Move snapshot number from Contest redeemer to Closed datum in Head sc…

…ript
cardano-scaling · Jan 16, 2023 · 4fc64f7 · 4fc64f7
1 parent 9cb4e1b
commit 4fc64f7
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Showing 4 changed files with 49 additions and 21 deletions.
diff --git a/hydra-node/src/Hydra/Chain/Direct/Tx.hs b/hydra-node/src/Hydra/Chain/Direct/Tx.hs
@@ -408,8 +408,7 @@ contestTx vk Snapshot{number, utxo} sig (slotNo, _) ClosedThreadOutput{closedThr
   headRedeemer =
     toScriptData
       Head.Contest
-        { snapshotNumber = toInteger number
-        , signature = toPlutusSignatures sig
+        { signature = toPlutusSignatures sig
         , utxoHash
         }
   headOutputAfter =
@@ -830,9 +829,10 @@ observeContestTx utxo tx = do
   datum <- fromData $ toPlutusData oldHeadDatum
   headId <- findStateToken headOutput
   case (datum, redeemer) of
-    (Head.Closed{}, Head.Contest{snapshotNumber = onChainSnapshotNumber}) -> do
+    (Head.Closed{}, Head.Contest{}) -> do
       (newHeadInput, newHeadOutput) <- findTxOutByScript @PlutusScriptV2 (utxoFromTx tx) headScript
       newHeadDatum <- lookupScriptData tx newHeadOutput
+      let onChainSnapshotNumber = closedSnapshotNumber newHeadDatum
       pure
         ContestObservation
           { contestedThreadOutput =
@@ -847,6 +847,11 @@ observeContestTx utxo tx = do
  where
   headScript = fromPlutusScript Head.validatorScript
 
+  closedSnapshotNumber headDatum =
+    case fromData $ toPlutusData headDatum of
+      Just Head.Closed{snapshotNumber} -> snapshotNumber
+      _ -> error "wrong state in output datum"
+
 data FanoutObservation = FanoutObservation
 
 -- | Identify a fanout tx by lookup up the input spending the Head output and

diff --git a/hydra-node/test/Hydra/Chain/Direct/Contract/Contest.hs b/hydra-node/test/Hydra/Chain/Direct/Contract/Contest.hs
@@ -177,20 +177,29 @@ genContestMutation
           mutatedSignature <- arbitrary :: Gen (MultiSignature (Snapshot Tx))
           pure $
             Head.Contest
-              { snapshotNumber = toInteger healthyContestSnapshotNumber
-              , utxoHash = healthyContestUTxOHash
+              { utxoHash = healthyContestUTxOHash
               , signature = toPlutusSignatures mutatedSignature
               }
-      , SomeMutation MutateToNonNewerSnapshot . ChangeHeadRedeemer <$> do
+      , SomeMutation MutateToNonNewerSnapshot <$> do
           mutatedSnapshotNumber <- choose (0, toInteger healthyClosedSnapshotNumber)
           pure $
-            Head.Contest
-              { snapshotNumber = mutatedSnapshotNumber
-              , utxoHash = healthyContestUTxOHash
-              , signature =
-                  toPlutusSignatures $
-                    healthySignature (fromInteger mutatedSnapshotNumber)
-              }
+            Changes
+              [ ChangeHeadDatum $
+                  Head.Closed
+                    { snapshotNumber = mutatedSnapshotNumber
+                    , utxoHash = healthyClosedUTxOHash
+                    , parties = healthyOnChainParties
+                    , contestationDeadline = posixFromUTCTime healthyContestationDeadline
+                    , headId = toPlutusCurrencySymbol testPolicyId
+                    }
+              , ChangeHeadRedeemer $
+                  Head.Contest
+                    { utxoHash = healthyContestUTxOHash
+                    , signature =
+                        toPlutusSignatures $
+                          healthySignature (fromInteger mutatedSnapshotNumber)
+                    }
+              ]
       , SomeMutation MutateRequiredSigner <$> do
           newSigner <- verificationKeyHash <$> genVerificationKey
           pure $ ChangeRequiredSigners [newSigner]

diff --git a/hydra-plutus/src/Hydra/Contract/Head.hs b/hydra-plutus/src/Hydra/Contract/Head.hs
@@ -48,6 +48,7 @@ import qualified PlutusTx.AssocMap as Map
 import qualified PlutusTx.Builtins as Builtins
 
