choose and implement data structures for node state and cache

src/Hash2Pub/FediChord.hs

@@ -11,6 +11,15 @@ Modernised EpiChord + k-choices load balancing
 
 module Hash2Pub.FediChord where
 
+import qualified Data.Map.Strict as Map
+import qualified Data.String.UTF8 as U8S
+import Network.Socket
+import Data.Time.Clock.System
+
+-- define protocol constants
+idBits :: Integer
+idBits = 256
+
 newtype NodeID = NodeID { getNodeID :: Integer } deriving (Eq, Show, Enum)
 
 instance Bounded NodeID where
@@ -26,9 +35,50 @@ instance Num NodeID where
     signum = NodeID . signum . getNodeID
     abs = NodeID . abs . getNodeID  -- ToDo: make sure that at creation time only IDs within the range are used
 
--- Todo: Num Instanz selbst definieren
--- Todo: Ist es sinnvoll, das hier Teil von Ord zu machen?
+-- NodeIDs on a ring are assigned an Ordering for finding a preceding node
+-- main idea: a node is preceding (LT) if the way forwards to the other node is smaller than the way backwards
+-- problem: equality of ways /= (a == b), so even equal-way paths don't return EQ. The equality-of-ways case is assigned to LT,
+-- as preceding EpiChord nodes are nodes <=.
+instance Ord NodeID where
+    a `compare` b
+      | getNodeID a == getNodeID b = EQ
+      | wayForwards <= wayBackwards = LT
+      | wayForwards > wayBackwards = GT
+      where
+        wayForwards = getNodeID (b - a)
+        wayBackwards = getNodeID (a - b)
 
--- define protocol constants
-idBits :: Integer
-idBits = 256
+data NodeState = NodeState {
+    id :: NodeID
+  , domain :: String
+  -- ^ full public domain name the node is reachable under
+  , ipAddr :: HostAddress6
+  -- the node's public IPv6 address
+  , dhtPort :: PortNumber
+  -- ^ port of the DHT itself
+  , apPort :: Maybe PortNumber
+  -- ^ port of the ActivityPub relay and storage service
+  -- might have to be queried first
+  , nodeCache :: Map.Map NodeID CacheEntry
+  -- ^ EpiChord node cache with expiry times for nodes
+  -- as the map is ordered, lookups for the closes preceding node can be done using `lookupLE`
+  , successors :: [NodeID]
+  , predecessors :: [NodeID]
+  ----- protocol parameters -----
+  -- TODO: evaluate moving these somewhere else
+  , kNeighbours :: Int
+  -- ^ desired length of predecessor and successor list
+  -- needs to be parameterisable for simulation purposes
+  , lNumBestNodes :: Int
+  -- ^ number of best next hops to provide
+  -- needs to be parameterisable for simulation purposes
+  , pNumParallelQueries :: Int
+  -- ^ number of parallel sent queries
+  -- needs to be parameterisable for simulation purposes
+                           }
+
+type CacheEntry = ( NodeState, SystemTime)
+
+-- Todo: DHT backend can learn potential initial bootstrapping points through the instances mentioned in the received AP-relay messages
+-- needs to know its own domain anyways for ID generation
+-- persist them on disk so they can be used for all following bootstraps

src/shell.nix

@@ -6,6 +6,13 @@ pkgs.mkShell {
     (pkgs.haskellPackages.ghcWithPackages (pkgs: with pkgs;
       [
         mtl
+        cmdargs
+        cryptonite   # cryptographic hash functions
+        utf8-string  # could also be done with Data.Text
+        HUnit
+        network      # sockets
+        network-info # for getting local IP address
+        time
       ]))
   ];
 }