
     )
         where
 
+import           Control.Concurrent
 import           Control.Concurrent.Async
 import           Control.Concurrent.STM
 import           Control.Concurrent.STM.TBQueue
 import           Control.Concurrent.STM.TQueue
 import           Control.Concurrent.STM.TVar
 import           Control.Exception
-import           Control.Monad                  (foldM, forM, forM_)
+import           Control.Monad                  (foldM, forM, forM_, void, when)
+import           Control.Monad.Except           (MonadError (..), runExceptT)
+import           Control.Monad.IO.Class         (MonadIO (..))
 import qualified Data.ByteString                as BS
 import           Data.Either                    (rights)
-import           Data.Foldable                  (foldl', foldr')
+import           Data.Foldable                  (foldl', foldr', foldrM)
 import           Data.Functor.Identity
 import           Data.IP                        (IPv6, fromHostAddress6,
                                                  toHostAddress6)
@@ -73,10 +78,11 @@ import           Hash2Pub.FediChordTypes        (CacheEntry (..),
                                                  LocalNodeState (..),
                                                  LocalNodeStateSTM, NodeCache,
                                                  NodeID, NodeState (..),
-                                                 RealNode (..),
+                                                 RealNode (..), RealNodeSTM,
                                                  RemoteNodeState (..),
                                                  RingEntry (..), RingMap (..),
-                                                 addRMapEntry, addRMapEntryWith,
+                                                 Service (..), addRMapEntry,
+                                                 addRMapEntryWith,
                                                  cacheGetNodeStateUnvalidated,
                                                  cacheLookup, cacheLookupPred,
                                                  cacheLookupSucc, genNodeID,
@@ -92,7 +98,7 @@ import           Debug.Trace                    (trace)
 
 -- TODO: evaluate more fine-grained argument passing to allow granular locking
 -- | look up an ID to either claim responsibility for it or return the closest l nodes from the local cache
-queryLocalCache :: LocalNodeState -> NodeCache -> Int -> NodeID -> QueryResponse
+queryLocalCache :: LocalNodeState s -> 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
     -- This only makes sense if the node is part of the DHT by having joined.
@@ -102,9 +108,6 @@ queryLocalCache ownState nCache lBestNodes targetID
     -- the closest succeeding node (like with the p initiated parallel queries
       | otherwise = FORWARD $ closestSuccessor `Set.union` closestCachePredecessors (lBestNodes-1) targetID nCache
   where
-    ownID = getNid ownState
-    preds = predecessors ownState
-
     closestSuccessor :: Set.Set RemoteCacheEntry
     closestSuccessor = maybe Set.empty (Set.singleton . toRemoteCacheEntry) $ cacheLookupSucc targetID nCache
 
@@ -130,23 +133,25 @@ closestCachePredecessors remainingLookups lastID nCache
 -- Looks up the successor of the lookup key on a 'RingMap' representation of the
 -- predecessor list with the node itself added. If the result is the same as the node
 -- itself then it falls into the responsibility interval.
-isInOwnResponsibilitySlice :: HasKeyID a NodeID => a -> LocalNodeState -> Bool
-isInOwnResponsibilitySlice lookupTarget ownNs = (getKeyID <$> rMapLookupSucc (getKeyID lookupTarget :: NodeID) predecessorRMap) == pure (getNid ownNs)
+isInOwnResponsibilitySlice :: HasKeyID NodeID a => a -> LocalNodeState s -> Bool
+isInOwnResponsibilitySlice lookupTarget ownNs = (fst <$> rMapLookupSucc (getKeyID lookupTarget :: NodeID) predecessorRMap) == pure (getNid ownNs)
   where
     predecessorList = predecessors ownNs
     -- add node itself to RingMap representation, to distinguish between
     -- responsibility of own node and predecessor
-    predecessorRMap = addRMapEntry (toRemoteNodeState ownNs) $ rMapFromList predecessorList
+    predecessorRMap = addRMapEntry (getKeyID ownRemote) ownRemote $ rMapFromList (keyValuePair <$> predecessorList) :: RingMap NodeID RemoteNodeState
+    ownRemote = toRemoteNodeState ownNs
     closestPredecessor = headMay predecessorList
 
-isPossiblePredecessor :: HasKeyID a NodeID => a -> LocalNodeState -> Bool
+isPossiblePredecessor :: HasKeyID NodeID a => a -> LocalNodeState s -> Bool
 isPossiblePredecessor = isInOwnResponsibilitySlice
 
-isPossibleSuccessor :: HasKeyID a NodeID => a -> LocalNodeState -> Bool
-isPossibleSuccessor lookupTarget ownNs = (getKeyID <$> rMapLookupPred (getKeyID lookupTarget :: NodeID) successorRMap) == pure (getNid ownNs)
+isPossibleSuccessor :: HasKeyID NodeID a => a -> LocalNodeState s -> Bool
+isPossibleSuccessor lookupTarget ownNs = (fst <$> rMapLookupPred (getKeyID lookupTarget :: NodeID) successorRMap) == pure (getNid ownNs)
   where
     successorList = successors ownNs
-    successorRMap = addRMapEntry (toRemoteNodeState ownNs) $ rMapFromList successorList
+    successorRMap = addRMapEntry (getKeyID ownRemote) ownRemote $ rMapFromList (keyValuePair <$> successorList)
+    ownRemote = toRemoteNodeState ownNs
     closestSuccessor = headMay successorList
 
 -- cache operations
@@ -169,7 +174,8 @@ addCacheEntryPure now (RemoteCacheEntry ns ts) cache =
     let
         -- TODO: limit diffSeconds to some maximum value to prevent malicious nodes from inserting entries valid nearly until eternity
         timestamp' = if ts <= now then ts else now
-        newCache = addRMapEntryWith insertCombineFunction (CacheEntry False ns timestamp') cache
+        newEntry = CacheEntry False ns timestamp'
+        newCache = addRMapEntryWith insertCombineFunction (getKeyID newEntry) newEntry cache
         insertCombineFunction newVal@(KeyEntry (CacheEntry newValidationState newNode newTimestamp)) oldVal =
             case oldVal of
               ProxyEntry n _ -> ProxyEntry n (Just newVal)
@@ -202,7 +208,7 @@ addNodeAsVerifiedPure :: POSIXTime
                       -> RemoteNodeState
                       -> NodeCache
                       -> NodeCache
-addNodeAsVerifiedPure now node = addRMapEntry (CacheEntry True node now)
+addNodeAsVerifiedPure now node = addRMapEntry (getKeyID node) (CacheEntry True node now)
 
 
 
@@ -221,7 +227,7 @@ 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 :: LocalNodeState s -> Bool
 isJoined ns = not . all null $ [successors ns, predecessors ns]
 
 -- | the size limit to be used when serialising messages for sending
@@ -245,19 +251,20 @@ ackRequest _ _ = Map.empty
 
 -- | Dispatch incoming requests to the dedicated handling and response function, and enqueue
 -- the response to be sent.
-handleIncomingRequest :: LocalNodeStateSTM                     -- ^ the handling node
+handleIncomingRequest :: Service s (RealNodeSTM s)
+                      => LocalNodeStateSTM s                     -- ^ the handling node
                       -> TQueue (BS.ByteString, SockAddr)   -- ^ send queue
                       -> Set.Set FediChordMessage           -- ^ all parts of the request to handle
                       -> SockAddr                           -- ^ source address of the request
                       -> IO ()
 handleIncomingRequest nsSTM sendQ msgSet sourceAddr = do
-    putStrLn $ "handling incoming request: " <> show msgSet
     ns <- readTVarIO nsSTM
     -- add nodestate to cache
     now <- getPOSIXTime
     case headMay . Set.elems $ msgSet of
       Nothing -> pure ()
       Just aPart -> do
+        let (SockAddrInet6 _ _ sourceIP _) = sourceAddr
         queueAddEntries (Identity $ RemoteCacheEntry (sender aPart) now) ns
         -- distinguish on whether and how to respond. If responding, pass message to response generating function and write responses to send queue
         maybe (pure ()) (
@@ -265,17 +272,36 @@ handleIncomingRequest nsSTM sendQ msgSet sourceAddr = do
                         )
             =<< (case action aPart of
                 Ping -> Just <$> respondPing nsSTM msgSet
-                Join -> Just <$> respondJoin nsSTM msgSet
+                Join -> dropSpoofedIDs sourceIP nsSTM msgSet respondJoin
                 -- 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 dropSpoofedIDs sourceIP nsSTM msgSet respondLeave else pure Nothing
+                Stabilise -> if isJoined ns then dropSpoofedIDs sourceIP nsSTM msgSet respondStabilise else pure Nothing
             )
       -- for single part request, response starts with part number 1. For multipart requests, response starts with part number n+1.
 
       -- TODO: determine request type only from first part, but catch RecSelError on each record access when folding, because otherwise different request type parts can make this crash
       -- TODO: test case: mixed message types of parts
+  where
+      -- | Filter out requests with spoofed node IDs by recomputing the ID using
+      -- the sender IP.
+      -- For valid (non-spoofed) sender IDs, the passed responder function is invoked.
+      dropSpoofedIDs :: HostAddress6        -- msg source address
+                     -> LocalNodeStateSTM s
+                     -> Set.Set FediChordMessage    -- message parts of the request
+                     -> (LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString))     -- reponder function to be invoked for valid requests
+                     -> IO (Maybe (Map.Map Integer BS.ByteString))
+      dropSpoofedIDs addr nsSTM' msgSet' responder =
+          let
+            aRequestPart = Set.elemAt 0 msgSet
+            senderNs = sender aRequestPart
+            givenSenderID = getNid senderNs
+            recomputedID = genNodeID addr (getDomain senderNs) (fromInteger $ getVServerID senderNs)
+          in
+          if recomputedID == givenSenderID
+             then Just <$> responder nsSTM' msgSet'
+             else pure Nothing
 
 
 -- ....... response sending .......
@@ -284,9 +310,8 @@ handleIncomingRequest nsSTM sendQ msgSet sourceAddr = do
 
 
 -- | execute a key ID lookup on local cache and respond with the result
-respondQueryID :: LocalNodeStateSTM -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
+respondQueryID :: LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
 respondQueryID nsSTM msgSet = do
-    putStrLn "responding to a QueryID request"
     -- this message cannot be split reasonably, so just
     -- consider the first payload
     let
@@ -324,8 +349,7 @@ respondQueryID nsSTM msgSet = do
 
 -- | Respond to a Leave request by removing the leaving node from local data structures
 -- and confirming with response.
--- TODO: copy over key data from leaver and confirm
-respondLeave :: LocalNodeStateSTM -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
+respondLeave :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
 respondLeave nsSTM msgSet = do
     -- combine payload of all parts
     let (requestPreds, requestSuccs) = foldr' (\msg (predAcc, succAcc) ->
@@ -334,16 +358,15 @@ respondLeave nsSTM msgSet = do
                                               )
                                               ([],[]) msgSet
         aRequestPart = Set.elemAt 0 msgSet
-        senderID = getNid . sender $ aRequestPart
+        leaveSenderID = getNid . sender $ aRequestPart
     responseMsg <- atomically $ do
         nsSnap <- readTVar nsSTM
         -- remove leaving node from successors, predecessors and NodeCache
-        writeTQueue (cacheWriteQueue nsSnap) $ deleteCacheEntry senderID
+        writeTQueue (cacheWriteQueue nsSnap) $ deleteCacheEntry leaveSenderID
         writeTVar nsSTM $
             -- add predecessors and successors of leaving node to own lists
-            setPredecessors (filter ((/=) senderID . getNid) $ requestPreds <> predecessors nsSnap)
-          . setSuccessors (filter ((/=) senderID . getNid) $ requestSuccs <> successors nsSnap) $ nsSnap
-        -- TODO: handle handover of key data
+            setPredecessors (filter ((/=) leaveSenderID . getNid) $ requestPreds <> predecessors nsSnap)
+          . setSuccessors (filter ((/=) leaveSenderID . getNid) $ requestSuccs <> successors nsSnap) $ nsSnap
         let leaveResponse = Response {
                 requestID = requestID aRequestPart
               , senderID = getNid nsSnap
@@ -353,10 +376,14 @@ respondLeave nsSTM msgSet = do
               , payload = Just LeaveResponsePayload
                                      }
         pure leaveResponse
+    -- if awaiting an incoming service data migration, collect the lock without blocking this thread
+    when (maybe False leaveDoMigration (payload  aRequestPart)) $ do
+        ownService <- atomically $ nodeService <$> (readTVar nsSTM >>= (readTVar . parentRealNode))
+        void (forkIO $ waitForMigrationFrom ownService leaveSenderID)
     pure $ serialiseMessage sendMessageSize responseMsg
 
 -- | respond to stabilise requests by returning successor and predecessor list
-respondStabilise :: LocalNodeStateSTM -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
+respondStabilise :: LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
 respondStabilise nsSTM msgSet = do
     nsSnap <- readTVarIO nsSTM
     let
@@ -378,7 +405,7 @@ respondStabilise nsSTM msgSet = do
 
 
 -- | respond to Ping request by returning all active vserver NodeStates
-respondPing :: LocalNodeStateSTM -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
+respondPing :: LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
 respondPing nsSTM msgSet = do
     -- TODO: respond with all active VS when implementing k-choices
     nsSnap <- readTVarIO nsSTM
@@ -395,18 +422,19 @@ respondPing nsSTM msgSet = do
                                 }
     pure $ serialiseMessage sendMessageSize pingResponse
 
--- this modifies node state, so locking and IO seems to be necessary.
--- Still try to keep as much code as possible pure
-respondJoin :: LocalNodeStateSTM -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
+
+respondJoin :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> Set.Set FediChordMessage -> IO (Map.Map Integer BS.ByteString)
 respondJoin nsSTM msgSet = do
     -- atomically read and modify the node state according to the parsed request
-    responseMsg <- atomically $ do
+    (dataMigration, responseMsg) <- atomically $ do
         nsSnap <- readTVar nsSTM
         cache <- readTVar $ nodeCacheSTM nsSnap
         let
             aRequestPart = Set.elemAt 0 msgSet
             senderNS = sender aRequestPart
-            responsibilityLookup = queryLocalCache nsSnap cache 1 (getNid senderNS)
+            -- if not joined yet, attract responsibility for
+            -- all keys to make bootstrapping possible
+            responsibilityLookup = if isJoined nsSnap then queryLocalCache nsSnap cache 1 (getNid senderNS) else FOUND (toRemoteNodeState nsSnap)
             thisNodeResponsible (FOUND _)   = True
             thisNodeResponsible (FORWARD _) = False
         -- check whether the joining node falls into our responsibility
@@ -430,33 +458,41 @@ respondJoin nsSTM msgSet = do
                , payload = Just responsePayload
                                      }
            writeTVar nsSTM joinedNS
-           pure joinResponse
+           ownService <- nodeService <$> readTVar (parentRealNode nsSnap)
+           let
+             serviceDataMigrator = migrateData ownService (getNid nsSnap) lowerKeyBound (getNid senderNS) (getDomain senderNS, fromIntegral $ getServicePort senderNS)
+             lowerKeyBound = maybe (getNid nsSnap) getNid $ headMay (predecessors nsSnap)
+           pure (Just serviceDataMigrator, joinResponse)
         -- otherwise respond with empty payload
-        else pure Response {
+        else pure (Nothing, Response {
              requestID = requestID aRequestPart
            , senderID = getNid nsSnap
            , part = if Set.size msgSet == 1 then 1 else fromIntegral $ Set.size msgSet + 1
            , isFinalPart = False
            , action = Join
            , payload = Nothing
-                           }
+                           })
 
+    -- as DHT response is required immediately, fork the service data migration push
+    -- into a new thread. That's kind of ugly but the best I can think of so far
+    when (isJust dataMigration) (forkIO (fromJust dataMigration >> pure ()) >> pure ())
     pure $ serialiseMessage sendMessageSize responseMsg
     -- TODO: notify service layer to copy over data now handled by the new joined node
 
 -- ....... request sending .......
 
