btcstaking: recording slashed height and disallowing slashed validato…

…r to vote (#50)

proto/babylon/btcstaking/v1/btcstaking.proto

@@ -15,8 +15,14 @@ message BTCValidator {
     bytes btc_pk = 2 [ (gogoproto.customtype) = "github.com/babylonchain/babylon/types.BIP340PubKey" ];
     // pop is the proof of possession of babylon_pk and btc_pk
     ProofOfPossession pop = 3;
-    // slashed indicates whether the BTC validator is slashed or not
-    bool slashed = 4;
+    // slashed_babylon_height indicates the Babylon height when
+    // the BTC validator is slashed.
+    // if it's 0 then the BTC validator is not slashed
+    uint64 slashed_babylon_height = 4;
+    // slashed_btc_height indicates the BTC height when
+    // the BTC validator is slashed.
+    // if it's 0 then the BTC validator is not slashed
+    uint64 slashed_btc_height = 5;
 }
 
 // BTCValidatorWithMeta wraps the BTCValidator with meta data.
@@ -28,6 +34,14 @@ message BTCValidatorWithMeta {
     uint64 height = 2;
     // voting_power is the voting power of this BTC validator at the given height
     uint64 voting_power = 3;
+    // slashed_babylon_height indicates the Babylon height when
+    // the BTC validator is slashed.
+    // if it's 0 then the BTC validator is not slashed
+    uint64 slashed_babylon_height = 4;
+    // slashed_btc_height indicates the BTC height when
+    // the BTC validator is slashed.
+    // if it's 0 then the BTC validator is not slashed
+    uint64 slashed_btc_height = 5;
 }
 
 // BTCDelegation defines a BTC delegation

x/btcstaking/keeper/btc_validators.go

@@ -1,6 +1,8 @@
 package keeper
 
 import (
+	"fmt"
+
 	"github.com/babylonchain/babylon/x/btcstaking/types"
 	"github.com/cosmos/cosmos-sdk/store/prefix"
 	sdk "github.com/cosmos/cosmos-sdk/types"
@@ -38,10 +40,14 @@ func (k Keeper) SlashBTCValidator(ctx sdk.Context, valBTCPK []byte) error {
 	if err != nil {
 		return err
 	}
-	if btcVal.Slashed {
+	if btcVal.IsSlashed() {
 		return types.ErrBTCValAlreadySlashed
 	}
-	btcVal.Slashed = true
+	btcVal.SlashedBabylonHeight = uint64(ctx.BlockHeight())
+	btcVal.SlashedBtcHeight, err = k.GetCurrentBTCHeight(ctx)
+	if err != nil {
+		panic(fmt.Errorf("failed to get current BTC height: %w", err))
+	}
 	k.SetBTCValidator(ctx, btcVal)
 	return nil
 }

x/btcstaking/keeper/grpc_query.go

@@ -127,9 +127,11 @@ func (k Keeper) ActiveBTCValidatorsAtHeight(ctx context.Context, req *types.Quer
 		votingPower := k.GetVotingPower(sdkCtx, key, req.Height)
 		if votingPower > 0 {
 			btcValidatorWithMeta := types.BTCValidatorWithMeta{
-				BtcPk:       btcValidator.BtcPk,
-				Height:      req.Height,
-				VotingPower: votingPower,
+				BtcPk:                btcValidator.BtcPk,
+				Height:               req.Height,
+				VotingPower:          votingPower,
+				SlashedBabylonHeight: btcValidator.SlashedBabylonHeight,
+				SlashedBtcHeight:     btcValidator.SlashedBtcHeight,
 			}
 			btcValidatorsWithMeta = append(btcValidatorsWithMeta, &btcValidatorWithMeta)
 		}

x/btcstaking/keeper/voting_power_table.go

@@ -37,7 +37,7 @@ func (k Keeper) RecordVotingPowerTable(ctx sdk.Context) {
 			// failed to get a BTC validator with voting power is a programming error
 			panic(err)
 		}
-		if btcVal.Slashed {
+		if btcVal.IsSlashed() {
 			// slashed BTC validator is removed from BTC validator set
 			continue
 		}

