feat(ADR-028): refunding transaction fee for certain txs (#125)

Resolves babylonlabs-io/pm#64

This PR introduces the functionality of refunding fee for certain txs,
including BTC headers/checkpoints in BTC timestamping protocol, and
finality signature, BTC delegation inclusion proof, covenant signatures,
undelegation, selective slashing evidence in BTC staking protocol.

The implementation leverages a new key-only KV store in the incentive
module for storing refundable messages, and a new PostHandler for
refunding a tx if all msgs in it are refundable.

Along the way, this PR also adds dependency from BTC light client / BTC
staking modules to the incentive module, and adds relevant e2e tests to
ensure that the tx fee refunding indeed works.

- RFC:
https://github.com/babylonlabs-io/pm/blob/main/rfc/rfc-010-transaction-fee-refund-protocol.md
- ADR:
https://github.com/babylonlabs-io/pm/blob/main/adr/adr-028-transaction-fee-refund-protocol.md

CHANGELOG.md

@@ -41,6 +41,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ### State Machine Breaking
 
+* [#125](https://github.com/babylonlabs-io/babylon/pull/125) Implement ADR-028 and
+refund transaction fee for certain transactions from protocol stakeholders
 * [#107](https://github.com/babylonlabs-io/babylon/pull/107) Implement ADR-027 and
 enable in-protocol minimum gas price
 * [#103](https://github.com/babylonlabs-io/babylon/pull/103) Add token distribution

Makefile

@@ -160,7 +160,6 @@ mockgen_cmd=go run github.com/golang/mock/[email protected]
 mocks: $(MOCKS_DIR) ## Generate mock objects for testing
 	$(mockgen_cmd) -source=x/checkpointing/types/expected_keepers.go -package mocks -destination testutil/mocks/checkpointing_expected_keepers.go
 	$(mockgen_cmd) -source=x/checkpointing/keeper/bls_signer.go -package mocks -destination testutil/mocks/bls_signer.go
-	$(mockgen_cmd) -source=x/zoneconcierge/types/expected_keepers.go -package types -destination x/zoneconcierge/types/mocked_keepers.go
 	$(mockgen_cmd) -source=x/btcstaking/types/expected_keepers.go -package types -destination x/btcstaking/types/mocked_keepers.go
 	$(mockgen_cmd) -source=x/finality/types/expected_keepers.go -package types -destination x/finality/types/mocked_keepers.go
 	$(mockgen_cmd) -source=x/incentive/types/expected_keepers.go -package types -destination x/incentive/types/mocked_keepers.go

app/app.go

@@ -111,6 +111,7 @@ import (
 	"github.com/babylonlabs-io/babylon/x/finality"
 	finalitytypes "github.com/babylonlabs-io/babylon/x/finality/types"
 	"github.com/babylonlabs-io/babylon/x/incentive"
+	incentivekeeper "github.com/babylonlabs-io/babylon/x/incentive/keeper"
 	incentivetypes "github.com/babylonlabs-io/babylon/x/incentive/types"
 	"github.com/babylonlabs-io/babylon/x/monitor"
 	monitortypes "github.com/babylonlabs-io/babylon/x/monitor/types"
@@ -513,6 +514,12 @@ func NewBabylonApp(
 	app.SetEndBlocker(app.EndBlocker)
 	app.SetAnteHandler(anteHandler)
 
+	// set postHandler
+	postHandler := sdk.ChainPostDecorators(
+		incentivekeeper.NewRefundTxDecorator(&app.IncentiveKeeper),
+	)
+	app.SetPostHandler(postHandler)
+
 	// must be before Loading version
 	// requires the snapshot store to be created and registered as a BaseAppOption
 	// see cmd/wasmd/root.go: 206 - 214 approx

app/keepers/keepers.go

@@ -432,6 +432,7 @@ func (ak *AppKeepers) InitKeepers(
 		appCodec,
 		runtime.NewKVStoreService(keys[btclightclienttypes.StoreKey]),
 		*btcConfig,
+		&ak.IncentiveKeeper,
 		authtypes.NewModuleAddress(govtypes.ModuleName).String(),
 	)
 
