Add HasEventId class to ensure events can be identified

We kept the EventSource/EventSink very abstract to make implementations
not realy on the internas of the actual data type used. However, an
event source / sink will need at least identify individual events to
tell them apart, e.g. to deduplicate them in memory.

Author: ch1bo

hydra-node/src/Hydra/Events.hs

@@ -6,21 +6,23 @@ module Hydra.Events where
 
 import Hydra.Prelude
 
--- TODO: Need to add a concept of identification to 'e' as used in these
--- definitions to enable deduplication etc.
+-- FIXME(Elaine): we have to figure out a better taxonomy/nomenclature for the events/statechange stuff
+-- the eventID here is not the same as the eventID in Queued, that one is more fickle and influenced by non state change events
+-- this one is only incremented when we have a new state change event
+type EventId = Word64
 
-newtype EventSource e m = EventSource {getEvents' :: m [e]}
+class HasEventId a where
+  getEventId :: a -> EventId
 
-newtype EventSink e m = EventSink {putEvent' :: e -> m ()}
+instance HasEventId (EventId, a) where
+  getEventId = fst
 
-putEventToSinks :: Monad m => [EventSink e m] -> e -> m ()
-putEventToSinks sinks e = forM_ sinks (\sink -> putEvent' sink e)
+newtype EventSource e m = EventSource {getEvents' :: HasEventId e => m [e]}
 
-putEventsToSinks :: Monad m => [EventSink e m] -> [e] -> m ()
-putEventsToSinks sinks es = forM_ es (\e -> putEventToSinks sinks e)
+newtype EventSink e m = EventSink {putEvent' :: HasEventId e => e -> m ()}
 
-type EventID = Word64
+putEventToSinks :: (Monad m, HasEventId e) => [EventSink e m] -> e -> m ()
+putEventToSinks sinks e = forM_ sinks (\sink -> putEvent' sink e)
 
--- FIXME(Elaine): we have to figure out a better taxonomy/nomenclature for the events/statechange stuff
--- the eventID here is not the same as the eventID in Queued, that one is more fickle and influenced by non state change events
--- this one is only incremented when we have a new state change event
+putEventsToSinks :: (Monad m, HasEventId e) => [EventSink e m] -> [e] -> m ()
+putEventsToSinks sinks es = forM_ es (\e -> putEventToSinks sinks e)

hydra-node/src/Hydra/HeadLogic/Outcome.hs

@@ -8,6 +8,7 @@ import Hydra.Prelude
 import Hydra.API.ServerOutput (ServerOutput)
 import Hydra.Chain (ChainStateType, HeadParameters, IsChainState, PostChainTx)
 import Hydra.Crypto (MultiSignature, Signature)
+import Hydra.Events (HasEventId (..))
 import Hydra.HeadId (HeadId, HeadSeed)
 import Hydra.HeadLogic.Error (LogicError)
 import Hydra.HeadLogic.State (HeadState)
@@ -85,23 +86,23 @@ data StateChanged tx
   | TickObserved {chainSlot :: ChainSlot, stateChangeID :: Word64}
   deriving stock (Generic)
 