 -- | send a join request and return the joined 'LocalNodeState' including neighbours
-requestJoin :: NodeState a => a             -- ^ currently responsible node to be contacted
-            -> LocalNodeStateSTM               -- ^ joining NodeState
-            -> IO (Either String LocalNodeStateSTM)    -- ^ node after join with all its new information
+requestJoin :: (NodeState a, Service s (RealNodeSTM s)) => a             -- ^ currently responsible node to be contacted
+            -> LocalNodeStateSTM s               -- ^ joining NodeState
+            -> IO (Either String (LocalNodeStateSTM s))    -- ^ node after join with all its new information
 requestJoin toJoinOn ownStateSTM = do
     ownState <- readTVarIO ownStateSTM
     prn <- readTVarIO $ parentRealNode ownState
-    srcAddr <- confIP . nodeConfig <$> readTVarIO (parentRealNode ownState)
+    nodeConf <- nodeConfig <$> readTVarIO (parentRealNode ownState)
+    let srcAddr = confIP nodeConf
     bracket (mkSendSocket srcAddr (getDomain toJoinOn) (getDhtPort toJoinOn)) close (\sock -> do
         -- extract own state for getting request information
-        responses <- sendRequestTo 5000 3 (\rid -> Request rid (toRemoteNodeState ownState) 1 True Join (Just JoinRequestPayload)) sock
+        responses <- sendRequestTo (confRequestTimeout nodeConf) (confRequestRetries nodeConf) (\rid -> Request rid (toRemoteNodeState ownState) 1 True Join (Just JoinRequestPayload)) sock
         (cacheInsertQ, joinedState) <- atomically $ do
             stateSnap <- readTVar ownStateSTM
             let
@@ -481,25 +517,28 @@ 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
-        pure $ if responses == Set.empty
-                  then Left $ "join error: got no response from " <> show (getNid toJoinOn)
-           else if null (predecessors joinedState) && null (successors joinedState)
-                then Left "join error: no predecessors or successors"
-                -- successful join
-                else Right ownStateSTM
+        if responses == Set.empty
+                  then pure . Left $ "join error: got no response from " <> show (getNid toJoinOn)
+           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))
 
 
 -- | Send a 'QueryID' 'Request' for getting the node that handles a certain key ID.
-requestQueryID :: LocalNodeState        -- ^ NodeState of the querying node
+requestQueryID :: (MonadIO m, MonadError String m)
+               => LocalNodeState s        -- ^ NodeState of the querying node
                -> NodeID                -- ^ target key ID to look up
-               -> IO RemoteNodeState    -- ^ the node responsible for handling that key
+               -> m RemoteNodeState    -- ^ the node responsible for handling that key
 -- 1. do a local lookup for the l closest nodes
 -- 2. create l sockets
 -- 3. send a message async concurrently to all l nodes
@@ -507,23 +546,23 @@ requestQueryID :: LocalNodeState        -- ^ NodeState of the querying node
 -- 5. repeat until FOUND (problem: new entries not necessarily already in cache, explicitly compare with closer results)
 -- TODO: deal with lookup failures
 requestQueryID ns targetID = do
-    firstCacheSnapshot <- readTVarIO . nodeCacheSTM $ ns
+    firstCacheSnapshot <- liftIO . readTVarIO . nodeCacheSTM $ ns
     -- TODO: make maxAttempts configurable
     queryIdLookupLoop firstCacheSnapshot ns 50 targetID
 
 -- | like 'requestQueryID, but allows passing of a custom cache, e.g. for joining
-queryIdLookupLoop :: NodeCache -> LocalNodeState -> Int -> NodeID -> IO RemoteNodeState
+queryIdLookupLoop :: (MonadIO m, MonadError String m) => NodeCache -> LocalNodeState s -> Int -> NodeID -> m RemoteNodeState
 -- return node itself as default fallback value against infinite recursion.
 -- TODO: consider using an Either instead of a default value
-queryIdLookupLoop _ ns 0 _ = pure $ toRemoteNodeState ns
+queryIdLookupLoop _ ns 0 _ = throwError "exhausted maximum lookup attempts"
 queryIdLookupLoop cacheSnapshot ns maxAttempts targetID = do
     let localResult = queryLocalCache ns cacheSnapshot (lNumBestNodes ns) targetID
     -- FOUND can only be returned if targetID is owned by local node
     case localResult of
       FOUND thisNode -> pure thisNode
       FORWARD nodeSet -> do
-          responseEntries <- sendQueryIdMessages targetID ns Nothing (remoteNode <$> Set.elems nodeSet)
-          now <- getPOSIXTime
+          responseEntries <- liftIO $ sendQueryIdMessages targetID ns Nothing (remoteNode <$> Set.elems nodeSet)
+          now <- liftIO getPOSIXTime
           -- check for a FOUND and return it
           case responseEntries of
             FOUND foundNode -> pure foundNode
@@ -538,7 +577,7 @@ queryIdLookupLoop cacheSnapshot ns maxAttempts targetID = do
 
 sendQueryIdMessages :: (Integral i)
                     => NodeID                        -- ^ target key ID to look up
-                    -> LocalNodeState                -- ^ node state of the node doing the query
+                    -> LocalNodeState s                -- ^ node state of the node doing the query
                     -> Maybe i                       -- ^ optionally provide an explicit @l@ parameter of number of nodes to be returned
                    -> [RemoteNodeState]             -- ^ nodes to query
                    -> IO QueryResponse -- ^ accumulated response
@@ -546,10 +585,10 @@ sendQueryIdMessages targetID ns lParam targets = do
 
           -- create connected sockets to all query targets and use them for request handling
 
-          srcAddr <- confIP . nodeConfig <$> readTVarIO (parentRealNode ns)
-          -- ToDo: make attempts and timeout configurable
+          nodeConf <- nodeConfig <$> readTVarIO (parentRealNode ns)
+          let srcAddr = confIP nodeConf
           queryThreads <- mapM (\resultNode -> async $ bracket (mkSendSocket srcAddr (getDomain resultNode) (getDhtPort resultNode)) close (
-              sendRequestTo 5000 3 (lookupMessage targetID ns Nothing)
+              sendRequestTo (confRequestTimeout nodeConf) (confRequestRetries nodeConf) (lookupMessage targetID ns Nothing)
                                                                                                                                    )) targets
           -- ToDo: process results immediately instead of waiting for the last one to finish, see https://stackoverflow.com/a/38815224/9198613
           -- ToDo: exception handling, maybe log them
@@ -557,8 +596,10 @@ sendQueryIdMessages targetID ns lParam targets = do
           -- insert new cache entries both into global cache as well as return accumulated QueryResponses for further processing
           now <- getPOSIXTime
           -- collect cache entries from all responses
-          foldM (\acc resp -> do
-            let entrySet = case queryResult <$> payload resp of
+          foldrM (\resp acc -> do
+            let
+                responseResult = queryResult <$> payload resp
+                entrySet = case responseResult of
                              Just (FOUND result1) -> Set.singleton (RemoteCacheEntry result1 now)
                              Just (FORWARD resultset) -> resultset
                              _ -> Set.empty
@@ -568,15 +609,20 @@ sendQueryIdMessages targetID ns lParam targets = do
             -- return accumulated QueryResult
             pure $ case acc of
               -- once a FOUND as been encountered, return this as a result
-              isFound@FOUND{} -> isFound
-              FORWARD accSet  -> FORWARD $ entrySet `Set.union` accSet
+              FOUND{} -> acc
+              FORWARD accSet
+                | maybe False isFound responseResult -> fromJust responseResult
+                | otherwise -> FORWARD $ entrySet `Set.union` accSet
 
                             ) (FORWARD Set.empty) responses
+  where
+      isFound FOUND{} = True
+      isFound _       = False
 
 -- | Create a QueryID message to be supplied to 'sendRequestTo'
 lookupMessage :: Integral i
               => NodeID         -- ^ target ID
-              -> LocalNodeState -- ^ sender node state
+              -> LocalNodeState s -- ^ sender node state
               -> Maybe i        -- ^ optionally provide a different l parameter
               ->  (Integer -> FediChordMessage)
 lookupMessage targetID ns lParam = \rID -> Request rID (toRemoteNodeState ns) 1 True QueryID (Just $ pl ns targetID)
@@ -586,12 +632,13 @@ lookupMessage targetID ns lParam = \rID -> Request rID (toRemoteNodeState ns) 1
 
 -- | Send a stabilise request to provided 'RemoteNode' and, if successful,
 -- return parsed neighbour lists
-requestStabilise :: LocalNodeState      -- ^ sending node
+requestStabilise :: LocalNodeState s      -- ^ sending node
                  -> RemoteNodeState     -- ^ neighbour node to send to
                  -> IO (Either String ([RemoteNodeState], [RemoteNodeState]))   -- ^ (predecessors, successors) of responding node
 requestStabilise ns neighbour = do
-    srcAddr <- confIP . nodeConfig <$> readTVarIO (parentRealNode ns)
-    responses <- bracket (mkSendSocket srcAddr (getDomain neighbour) (getDhtPort neighbour)) close (fmap Right . sendRequestTo 5000 3 (\rid ->
+    nodeConf <- nodeConfig <$> readTVarIO (parentRealNode ns)
+    let srcAddr = confIP nodeConf
+    responses <- bracket (mkSendSocket srcAddr (getDomain neighbour) (getDhtPort neighbour)) close (fmap Right . sendRequestTo (confRequestTimeout nodeConf) (confRequestRetries nodeConf) (\rid ->
         Request {
             requestID = rid
           , sender = toRemoteNodeState ns
@@ -613,22 +660,55 @@ requestStabilise ns neighbour = do
                                                       )
                                                       ([],[]) respSet
             -- update successfully responded neighbour in cache
-            now <- getPOSIXTime
-            maybe (pure ()) (\p -> queueAddEntries (Identity $ RemoteCacheEntry (sender p) now) ns) $ headMay (Set.elems respSet)
+            maybe (pure ()) (\p -> queueUpdateVerifieds (Identity $ senderID p) ns) $ headMay (Set.elems respSet)
             pure $ if null responsePreds && null responseSuccs
                       then Left "no neighbours returned"
                       else Right (responsePreds, responseSuccs)
         ) responses
 
 
-requestPing :: LocalNodeState      -- ^ sending node
+-- | Send a Leave request to the specified node.
+-- Service data transfer needs to be done separately, as not all neighbours
+-- that need to know about the leaving handle the new service data.
+requestLeave :: LocalNodeState s
+             -> Bool                -- whether to migrate service data
+             -> RemoteNodeState     -- target node
+             -> IO (Either String ())   -- error or success
+requestLeave ns doMigration target = do
+    nodeConf <- nodeConfig <$> readTVarIO (parentRealNode ns)
+    let srcAddr = confIP nodeConf
+        leavePayload = LeaveRequestPayload {
+        leaveSuccessors = successors ns
+      , leavePredecessors = predecessors ns
+      , leaveDoMigration = doMigration
+                                           }
+    responses <- bracket (mkSendSocket srcAddr (getDomain target) (getDhtPort target)) close (fmap Right . sendRequestTo (confRequestTimeout nodeConf) (confRequestRetries nodeConf) (\rid ->
+        Request {
+            requestID = rid
+          , sender = toRemoteNodeState ns
+          , part = 1
+          , isFinalPart = False
+          , action = Leave
+          , payload = Just leavePayload
+                }
+                         )
+                                                                                           ) `catch`  (\e -> pure . Left $ displayException (e :: IOException))
+    either
+        -- forward IO error messages
+        (pure . Left)
+        -- empty payload, so no processing required
+        (const . pure . Right $ ())
+        responses
+
+requestPing :: LocalNodeState s      -- ^ sending node
                  -> RemoteNodeState     -- ^ node to be PINGed
                  -> IO (Either String [RemoteNodeState])   -- ^ all active vServers of the pinged node
 requestPing ns target = do
-    srcAddr <- confIP . nodeConfig <$> readTVarIO (parentRealNode ns)
+    nodeConf <- nodeConfig <$> readTVarIO (parentRealNode ns)
+    let srcAddr = confIP nodeConf
     responses <- bracket (mkSendSocket srcAddr (getDomain target) (getDhtPort target)) close
         (\sock -> do
-            resp <- sendRequestTo 5000 3 (\rid ->
+            resp <- sendRequestTo (confRequestTimeout nodeConf) (confRequestRetries nodeConf) (\rid ->
                 Request {
                     requestID = rid
                   , sender = toRemoteNodeState ns
@@ -664,10 +744,9 @@ requestPing ns target = do
         ) responses
 
 
-
 -- | Generic function for sending a request over a connected socket and collecting the response.
 -- Serialises the message and tries to deliver its parts for a number of attempts within a specified timeout.
-sendRequestTo :: Int                    -- ^ timeout in seconds
+sendRequestTo :: Int                    -- ^ timeout in milliseconds
               -> Int                    -- ^ number of retries
               -> (Integer -> FediChordMessage)       -- ^ the message to be sent, still needing a requestID
               -> Socket                 -- ^ connected socket to use for sending
@@ -678,11 +757,10 @@ sendRequestTo timeoutMillis numAttempts msgIncomplete sock = do
     let
         msgComplete = msgIncomplete randomID
         requests = serialiseMessage sendMessageSize msgComplete
-    putStrLn $ "sending request message " <> show msgComplete
     -- create a queue for passing received response messages back, even after a timeout
     responseQ <- newTBQueueIO $ 2*maximumParts  -- keep room for duplicate packets
     -- start sendAndAck with timeout
-    attempts numAttempts . timeout timeoutMillis $ sendAndAck responseQ sock requests
+    _ <- attempts numAttempts . timeout (timeoutMillis*1000) $ sendAndAck responseQ sock requests
     -- after timeout, check received responses, delete them from unacked message set/ map and rerun senAndAck with that if necessary.
     recvdParts <- atomically $ flushTBQueue responseQ
     pure $ Set.fromList recvdParts
@@ -691,19 +769,20 @@ sendRequestTo timeoutMillis numAttempts msgIncomplete sock = do
                -> Socket                            -- ^ the socket used for sending and receiving for this particular remote node
                -> Map.Map Integer BS.ByteString     -- ^ the remaining unacked request parts
                -> IO ()
-    sendAndAck responseQueue sock remainingSends = do
-        sendMany sock $ Map.elems remainingSends
+    sendAndAck responseQueue sock' remainingSends = do
+        sendMany sock' $ Map.elems remainingSends
         -- if all requests have been acked/ responded to, return prematurely
-        recvLoop responseQueue remainingSends Set.empty Nothing
-    recvLoop :: TBQueue FediChordMessage          -- ^ the queue for putting in the received responses
+        recvLoop sock' responseQueue remainingSends Set.empty Nothing
+    recvLoop :: Socket
+             -> TBQueue FediChordMessage          -- ^ the queue for putting in the received responses
              -> Map.Map Integer BS.ByteString       -- ^ the remaining unacked request parts
              -> Set.Set Integer                     -- ^ already received response part numbers
              -> Maybe Integer                     -- ^ total number of response parts if already known
              -> IO ()
-    recvLoop responseQueue remainingSends' receivedPartNums totalParts = do
+    recvLoop sock' responseQueue remainingSends' receivedPartNums totalParts = do
         -- 65535 is maximum length of UDP packets, as long as
         -- no IPv6 jumbograms are used
-        response <- deserialiseMessage <$> recv sock 65535
+        response <- deserialiseMessage <$> recv sock' 65535
         case response of
           Right msg@Response{} -> do
               atomically $ writeTBQueue responseQueue msg
@@ -711,16 +790,17 @@ sendRequestTo timeoutMillis numAttempts msgIncomplete sock = do
                 newTotalParts = if isFinalPart msg then Just (part msg) else totalParts
                 newRemaining = Map.delete (part msg) remainingSends'
                 newReceivedParts = Set.insert (part msg) receivedPartNums
-              if Map.null newRemaining && maybe False (\p -> Set.size receivedPartNums == fromIntegral p) newTotalParts
+              if  Map.null newRemaining && maybe False (\p -> Set.size newReceivedParts == fromIntegral p) newTotalParts
                  then pure ()
-                 else recvLoop responseQueue newRemaining receivedPartNums newTotalParts
+                 else recvLoop sock' responseQueue newRemaining newReceivedParts newTotalParts
           -- drop errors and invalid messages
-          Left _ -> recvLoop responseQueue remainingSends' receivedPartNums totalParts
+          Right Request{} -> pure ()    -- expecting a response, not a request
+          Left _ -> recvLoop sock' responseQueue remainingSends' receivedPartNums totalParts
 
 
 -- | enqueue a list of RemoteCacheEntries to be added to the global NodeCache
 queueAddEntries :: Foldable c => c RemoteCacheEntry
-                -> LocalNodeState
+                -> LocalNodeState s
                 -> IO ()
 queueAddEntries entries ns = do
     now <- getPOSIXTime
@@ -730,17 +810,29 @@ queueAddEntries entries ns = do
 -- | enque a list of node IDs to be deleted from the global NodeCache
 queueDeleteEntries :: Foldable c
                    => c NodeID
-                   -> LocalNodeState
+                   -> LocalNodeState s
                    -> IO ()
 queueDeleteEntries ids ns = forM_ ids $ atomically . writeTQueue (cacheWriteQueue ns) . deleteCacheEntry
 
 
 -- | enque a single node ID to be deleted from the global NodeCache
 queueDeleteEntry :: NodeID
-                 -> LocalNodeState
+                 -> LocalNodeState s
                  -> IO ()
 queueDeleteEntry toDelete = queueDeleteEntries $ Identity toDelete
 
+
+-- | enqueue the timestamp update and verification marking of an entry in the
+-- global 'NodeCache'.
+queueUpdateVerifieds :: Foldable c
+                     => c NodeID
+                     -> LocalNodeState s
+                     -> IO ()
+queueUpdateVerifieds nIds ns = do
+    now <- getPOSIXTime
+    forM_ nIds $ \nid' -> atomically $ writeTQueue (cacheWriteQueue ns) $
+        markCacheEntryAsVerified (Just now) nid'
+
 -- | retry an IO action at most *i* times until it delivers a result
 attempts :: Int             -- ^ number of retries *i*
          -> IO (Maybe a)    -- ^ action to retry
@@ -773,7 +865,7 @@ mkServerSocket ip port = do
     sockAddr <- addrAddress <$> resolve (Just $ show . fromHostAddress6 $ ip) (Just port)
     sock <- socket AF_INET6 Datagram defaultProtocol
     setSocketOption sock IPv6Only 1
-    bind sock sockAddr
+    bind sock sockAddr `catch` (\e -> putStrLn $ "Caught exception while bind " <> show sock <> " " <> show sockAddr <> ": " <> show (e :: SomeException))
     pure sock
 
 -- | create a UDP datagram socket, connected to a destination.
@@ -789,6 +881,6 @@ mkSendSocket srcIp dest destPort = do
     setSocketOption sendSock IPv6Only 1
     -- bind to the configured local IP to make sure that outgoing packets are sent from
     -- this source address
-    bind sendSock srcAddr
+    bind sendSock srcAddr `catch` (\e -> putStrLn $ "Caught exception while mkSendSocket bind " <> show sendSock <> " " <> show srcAddr <> ": " <> show (e :: SomeException))
     connect sendSock destAddr
     pure sendSock

src/Hash2Pub/FediChord.hs

@@ -3,7 +3,6 @@
 {-# LANGUAGE FlexibleContexts   #-}
 {-# LANGUAGE FlexibleInstances  #-}
 {-# LANGUAGE OverloadedStrings  #-}
-{-# LANGUAGE TypeSynonymInstances #-}
 {- |
 Module      : FediChord
 Description : An opinionated implementation of the EpiChord DHT by Leong et al.
@@ -40,7 +39,7 @@ module Hash2Pub.FediChord (
   , bsAsIpAddr
   , FediChordConf(..)
   , fediChordInit
-  , fediChordJoin
+  , fediChordVserverJoin
   , fediChordBootstrapJoin
   , tryBootstrapJoining
   , fediMainThreads
@@ -78,7 +77,6 @@ import           Data.Maybe                    (catMaybes, fromJust, fromMaybe,
                                                 isJust, isNothing, mapMaybe)
 import qualified Data.Set                      as Set
 import           Data.Time.Clock.POSIX
-import           Data.Typeable                 (Typeable (..), typeOf)
 import           Data.Word
 import qualified Network.ByteOrder             as NetworkBytes
 import           Network.Socket                hiding (recv, recvFrom, send,
@@ -95,24 +93,34 @@ import           Debug.Trace                   (trace)
 