 -- REVIEW: Functions not re-exported "as V2", but using the same data types.
+
 import Plutus.V1.Ledger.Time (fromMilliSeconds)
 import Plutus.V1.Ledger.Value (assetClass, assetClassValue, valueOf)
 
@@ -72,8 +73,8 @@ headValidator oldState input ctx =
       checkAbort ctx headId parties
     (Open{parties, utxoHash = initialUtxoHash, contestationPeriod, headId}, Close{snapshotNumber, utxoHash = closedUtxoHash, signature}) ->
       checkClose ctx parties initialUtxoHash snapshotNumber closedUtxoHash signature contestationPeriod headId
-    (Closed{parties, snapshotNumber = closedSnapshotNumber, contestationDeadline, headId}, Contest{snapshotNumber = contestSnapshotNumber, utxoHash = contestUtxoHash, signature}) ->
-      checkContest ctx contestationDeadline parties closedSnapshotNumber contestSnapshotNumber contestUtxoHash signature headId
+    (Closed{parties, snapshotNumber = closedSnapshotNumber, contestationDeadline, headId}, Contest{utxoHash = contestUtxoHash, signature}) ->
+      checkContest ctx contestationDeadline parties closedSnapshotNumber contestUtxoHash signature headId
     (Closed{utxoHash, contestationDeadline}, Fanout{numberOfFanoutOutputs}) ->
       checkFanout utxoHash contestationDeadline numberOfFanoutOutputs ctx
     _ ->
@@ -311,16 +312,13 @@ checkContest ::
   POSIXTime ->
   [Party] ->
   -- | Snapshot number of the closed state.
-  -- XXX: Having two snapshot numbers here is FRAGILE
-  SnapshotNumber ->
-  -- | Snapshot number of the contestin snapshot.
   SnapshotNumber ->
   BuiltinByteString ->
   [Signature] ->
   -- | Head id
   CurrencySymbol ->
   Bool
-checkContest ctx@ScriptContext{scriptContextTxInfo} contestationDeadline parties closedSnapshotNumber contestSnapshotNumber contestUtxoHash sig headPolicyId =
+checkContest ctx@ScriptContext{scriptContextTxInfo} contestationDeadline parties closedSnapshotNumber contestUtxoHash sig headPolicyId =
   mustBeNewer
     && mustBeMultiSigned
     && checkHeadOutputDatum
@@ -332,6 +330,23 @@ checkContest ctx@ScriptContext{scriptContextTxInfo} contestationDeadline parties
  where
   outValue =
     maybe mempty (txOutValue . txInInfoResolved) $ findOwnInput ctx
+
+  contestSnapshotNumber =
+    case fromBuiltinData @DatumType $ getDatum continuingDatum of
+      Just Closed{snapshotNumber} -> snapshotNumber
+      _ -> traceError "wrong state in output datum"
+
+  continuingDatum =
+    case ownDatum of
+      NoOutputDatum -> traceError "no output datum"
+      OutputDatumHash dh -> fromMaybe (traceError "datum not found") $ findDatum dh scriptContextTxInfo
+      OutputDatum d -> d
+   where
+    ownDatum =
+      case getContinuingOutputs ctx of
+        [o] -> txOutDatum o
+        _ -> traceError "expected only one head output"
+
   mustBeNewer =
     traceIfFalse "too old snapshot" $ contestSnapshotNumber > closedSnapshotNumber
 

diff --git a/hydra-plutus/src/Hydra/Contract/HeadState.hs b/hydra-plutus/src/Hydra/Contract/HeadState.hs
@@ -52,8 +52,7 @@ data Input
       , signature :: [Signature]
       }
   | Contest
-      { snapshotNumber :: SnapshotNumber
-      , utxoHash :: Hash
+      { utxoHash :: Hash
       , signature :: [Signature]
       }
   | Abort