-getStateChangeID :: StateChanged tx -> Word64
-getStateChangeID = \case
-  HeadInitialized{stateChangeID} -> stateChangeID
-  CommittedUTxO{stateChangeID} -> stateChangeID
-  HeadAborted{stateChangeID} -> stateChangeID
-  HeadOpened{stateChangeID} -> stateChangeID
-  TransactionAppliedToLocalUTxO{stateChangeID} -> stateChangeID
-  SnapshotRequestDecided{stateChangeID} -> stateChangeID
-  SnapshotRequested{stateChangeID} -> stateChangeID
-  TransactionReceived{stateChangeID} -> stateChangeID
-  PartySignedSnapshot{stateChangeID} -> stateChangeID
-  SnapshotConfirmed{stateChangeID} -> stateChangeID
-  HeadClosed{stateChangeID} -> stateChangeID
-  HeadIsReadyToFanout{stateChangeID} -> stateChangeID
-  HeadFannedOut{stateChangeID} -> stateChangeID
-  ChainRolledBack{stateChangeID} -> stateChangeID
-  TickObserved{stateChangeID} -> stateChangeID
+instance HasEventId (StateChanged tx) where
+  getEventId = \case
+    HeadInitialized{stateChangeID} -> stateChangeID
+    CommittedUTxO{stateChangeID} -> stateChangeID
+    HeadAborted{stateChangeID} -> stateChangeID
+    HeadOpened{stateChangeID} -> stateChangeID
+    TransactionAppliedToLocalUTxO{stateChangeID} -> stateChangeID
+    SnapshotRequestDecided{stateChangeID} -> stateChangeID
+    SnapshotRequested{stateChangeID} -> stateChangeID
+    TransactionReceived{stateChangeID} -> stateChangeID
+    PartySignedSnapshot{stateChangeID} -> stateChangeID
+    SnapshotConfirmed{stateChangeID} -> stateChangeID
+    HeadClosed{stateChangeID} -> stateChangeID
+    HeadIsReadyToFanout{stateChangeID} -> stateChangeID
+    HeadFannedOut{stateChangeID} -> stateChangeID
+    ChainRolledBack{stateChangeID} -> stateChangeID
+    TickObserved{stateChangeID} -> stateChangeID
 
 -- FIXME(Elaine): these stateChangeID fields were added in an attempt to make every StateChanged keep track of its ID
 -- it's not clear how to handle the state for this. but for now the field is kept so that the type of putEvent' can be kept simple, and shouldn't do harm

hydra-node/test/Hydra/HeadLogicSnapshotSpec.hs

@@ -24,7 +24,7 @@ import Hydra.HeadLogic (
   update,
  )
 import Hydra.HeadLogic.Outcome (collectEffects)
-import Hydra.HeadLogicSpec (getState, getStateAndEventID, inOpenState, inOpenState', runEvents, step)
+import Hydra.HeadLogicSpec (getState, getStateAndEventId, inOpenState, inOpenState', runEvents, step)
 import Hydra.Ledger (txId)
 import Hydra.Ledger.Simple (SimpleTx (..), aValidTx, simpleLedger, utxoRef)
 import Hydra.Network.Message (Message (..))
@@ -118,7 +118,7 @@ spec = do
 
         (actualState, actualEventID) <- runEvents (envFor aliceSk) simpleLedger st stEventID $ do
           step $ NetworkEvent defaultTTL alice $ ReqTx tx
-          getStateAndEventID
+          getStateAndEventId
         actualState `shouldBe` st'
         actualEventID `shouldBe` st'EventID
 
@@ -131,7 +131,7 @@ spec = do
           step (NetworkEvent defaultTTL carol $ ReqTx $ aValidTx 1)
           step (ackFrom carolSk carol)
           step (ackFrom aliceSk alice)
-          getStateAndEventID
+          getStateAndEventId
 
         let outcome = update bobEnv simpleLedger headStateEventID headState $ ackFrom bobSk bob
         collectEffects outcome `shouldSatisfy` sendReqSn
@@ -141,7 +141,7 @@ spec = do
           step (NetworkEvent defaultTTL alice $ ReqSn 1 [])
           step (ackFrom carolSk carol)
           step (ackFrom aliceSk alice)
-          getStateAndEventID
+          getStateAndEventId
 
         let outcome = update bobEnv simpleLedger headStateEventID headState $ ackFrom bobSk bob
         collectEffects outcome `shouldNotSatisfy` sendReqSn
@@ -160,7 +160,7 @@ spec = do
           step (ackFrom carolSk carol)
           newTxBeforeSnapshotAcknowledged
           step (ackFrom aliceSk alice)
-          getStateAndEventID
+          getStateAndEventId
 
         let everybodyAcknowleged = update notLeaderEnv simpleLedger headStateEventID headState $ ackFrom bobSk bob
         collectEffects everybodyAcknowleged `shouldNotSatisfy` sendReqSn