 -- | initialise data structures, compute own IDs and bind to listening socket
 -- ToDo: load persisted state, thus this function already operates in IO
-fediChordInit :: FediChordConf -> IO (Socket, LocalNodeStateSTM)
-fediChordInit initConf = do
+fediChordInit :: (Service s (RealNodeSTM s))
+              => FediChordConf
+              -> (RealNodeSTM s -> IO (s (RealNodeSTM s)))     -- ^ runner function for service
+              -> IO (Socket, LocalNodeStateSTM s)
+fediChordInit initConf serviceRunner = do
     emptyLookupCache <- newTVarIO Map.empty
     let realNode = RealNode {
             vservers = []
           , nodeConfig = initConf
           , bootstrapNodes = confBootstrapNodes initConf
           , lookupCacheSTM = emptyLookupCache
+          , nodeService = undefined
                             }
     realNodeSTM <- newTVarIO realNode
+    -- launch service and set the reference in the RealNode
+    serv <- serviceRunner realNodeSTM
+    atomically . modifyTVar' realNodeSTM $ \rn -> rn { nodeService = serv }
+    -- initialise a single vserver
     initialState <- nodeStateInit realNodeSTM
     initialStateSTM <- newTVarIO initialState
+    -- add vserver to list at RealNode
+    atomically . modifyTVar' realNodeSTM $ \rn -> rn { vservers = initialStateSTM:vservers rn }
     serverSock <- mkServerSocket (getIpAddr initialState) (getDhtPort initialState)
     pure (serverSock, initialStateSTM)
 
 -- | initialises the 'NodeState' for this local node.
 -- Separated from 'fediChordInit' to be usable in tests.
-nodeStateInit :: RealNodeSTM -> IO LocalNodeState
+nodeStateInit :: Service s (RealNodeSTM s) => RealNodeSTM s -> IO (LocalNodeState s)
 nodeStateInit realNodeSTM = do
     realNode <- readTVarIO realNodeSTM
     cacheSTM <- newTVarIO initCache
@@ -125,7 +133,7 @@ nodeStateInit realNodeSTM = do
           , ipAddr = confIP conf
           , nid = genNodeID (confIP conf) (confDomain conf) $ fromInteger vsID
           , dhtPort = toEnum $ confDhtPort conf
-          , servicePort = 0
+          , servicePort = getListeningPortFromService $ nodeService realNode
           , vServerID = vsID
                                           }
         initialState = LocalNodeState {
@@ -144,9 +152,10 @@ nodeStateInit realNodeSTM = do
 
 -- | Join a new node into the DHT, using a provided bootstrap node as initial cache seed
 -- for resolving the new node's position.
-fediChordBootstrapJoin :: LocalNodeStateSTM              -- ^ the local 'NodeState'
+fediChordBootstrapJoin :: Service s (RealNodeSTM s)
+                       => LocalNodeStateSTM s            -- ^ the local 'NodeState'
                        -> (String, PortNumber)   -- ^ domain and port of a bootstrapping node
-                        -> IO (Either String LocalNodeStateSTM) -- ^ the joined 'NodeState' after a
+                       -> IO (Either String (LocalNodeStateSTM s)) -- ^ the joined 'NodeState' after a
                                             -- successful join, otherwise an error message
 fediChordBootstrapJoin nsSTM bootstrapNode = do
     -- can be invoked multiple times with all known bootstrapping nodes until successfully joined
@@ -157,12 +166,13 @@ fediChordBootstrapJoin nsSTM bootstrapNode = do
         currentlyResponsible <- liftEither lookupResp
         liftIO . putStrLn $ "Trying to join on " <> show (getNid currentlyResponsible)
         -- 2. then send a join to the currently responsible node
+        liftIO $ putStrLn "send a bootstrap Join"
         joinResult <- liftIO $ requestJoin currentlyResponsible nsSTM
         liftEither joinResult
 
 -- Periodically lookup own ID through a random bootstrapping node to discover and merge separated DHT clusters.
 -- Unjoined try joining instead.
-convergenceSampleThread :: LocalNodeStateSTM -> IO ()
+convergenceSampleThread :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> IO ()
 convergenceSampleThread nsSTM = forever $ do
     nsSnap <- readTVarIO nsSTM
     parentNode <- readTVarIO $ parentRealNode nsSnap
@@ -189,11 +199,11 @@ convergenceSampleThread nsSTM = forever $ do
     -- unjoined node: try joining through all bootstrapping nodes
     else tryBootstrapJoining nsSTM >> pure ()
     let delaySecs = confBootstrapSamplingInterval . nodeConfig $ parentNode
-    threadDelay $ delaySecs * 10^6
+    threadDelay delaySecs
 
 
 -- | Try joining the DHT through any of the bootstrapping nodes until it succeeds.
-tryBootstrapJoining :: LocalNodeStateSTM -> IO (Either String LocalNodeStateSTM)
+tryBootstrapJoining :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> IO (Either String (LocalNodeStateSTM s))
 tryBootstrapJoining nsSTM = do
     bss <- atomically $ do
         nsSnap <- readTVar nsSTM
@@ -210,13 +220,14 @@ tryBootstrapJoining nsSTM = do
 
 
 -- | Look up a key just based on the responses of a single bootstrapping node.
-bootstrapQueryId :: LocalNodeStateSTM -> (String, PortNumber) -> NodeID -> IO (Either String RemoteNodeState)
+bootstrapQueryId :: LocalNodeStateSTM s -> (String, PortNumber) -> NodeID -> IO (Either String RemoteNodeState)
 bootstrapQueryId nsSTM (bootstrapHost, bootstrapPort) targetID = do
     ns <- readTVarIO nsSTM
-    srcAddr <- confIP . nodeConfig <$> readTVarIO (parentRealNode ns)
+    nodeConf <- nodeConfig <$> readTVarIO (parentRealNode ns)
+    let srcAddr = confIP nodeConf
     bootstrapResponse <- bracket (mkSendSocket srcAddr bootstrapHost bootstrapPort) close (
         -- Initialise an empty cache only with the responses from a bootstrapping node
-        fmap Right . sendRequestTo 5000 3 (lookupMessage targetID ns Nothing)
+        fmap Right . sendRequestTo (confRequestTimeout nodeConf) (confRequestRetries nodeConf) (lookupMessage targetID ns Nothing)
                                                                                   )
        `catch` (\e -> pure . Left $ "Error at bootstrap QueryId: " <> displayException (e :: IOException))
 
@@ -235,60 +246,95 @@ bootstrapQueryId nsSTM (bootstrapHost, bootstrapPort) targetID = do
                            Just (FORWARD resultset) -> foldr' (addCacheEntryPure now) cacheAcc resultset
                               )
                            initCache resp
-               currentlyResponsible <- queryIdLookupLoop bootstrapCache ns 50 $ getNid ns
-               pure $ Right currentlyResponsible
+               currentlyResponsible <- runExceptT $ queryIdLookupLoop bootstrapCache ns 50 $ getNid ns
+               pure currentlyResponsible
 
 
 -- | join a node to the DHT using the global node cache
 -- node's position.
-fediChordJoin :: LocalNodeStateSTM                    -- ^ the local 'NodeState'
-              -> IO (Either String LocalNodeStateSTM)  -- ^ the joined 'NodeState' after a
+fediChordVserverJoin :: (MonadError String m, MonadIO m, Service s (RealNodeSTM s))
+                     => LocalNodeStateSTM s                    -- ^ the local 'NodeState'
+                     -> m (LocalNodeStateSTM s)  -- ^ the joined 'NodeState' after a
                                                     -- successful join, otherwise an error message
-fediChordJoin nsSTM = do
-    ns <- readTVarIO nsSTM
+fediChordVserverJoin nsSTM = do
+    ns <- liftIO $ readTVarIO nsSTM
     -- 1. get routed to the currently responsible node
     currentlyResponsible <- requestQueryID ns $ getNid ns
-    putStrLn $ "Trying to join on " <> show (getNid currentlyResponsible)
+    liftIO . putStrLn $ "Trying to join on " <> show (getNid currentlyResponsible)
     -- 2. then send a join to the currently responsible node
-    joinResult <- requestJoin currentlyResponsible nsSTM
-    case joinResult of
-      Left err       -> pure . Left $ "Error joining on " <> err
-      Right joinedNS -> pure . Right $ joinedNS
+    joinResult <- liftIO $ requestJoin currentlyResponsible nsSTM
+    liftEither joinResult
+
+fediChordVserverLeave :: (MonadError String m, MonadIO m, Service s (RealNodeSTM s)) => LocalNodeState s -> m ()
+fediChordVserverLeave ns = do
+    -- TODO: deal with failure of all successors, e.g. by invoking a stabilise
+    -- and looking up further successors. So far we just fail here.
+    _ <- migrateSuccessor
+    -- then send leave messages to all other neighbours
+    -- TODO: distinguish between sending error causes on our side and on the
+    -- network/ target side. The latter cannot be fixed anyways while the
+    -- former could be worked around
+
+    -- send a leave message to all neighbours
+    forM_ (predecessors ns <> successors ns) $ liftIO . requestLeave ns False
+  where
+    sendUntilSuccess i = maybe
+                     (pure $ Left "Exhausted all successors")
+                     (\neighb -> do
+                         leaveResponse <- requestLeave ns True neighb
+                         case leaveResponse of
+                           Left _  -> sendUntilSuccess (i+1)
+                           -- return first successfully contacted neighbour,
+                           -- so it can be contacted by the service layer for migration
+                           Right _ -> pure $ Right neighb
+                     )
+                     $ atMay (successors ns) i
+    migrateSuccessor :: (MonadError String m, MonadIO m) => m ()
+    migrateSuccessor = do
+        -- send leave message to first responding successor
+        successorLeave <- liftIO $ sendUntilSuccess 0
+        -- trigger service data transfer for abandoned key space
+        migrateToNode <- liftEither successorLeave
+        let lowerKeyBound = maybe (getNid ns) getNid $ headMay (predecessors ns)
+        ownService <- nodeService <$> (liftIO . readTVarIO $ parentRealNode ns)
+        -- previously held data is the one between the immediate predecessor and
+        -- the own ID
+        migrationResult <- liftIO $ migrateData ownService (getNid ns) lowerKeyBound (getNid ns) (getDomain migrateToNode, fromIntegral $ getServicePort migrateToNode)
+        liftEither migrationResult
+
 
 
 -- | Wait for new cache entries to appear and then try joining on them.
 -- Exits after successful joining.
-joinOnNewEntriesThread :: LocalNodeStateSTM -> IO ()
+joinOnNewEntriesThread :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> IO ()
 joinOnNewEntriesThread nsSTM = loop
   where
     loop = do
         nsSnap <- readTVarIO nsSTM
-        (lookupResult, cache) <- atomically $ do
+        (lookupResult, parentNode) <- atomically $ do
             cache <- readTVar $ nodeCacheSTM nsSnap
+            parentNode <- readTVar $ parentRealNode nsSnap
             case queryLocalCache nsSnap cache 1 (getNid nsSnap) of
               -- empty cache, block until cache changes and then retry
               (FORWARD s) | Set.null s -> retry
-              result                   -> pure (result, cache)
+              result                   -> pure (result, parentNode)
         case lookupResult of
           -- already joined
-          FOUND _ -> do
-              print =<< readTVarIO nsSTM
+          FOUND _ ->
               pure ()
           -- otherwise try joining
           FORWARD _ -> do
-              joinResult <- fediChordJoin nsSTM
+              joinResult <- runExceptT $ fediChordVserverJoin nsSTM
               either
                 -- on join failure, sleep and retry
-                -- TODO: make delay configurable
-                (const $ threadDelay (30 * 10^6) >> loop)
+                (const $ threadDelay (confJoinAttemptsInterval . nodeConfig $ parentNode) >> loop)
                 (const $ pure ())
                 joinResult
-    emptyset = Set.empty    -- because pattern matches don't accept qualified names
 
 
 -- | cache updater thread that waits for incoming NodeCache update instructions on
 -- the node's cacheWriteQueue and then modifies the NodeCache as the single writer.
-nodeCacheWriter :: LocalNodeStateSTM -> IO ()
+nodeCacheWriter :: LocalNodeStateSTM s -> IO ()
 nodeCacheWriter nsSTM =
     forever $ atomically $ do
         ns <- readTVar nsSTM
@@ -296,20 +342,15 @@ nodeCacheWriter nsSTM =
         modifyTVar' (nodeCacheSTM ns) cacheModifier
 
 
--- TODO: make max entry age configurable
-maxEntryAge :: POSIXTime
-maxEntryAge = 600
-
-
 -- | Periodically iterate through cache, clean up expired entries and verify unverified ones
-nodeCacheVerifyThread :: LocalNodeStateSTM -> IO ()
+nodeCacheVerifyThread :: LocalNodeStateSTM s -> IO ()
 nodeCacheVerifyThread nsSTM = forever $ do
-    putStrLn "cache verify run: begin"
     -- get cache
-    (ns, cache) <- atomically $ do
+    (ns, cache, maxEntryAge) <- atomically $ do
         ns <- readTVar nsSTM
         cache <- readTVar $ nodeCacheSTM ns
-        pure (ns, cache)
+        maxEntryAge <- confMaxNodeCacheAge . nodeConfig <$> readTVar (parentRealNode ns)
+        pure (ns, cache, maxEntryAge)
     -- iterate entries:
     -- for avoiding too many time syscalls, get current time before iterating.
     now <- getPOSIXTime
@@ -356,14 +397,13 @@ nodeCacheVerifyThread nsSTM = forever $ do
         forkIO $ sendQueryIdMessages targetID latestNs (Just (1 + jEntriesPerSlice latestNs)) (nodesToQuery targetID) >> pure () -- ask for 1 entry more than j because of querying the middle
                                                              )
 
-    putStrLn "cache verify run: end"
-    threadDelay $ 10^6 * round maxEntryAge `div` 20
+    threadDelay $ fromEnum (maxEntryAge / 20) `div` 10^6    -- convert from pico to milliseconds
 
 
 -- | Checks the invariant of at least @jEntries@ per cache slice.
 -- If this invariant does not hold, the middle of the slice is returned for
 -- making lookups to that ID
-checkCacheSliceInvariants :: LocalNodeState
+checkCacheSliceInvariants :: LocalNodeState s
                           -> NodeCache
                           -> [NodeID]   -- ^ list of middle IDs of slices not
                                         -- ^ fulfilling the invariant
@@ -419,12 +459,10 @@ checkCacheSliceInvariants ns
 -- | Periodically send @StabiliseRequest' s to the closest neighbour nodes, until
 -- one responds, and get their neighbours for maintaining the own neighbour lists.
 -- If necessary, request new neighbours.
-stabiliseThread :: LocalNodeStateSTM -> IO ()
+stabiliseThread :: Service s (RealNodeSTM s) => LocalNodeStateSTM s -> IO ()
 stabiliseThread nsSTM = forever $ do
-    ns <- readTVarIO nsSTM
+    oldNs <- readTVarIO nsSTM
 
-    putStrLn "stabilise run: begin"
-    print ns
 
     -- iterate through the same snapshot, collect potential new neighbours
     -- and nodes to be deleted, and modify these changes only at the end of
@@ -433,8 +471,8 @@ stabiliseThread nsSTM = forever $ do
 
     -- don't contact all neighbours unless the previous one failed/ Left ed
 
-    predStabilise <- stabiliseClosestResponder ns predecessors 1 []
-    succStabilise <- stabiliseClosestResponder ns predecessors 1 []
+    predStabilise <- stabiliseClosestResponder oldNs predecessors 1 []
+    succStabilise <- stabiliseClosestResponder oldNs predecessors 1 []
 
     let
         (predDeletes, predNeighbours) = either (const ([], [])) id predStabilise
@@ -459,31 +497,60 @@ 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 $ lastDef (toRemoteNodeState ns') (predecessors ns')
-        atomically $ do
+        nextEntry <- runExceptT . requestQueryID ns' $ pred . getNid $ lastDef (toRemoteNodeState ns') (predecessors ns')
+        either
+            (const $ pure ())
+            (\entry -> atomically $ do
                 latestNs <- readTVar nsSTM
-            writeTVar nsSTM $ addPredecessors [nextEntry] latestNs
+                writeTVar nsSTM $ addPredecessors [entry] latestNs
+            )
+            nextEntry
                                                                        )
 
     forM_ [(length $ successors updatedNs)..(kNeighbours updatedNs)] (\_ -> do
         ns' <- readTVarIO nsSTM
-        nextEntry <- requestQueryID ns' $ succ . getNid $ lastDef (toRemoteNodeState ns') (successors ns')
-        atomically $ do
+        nextEntry <- runExceptT . requestQueryID ns' $ succ . getNid $ lastDef (toRemoteNodeState ns') (successors ns')
+        either
+            (const $ pure ())
+            (\entry -> atomically $ do
                 latestNs <- readTVar nsSTM
-            writeTVar nsSTM $ addSuccessors [nextEntry] latestNs
+                writeTVar nsSTM $ addSuccessors [entry] latestNs
+            )
+            nextEntry
                                                                      )
 