@@ -498,6 +499,7 @@ func (ak *AppKeepers) InitKeepers(
 		// setting the finality keeper as nil for now
 		// need to set it after finality keeper is initiated
 		nil,
+		&ak.IncentiveKeeper,
 		btcNetParams,
 		authtypes.NewModuleAddress(govtypes.ModuleName).String(),
 	)

test/e2e/btc_staking_e2e_test.go

@@ -228,15 +228,18 @@ func (s *BTCStakingTestSuite) Test2SubmitCovenantSignature() {
 	s.NoError(err)
 
 	for i := 0; i < int(s.covenantQuorum); i++ {
-		nonValidatorNode.AddCovenantSigs(
-			covenantSlashingSigs[i].CovPk,
-			stakingTxHash,
-			covenantSlashingSigs[i].AdaptorSigs,
-			bbn.NewBIP340SignatureFromBTCSig(covUnbondingSigs[i]),
-			covenantUnbondingSlashingSigs[i].AdaptorSigs,
-		)
-		// wait for a block so that above txs take effect
-		nonValidatorNode.WaitForNextBlock()
+		nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+			// add covenant sigs
+			nonValidatorNode.AddCovenantSigs(
+				covenantSlashingSigs[i].CovPk,
+				stakingTxHash,
+				covenantSlashingSigs[i].AdaptorSigs,
+				bbn.NewBIP340SignatureFromBTCSig(covUnbondingSigs[i]),
+				covenantUnbondingSlashingSigs[i].AdaptorSigs,
+			)
+			// wait for a block so that above txs take effect
+			nonValidatorNode.WaitForNextBlock()
+		}, true)
 	}
 
 	// wait for a block so that above txs take effect
@@ -345,18 +348,21 @@ func (s *BTCStakingTestSuite) Test3CommitPublicRandomnessAndSubmitFinalitySignat
 	sig, err := eots.Sign(s.fptBTCSK, randListInfo.SRList[idx], msgToSign)
 	s.NoError(err)
 	eotsSig := bbn.NewSchnorrEOTSSigFromModNScalar(sig)
-	// submit finality signature
-	nonValidatorNode.AddFinalitySig(s.cacheFP.BtcPk, activatedHeight, &randListInfo.PRList[idx], *randListInfo.ProofList[idx].ToProto(), appHash, eotsSig)
 
-	// ensure vote is eventually cast
-	var finalizedBlocks []*ftypes.IndexedBlock
-	s.Eventually(func() bool {
-		finalizedBlocks = nonValidatorNode.QueryListBlocks(ftypes.QueriedBlockStatus_FINALIZED)
-		return len(finalizedBlocks) > 0
-	}, time.Minute, time.Millisecond*50)
-	s.Equal(activatedHeight, finalizedBlocks[0].Height)
-	s.Equal(appHash.Bytes(), finalizedBlocks[0].AppHash)
-	s.T().Logf("the block %d is finalized", activatedHeight)
+	nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+		// submit finality signature
+		nonValidatorNode.AddFinalitySig(s.cacheFP.BtcPk, activatedHeight, &randListInfo.PRList[idx], *randListInfo.ProofList[idx].ToProto(), appHash, eotsSig)
+
+		// ensure vote is eventually cast
+		var finalizedBlocks []*ftypes.IndexedBlock
+		s.Eventually(func() bool {
+			finalizedBlocks = nonValidatorNode.QueryListBlocks(ftypes.QueriedBlockStatus_FINALIZED)
+			return len(finalizedBlocks) > 0
+		}, time.Minute, time.Millisecond*50)
+		s.Equal(activatedHeight, finalizedBlocks[0].Height)
+		s.Equal(appHash.Bytes(), finalizedBlocks[0].AppHash)
+		s.T().Logf("the block %d is finalized", activatedHeight)
+	}, true)
 