x/btcstaking/keeper/voting_power_table_test.go

@@ -60,7 +60,9 @@ func FuzzVotingPowerTable(f *testing.F) {
 			}
 		}
 
-		// Case 1: assert none of validators has voting power (since BTC height is 0)
+		/*
+			Case 1: assert none of validators has voting power (since BTC height is 0)
+		*/
 		babylonHeight := datagen.RandomInt(r, 10) + 1
 		ctx = ctx.WithBlockHeight(int64(babylonHeight))
 		btclcKeeper.EXPECT().GetTipInfo(gomock.Any()).Return(&btclctypes.BTCHeaderInfo{Height: 0}).Times(1)
@@ -75,7 +77,9 @@ func FuzzVotingPowerTable(f *testing.F) {
 		_, err = keeper.GetBTCStakingActivatedHeight(ctx)
 		require.Error(t, err)
 
-		// Case 2: move to 1st BTC block, then assert the first numBTCValsWithVotingPower validators have voting power
+		/*
+			Case 2: move to 1st BTC block, then assert the first numBTCValsWithVotingPower validators have voting power
+		*/
 		babylonHeight += datagen.RandomInt(r, 10) + 1
 		ctx = ctx.WithBlockHeight(int64(babylonHeight))
 		btclcKeeper.EXPECT().GetTipInfo(gomock.Any()).Return(&btclctypes.BTCHeaderInfo{Height: 1}).Times(1)
@@ -102,19 +106,23 @@ func FuzzVotingPowerTable(f *testing.F) {
 		require.NoError(t, err)
 		require.Equal(t, babylonHeight, activatedHeight)
 
-		// Case 3: move to 2nd BTC block and slash a random BTC validator,
-		// then assert the slashed BTC validator does not have voting power
-		babylonHeight += datagen.RandomInt(r, 10) + 1
-		ctx = ctx.WithBlockHeight(int64(babylonHeight))
-		btclcKeeper.EXPECT().GetTipInfo(gomock.Any()).Return(&btclctypes.BTCHeaderInfo{Height: 2}).Times(1)
+		/*
+			Case 3: slash a random BTC validator and move on
+			then assert the slashed BTC validator does not have voting power
+		*/
 		// slash a random BTC validator
 		slashedIdx := datagen.RandomInt(r, int(numBTCValsWithVotingPower))
 		slashedVal := btcVals[slashedIdx]
 		err = keeper.SlashBTCValidator(ctx, slashedVal.BtcPk.MustMarshal())
 		require.NoError(t, err)
+		// move to later Babylon height and 2nd BTC height
+		babylonHeight += datagen.RandomInt(r, 10) + 1
+		ctx = ctx.WithBlockHeight(int64(babylonHeight))
+		btclcKeeper.EXPECT().GetTipInfo(gomock.Any()).Return(&btclctypes.BTCHeaderInfo{Height: 2}).Times(1)
 		// index height and record power table
 		keeper.IndexBTCHeight(ctx)
 		keeper.RecordVotingPowerTable(ctx)
+		// check if the slashed BTC validator's voting power becomes zero
 		for i := uint64(0); i < numBTCValsWithVotingPower; i++ {
 			power := keeper.GetVotingPower(ctx, *btcVals[i].BtcPk, babylonHeight)
 			if i == slashedIdx {
@@ -139,7 +147,9 @@ func FuzzVotingPowerTable(f *testing.F) {
 			require.Equal(t, powerTable[btcVals[i].BtcPk.MarshalHex()], power)
 		}
 
-		// Case 4: move to 999th BTC block, then assert none of validators has voting power (since end height - w < BTC height)
+		/*
+			Case 4: move to 999th BTC block, then assert none of validators has voting power (since end height - w < BTC height)
+		*/
 		babylonHeight += datagen.RandomInt(r, 10) + 1
 		ctx = ctx.WithBlockHeight(int64(babylonHeight))
 		btclcKeeper.EXPECT().GetTipInfo(gomock.Any()).Return(&btclctypes.BTCHeaderInfo{Height: 999}).Times(1)

x/btcstaking/types/btcstaking.go

@@ -12,6 +12,10 @@ import (
 	"github.com/btcsuite/btcd/wire"
 )
 
+func (v *BTCValidator) IsSlashed() bool {
+	return v.SlashedBabylonHeight > 0
+}
+
 func (v *BTCValidator) ValidateBasic() error {
 	// ensure fields are non-empty and well-formatted
 	if v.BabylonPk == nil {