-    putStrLn "stabilise run: end"
-    -- TODO: make delay configurable
-    threadDelay (60 * 10^6)
+    newNs <- readTVarIO nsSTM
+
+    let
+        oldPredecessor = headDef (toRemoteNodeState oldNs) $ predecessors oldNs
+        newPredecessor = headMay $ predecessors newNs
+    -- manage need for service data migration:
+    maybe (pure ()) (\newPredecessor' ->
+        when (
+            isJust newPredecessor
+            && oldPredecessor /= newPredecessor'
+        -- case: predecessor has changed in some way => own responsibility has changed in some way
+        -- case 1: new predecessor is further away => broader responsibility, but new pred needs to push the data
+        -- If this is due to a node leaving without transfering its data, try getting it from a redundant copy
+        -- case 2: new predecessor is closer, it takes some of our data but somehow didn't join on us => push data to it
+            && isInOwnResponsibilitySlice newPredecessor' oldNs) $ do
+                ownService <- nodeService <$> (liftIO . readTVarIO $ parentRealNode newNs)
+                migrationResult <- migrateData ownService (getNid newNs) (getNid oldPredecessor) (getNid newPredecessor') (getDomain newPredecessor', fromIntegral $ getServicePort newPredecessor')
+                -- TODO: deal with migration failure, e.g retry
+                pure ()
+                    )
+                    newPredecessor
+
+    stabiliseDelay <- confStabiliseInterval . nodeConfig <$> readTVarIO (parentRealNode newNs)
+    threadDelay stabiliseDelay
   where
     -- | send a stabilise request to the n-th neighbour
-    -- (specified by the provided getter function) and on failure retr
+    -- (specified by the provided getter function) and on failure retry
     -- with the n+1-th neighbour.
     -- On success, return 2 lists: The failed nodes and the potential neighbours
     -- returned by the queried node.
-    stabiliseClosestResponder :: LocalNodeState     -- ^ own node
-                              -> (LocalNodeState -> [RemoteNodeState])  -- ^ getter function for either predecessors or successors
+    stabiliseClosestResponder :: LocalNodeState s    -- ^ own node
+                              -> (LocalNodeState s -> [RemoteNodeState])  -- ^ getter function for either predecessors or successors
                               -> Int    -- ^ index of neighbour to query
                               -> [RemoteNodeState]     -- ^ delete accumulator
                               -> IO (Either String ([RemoteNodeState], [RemoteNodeState])) -- ^ (nodes to be deleted, successfully pinged potential neighbours)
@@ -507,7 +574,7 @@ stabiliseThread nsSTM = forever $ do
 
     currentNeighbour ns neighbourGetter = atMay $ neighbourGetter ns
 
-    checkReachability :: LocalNodeState         -- ^ this node
+    checkReachability :: LocalNodeState s       -- ^ this node
                       -> RemoteNodeState        -- ^ node to Ping for reachability
                       -> IO (Maybe RemoteNodeState)     -- ^ if the Pinged node handles the requested node state then that one
     checkReachability ns toCheck = do
@@ -536,10 +603,10 @@ sendThread sock sendQ = forever $ do
     sendAllTo sock packet addr
 
 -- | Sets up and manages the main server threads of FediChord
-fediMainThreads :: Socket -> LocalNodeStateSTM -> IO ()
+fediMainThreads :: Service s (RealNodeSTM s) => Socket -> LocalNodeStateSTM s -> IO ()
 fediMainThreads sock nsSTM = do
     ns <- readTVarIO nsSTM
-    putStrLn $ "launching threads, ns: " <> show ns
+    putStrLn "launching threads"
     sendQ <- newTQueueIO
     recvQ <- newTQueueIO
     -- concurrently launch all handler threads, if one of them throws an exception
@@ -562,38 +629,36 @@ type RequestMap = Map.Map (SockAddr, Integer) RequestMapEntry
 data RequestMapEntry = RequestMapEntry (Set.Set FediChordMessage) (Maybe Integer)
                   POSIXTime
 
--- TODO: make purge age configurable
--- | periodically clean up old request parts
-responsePurgeAge :: POSIXTime
-responsePurgeAge = 60 -- seconds
 
-requestMapPurge :: MVar RequestMap -> IO ()
-requestMapPurge mapVar = forever $ do
+requestMapPurge :: POSIXTime -> MVar RequestMap -> IO ()
+requestMapPurge purgeAge mapVar = forever $ do
     rMapState <- takeMVar mapVar
     now <- getPOSIXTime
-    putMVar mapVar $ Map.filter (\entry@(RequestMapEntry _ _ ts)  ->
-        now - ts < responsePurgeAge
+    putMVar mapVar $ Map.filter (\(RequestMapEntry _ _ ts)  ->
+        now - ts < purgeAge
                                 ) rMapState
-    threadDelay $ round responsePurgeAge * 2 * 10^6
+    threadDelay $ (fromEnum purgeAge * 2) `div` 10^6
 
 
 -- | Wait for messages, deserialise them, manage parts and acknowledgement status,
 -- and pass them to their specific handling function.
-fediMessageHandler :: TQueue (BS.ByteString, SockAddr)  -- ^ send queue
+fediMessageHandler :: Service s (RealNodeSTM s)
+                   => TQueue (BS.ByteString, SockAddr)  -- ^ send queue
                    -> TQueue (BS.ByteString, SockAddr)  -- ^ receive queue
-                   -> LocalNodeStateSTM                    -- ^ acting NodeState
+                   -> LocalNodeStateSTM s                  -- ^ 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
+    nodeConf <- nodeConfig <$> readTVarIO (parentRealNode nsSnap)
     -- 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.
     requestMap <- newMVar (Map.empty :: RequestMap)
     -- run receive loop and requestMapPurge concurrently, so that an exception makes
     -- both of them fail
-    concurrently_ (requestMapPurge requestMap) $ forever $ do
+    concurrently_ (requestMapPurge (confResponsePurgeAge nodeConf) requestMap) $ forever $ do
         -- wait for incoming messages
         (rawMsg, sourceAddr) <- atomically $ readTQueue recvQ
         let aMsg = deserialiseMessage rawMsg
@@ -646,14 +711,33 @@ fediMessageHandler sendQ recvQ nsSTM = do
 
 -- ==== interface to service layer ====
 
-instance DHT RealNodeSTM where
+instance DHT (RealNodeSTM s) where
     lookupKey nodeSTM keystring = getKeyResponsibility nodeSTM $ genKeyID keystring
-    forceLookupKey nodeSTM keystring = updateLookupCache nodeSTM $ genKeyID keystring
+    forceLookupKey nodeSTM keystring = (putStrLn $ "forced responsibility lookup of #" <> keystring) >> (updateLookupCache nodeSTM $ genKeyID keystring)
+    -- potential better implementation: put all neighbours of all vservers and the vservers on a ringMap, look the key up and see whether it results in a LocalNodeState
+    isResponsibleFor nodeSTM key = do
+        node <- readTVarIO nodeSTM
+        foldM (\responsible vsSTM -> do
+            vs <- readTVarIO vsSTM
+            pure $ responsible || isInOwnResponsibilitySlice key vs
+              )
+              False
+              $ vservers node
+    isResponsibleForSTM nodeSTM key = do
+        node <- readTVar nodeSTM
+        foldM (\responsible vsSTM -> do
+            vs <- readTVar vsSTM
+            pure $ responsible || isInOwnResponsibilitySlice key vs
+              )
+              False
+              $ vservers node
+
+
 
 -- | Returns the hostname and port of the host responsible for a key.
 -- Information is provided from a cache, only on a cache miss a new DHT lookup
 -- is triggered.
-getKeyResponsibility :: RealNodeSTM -> NodeID -> IO (Maybe (String, PortNumber))
+getKeyResponsibility :: RealNodeSTM s -> NodeID -> IO (Maybe (String, PortNumber))
 getKeyResponsibility nodeSTM lookupKey = do
     node <- readTVarIO nodeSTM
     cache <- readTVarIO $ lookupCacheSTM node
@@ -669,8 +753,8 @@ getKeyResponsibility nodeSTM lookupKey = do
 -- | Triggers a new DHT lookup for a key, updates the lookup cache and returns the
 -- new entry.
 -- If no vserver is active in the DHT, 'Nothing' is returned.
-updateLookupCache :: RealNodeSTM -> NodeID -> IO (Maybe (String, PortNumber))
-updateLookupCache nodeSTM lookupKey = do
+updateLookupCache :: RealNodeSTM s -> NodeID -> IO (Maybe (String, PortNumber))
+updateLookupCache nodeSTM keyToLookup = do
     (node, lookupSource) <- atomically $ do
         node <- readTVar nodeSTM
         let firstVs = headMay (vservers node)
@@ -680,23 +764,30 @@ updateLookupCache nodeSTM lookupKey = do
         pure (node, lookupSource)
     maybe (do
         -- if no local node available, delete cache entry and return Nothing
-        atomically $ modifyTVar' (lookupCacheSTM node) $ Map.delete lookupKey
+        atomically $ modifyTVar' (lookupCacheSTM node) $ Map.delete keyToLookup
         pure Nothing
           )
           (\n -> do
         -- start a lookup from the node, update the cache with the lookup result and return it
-        newResponsible <- requestQueryID n lookupKey
-        let newEntry = (getDomain newResponsible, getServicePort newResponsible)
+        -- TODO: better retry management, because having no vserver joined yet should
+        -- be treated differently than other reasons for not getting a result.
+        newResponsible <- runExceptT $ requestQueryID n keyToLookup
+        either
+            (const $ pure Nothing)
+            (\result -> do
+                let newEntry = (getDomain result, getServicePort result)
                 now <- getPOSIXTime
                 -- atomic update against lost updates
                 atomically $ modifyTVar' (lookupCacheSTM node) $
-            Map.insert lookupKey (CacheEntry False newEntry now)
+                    Map.insert keyToLookup (CacheEntry False newEntry now)
                 pure $ Just newEntry
+            )
+            newResponsible
            ) lookupSource
 
 
 -- | Periodically clean the lookup cache from expired entries.
-lookupCacheCleanup :: RealNodeSTM -> IO ()
+lookupCacheCleanup :: RealNodeSTM s -> IO ()
 lookupCacheCleanup nodeSTM = do
     node <- readTVarIO nodeSTM
     forever $ do
@@ -706,4 +797,4 @@ lookupCacheCleanup nodeSTM = do
                 now - ts < confMaxLookupCacheAge (nodeConfig node)
                        )
                                                        )
-        threadDelay $ round (confMaxLookupCacheAge $ nodeConfig node) * (10^5)
+        threadDelay $ fromEnum (2 * confMaxLookupCacheAge (nodeConfig node)) `div` 10^6

src/Hash2Pub/FediChordTypes.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE DataKinds                  #-}
 {-# LANGUAGE DerivingStrategies         #-}
+{-# LANGUAGE FlexibleContexts           #-}
 {-# LANGUAGE FlexibleInstances          #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses      #-}
@@ -26,8 +27,7 @@ module Hash2Pub.FediChordTypes (
   , CacheEntry(..)
   , RingEntry(..)
   , RingMap(..)
-  , HasKeyID
-  , getKeyID
+  , HasKeyID(..)
   , rMapSize
   , rMapLookup
   , rMapLookupPred
@@ -58,11 +58,14 @@ module Hash2Pub.FediChordTypes (
   , bsAsIpAddr
   , FediChordConf(..)
   , DHT(..)
+  , Service(..)
+  , ServiceConf(..)
                            ) where
 
 import           Control.Exception
 import           Data.Foldable                 (foldr')
 import           Data.Function                 (on)
+import qualified Data.Hashable                 as Hashable
 import           Data.List                     (delete, nub, sortBy)
 import qualified Data.Map.Strict               as Map
 import           Data.Maybe                    (fromJust, fromMaybe, isJust,
@@ -144,8 +147,8 @@ a `localCompare` b
 -- | Data for managing the virtual server nodes of this real node.
 -- Also contains shared data and config values.
 -- TODO: more data structures for k-choices bookkeeping
-data RealNode = RealNode
-    { vservers       :: [LocalNodeStateSTM]
+data RealNode s = RealNode
+    { vservers       :: [LocalNodeStateSTM s]
     -- ^ references to all active versers
     , nodeConfig     :: FediChordConf
     -- ^ holds the initial configuration read at program start
@@ -153,9 +156,10 @@ data RealNode = RealNode
     -- ^ nodes to be used as bootstrapping points, new ones learned during operation
     , lookupCacheSTM :: TVar LookupCache
     -- ^ a global cache of looked up keys and their associated nodes
+    , nodeService    :: s (RealNodeSTM s)
     }
 
-type RealNodeSTM = TVar RealNode
+type RealNodeSTM s = TVar (RealNode s)
 
 -- | represents a node and all its important state
 data RemoteNodeState = RemoteNodeState
@@ -177,7 +181,7 @@ instance Ord RemoteNodeState where
     a `compare` b = nid a `compare` nid b
 
 -- | represents a node and encapsulates all data and parameters that are not present for remote nodes
-data LocalNodeState = LocalNodeState
+data LocalNodeState s = LocalNodeState
     { nodeState           :: RemoteNodeState
     -- ^ represents common data present both in remote and local node representations
     , nodeCacheSTM        :: TVar NodeCache
@@ -196,13 +200,13 @@ data LocalNodeState = LocalNodeState
     -- ^ number of parallel sent queries
     , jEntriesPerSlice    :: Int
     -- ^ number of desired entries per cache slice
-    , parentRealNode      :: RealNodeSTM
+    , parentRealNode      :: RealNodeSTM s
     -- ^ the parent node managing this vserver instance
     }
     deriving (Show, Eq)
 
 -- | for concurrent access, LocalNodeState is wrapped in a TVar
-type LocalNodeStateSTM = TVar LocalNodeState
+type LocalNodeStateSTM s = TVar (LocalNodeState s)
 
 -- | class for various NodeState representations, providing
 -- getters and setters for common values
@@ -239,14 +243,14 @@ instance NodeState RemoteNodeState where
     toRemoteNodeState = id
 
 -- | helper function for setting values on the 'RemoteNodeState' contained in the 'LocalNodeState'
-propagateNodeStateSet_ :: (RemoteNodeState -> RemoteNodeState) -> LocalNodeState -> LocalNodeState
+propagateNodeStateSet_ :: (RemoteNodeState -> RemoteNodeState) -> LocalNodeState s -> LocalNodeState s
 propagateNodeStateSet_ func ns = let
         newNs = func $ nodeState ns
     in
         ns {nodeState = newNs}
 
 
-instance NodeState LocalNodeState where
+instance NodeState (LocalNodeState s) where
     getNid = getNid . nodeState
     getDomain = getDomain . nodeState
     getIpAddr = getIpAddr . nodeState
@@ -268,34 +272,37 @@ instance Typeable a => Show (TVar a) where
 instance Typeable a => Show (TQueue a) where
     show x = show (typeOf x)
 
+instance Typeable a => Show (TChan a) where
+    show x = show (typeOf x)
+
 
 -- | convenience function that replaces the predecessors of a 'LocalNodeState' with the k closest nodes from the provided list
-setPredecessors :: [RemoteNodeState] -> LocalNodeState -> LocalNodeState
-setPredecessors preds ns = ns {predecessors = takeRMapPredecessors (getNid ns) (kNeighbours ns) . rMapFromList . filter ((/=) (getNid ns) . getNid) $ preds}
+setPredecessors :: [RemoteNodeState] -> LocalNodeState s -> LocalNodeState s
+setPredecessors preds ns = ns {predecessors = takeRMapPredecessors (getNid ns) (kNeighbours ns) . rMapFromList . fmap keyValuePair . filter ((/=) (getNid ns) . getNid) $ preds}
 
 -- | convenience function that replaces the successors of a 'LocalNodeState' with the k closest nodes from the provided list
-setSuccessors :: [RemoteNodeState] -> LocalNodeState -> LocalNodeState
-setSuccessors succs ns = ns {successors = takeRMapSuccessors (getNid ns) (kNeighbours ns) . rMapFromList . filter ((/=) (getNid ns) . getNid) $ succs}
+setSuccessors :: [RemoteNodeState] -> LocalNodeState s -> LocalNodeState s
+setSuccessors succs ns = ns {successors = takeRMapSuccessors (getNid ns) (kNeighbours ns) . rMapFromList . fmap keyValuePair . filter ((/=) (getNid ns) . getNid) $ succs}
 
 -- | sets the predecessors of a 'LocalNodeState' to the closest k nodes of the current predecessors and the provided list, combined
-addPredecessors :: [RemoteNodeState] -> LocalNodeState -> LocalNodeState
-addPredecessors preds ns = ns {predecessors = takeRMapPredecessors (getNid ns) (kNeighbours ns) . addRMapEntries (filter ((/=) (getNid ns) . getNid) preds) . rMapFromList  $ predecessors ns}
+addPredecessors :: [RemoteNodeState] -> LocalNodeState s -> LocalNodeState s
+addPredecessors preds ns = ns {predecessors = takeRMapPredecessors (getNid ns) (kNeighbours ns) . addRMapEntries (keyValuePair <$> filter ((/=) (getNid ns) . getNid) preds) . rMapFromList . fmap keyValuePair  $ predecessors ns}
 
 -- | sets the successors of a 'LocalNodeState' to the closest k nodes of the current successors and the provided list, combined
-addSuccessors :: [RemoteNodeState] -> LocalNodeState -> LocalNodeState
-addSuccessors succs ns = ns {successors = takeRMapSuccessors (getNid ns) (kNeighbours ns) . addRMapEntries (filter ((/=) (getNid ns) . getNid) succs) . rMapFromList  $ successors ns}
+addSuccessors :: [RemoteNodeState] -> LocalNodeState s -> LocalNodeState s
+addSuccessors succs ns = ns {successors = takeRMapSuccessors (getNid ns) (kNeighbours ns) . addRMapEntries (keyValuePair <$> filter ((/=) (getNid ns) . getNid) succs) . rMapFromList . fmap keyValuePair $ successors ns}
 
-instance HasKeyID RemoteNodeState NodeID where
+instance HasKeyID NodeID RemoteNodeState where
     getKeyID = getNid
 