 	// ensure finality provider has received rewards after the block is finalised
 	fpRewardGauges, err := nonValidatorNode.QueryRewardGauge(fpBabylonAddr)
@@ -463,10 +469,12 @@ func (s *BTCStakingTestSuite) Test5SubmitStakerUnbonding() {
 	delUnbondingSig, err := activeDel.SignUnbondingTx(params, s.net, s.delBTCSK)
 	s.NoError(err)
 
-	// submit the message for creating BTC undelegation
-	nonValidatorNode.BTCUndelegate(&stakingTxHash, delUnbondingSig)
-	// wait for a block so that above txs take effect
-	nonValidatorNode.WaitForNextBlock()
+	nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+		// submit the message for creating BTC undelegation
+		nonValidatorNode.BTCUndelegate(&stakingTxHash, delUnbondingSig)
+		// wait for a block so that above txs take effect
+		nonValidatorNode.WaitForNextBlock()
+	}, true)
 
 	// Wait for unbonded delegations to be created
 	var unbondedDelsResp []*bstypes.BTCDelegationResponse

test/e2e/btc_staking_pre_approval_e2e_test.go

@@ -220,15 +220,17 @@ func (s *BTCStakingPreApprovalTestSuite) Test2SubmitCovenantSignature() {
 	s.NoError(err)
 
 	for i := 0; i < int(s.covenantQuorum); i++ {
-		nonValidatorNode.AddCovenantSigs(
-			covenantSlashingSigs[i].CovPk,
-			stakingTxHash,
-			covenantSlashingSigs[i].AdaptorSigs,
-			bbn.NewBIP340SignatureFromBTCSig(covUnbondingSigs[i]),
-			covenantUnbondingSlashingSigs[i].AdaptorSigs,
-		)
-		// wait for a block so that above txs take effect
-		nonValidatorNode.WaitForNextBlock()
+		nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+			nonValidatorNode.AddCovenantSigs(
+				covenantSlashingSigs[i].CovPk,
+				stakingTxHash,
+				covenantSlashingSigs[i].AdaptorSigs,
+				bbn.NewBIP340SignatureFromBTCSig(covUnbondingSigs[i]),
+				covenantUnbondingSlashingSigs[i].AdaptorSigs,
+			)
+			// wait for a block so that above txs take effect
+			nonValidatorNode.WaitForNextBlock()
+		}, true)
 	}
 
 	// wait for a block so that above txs take effect
@@ -266,13 +268,14 @@ func (s *BTCStakingPreApprovalTestSuite) Test3SendStakingTransctionInclusionProo
 	s.NoError(err)
 	stakingTxHash := stakingMsgTx.TxHash()
 
-	nonValidatorNode.AddBTCDelegationInclusionProof(
-		&stakingTxHash,
-		s.cachedInclusionProof,
-	)
-
-	nonValidatorNode.WaitForNextBlock()
-	nonValidatorNode.WaitForNextBlock()
+	nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+		nonValidatorNode.AddBTCDelegationInclusionProof(
+			&stakingTxHash,
+			s.cachedInclusionProof,
+		)
+		nonValidatorNode.WaitForNextBlock()
+		nonValidatorNode.WaitForNextBlock()
+	}, true)
 
