1 files changed, 23 insertions, 1 deletions

diff --git a/src/Network/RPC.hs b/src/Network/RPC.hs
index 727422fd..7fb0e571 100644
--- a/src/Network/RPC.hs
+++ b/src/Network/RPC.hs
@@ -1,16 +1,22 @@
 {-# LANGUAGE ConstraintKinds        #-}
+{-# LANGUAGE DeriveDataTypeable     #-}
+{-# LANGUAGE FlexibleContexts       #-}
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE MultiParamTypeClasses  #-}
 {-# LANGUAGE RankNTypes             #-}
 {-# LANGUAGE ScopedTypeVariables    #-}
 {-# LANGUAGE TypeFamilies           #-}
-{-# LANGUAGE DeriveDataTypeable     #-}
 module Network.RPC where
 
+import Data.Bits
 import Data.ByteString (ByteString)
 import Data.Kind       (Constraint)
 import Data.Data
 import Network.Socket
+import Text.PrettyPrint.HughesPJClass  hiding (($$), (<>))
+import Data.Serialize                  as S
+import qualified Data.ByteString.Char8 as Char8
+import Data.ByteString.Base16          as Base16
 
 data MessageClass = Error | Query | Response
  deriving (Eq,Ord,Enum,Bounded,Data,Show,Read)
@@ -36,6 +42,22 @@ class Envelope envelope where
     -- Returns: response message envelope
     buildReply :: NodeId envelope -> SockAddr -> envelope a -> b -> envelope b
 
+-- | In Kademlia, the distance metric is XOR and the result is
+-- interpreted as an unsigned integer.
+newtype NodeDistance nodeid = NodeDistance nodeid
+  deriving (Eq, Ord)
+
+-- | distance(A,B) = |A xor B| Smaller values are closer.
+distance :: Bits nid => nid -> nid -> NodeDistance nid
+distance a b = NodeDistance $ xor a b
+
+instance Serialize nodeid => Show (NodeDistance nodeid) where
+  show (NodeDistance w) = Char8.unpack $ Base16.encode $ S.encode w
+
+instance Serialize nodeid => Pretty (NodeDistance nodeid) where
+  pPrint n = text $ show n
+
+
 class Envelope envelope => WireFormat raw envelope where
     type SerializableTo raw :: * -> Constraint
     type CipherContext raw envelope