-instance HasKeyID a k => HasKeyID (CacheEntry a) k where
+instance HasKeyID k a => HasKeyID k (CacheEntry a) where
     getKeyID (CacheEntry _ obj _) = getKeyID obj
 
 instance HasKeyID NodeID NodeID where
     getKeyID = id
 
 type NodeCacheEntry = CacheEntry RemoteNodeState
-type NodeCache = RingMap NodeCacheEntry NodeID
+type NodeCache = RingMap NodeID NodeCacheEntry
 
 type LookupCacheEntry = CacheEntry (String, PortNumber)
 type LookupCache = Map.Map NodeID LookupCacheEntry
@@ -319,12 +326,15 @@ cacheLookup = rMapLookup
 cacheLookupSucc :: NodeID           -- ^lookup key
                 -> NodeCache        -- ^ring cache
                 -> Maybe NodeCacheEntry
-cacheLookupSucc = rMapLookupSucc
+cacheLookupSucc key cache = snd <$> rMapLookupSucc key cache
 
 cacheLookupPred :: NodeID           -- ^lookup key
                 -> NodeCache        -- ^ring cache
                 -> Maybe NodeCacheEntry
-cacheLookupPred = rMapLookupPred
+cacheLookupPred key cache = snd <$> rMapLookupPred key cache
+
+-- clean up cache entries: once now - entry > maxAge
+-- transfer difference now - entry to other node
 
 -- | return the @NodeState@ data from a cache entry without checking its validation status
 cacheGetNodeStateUnvalidated :: CacheEntry RemoteNodeState -> RemoteNodeState
@@ -401,18 +411,67 @@ data FediChordConf = FediChordConf
     -- ^ listening port for the FediChord DHT
     , confBootstrapNodes            :: [(String, PortNumber)]
     -- ^ list of potential bootstrapping nodes
+    , confStabiliseInterval         :: Int
+    -- ^ pause between stabilise runs, in milliseconds
     , confBootstrapSamplingInterval :: Int
-    -- ^ pause between sampling the own ID through bootstrap nodes, in seconds
+    -- ^ pause between sampling the own ID through bootstrap nodes, in milliseconds
     , confMaxLookupCacheAge         :: POSIXTime
-    -- ^ maximum age of lookup cache entries in seconds
+    -- ^ maximum age of key lookup cache entries in seconds
+    , confJoinAttemptsInterval      :: Int
+    -- ^ interval between join attempts on newly learned nodes, in milliseconds
+    , confMaxNodeCacheAge           :: POSIXTime
+    -- ^ maximum age of entries in the node cache, in milliseconds
+    , confResponsePurgeAge          :: POSIXTime
+    -- ^ maximum age of message parts in response part cache, in seconds
+    , confRequestTimeout            :: Int
+    -- ^ how long to wait until response has arrived, in milliseconds
+    , confRequestRetries            :: Int
+    -- ^ how often re-sending a timed-out request can be retried
     }
     deriving (Show, Eq)
 
+-- ====== Service Types ============
+
+class Service s d where
+    -- | run the service
+    runService :: ServiceConf -> d -> IO (s d)
+    getListeningPortFromService :: (Integral i) => s d -> i
+    -- | trigger a service data migration of data between the two given keys
+    migrateData :: s d
+                -> NodeID       -- ^ source/ sender node ID
+                -> NodeID       -- ^ start key
+                -> NodeID       -- ^ end key
+                -> (String, Int)    -- ^ hostname and port of target service
+                -> IO (Either String ())    -- ^ success or failure
+    -- | Wait for an incoming migration from a given node to succeed, may block forever
+    waitForMigrationFrom :: s d -> NodeID -> IO ()
+
+instance Hashable.Hashable NodeID where
+    hashWithSalt salt = Hashable.hashWithSalt salt . getNodeID
+    hash = Hashable.hash . getNodeID
+
+data ServiceConf = ServiceConf
+    { confSubscriptionExpiryTime :: POSIXTime
+    -- ^ subscription lease expiration in seconds
+    , confServicePort            :: Int
+    -- ^ listening port for service
+    , confServiceHost            :: String
+    -- ^ hostname of service
+    , confLogfilePath            :: String
+    -- ^ where to store the (measurement) log file
+    , confStatsEvalDelay         :: Int
+    -- ^ delay between statistic rate measurement samplings, in microseconds
+    , confSpeedupFactor          :: Int
+    -- While the speedup factor needs to be already included in all
+    }
+
 class DHT d where
     -- | lookup the responsible host handling a given key string,
-    -- possibly from a lookup cache
+    -- possiblggy from a lookup cache
     lookupKey :: d -> String -> IO (Maybe (String, PortNumber))
     -- | lookup the responsible host handling a given key string,
     -- but force the DHT to do a fresh lookup instead of returning a cached result.
     -- Also invalidates old cache entries.
     forceLookupKey :: d -> String -> IO (Maybe (String, PortNumber))
+    isResponsibleFor :: d -> NodeID -> IO Bool
+    isResponsibleForSTM :: d -> NodeID -> STM Bool

src/Hash2Pub/PostService.hs

@@ -1,117 +1,884 @@
 {-# LANGUAGE DataKinds             #-}
 {-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE InstanceSigs          #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings     #-}
 {-# LANGUAGE RankNTypes            #-}
 {-# LANGUAGE TypeOperators         #-}
-{-# LANGUAGE InstanceSigs          #-}
 
 module Hash2Pub.PostService where
 
 import           Control.Concurrent
-import qualified Data.ByteString.Lazy.UTF8 as BSU
-import           Data.Maybe                (fromMaybe)
+import           Control.Concurrent.Async
+import           Control.Concurrent.STM
+import           Control.Exception         (Exception (..), try)
+import           Control.Monad             (foldM, forM, forM_, forever, unless,
+                                            void, when)
+import           Control.Monad.IO.Class    (liftIO)
+import           Data.Bifunctor
+import qualified Data.ByteString.Lazy.UTF8 as BSUL
+import qualified Data.ByteString.UTF8      as BSU
+import qualified Data.DList                as D
+import           Data.Either               (lefts, rights)
+import qualified Data.HashMap.Strict       as HMap
+import qualified Data.HashSet              as HSet
+import           Data.Maybe                (fromJust, isJust)
 import           Data.String               (fromString)
-import qualified Data.Text                 as Txt
+import           Data.Text.Lazy            (Text)
+import qualified Data.Text.Lazy            as Txt
+import qualified Data.Text.Lazy.IO         as TxtI
+import           Data.Text.Normalize       (NormalizationMode (NFC), normalize)
+import           Data.Time.Clock.POSIX
+import           Data.Typeable             (Typeable)
+import qualified Network.HTTP.Client       as HTTP
+import qualified Network.HTTP.Types        as HTTPT
+import           System.IO
+import           System.Random
+import           Text.Read                 (readEither)
 
+import           Formatting                (fixed, format, int, (%))
 import qualified Network.Wai.Handler.Warp  as Warp
 import           Servant
+import           Servant.Client
 
-import           Hash2Pub.FediChord
-import           Hash2Pub.ServiceTypes
+import           Hash2Pub.FediChordTypes
+import           Hash2Pub.PostService.API
+import           Hash2Pub.RingMap
+import           Hash2Pub.Utils
 
+import           Debug.Trace
 
 data PostService d = PostService
-    { psPort        :: Warp.Port
-    , psHost        :: String
+    { serviceConf          :: ServiceConf
     -- queues, other data structures
     , baseDHT              ::   (DHT d) => d
-    , serviceThread :: ThreadId
+    , serviceThread        :: TVar ThreadId
+    , subscribers          :: TVar RelayTags
+    -- ^ for each tag store the subscribers + their queue
+    , ownSubscriptions     :: TVar (HMap.HashMap NodeID POSIXTime)
+    -- ^ tags subscribed by the own node have an assigned lease time
+    , relayInQueue         :: TQueue (Hashtag, PostID, PostContent)
+    -- ^ Queue for processing incoming posts of own instance asynchronously
+    , postFetchQueue       :: TQueue PostID
+    -- ^ queue of posts to be fetched
+    , migrationsInProgress :: TVar (HMap.HashMap NodeID (MVar ()))
+    , httpMan              :: HTTP.Manager
+    , statsQueue           :: TQueue StatsEvent
+    , loadStats            :: TVar RelayStats
+    -- ^ current load stats, replaced periodically
+    , logFileHandle        :: Handle
     }
+    deriving (Typeable)
+
+type Hashtag = Text
+type PostID = Text
+type PostContent = Text
+-- | For each handled tag, store its subscribers and provide a
+-- broadcast 'TChan' for enqueuing posts
+type RelayTags = RingMap NodeID (TagSubscribersSTM, TChan PostID, Hashtag)
+type TagSubscribersSTM = TVar TagSubscribers
+-- | each subscriber is identified by its contact data "hostname" "port"
+-- and holds a TChan duplicated from the broadcast TChan of the tag
+-- + an expiration timestamp
+type TagSubscribers = (HMap.HashMap (String, Int) (TChan PostID, POSIXTime))
+
 
 instance DHT d => Service PostService d where
-    runService dht host port = do
+    -- | initialise 'PostService' data structures and run server
+    runService conf dht = do
+        -- create necessary TVars
+        threadVar <- newTVarIO =<< myThreadId -- own thread ID as placeholder
+        subscriberVar <- newTVarIO emptyRMap
+        ownSubsVar <- newTVarIO HMap.empty
+        --ownPostVar <- newTVarIO HSet.empty
+        relayInQueue' <- newTQueueIO
+        postFetchQueue' <- newTQueueIO
+        migrationsInProgress' <- newTVarIO HMap.empty
+        httpMan' <- HTTP.newManager HTTP.defaultManagerSettings
+        statsQueue' <- newTQueueIO
+        loadStats' <- newTVarIO emptyStats
+        loggingFile <- openFile (confLogfilePath conf) WriteMode
+        hSetBuffering loggingFile LineBuffering
         let
-            port' = fromIntegral port
-            warpSettings = Warp.setPort port' . Warp.setHost (fromString host) $ Warp.defaultSettings
-        servThread <- forkIO $ Warp.runSettings warpSettings postServiceApplication
-        pure $ PostService {
-            psPort = port'
-          , psHost = host
+            thisService = PostService
+              { serviceConf = conf
               , baseDHT = dht
-          , serviceThread = servThread
+              , serviceThread = threadVar
+              , subscribers = subscriberVar
+              , ownSubscriptions = ownSubsVar
+              --, ownPosts = ownPostVar
+              , relayInQueue = relayInQueue'
+              , postFetchQueue = postFetchQueue'
+              , migrationsInProgress = migrationsInProgress'
+              , httpMan = httpMan'
+              , statsQueue = statsQueue'
+              , loadStats = loadStats'
+              , logFileHandle = loggingFile
               }
-    getServicePort s = fromIntegral $ psPort s
+            port' = fromIntegral (confServicePort conf)
+            warpSettings = Warp.setPort port' . Warp.setHost (fromString . confServiceHost $ conf) $ Warp.defaultSettings
+        -- log a start message, this also truncates existing files
+        TxtI.hPutStrLn loggingFile $ Txt.unlines
+            [ "# Starting mock relay implementation"
+            , "#time stamp         ; relay receive rate   ;relay delivery rate   ;instance publish rate ;instance fetch rate   ;total subscriptions"
+            ]
+        -- Run 'concurrently_' from another thread to be able to return the
+        -- 'PostService'.
+        -- Terminating that parent thread will make all child threads terminate as well.
+        servThreadID <- forkIO $
+            concurrently_
+                -- web server
+                (Warp.runSettings warpSettings $ postServiceApplication thisService)
+                $ concurrently
+                    -- background processing workers
+                    (launchWorkerThreads thisService)
+                    -- statistics/ measurements
+                    (launchStatsThreads thisService)
+        -- update thread ID after fork
+        atomically $ writeTVar threadVar servThreadID
+        pure thisService
+
+    getListeningPortFromService = fromIntegral . confServicePort . serviceConf
+
+    migrateData = clientDeliverSubscriptions
+
+    waitForMigrationFrom serv fromID = do
+        migrationSynchroniser <- atomically $ do
+            syncPoint <- HMap.lookup fromID <$> readTVar (migrationsInProgress serv)
+            maybe
+              -- decision: this function blocks until it gets an incoming migration from given ID
+              retry
+              pure
+              syncPoint
+        -- block until migration finished
+        takeMVar migrationSynchroniser
 
 
 -- | return a WAI application
-postServiceApplication :: Application
-postServiceApplication = serve exposedPostServiceAPI postServer
-
-servicePort = 8081
-
--- | needed for guiding type inference
-exposedPostServiceAPI :: Proxy PostServiceAPI
-exposedPostServiceAPI = Proxy
+postServiceApplication :: DHT d => PostService d -> Application
+postServiceApplication serv = serve exposedPostServiceAPI $ postServer serv
 
 
+-- ========= constants ===========
+
+placeholderPost :: Text
+placeholderPost = Txt.take 5120 . Txt.repeat $ 'O' -- size 5KiB
 
 -- ========= HTTP API and handlers =============
 
-type PostServiceAPI = "relay" :> "inbox" :> ReqBody '[PlainText] Txt.Text :> PostCreated '[PlainText] Txt.Text
-                 -- ^ delivery endpoint of newly published posts of the relay's instance
-                 :<|> "relay" :> "subscribers" :> ReqBody '[PlainText] Txt.Text :> Post '[PlainText] Txt.Text
-                 -- ^ endpoint for delivering the subscriptions and outstanding queue
-                 :<|> "post" :> Capture "postid" Txt.Text :> Get '[PlainText] Txt.Text
-                 -- ^ fetch endpoint for posts, full post ID is http://$domain/post/$postid
-                 :<|> "posts" :> ReqBody '[PlainText] Txt.Text :> Post '[PlainText] Txt.Text
-                 -- ^ endpoint for fetching multiple posts at once
-                 :<|> "tags" :> Capture "hashtag" Txt.Text :> ReqBody '[PlainText] Txt.Text :> PostCreated '[PlainText] Txt.Text
-                 -- ^ delivery endpoint for posts of $tag at subscribing instance
-                 :<|> "tags" :> Capture "hashtag" Txt.Text :> "subscribe" :> Header "Origin" Txt.Text :> Get '[PlainText] Integer
-                 -- ^ endpoint for subscribing the instance specified in
-                 -- the Origin header to $hashtag.
-                 -- Returns subscription lease time in seconds.
-                 :<|> "tags" :> Capture "hashtag" Txt.Text :> "unsubscribe" :> Header "Origin" Txt.Text :> Get '[PlainText] Txt.Text
-                 -- ^ endpoint for unsubscribing the instance specified in
-                 -- the Origin header to $hashtag
+postServer :: DHT d => PostService d -> Server PostServiceAPI
+postServer service = relayInbox service
+        :<|> subscriptionDelivery service
+        :<|> postFetch service
+        :<|> postMultiFetch service
+        :<|> postInbox service
+        :<|> tagDelivery service
+        :<|> tagSubscribe service
+        :<|> tagUnsubscribe service
 
 
-postServer :: Server PostServiceAPI
-postServer = relayInbox
-        :<|> subscriptionDelivery
-        :<|> postFetch
-        :<|> postMultiFetch
-        :<|> tagDelivery
-        :<|> tagSubscribe
-        :<|> tagUnsubscribe
+-- | delivery endpoint: receive posts of a handled tag and enqueue them for relaying
+relayInbox :: DHT d => PostService d -> Hashtag -> Text -> Handler NoContent
+relayInbox serv tag posts = do
+    let
+    -- skip checking whether the post actually contains the tag, just drop full post
+        postIDs = head . Txt.splitOn "," <$> Txt.lines posts
+    -- if tag is not in own responsibility, return a 410 Gone
+    responsible <- liftIO $ isResponsibleFor (baseDHT serv) (hashtagToId tag)
+    if responsible
+       then pure ()
+       else
+        throwError $ err410 { errBody = "Relay is not responsible for this tag"}
+    broadcastChan <- liftIO $ atomically $ getTagBroadcastChannel serv tag
+    maybe
+    -- if noone subscribed to the tag, nothing needs to be done
+        (pure ())
+    -- otherwise enqueue posts into broadcast queue of the tag
+        (\queue -> do
+            liftIO $ forM_ postIDs (atomically . writeTChan queue)
+            -- report the received post for statistic purposes
+            liftIO . atomically . writeTQueue (statsQueue serv) $ StatsEvent RelayReceiveEvent (length postIDs) (hashtagToId tag)
+        )
+        broadcastChan
+    pure NoContent
+
+-- exception to be thrown when a tag is not in the responsibility of a relay
+newtype UnhandledTagException = UnhandledTagException String
+    deriving (Show, Typeable)
+
+instance Exception UnhandledTagException
+
+-- | delivery endpoint: receives a list of subscribers of tags and their outstanding queues for migration
+subscriptionDelivery :: DHT d => PostService d -> Integer -> Text -> Handler Text
+subscriptionDelivery serv senderID subList = do
+    let
+        tagSubs = Txt.lines subList
+    -- signal that the migration is in progress
+    syncMVar <- liftIO newEmptyMVar
+    liftIO . atomically $ modifyTVar' (migrationsInProgress serv) $
+        HMap.insert (fromInteger senderID) syncMVar
+    -- In favor of having the convenience of rolling back the transaction once a
+    -- not-handled tag occurs, this results in a single large transaction.
+    -- Hopefully the performance isn't too bad.
+    res <- liftIO . atomically $ (foldM (\_ tag' -> do
+        responsible <- isResponsibleForSTM (baseDHT serv) (hashtagToId tag')
+        if responsible
+           then processTag (subscribers serv) tag'
+           else throwSTM $ UnhandledTagException (Txt.unpack tag' <> " not handled by this relay")
+        pure $ Right ()
+           ) (pure ()) tagSubs
+           `catchSTM` (\e -> pure . Left $ show (e :: UnhandledTagException))
+           -- TODO: potentially log this
+                          :: STM (Either String ()))
+    -- TODO: should this always signal migration finished to avoid deadlocksP
+    liftIO $ putMVar syncMVar ()    -- wakes up waiting thread
+    -- allow response to be completed independently from waiting thread
+    _ <- liftIO . forkIO $ do
+        putMVar syncMVar ()    -- blocks until waiting thread has resumed
+        -- delete this migration from ongoing ones
+        liftIO . atomically $ modifyTVar' (migrationsInProgress serv) $
+            HMap.delete (fromInteger senderID)
+    case res of
+      Left err -> throwError err410 {errBody = BSUL.fromString err}
+      Right _  -> pure ""
+    -- TODO: check and only accept tags in own (future?) responsibility
+  where
+      processTag :: TVar RelayTags -> Text -> STM ()
+      processTag subscriberSTM tagData = do
+          let
+            tag:subText:lease:posts:_ = Txt.splitOn "," tagData
+            -- ignore checking of lease time
+            leaseTime = fromIntegral (read . Txt.unpack $ lease :: Integer)
+            sub = read . Txt.unpack $ subText :: (String, Int)
+            postList = Txt.words posts
+          enqueueSubscription subscriberSTM (normaliseTag tag) sub postList leaseTime
 