 	activeBTCDelegations := nonValidatorNode.QueryActiveDelegations()
 	s.Len(activeBTCDelegations, 1)
@@ -366,17 +369,28 @@ func (s *BTCStakingPreApprovalTestSuite) Test4CommitPublicRandomnessAndSubmitFin
 	s.NoError(err)
 	eotsSig := bbn.NewSchnorrEOTSSigFromModNScalar(sig)
 	// submit finality signature
-	nonValidatorNode.AddFinalitySig(s.cacheFP.BtcPk, activatedHeight, &randListInfo.PRList[idx], *randListInfo.ProofList[idx].ToProto(), appHash, eotsSig)
-
-	// ensure vote is eventually cast
-	var finalizedBlocks []*ftypes.IndexedBlock
-	s.Eventually(func() bool {
-		finalizedBlocks = nonValidatorNode.QueryListBlocks(ftypes.QueriedBlockStatus_FINALIZED)
-		return len(finalizedBlocks) > 0
-	}, time.Minute, time.Millisecond*50)
-	s.Equal(activatedHeight, finalizedBlocks[0].Height)
-	s.Equal(appHash.Bytes(), finalizedBlocks[0].AppHash)
-	s.T().Logf("the block %d is finalized", activatedHeight)
+	nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+		nonValidatorNode.AddFinalitySig(s.cacheFP.BtcPk, activatedHeight, &randListInfo.PRList[idx], *randListInfo.ProofList[idx].ToProto(), appHash, eotsSig)
+
+		// ensure vote is eventually cast
+		var finalizedBlocks []*ftypes.IndexedBlock
+		s.Eventually(func() bool {
+			finalizedBlocks = nonValidatorNode.QueryListBlocks(ftypes.QueriedBlockStatus_FINALIZED)
+			return len(finalizedBlocks) > 0
+		}, time.Minute, time.Millisecond*50)
+		s.Equal(activatedHeight, finalizedBlocks[0].Height)
+		s.Equal(appHash.Bytes(), finalizedBlocks[0].AppHash)
+		s.T().Logf("the block %d is finalized", activatedHeight)
+	}, true)
+
+	// submit an invalid finality signature, and tx should NOT be refunded
+	nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+		_, pk, err := datagen.GenRandomBTCKeyPair(s.r)
+		s.NoError(err)
+		btcPK := bbn.NewBIP340PubKeyFromBTCPK(pk)
+		nonValidatorNode.AddFinalitySig(btcPK, activatedHeight, &randListInfo.PRList[idx], *randListInfo.ProofList[idx].ToProto(), appHash, eotsSig)
+		nonValidatorNode.WaitForNextBlock()
+	}, false)
 
 	// ensure finality provider has received rewards after the block is finalised
 	fpRewardGauges, err := nonValidatorNode.QueryRewardGauge(fpBabylonAddr)
@@ -483,10 +497,12 @@ func (s *BTCStakingPreApprovalTestSuite) Test5SubmitStakerUnbonding() {
 	delUnbondingSig, err := activeDel.SignUnbondingTx(params, s.net, s.delBTCSK)
 	s.NoError(err)
 
-	// submit the message for creating BTC undelegation
-	nonValidatorNode.BTCUndelegate(&stakingTxHash, delUnbondingSig)
-	// wait for a block so that above txs take effect
-	nonValidatorNode.WaitForNextBlock()
+	nonValidatorNode.SubmitRefundableTxWithAssertion(func() {
+		// submit the message for creating BTC undelegation
+		nonValidatorNode.BTCUndelegate(&stakingTxHash, delUnbondingSig)
+		// wait for a block so that above txs take effect
+		nonValidatorNode.WaitForNextBlock()
+	}, true)
 
 	// Wait for unbonded delegations to be created
 	var unbondedDelsResp []*bstypes.BTCDelegationResponse

test/e2e/configurer/chain/commands.go

@@ -232,9 +232,13 @@ func (n *NodeConfig) FinalizeSealedEpochs(startEpoch uint64, lastEpoch uint64) {
 		tx2 := datagen.CreatOpReturnTransaction(r, p2)
 		opReturn2 := datagen.CreateBlockWithTransaction(r, opReturn1.HeaderBytes.ToBlockHeader(), tx2)
 