 
-relayInbox :: Txt.Text -> Handler Txt.Text
-relayInbox post = pure $ "Here be InboxDragons with " <> post
+-- | endpoint for fetching a post by its ID
+postFetch :: PostService d -> Text -> Handler Text
+postFetch serv _ = do
+    -- decision: for saving memory do not store published posts, just
+    -- pretend there is a post for each requested ID
+    liftIO . atomically . writeTQueue (statsQueue serv) $ StatsEvent IncomingPostFetchEvent 1 0  -- tag fetched for is irrelevant
+    pure placeholderPost
 
-subscriptionDelivery :: Txt.Text -> Handler Txt.Text
-subscriptionDelivery subList = pure $ "Here be Subscription List dragons: " <> subList
 
-postFetch :: Txt.Text -> Handler Txt.Text
-postFetch postID = pure $ "Here be a post with dragon ID " <> postID
+-- | endpoint for fetching multiple posts of this instance by their IDs
+postMultiFetch :: PostService d -> Text -> Handler Text
+postMultiFetch serv postIDs = do
+    let
+        idList = Txt.lines postIDs
+        -- decision: for saving memory do not store published posts, just
+        -- pretend there is a post for each requested ID
+        response = foldl (\response' _ ->
+           placeholderPost <> "\n" <> response'
+          ) "" idList
+    liftIO . atomically . writeTQueue (statsQueue serv) $ StatsEvent IncomingPostFetchEvent (length idList) 0  -- tag fetched for is irrelevant
+    pure response
 
-postMultiFetch :: Txt.Text -> Handler Txt.Text
-postMultiFetch postIDs = pure $ "Here be multiple post dragons: "
-                      <> (Txt.unwords . Txt.lines $ postIDs)
 
-tagDelivery :: Txt.Text -> Txt.Text -> Handler Txt.Text
-tagDelivery hashtag posts = pure $ "Here be #" <> hashtag <> " dragons with " <> posts
+-- | delivery endpoint: inbox for initially publishing a post at an instance
+postInbox :: PostService d -> Text -> Handler NoContent
+postInbox serv post = do
+    -- extract contained hashtags
+    let
+        containedTags = fmap (normaliseTag . Txt.tail) . filter ((==) '#' . Txt.head) . Txt.words $ post
+    -- generate post ID
+    postId <- liftIO $ Txt.pack . show <$> (randomRIO (0, 2^(128::Integer)-1) :: IO Integer)
+    -- decision: for saving memory do not store published post IDs, just deliver a post for any requested ID
+    -- enqueue a relay job for each tag
+    liftIO $ forM_ (containedTags :: [Text]) (\tag ->
+        atomically $ writeTQueue (relayInQueue serv) (tag, postId,  post)
+                                 )
+    pure NoContent
 
-tagSubscribe :: Txt.Text -> Maybe Txt.Text -> Handler Integer
-tagSubscribe hashtag origin = pure 42
 
-tagUnsubscribe :: Txt.Text -> Maybe Txt.Text -> Handler Txt.Text
-tagUnsubscribe hashtag origin = pure $ "Here be a dragon unsubscription from " <> fromMaybe "Nothing" origin <> " to " <> hashtag
+-- | delivery endpoint: receive postIDs of a certain subscribed hashtag
+tagDelivery :: PostService d -> Text -> Text -> Handler Text
+tagDelivery serv hashtag posts = do
+    let postIDs = Txt.lines posts
+    subscriptions <- liftIO . readTVarIO . ownSubscriptions $ serv
+    if isJust (HMap.lookup (hashtagToId hashtag) subscriptions)
+       then -- TODO: increase a counter/ statistics for received posts of this tag
+            liftIO $ forM_ postIDs $ atomically . writeTQueue (postFetchQueue serv)
+        else -- silently drop posts from unsubscribed tags
+            pure ()
+    pure $ "Received a postID for tag " <> hashtag
 
 
+-- | receive subscription requests to a handled hashtag
+tagSubscribe :: DHT d => PostService d -> Text -> Maybe Text -> Handler Integer
+tagSubscribe serv hashtag origin = do
+    responsible <- liftIO $ isResponsibleFor (baseDHT serv) (hashtagToId hashtag)
+    if not responsible
+       -- GONE if not responsible
+       then throwError err410 { errBody = "not responsible for this tag" }
+       else pure ()
+    originURL <- maybe
+        (throwError $ err400 { errBody = "Missing Origin header" })
+        pure
+        origin
+    req <- HTTP.parseUrlThrow (Txt.unpack originURL)
+    now <- liftIO getPOSIXTime
+    let leaseTime = now + confSubscriptionExpiryTime (serviceConf serv)
+    -- setup subscription entry
+    _ <- liftIO . atomically $ setupSubscriberChannel (subscribers serv) hashtag (BSU.toString $ HTTP.host req, HTTP.port req) leaseTime
+    --liftIO . putStrLn $ "just got a subscription to " <> Txt.unpack hashtag
+    pure $ round leaseTime
+
+
+-- | receive and handle unsubscription requests regarding a handled tag
+tagUnsubscribe :: DHT d => PostService d -> Text -> Maybe Text -> Handler Text
+tagUnsubscribe serv hashtag origin = do
+    responsible <- liftIO $ isResponsibleFor (baseDHT serv) (hashtagToId hashtag)
+    if not responsible
+       -- GONE if not responsible
+       then throwError err410 { errBody = "not responsible for this tag" }
+       else pure ()
+    originURL <- maybe
+        (throwError $ err400 { errBody = "Missing Origin header" })
+        pure
+        origin
+    req <- HTTP.parseUrlThrow (Txt.unpack originURL)
+    liftIO . atomically $ deleteSubscription (subscribers serv) hashtag (BSU.toString $ HTTP.host req, HTTP.port req)
+    pure "bye bye"
+
+-- client/ request functions
+
+clientAPI :: Proxy PostServiceAPI
+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 d
+                           -> NodeID -- ^ sender node ID
+                           -> NodeID -- ^ fromTag
+                           -> NodeID -- ^ toTag
+                           -> (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 interval
+    intervalTags <- takeRMapSuccessorsFromTo fromKey toKey <$> 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
+    resp <- runClientM (subscriptionDeliveryClient (getNodeID fromNode) subscriberData) (mkClientEnv (httpMan serv) (BaseUrl Http toHost (fromIntegral toPort) ""))
+    -- on failure return a Left, otherwise delete subscription entry
+    case resp of
+      Left err -> pure . Left . show $ err
+      Right _ -> do
+          atomically $
+              modifyTVar' (subscribers serv) $ \tagMap ->
+                  foldr deleteRMapEntry tagMap ((\(_, _, t) -> hashtagToId t) <$> intervalTags)
+          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
+
+
+-- | Subscribe the client to the given hashtag. On success it returns the given lease time,
+-- but also records the subscription in its own data structure.
+clientSubscribeTo :: DHT d => PostService d -> Hashtag -> IO (Either String Integer)
+clientSubscribeTo serv tag = do
+    lookupRes <- lookupKey (baseDHT serv) (Txt.unpack tag)
+    doSubscribe lookupRes True
+  where
+      doSubscribe lookupResponse allowRetry = maybe
+          (pure . Left $ "No node found")
+          (\(foundHost, foundPort) -> do
+              let origin = "http://" <> Txt.pack (confServiceHost $ serviceConf serv) <> ":" <> Txt.pack (show (getListeningPortFromService serv :: Integer))
+              resp <- runClientM (tagSubscribeClient tag (Just origin)) (mkClientEnv (httpMan serv) (BaseUrl Http foundHost (fromIntegral foundPort) ""))
+              case resp of
+                Left (FailureResponse _ fresp)
+                  |(HTTPT.statusCode . responseStatusCode $ fresp) == 410 && allowRetry -> do  -- responsibility gone, force new lookup
+                      newRes <- forceLookupKey (baseDHT serv) (Txt.unpack tag)
+                      --putStrLn $ "failed subscribing to " <> Txt.unpack tag <> " on " <> foundHost
+                      doSubscribe newRes False
+                Left err    -> pure . Left . show $ err
+                Right lease -> do
+                    atomically . modifyTVar' (ownSubscriptions serv) $ HMap.insert (hashtagToId tag) (fromInteger lease)
+                    --putStrLn $ "just subscribed to " <> Txt.unpack tag <> " on " <> foundHost
+                    pure . Right $ lease
+          )
+          lookupResponse
+
+
+-- | Unsubscribe the client from the given hashtag.
+clientUnsubscribeFrom :: DHT d => PostService d -> Hashtag -> IO (Either String ())
+clientUnsubscribeFrom serv tag = do
+    lookupRes <- lookupKey (baseDHT serv) (Txt.unpack tag)
+    doUnsubscribe lookupRes True
+  where
+      doUnsubscribe lookupResponse allowRetry = maybe
+          (pure . Left $ "No node found")
+          (\(foundHost, foundPort) -> do
+              let origin = "http://" <> Txt.pack (confServiceHost $ serviceConf serv) <> ":" <> Txt.pack (show (getListeningPortFromService serv :: Integer))
+              resp <- runClientM (tagUnsubscribeClient tag (Just origin)) (mkClientEnv (httpMan serv) (BaseUrl Http foundHost (fromIntegral foundPort) ""))
+              case resp of
+                Left (FailureResponse _ fresp)
+                  |(HTTPT.statusCode . responseStatusCode $ fresp) == 410 && allowRetry -> do  -- responsibility gone, force new lookup
+                      newRes <- forceLookupKey (baseDHT serv) (Txt.unpack tag)
+                      doUnsubscribe newRes False
+                Left err    -> pure . Left . show $ err
+                Right _ -> do
+                    atomically . modifyTVar' (ownSubscriptions serv) $ HMap.delete (hashtagToId tag)
+                    pure . Right $ ()
+          )
+          lookupResponse
+
+
+-- | publish a new post to the inbox of a specified relay instance. This
+-- instance will then be the originating instance of the post and will forward
+-- the post to the responsible relays.
+-- As the initial publishing isn't done by a specific relay (but *to* a specific relay
+-- instead), the function does *not* take a PostService as argument.
+clientPublishPost :: HTTP.Manager   -- ^ for better performance, a shared HTTP manager has to be provided
+                  -> String         -- ^ hostname
+                  -> Int            -- ^ port
+                  -> PostContent    -- ^ post content
+                  -> IO (Either String ())  -- ^ error or success
+clientPublishPost httpman hostname port postC = do
+    resp <- runClientM (postInboxClient postC) (mkClientEnv httpman (BaseUrl Http hostname port ""))
+    pure . bimap show (const ()) $ resp
+
+-- currently this is unused code
+getClients :: String -> Int -> HTTP.Manager -> Client IO PostServiceAPI
+getClients hostname' port' httpMan = hoistClient clientAPI
+    (fmap (either (error . show) id)
+    . flip runClientM clientEnv
+    )
+    (client clientAPI)
+  where
+      clientEnv = mkClientEnv httpMan (BaseUrl Http hostname' port' "")
+
+-- ======= data structure manipulations =========
+
+-- | Write all pending posts of a subscriber-tag-combination to its queue.
+-- Sets up all necessary data structures if they are still missing.
+enqueueSubscription :: TVar RelayTags    -- tag-subscriber map
+                     -> Hashtag         -- hashtag of pending posts
+                     -> (String, Int)   -- subscriber's connection information
+                     -> [PostID]        -- pending posts
+                     -> POSIXTime       -- lease expiry time
+                     -> STM ()
+enqueueSubscription tagMapSTM tag subscriber posts leaseTime = do
+    -- get the tag output queue and, if necessary, create it
+    subChan <- setupSubscriberChannel tagMapSTM tag subscriber leaseTime
+    forM_ posts (writeTChan subChan)
+
+
+-- | STM operation to return the outgoing post queue of a tag to a specified subscriber.
+-- If the queue doesn't exist yet, all necessary data structures are set up accordingly.
+setupSubscriberChannel :: TVar RelayTags -> Hashtag -> (String, Int) -> POSIXTime -> STM (TChan PostID)
+setupSubscriberChannel tagMapSTM tag subscriber leaseTime = do
+    tagMap <- readTVar tagMapSTM
+    case lookupTagSubscriptions tag tagMap of
+      Nothing -> do
+        -- if no collision/ tag doesn't exist yet, just initialize a
+        -- new subscriber map
+        broadcastChan <- newBroadcastTChan
+        tagOutChan <- dupTChan broadcastChan
+        newSubMapSTM <- newTVar $ HMap.singleton subscriber (tagOutChan, leaseTime)
+        writeTVar tagMapSTM $ addRMapEntry (hashtagToId tag) (newSubMapSTM, broadcastChan, tag) tagMap
+        pure tagOutChan
+      Just (foundSubMapSTM, broadcastChan, _) -> do
+        -- otherwise use the existing subscriber map
+        foundSubMap <- readTVar foundSubMapSTM
+        case HMap.lookup subscriber foundSubMap of
+          Nothing -> do
+            -- for new subscribers, create new output channel
+            tagOutChan <- dupTChan broadcastChan
+            writeTVar foundSubMapSTM $ HMap.insert subscriber (tagOutChan, leaseTime) foundSubMap
+            pure tagOutChan
+          -- existing subscriber's channels are just returned
+          Just (tagOutChan, _) -> pure tagOutChan
+
+
+-- | deletes a subscription from the passed subscriber map
+deleteSubscription :: TVar RelayTags -> Hashtag -> (String, Int) -> STM ()
+deleteSubscription tagMapSTM tag subscriber = do
+    tagMap <- readTVar tagMapSTM
+    case lookupTagSubscriptions tag tagMap of
+      -- no subscribers to that tag, just return
+      Nothing -> pure ()
+      Just (foundSubMapSTM, _, _) -> do
+          foundSubMap <- readTVar foundSubMapSTM
+          let newSubMap = HMap.delete subscriber foundSubMap
+          -- if there are no subscriptions for the tag anymore, remove its
+          -- data sttructure altogether
+          if HMap.null newSubMap
+             then writeTVar tagMapSTM $ deleteRMapEntry (hashtagToId tag) tagMap
+          -- otherwise just remove the subscription of that node
+             else writeTVar foundSubMapSTM newSubMap
+
+
+
+-- | returns the broadcast channel of a hashtag if there are any subscribers to it
+getTagBroadcastChannel :: PostService d -> Hashtag -> STM (Maybe (TChan PostID))
+getTagBroadcastChannel serv tag = do
+    tagMap <- readTVar $ subscribers serv
+    case lookupTagSubscriptions tag tagMap of
+      Nothing -> pure Nothing
+      Just (subscriberSTM, broadcastChan, _) -> do
+          subscriberMap <- readTVar subscriberSTM
+          if HMap.null subscriberMap
+             then pure Nothing
+             else pure (Just broadcastChan)
+
+
+-- | look up the subscription data of a tag
+lookupTagSubscriptions :: Hashtag -> RingMap NodeID a -> Maybe a
+lookupTagSubscriptions tag = rMapLookup (hashtagToId tag)
+
+
+-- normalise the unicode representation of a string to NFC and convert to lower case
+normaliseTag :: Text -> Text
+normaliseTag = Txt.toLower . Txt.fromStrict . normalize NFC . Txt.toStrict
+
+
+-- | convert a hashtag to its representation on the DHT
+hashtagToId :: Hashtag -> NodeID
+hashtagToId = genKeyID . Txt.unpack
+
+
+readUpToTChan :: Int -> TChan a -> STM [a]
+readUpToTChan 0 _ = pure []
+readUpToTChan n chan = do
+  readFromChan <- tryReadTChan chan
+  case readFromChan of
+       Nothing -> pure []
+       Just val -> do
+           moreReads <- readUpToTChan (pred n) chan
+           pure (val:moreReads)
+
+
+readUpToTQueue :: Int -> TQueue a -> STM [a]
+readUpToTQueue 0 _ = pure []
+readUpToTQueue n q = do
+    readFromQueue <- tryReadTQueue q
+    case readFromQueue of
+      Nothing -> pure []
+      Just val -> do
+          moreReads <- readUpToTQueue (pred n) q
+          pure (val:moreReads)
+
 -- | define how to convert all showable types to PlainText
 -- No idea what I'm doing with these overlappable instances though ¯\_(ツ)_/¯
 -- TODO: figure out how this overlapping stuff actually works https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#instance-overlap
 instance {-# OVERLAPPABLE #-} Show a => MimeRender PlainText a where
-    mimeRender _ = BSU.fromString . show
+    mimeRender _ = BSUL.fromString . show
+
+instance {-# OVERLAPPABLE #-} Read a => MimeUnrender PlainText a where
+    mimeUnrender _ = readEither . BSUL.toString
+
+-- ====== worker threads ======
+
+-- TODO: make configurable
+numParallelDeliveries = 10
+
+launchWorkerThreads :: DHT d => PostService d -> IO ()
+launchWorkerThreads serv = concurrently_
+    (processIncomingPosts serv)
+    $ concurrently_
+        (purgeSubscriptionsThread serv)
+        $ concurrently_
+            (fetchTagPosts serv)
+            (relayWorker serv)
+
+
+-- | periodically remove expired subscription entries from relay subscribers
+purgeSubscriptionsThread :: PostService d -> IO ()
+purgeSubscriptionsThread serv = forever $ do
+    -- read config
+    now <- getPOSIXTime
+    let
+        purgeInterval = confSubscriptionExpiryTime (serviceConf serv) / 10
+    -- no need to atomically lock this, as newly incoming subscriptions do not
+    -- need to be purged
+    tagMap <- readTVarIO $ subscribers serv
+    forM_ tagMap $ \(subscriberMapSTM, _, _) ->
+        -- but each subscriberMap needs to be modified atomically
+        atomically . modifyTVar' subscriberMapSTM $ HMap.filter (\(_, ts) -> ts > now)
+    threadDelay $ fromEnum purgeInterval `div` 10^6
+
+
+-- | process the pending relay inbox of incoming posts from the internal queue:
+-- Look up responsible relay node for given hashtag and forward post to it
+processIncomingPosts :: DHT d => PostService d -> IO ()
+processIncomingPosts serv = forever $ do
+    -- blocks until available
+    deliveriesToProcess <- atomically $ do
+        readResult <- readUpToTQueue numParallelDeliveries $ relayInQueue serv
+        if null readResult
+           then retry
+           else pure readResult
+    runningJobs <- forM deliveriesToProcess $ \(tag, pID, pContent) -> async $ do
+        let pIdUri = "http://" <> (Txt.pack . confServiceHost . serviceConf $ serv) <> ":" <> (fromString . show . confServicePort . serviceConf $ serv) <> "/post/" <> pID
+        lookupRes <- lookupKey (baseDHT serv) (Txt.unpack tag)
+        case lookupRes of
+          -- no vserver active => wait and retry
+          Nothing -> threadDelay (10 * 10^6) >> pure (Left "no vserver active")
+          Just (responsibleHost, responsiblePort) -> do
+            resp <- runClientM (relayInboxClient tag $ pIdUri <> "," <> pContent) (mkClientEnv (httpMan serv) (BaseUrl Http responsibleHost (fromIntegral responsiblePort) ""))
+            case resp of
+              Left err  -> do
+                  -- 410 error indicates outdated responsibility mapping
+                  -- Simplification: just invalidate the mapping entry on all errors, force a re-lookup and re-queue the post
+                  -- TODO: keep track of maximum retries
+                  _ <- forceLookupKey (baseDHT serv) (Txt.unpack tag)
+                  atomically . writeTQueue (relayInQueue serv) $ (tag, pID, pContent)
+                  pure . Left $ "Error: " <> show err
+              Right _ -> do
+                  -- idea for the experiment: each post publication makes the initial posting instance subscribe to all contained tags
+                  now <- getPOSIXTime
+                  subscriptionStatus <- HMap.lookup (hashtagToId tag) <$> readTVarIO (ownSubscriptions serv)
+                  -- if not yet subscribed or subscription expires within 5 minutes, (re)subscribe to tag
+                  when (maybe True (\subLease -> now - subLease < 300) subscriptionStatus) $
+                      void $ clientSubscribeTo serv tag
+
+                  -- for evaluation, return the tag of the successfully forwarded post
+                  pure $ Right tag
+
+    -- collect async results
+    results <- mapM waitCatch runningJobs
+    -- report the count of published posts for statistics
+    atomically . writeTQueue (statsQueue serv) $ StatsEvent PostPublishEvent (length . rights $ results) 0    -- hashtag published to doesn't matter
+    pure ()
+
+
+
+-- | process the pending fetch jobs of delivered post IDs: Delivered posts are tried to be fetched from their URI-ID
+fetchTagPosts :: DHT d => PostService d -> IO ()
+fetchTagPosts serv = forever $ do
+    -- blocks until available
+    -- TODO: batching, retry
+    -- TODO: process multiple in parallel
+    pIdUri <- atomically . readTQueue $ postFetchQueue serv
+    fetchReq <- HTTP.parseRequest . Txt.unpack $ pIdUri
+    resp <- try $ HTTP.httpLbs fetchReq (httpMan serv) :: IO (Either HTTP.HttpException (HTTP.Response BSUL.ByteString))
+    case resp of
+      Right response ->
+          -- TODO error handling, retry
+          --if HTTPT.statusCode (HTTP.responseStatus response) == 200
+          --   then
+          --   -- success, TODO: statistics
+          --   else
+          pure ()
+      Left _ ->
+             -- TODO error handling, retry
+             pure ()
+
+
+relayWorker :: PostService d -> IO ()
+relayWorker serv = forever $ do
+    -- atomically (to be able to retry) fold a list of due delivery actions
+    jobsToProcess <- atomically $ do
+        subscriptionMap <- readTVar $ subscribers serv
+        jobList <- D.toList <$> foldM (\jobAcc (subscriberMapSTM, _, tag) -> do
+            subscriberMap <- readTVar subscriberMapSTM
+            foldM (\jobAcc' ((subHost, subPort), (postChan, _)) -> do
+                postsToDeliver <- readUpToTChan 500 postChan
+                let postDeliveryAction = runClientM (tagDeliveryClient tag (Txt.unlines postsToDeliver)) (mkClientEnv (httpMan serv) (BaseUrl Http subHost (fromIntegral subPort) ""))
+                -- append relay push job to job list
+                pure $ if not (null postsToDeliver)
+                          then jobAcc' `D.snoc` (do
+                              deliveryResult <- postDeliveryAction
+                              either
+                                (const $ pure ())
+                                -- on successful push, record that event for statistics
+                                (const . atomically . writeTQueue (statsQueue serv) $ StatsEvent RelayDeliveryEvent (length postsToDeliver) (hashtagToId tag))
+                                deliveryResult
+                              pure deliveryResult
+                                                )
+                   else jobAcc'
+                ) jobAcc $ HMap.toList subscriberMap
+            ) D.empty subscriptionMap
+        -- if no relay jobs, then retry
+        if null jobList
+           then retry
+           else pure jobList
+
+    -- when processing the list, send several deliveries in parallel
+    forM_ (chunksOf numParallelDeliveries jobsToProcess) $ \jobset -> do
+        runningJobs <- mapM async jobset
+        -- so far just dropping failed attempts, TODO: retry mechanism
+        results <- mapM waitCatch runningJobs
+        let
+            successfulResults =  rights results
+            unsuccessfulResults = lefts results
+        unless (null unsuccessfulResults) $ putStrLn ("ERR: " <> show (length unsuccessfulResults) <> " failed deliveries!")
+        putStrLn $ "successfully relayed " <> show (length successfulResults)
+        pure ()
+
+
+-- ======= statistics/measurement and logging =======
+
+data StatsEventType = PostPublishEvent
+    | RelayReceiveEvent
+    | RelayDeliveryEvent
+    | IncomingPostFetchEvent
+    deriving (Enum, Show, Eq)
+
+-- | Represents measurement event of a 'StatsEventType' with a count relevant for a certain key
+data StatsEvent = StatsEvent StatsEventType Int NodeID
+    deriving (Show, Eq)
+
+
+-- | measured rates of relay performance
+-- TODO: maybe include other metrics in here as well, like number of subscribers?
+data RelayStats = RelayStats
+    { relayReceiveRates  :: RingMap NodeID Double
+    -- ^ rate of incoming posts in the responsibility of this relay
+    , relayDeliveryRates :: RingMap NodeID Double
+    -- ^ rate of relayed outgoing posts
+    , postFetchRate      :: Double -- no need to differentiate between tags
+    -- ^ number of post-fetches delivered
+    , postPublishRate    :: Double
+    -- ^ rate of initially publishing posts through this instance
+    }
+    deriving (Show, Eq)
+
+
+
+launchStatsThreads :: PostService d -> IO ()
+launchStatsThreads serv = do
+    -- create shared accumulator
+    sharedAccum <- newTVarIO emptyStats
+    concurrently_
+        (accumulateStatsThread sharedAccum $ statsQueue serv)
+        (evaluateStatsThread serv sharedAccum)
+
+
+-- | Read stats events from queue and add them to a shared accumulator.
+-- Instead of letting the events accumulate in the queue and allocate linear memory, immediately fold the result.
+accumulateStatsThread :: TVar RelayStats -> TQueue StatsEvent -> IO ()
+accumulateStatsThread statsAccumulator statsQ = forever $ do
+    -- blocks until stats event arrives
+    event <- atomically $ readTQueue statsQ
+    -- add the event number to current accumulator
+    atomically $ modifyTVar' statsAccumulator $ statsAdder event
+
+
+-- | add incoming stats events to accumulator value
+statsAdder :: StatsEvent -> RelayStats -> RelayStats
+statsAdder event stats = case event of
+    StatsEvent PostPublishEvent num _ ->
+        stats {postPublishRate = fromIntegral num + postPublishRate stats}
+    StatsEvent RelayReceiveEvent num key ->
+        stats {relayReceiveRates = sumIfEntryExists key (fromIntegral num) (relayReceiveRates stats)}
+    StatsEvent RelayDeliveryEvent num key ->
+        stats {relayDeliveryRates = sumIfEntryExists key (fromIntegral num) (relayDeliveryRates stats)}
+    StatsEvent IncomingPostFetchEvent num _ ->
+        stats {postFetchRate = fromIntegral num + postFetchRate stats}
+  where
+      sumIfEntryExists = addRMapEntryWith (\newVal oldVal ->
+          let toInsert = fromJust $ extractRingEntry newVal
+          in
+          case oldVal of
+            KeyEntry n -> KeyEntry (n + toInsert)
+            ProxyEntry pointer (Just (KeyEntry n)) -> ProxyEntry pointer (Just (KeyEntry $ n + toInsert))
+            ProxyEntry pointer Nothing -> ProxyEntry pointer (Just newVal)
+            _ -> error "RingMap nested too deeply"
+                                          )
+
+
+-- Periodically exchange the accumulated statistics with empty ones, evaluate them
+-- and make them the current statistics of the service.
+evaluateStatsThread :: PostService d -> TVar RelayStats -> IO ()
+evaluateStatsThread serv statsAcc = getPOSIXTime >>= loop
+  where
+      loop previousTs = do
+          threadDelay $ confStatsEvalDelay (serviceConf serv)
+          -- get and reset the stats accumulator
+          summedStats <- atomically $ do
+              stats <- readTVar statsAcc
+              writeTVar statsAcc emptyStats
+              pure stats
+          -- as the transaction might retry several times, current time needs to
+          -- be read afterwards
+          now <- getPOSIXTime
+          -- evaluate stats rate and replace server stats
+          -- persistently store in a TVar so it can be retrieved later by the DHT
+          let timePassed = (now - previousTs) * fromIntegral (confSpeedupFactor $ serviceConf serv)
+              rateStats = evaluateStats timePassed summedStats
+          atomically $ writeTVar (loadStats serv) rateStats
+          -- and now what? write a log to file
+          -- format: total relayReceiveRates;total relayDeliveryRates;postFetchRate;postPublishRate; subscriberSum
+          -- later: current (reported) load, target load
+          subscriberSum <- sumSubscribers
+          TxtI.hPutStrLn (logFileHandle serv) $
+              format (fixed 9 % ";" % fixed 20 % ";" % fixed 20 % ";" % fixed 20 % ";" % fixed 20 % ";" % int )
+                  (realToFrac now :: Double)
+                  (sum . relayReceiveRates $ rateStats)
+                  (sum . relayDeliveryRates $ rateStats)
+                  (postPublishRate rateStats)
+                  (postFetchRate rateStats)
+                  subscriberSum
+          loop now
+
+      sumSubscribers = do
+          tagMap <- readTVarIO $ subscribers serv
+          foldM (\subscriberSum (subscriberMapSTM, _, _) -> do
+              subscriberMap <- readTVarIO subscriberMapSTM
+              pure $ subscriberSum + HMap.size subscriberMap
+                )
+                0 tagMap
+
+
+-- | Evaluate the accumulated statistic events: Currently mostly calculates the event
+-- rates by dividing through the collection time frame
+evaluateStats :: POSIXTime -> RelayStats -> RelayStats
+evaluateStats timeInterval summedStats =
+    -- first sum all event numbers, then divide through number of seconds passed to
+    -- get rate per second
+    RelayStats
+    { relayReceiveRates = (/ intervalSeconds) <$> relayReceiveRates summedStats
+    , relayDeliveryRates = (/ intervalSeconds) <$> relayDeliveryRates summedStats
+    , postPublishRate = postPublishRate summedStats / intervalSeconds
+    , postFetchRate = postFetchRate summedStats / intervalSeconds
+    }
+  where
+      intervalSeconds = realToFrac timeInterval
+
+
+emptyStats :: RelayStats
+emptyStats = RelayStats
+    { relayReceiveRates = emptyRMap
+    , relayDeliveryRates = emptyRMap
+    , postFetchRate = 0
+    , postPublishRate = 0
+    }

src/Hash2Pub/PostService/API.hs

@@ -0,0 +1,37 @@
+{-# LANGUAGE DataKinds             #-}
+{-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE InstanceSigs          #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings     #-}
+{-# LANGUAGE RankNTypes            #-}
+{-# LANGUAGE TypeOperators         #-}
+module Hash2Pub.PostService.API where
+
+import           Data.Text.Lazy (Text)
+
+import           Servant
+
+type PostServiceAPI = "relay" :> "inbox" :> Capture "hashtag" Text :> ReqBody '[PlainText] Text :> PutCreated '[PlainText] NoContent
+                 -- delivery endpoint at responsible relay for delivering posts of $tag for distribution
+                 :<|> "relay" :> "subscribers" :> Capture "senderID" Integer :> ReqBody '[PlainText] Text :> PostNoContent '[PlainText] Text
+                 -- endpoint for delivering the subscriptions and outstanding queue
+                 :<|> "post" :> Capture "postid" Text :> Get '[PlainText] Text
+                 -- fetch endpoint for posts, full post ID is http://$domain/post/$postid
+                 :<|> "posts" :> ReqBody '[PlainText] Text :> Post '[PlainText] Text
+                 -- endpoint for fetching multiple posts at once
+                 :<|> "posts" :> "inbox" :> ReqBody '[PlainText] Text :> PutCreated '[PlainText] NoContent
+                 -- delivery endpoint of newly published posts of the relay's instance
+                 :<|> "tags" :> Capture "hashtag" Text :> ReqBody '[PlainText] Text :> PostCreated '[PlainText] Text
+                 -- delivery endpoint for posts of $tag at subscribing instance
+                 :<|> "tags" :> Capture "hashtag" Text :> "subscribe" :> Header "Origin" Text :> Get '[PlainText] Integer
+                 -- endpoint for subscribing the instance specified in
+                 -- the Origin header to $hashtag.
+                 -- Returns subscription lease time in seconds.
+                 :<|> "tags" :> Capture "hashtag" Text :> "unsubscribe" :> Header "Origin" Text :> Get '[PlainText] Text
+                 -- endpoint for unsubscribing the instance specified in
+                 -- the Origin header to $hashtag
+
+-- | needed for guiding type inference
+exposedPostServiceAPI :: Proxy PostServiceAPI
+exposedPostServiceAPI = Proxy
+

src/Hash2Pub/ProtocolTypes.hs

@@ -1,7 +1,5 @@
 module Hash2Pub.ProtocolTypes where
 
-import qualified Data.Map                as Map
-import           Data.Maybe              (mapMaybe)
 import qualified Data.Set                as Set
 import           Data.Time.Clock.POSIX   (POSIXTime)
 
@@ -55,6 +53,7 @@ data ActionPayload = QueryIDRequestPayload
     | LeaveRequestPayload
     { leaveSuccessors   :: [RemoteNodeState]
     , leavePredecessors :: [RemoteNodeState]
+    , leaveDoMigration  :: Bool
     }
     | StabiliseRequestPayload
     | PingRequestPayload

src/Hash2Pub/RingMap.hs

@@ -5,36 +5,61 @@ module Hash2Pub.RingMap where
 
 import           Data.Foldable   (foldr')
 import qualified Data.Map.Strict as Map
-import           Data.Maybe      (fromJust, isJust, isNothing, mapMaybe)
+import           Data.Maybe      (isJust, isNothing, mapMaybe)
 
 
 -- | Class for all types that can be identified via a EpiChord key.
 -- Used for restricting the types a 'RingMap' can store
-class (Eq a, Show a, Bounded k, Ord k) => HasKeyID a k where
+class (Eq a, Show a, Bounded k, Ord k) => HasKeyID k a where
     getKeyID :: a -> k
+    keyValuePair :: a -> (k, a)
+    keyValuePair val = (getKeyID val, val)
 
 
 -- | generic data structure for holding elements with a key and modular lookup
-newtype RingMap a k = RingMap { getRingMap :: (HasKeyID a k, Bounded k, Ord k) => Map.Map k (RingEntry a k) }
+newtype RingMap k a = RingMap { getRingMap :: (Bounded k, Ord k) => Map.Map k (RingEntry k a) }
 
-instance (HasKeyID a k, Bounded k, Ord k) => Eq (RingMap a k) where
+instance (Bounded k, Ord k, Eq a) => Eq (RingMap k a) where
     a == b = getRingMap a == getRingMap b
 
-instance (HasKeyID a k, Bounded k, Ord k, Show k) => Show (RingMap a k) where
-    show rmap = shows "RingMap " (show $ getRingMap rmap)
+instance (Bounded k, Ord k, Show k, Show a) => Show (RingMap k a) where
+    show rmap = shows ("RingMap " :: String) (show $ getRingMap rmap)
+
+
+instance (Bounded k, Ord k) => Functor (RingMap k) where
+    -- | map a function over all payload values of a 'RingMap'
+    fmap f = RingMap . Map.map traversingF . getRingMap
+      where
+          traversingF (KeyEntry a) = KeyEntry (f a)
+          traversingF (ProxyEntry pointer (Just entry)) = ProxyEntry pointer (Just $ traversingF entry)
+          traversingF (ProxyEntry pointer Nothing) = ProxyEntry pointer Nothing
+
+
+instance (Bounded k, Ord k) => Foldable (RingMap k) where
+    foldr f initVal = Map.foldr traversingFR initVal . getRingMap
+      where
+          traversingFR (KeyEntry a) acc = f a acc
+          traversingFR (ProxyEntry _ Nothing) acc = acc
+          traversingFR (ProxyEntry _ (Just entry)) acc = traversingFR entry acc
+    foldl f initVal = Map.foldl traversingFL initVal . getRingMap
+      where
+          traversingFL acc (KeyEntry a) = f acc a
+          traversingFL acc (ProxyEntry _ Nothing) = acc
+          traversingFL acc (ProxyEntry _ (Just entry)) = traversingFL acc entry
+
 
 -- | entry of a 'RingMap' that holds a value and can also
 -- wrap around the lookup direction at the edges of the name space.
-data RingEntry a k = KeyEntry a
-    | ProxyEntry (k, ProxyDirection) (Maybe (RingEntry a k))
+data RingEntry k a = KeyEntry a
+    | ProxyEntry (k, ProxyDirection) (Maybe (RingEntry k a))
     deriving (Show, Eq)
 
 -- | as a compromise, only KeyEntry components are ordered by their key
 -- while ProxyEntry components should never be tried to be ordered.
-instance (HasKeyID a k, Eq k, Ord a, Bounded k, Ord k) => Ord (RingEntry a k) where
+instance (HasKeyID k a, Eq k, Ord a, Bounded k, Ord k) => Ord (RingEntry k a) where
     a `compare` b = compare (extractID a) (extractID b)
         where
-            extractID :: (HasKeyID a k, Ord a, Bounded k, Ord k) => RingEntry a k -> k
+            extractID :: (HasKeyID k a, Ord a, Bounded k, Ord k) => RingEntry k a -> k
             extractID (KeyEntry e) = getKeyID e
             extractID ProxyEntry{} = error "proxy entries should never appear outside of the RingMap"
 
@@ -49,51 +74,51 @@ instance Enum ProxyDirection where
     fromEnum Backwards = - 1
     fromEnum Forwards  = 1
 
--- | helper function for getting the a from a RingEntry a k
-extractRingEntry :: (HasKeyID a k, Bounded k, Ord k) => RingEntry a k -> Maybe a
+-- | helper function for getting the a from a RingEntry k a
+extractRingEntry :: (Bounded k, Ord k) => RingEntry k a -> Maybe a
 extractRingEntry (KeyEntry entry)                       = Just entry
 extractRingEntry (ProxyEntry _ (Just (KeyEntry entry))) = Just entry
 extractRingEntry _                                      = Nothing
 
 -- | An empty 'RingMap' needs to be initialised with 2 proxy entries,
 -- linking the modular name space together by connecting @minBound@ and @maxBound@
-emptyRMap :: (HasKeyID a k, Bounded k, Ord k) => RingMap a k
+emptyRMap :: (Bounded k, Ord k) => RingMap k a
 emptyRMap = RingMap . Map.fromList $ proxyEntry <$> [(maxBound, (minBound, Forwards)), (minBound, (maxBound, Backwards))]
   where
     proxyEntry (from,to) = (from, ProxyEntry to Nothing)
 
 -- | Maybe returns the entry stored at given key
-rMapLookup :: (HasKeyID a k, Bounded k, Ord k)
+rMapLookup :: (Bounded k, Ord k)
            => k       -- ^lookup key
-           -> RingMap a k    -- ^lookup cache
+           -> RingMap k a    -- ^lookup cache
            -> Maybe a
 rMapLookup key rmap =  extractRingEntry =<< Map.lookup key (getRingMap rmap)
 
 -- | returns number of present 'KeyEntry' in a properly initialised 'RingMap'
-rMapSize :: (HasKeyID a k, Integral i, Bounded k, Ord k)
-         => RingMap a k
+rMapSize :: (Integral i, Bounded k, Ord k)
+         => RingMap k a
          -> i
 rMapSize rmap = fromIntegral $ Map.size innerMap - oneIfEntry rmap minBound - oneIfEntry rmap maxBound
   where
     innerMap = getRingMap rmap
-    oneIfEntry :: (HasKeyID a k, Integral i, Bounded k, Ord k) => RingMap a k -> k -> i
+    oneIfEntry :: (Integral i, Bounded k, Ord k) => RingMap k a -> k -> i
     oneIfEntry rmap' nid
       | isNothing (rMapLookup nid rmap') = 1
       | otherwise = 0
 
 -- | a wrapper around lookup functions, making the lookup redirectable by a @ProxyEntry@
 -- to simulate a modular ring
-lookupWrapper :: (HasKeyID a k, Bounded k, Ord k, Num k)
-              => (k -> Map.Map k (RingEntry a k) -> Maybe (k, RingEntry a k))
-              -> (k -> Map.Map k (RingEntry a k) -> Maybe (k, RingEntry a k))
+lookupWrapper :: (Bounded k, Ord k, Num k)
+              => (k -> Map.Map k (RingEntry k a) -> Maybe (k, RingEntry k a))
+              -> (k -> Map.Map k (RingEntry k a) -> Maybe (k, RingEntry k a))
               -> ProxyDirection
               -> k
-              -> RingMap a k
-              -> Maybe a
+              -> RingMap k a
+              -> Maybe (k, a)
 lookupWrapper f fRepeat direction key rmap =
     case f key $ getRingMap rmap of
         -- the proxy entry found holds a
-        Just (_, ProxyEntry _ (Just (KeyEntry entry))) -> Just entry
+        Just (foundKey, ProxyEntry _ (Just (KeyEntry entry))) -> Just (foundKey, entry)
         -- proxy entry holds another proxy entry, this should not happen
         Just (_, ProxyEntry _ (Just (ProxyEntry _ _))) -> Nothing
         -- proxy entry without own entry is a pointer on where to continue
@@ -106,10 +131,10 @@ lookupWrapper f fRepeat direction key rmap =
                then lookupWrapper fRepeat fRepeat direction newKey rmap
                else Nothing
         -- normal entries are returned
-        Just (_, KeyEntry entry) -> Just entry
+        Just (foundKey, KeyEntry entry) -> Just (foundKey, entry)
         Nothing -> Nothing
   where
-    rMapNotEmpty :: (HasKeyID a k, Bounded k, Ord k) => RingMap a k -> Bool
+    rMapNotEmpty :: (Bounded k, Ord k) => RingMap k a -> Bool
     rMapNotEmpty rmap' = (Map.size (getRingMap rmap') > 2)     -- there are more than the 2 ProxyEntries
                    || isJust (rMapLookup minBound rmap') -- or one of the ProxyEntries holds a node
                    || isJust (rMapLookup maxBound rmap')
@@ -117,32 +142,34 @@ lookupWrapper f fRepeat direction key rmap =
 -- | find the successor node to a given key on a modular EpiChord ring.
 -- Note: The EpiChord definition of "successor" includes the node at the key itself,
 -- if existing.
-rMapLookupSucc :: (HasKeyID a k, Bounded k, Ord k, Num k)
+rMapLookupSucc :: (Bounded k, Ord k, Num k)
                => k           -- ^lookup key
-               -> RingMap a k       -- ^ring cache
-               -> Maybe a
+               -> RingMap k a       -- ^ring cache
+               -> Maybe (k, a)
 rMapLookupSucc = lookupWrapper Map.lookupGE Map.lookupGE Forwards
 
 -- | find the predecessor node to a given key on a modular EpiChord ring.
-rMapLookupPred :: (HasKeyID a k, Bounded k, Ord k, Num k)
+rMapLookupPred :: (Bounded k, Ord k, Num k)
                => k           -- ^lookup key
-               -> RingMap a k        -- ^ring cache
-               -> Maybe a
+               -> RingMap k a        -- ^ring cache
+               -> Maybe (k, a)
 rMapLookupPred = lookupWrapper Map.lookupLT Map.lookupLE Backwards
 
-addRMapEntryWith :: (HasKeyID a k, Bounded k, Ord k)
-                 => (RingEntry a k -> RingEntry a k -> RingEntry a k)
-                 -> a
-                 -> RingMap a k
-                 -> RingMap a k
-addRMapEntryWith combineFunc entry = RingMap
-    . Map.insertWith combineFunc (getKeyID entry) (KeyEntry entry)
+addRMapEntryWith :: (Bounded k, Ord k)
+                 => (RingEntry k a -> RingEntry k a -> RingEntry k a) -- ^ f new_value mold_value
+                 -> k   -- ^ key
+                 -> a   -- ^ value
+                 -> RingMap k a
+                 -> RingMap k a
+addRMapEntryWith combineFunc key entry = RingMap
+    . Map.insertWith combineFunc key (KeyEntry entry)
     . getRingMap
 
-addRMapEntry :: (HasKeyID a k, Bounded k, Ord k)
-             => a
-             -> RingMap a k
-             -> RingMap a k
+addRMapEntry :: (Bounded k, Ord k)
+             => k   -- ^ key
+             -> a   -- ^ value
+             -> RingMap k a
+             -> RingMap k a
 addRMapEntry = addRMapEntryWith insertCombineFunction
   where
     insertCombineFunction newVal oldVal =
@@ -151,30 +178,30 @@ addRMapEntry = addRMapEntryWith insertCombineFunction
           KeyEntry _     -> newVal
 
 
-addRMapEntries :: (Foldable t, HasKeyID a k, Bounded k, Ord k)
-               => t a
-               -> RingMap a k
-               -> RingMap a k
-addRMapEntries entries rmap = foldr' addRMapEntry rmap entries
+addRMapEntries :: (Foldable t, Bounded k, Ord k)
+               => t (k, a)
+               -> RingMap k a
+               -> RingMap k a
+addRMapEntries entries rmap = foldr' (\(k, v) rmap' -> addRMapEntry k v rmap') rmap entries
 
-setRMapEntries :: (Foldable t, HasKeyID a k, Bounded k, Ord k)
-               => t a
-               -> RingMap a k
+setRMapEntries :: (Foldable t, Bounded k, Ord k)
+               => t (k, a)
+               -> RingMap k a
 setRMapEntries entries = addRMapEntries entries emptyRMap
 
-deleteRMapEntry :: (HasKeyID a k, Bounded k, Ord k)
+deleteRMapEntry :: (Bounded k, Ord k)
                 => k
-                -> RingMap a k
-                -> RingMap a k
+                -> RingMap k a
+                -> RingMap k a
 deleteRMapEntry nid = RingMap . Map.update modifier nid . getRingMap
   where
     modifier (ProxyEntry idPointer _) = Just (ProxyEntry idPointer Nothing)
     modifier KeyEntry {}              = Nothing
 
-rMapToList :: (HasKeyID a k, Bounded k, Ord k) => RingMap a k -> [a]
+rMapToList :: (Bounded k, Ord k) => RingMap k a -> [a]
 rMapToList = mapMaybe extractRingEntry . Map.elems . getRingMap
 
-rMapFromList :: (HasKeyID a k, Bounded k, Ord k) => [a] -> RingMap a k
+rMapFromList :: (Bounded k, Ord k) => [(k, a)] -> RingMap k a
 rMapFromList = setRMapEntries
 
 -- | takes up to i entries from a 'RingMap' by calling a getter function on a
@@ -182,49 +209,64 @@ rMapFromList = setRMapEntries
 -- Stops once i entries have been taken or an entry has been encountered twice
 -- (meaning the ring has been traversed completely).
 -- Forms the basis for 'takeRMapSuccessors' and 'takeRMapPredecessors'.
-takeRMapEntries_ :: (HasKeyID a k, Integral i, Bounded k, Ord k)
-                 => (k -> RingMap a k -> Maybe a)
-                 -> k
-                 -> i
-                 -> RingMap a k
-                 -> [a]
+takeRMapEntries_ :: (Integral i, Bounded k, Ord k)
+                 => (k -> RingMap k a -> Maybe (k, a))   -- ^ parameterisable getter function to determine lookup direction
+                 -> k   -- ^ starting key
+                 -> i   -- ^ number of maximum values to take
+                 -> RingMap k a
+                 -> [a] -- ^ values taken
 -- TODO: might be more efficient with dlists
 takeRMapEntries_ getterFunc startAt num rmap = reverse $
     case getterFunc startAt rmap of
       Nothing -> []
-      Just anEntry -> takeEntriesUntil rmap getterFunc (getKeyID anEntry) (getKeyID anEntry) (num-1) [anEntry]
-  where
-    -- for some reason, just reusing the already-bound @rmap@ and @getterFunc@
-    -- variables leads to a type error, these need to be passed explicitly
-    takeEntriesUntil :: (HasKeyID a k, Integral i, Bounded k, Ord k)
-                     => RingMap a k
-                     -> (k -> RingMap a k -> Maybe a) -- getter function
-                     -> k
-                     -> k
-                     -> i
-                     -> [a]
-                     -> [a]
-    takeEntriesUntil rmap' getterFunc' havingReached previousEntry remaining takeAcc
-      | remaining <= 0 = takeAcc
-      | getKeyID (fromJust $ getterFunc' previousEntry rmap') == havingReached = takeAcc
-      | otherwise = let (Just gotEntry) = getterFunc' previousEntry rmap'
-                    in takeEntriesUntil rmap' getterFunc' havingReached (getKeyID gotEntry) (remaining-1) (gotEntry:takeAcc)
+      Just (foundKey, anEntry) -> takeEntriesUntil_ rmap getterFunc foundKey foundKey (Just $ num-1) [anEntry]
 
-takeRMapPredecessors :: (HasKeyID a k, Integral i, Bounded k, Ord k, Num k)
+
+takeEntriesUntil_ :: (Integral i, Bounded k, Ord k)
+                 => RingMap k a
+                 -> (k -> RingMap k a -> Maybe (k, a)) -- getter function
+                 -> k           -- limit value
+                 -> k           -- start value
+                 -> Maybe i     -- possible number limit
+                 -> [a]
+                 -> [a]
+takeEntriesUntil_ _rmap' _getterFunc' _havingReached _previousEntry (Just remaining) takeAcc
+  -- length limit reached
+  | remaining <= 0 = takeAcc
+takeEntriesUntil_ rmap' getterFunc' havingReached previousEntry numLimit takeAcc =
+    case nextEntry of
+                  Just (fKey, gotEntry)
+                    | fKey == havingReached -> takeAcc
+                    | otherwise -> takeEntriesUntil_ rmap' getterFunc' havingReached fKey (fmap pred numLimit) (gotEntry:takeAcc)
+                  Nothing -> takeAcc
+    where
+        nextEntry = getterFunc' previousEntry rmap'
+
+
+takeRMapPredecessors :: (Integral i, Bounded k, Ord k, Num k)
                  => k
                  -> i
-                 -> RingMap a k
+                 -> RingMap k a
                  -> [a]
 takeRMapPredecessors = takeRMapEntries_ rMapLookupPred
 
-takeRMapSuccessors :: (HasKeyID a k, Integral i, Bounded k, Ord k, Num k)
+takeRMapSuccessors :: (Integral i, Bounded k, Ord k, Num k)
                  => k
                  -> i
-                 -> RingMap a k
+                 -> RingMap k a
                  -> [a]
 takeRMapSuccessors = takeRMapEntries_ rMapLookupSucc
 
--- clean up cache entries: once now - entry > maxAge
--- transfer difference now - entry to other node
-
+takeRMapPredecessorsFromTo :: (Bounded k, Ord k, Num k)
+                           => k     -- start value for taking
+                           -> k     -- stop value for taking
+                           -> RingMap k a
+                           -> [a]
+takeRMapPredecessorsFromTo fromVal toVal rmap = takeEntriesUntil_ rmap rMapLookupPred toVal fromVal Nothing []
 
+takeRMapSuccessorsFromTo :: (Bounded k, Ord k, Num k)
+                           => k     -- start value for taking
+                           -> k     -- stop value for taking
+                           -> RingMap k a
+                           -> [a]
+takeRMapSuccessorsFromTo fromVal toVal rmap = takeEntriesUntil_ rmap rMapLookupSucc toVal fromVal Nothing []

src/Hash2Pub/ServiceTypes.hs

@@ -1,9 +0,0 @@
-{-# LANGUAGE MultiParamTypeClasses #-}
-module Hash2Pub.ServiceTypes where
-
-import           Hash2Pub.FediChord (DHT (..))
-
-class Service s d where
-    -- | run the service
-    runService :: (Integral i) => d -> String -> i -> IO (s d)
-    getServicePort :: (Integral i) => s d -> i

test/FediChordSpec.hs

@@ -1,3 +1,5 @@
+{-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings     #-}
 module FediChordSpec where
 
@@ -187,6 +189,7 @@ spec = do
             lReqPayload = LeaveRequestPayload {
                 leaveSuccessors = someNodes
               , leavePredecessors = someNodes
+              , leaveDoMigration = True
                                               }
             stabReqPayload = StabiliseRequestPayload
             pingReqPayload = PingRequestPayload
@@ -292,12 +295,15 @@ exampleNodeState = RemoteNodeState {
   , vServerID = 0
                    }
 
-exampleLocalNode :: IO LocalNodeState
-exampleLocalNode = nodeStateInit =<< (newTVarIO $ RealNode {
+exampleLocalNode :: IO (LocalNodeState MockService)
+exampleLocalNode = do
+    realNode <- newTVarIO $ RealNode {
             vservers = []
           , nodeConfig = exampleFediConf
           , bootstrapNodes = confBootstrapNodes exampleFediConf
-                                                        })
+          , nodeService = MockService
+                                                        }
+    nodeStateInit realNode
 
 
 exampleFediConf :: FediChordConf
@@ -313,3 +319,9 @@ exampleVs :: (Integral i) => i
 exampleVs = 4
 exampleIp :: HostAddress6
 exampleIp = tupleToHostAddress6 (0x2001, 0x16b8, 0x755a, 0xb110, 0x7d6a, 0x12ab, 0xf0c5, 0x386e)
+
+data MockService d = MockService
+
+instance DHT d => Service MockService d where
+    runService _ _ = pure MockService
+    getListeningPortFromService = const 1337