-		n.InsertHeader(&opReturn1.HeaderBytes)
-		n.InsertHeader(&opReturn2.HeaderBytes)
-		n.InsertProofs(opReturn1.SpvProof, opReturn2.SpvProof)
+		n.SubmitRefundableTxWithAssertion(func() {
+			n.InsertHeader(&opReturn1.HeaderBytes)
+			n.InsertHeader(&opReturn2.HeaderBytes)
+		}, true)
+		n.SubmitRefundableTxWithAssertion(func() {
+			n.InsertProofs(opReturn1.SpvProof, opReturn2.SpvProof)
+		}, true)
 
 		n.WaitForCondition(func() bool {
 			ckpt, err := n.QueryRawCheckpoint(checkpoint.Ckpt.EpochNum)
@@ -444,3 +448,26 @@ func (n *NodeConfig) TxGovVote(from string, propID int, option govv1.VoteOption,
 
 	n.LogActionF("successfully submitted vote %s to prop %d", option, propID)
 }
+
+// submitRefundableTxWithAssertion submits a refundable transaction,
+// and asserts that the tx fee is refunded
+func (n *NodeConfig) SubmitRefundableTxWithAssertion(
+	f func(),
+	shouldBeRefunded bool,
+) {
+	// balance before submitting the refundable tx
+	submitterBalanceBefore, err := n.QueryBalances(n.PublicAddress)
+	require.NoError(n.t, err)
+
+	// submit refundable tx
+	f()
+
+	// ensure the tx fee is refunded and the balance is not changed
+	submitterBalanceAfter, err := n.QueryBalances(n.PublicAddress)
+	require.NoError(n.t, err)
+	if shouldBeRefunded {
+		require.Equal(n.t, submitterBalanceBefore, submitterBalanceAfter)
+	} else {
+		require.True(n.t, submitterBalanceBefore.IsAllGT(submitterBalanceAfter))
+	}
+}

test/e2e/configurer/chain/commands_btcstaking.go

@@ -150,7 +150,7 @@ func (n *NodeConfig) AddCovenantSigs(covPK *bbn.BIP340PubKey, stakingTxHash stri
 	// used key
 	cmd = append(cmd, "--from=val")
 	// gas
-	cmd = append(cmd, "--gas=auto", "--gas-adjustment=1.3")
+	cmd = append(cmd, "--gas=auto", "--gas-adjustment=2")
 
 	_, _, err := n.containerManager.ExecTxCmd(n.t, n.chainId, n.Name, cmd)
 	require.NoError(n.t, err)

testutil/keeper/btclightclient.go

@@ -1,6 +1,7 @@
 package keeper
 
 import (
+	"context"
 	"testing"
 
 	"cosmossdk.io/core/header"
@@ -26,6 +27,10 @@ import (
 	btclightclientt "github.com/babylonlabs-io/babylon/x/btclightclient/types"
 )
 
+type MockIncentiveKeeper struct{}
+
+func (mik MockIncentiveKeeper) IndexRefundableMsg(ctx context.Context, msg sdk.Msg) {}
+
 func BTCLightClientKeeper(t testing.TB) (*btclightclientk.Keeper, sdk.Context) {
 	k, ctx, _ := BTCLightClientKeeperWithCustomParams(t, btclightclientt.DefaultParams())
 	return k, ctx
@@ -40,7 +45,10 @@ func NewBTCHeaderBytesList(chain []*wire.BlockHeader) []bbn.BTCHeaderBytes {
 	return chainBytes
 }
 
-func BTCLightClientKeeperWithCustomParams(t testing.TB, p btclightclientt.Params) (*btclightclientk.Keeper, sdk.Context, corestore.KVStoreService) {
+func BTCLightClientKeeperWithCustomParams(
+	t testing.TB,
+	p btclightclientt.Params,
+) (*btclightclientk.Keeper, sdk.Context, corestore.KVStoreService) {
 	storeKey := storetypes.NewKVStoreKey(btclightclientt.StoreKey)
 
 	db := dbm.NewMemDB()
@@ -52,12 +60,12 @@ func BTCLightClientKeeperWithCustomParams(t testing.TB, p btclightclientt.Params
 	cdc := codec.NewProtoCodec(registry)
 
 	testCfg := bbn.ParseBtcOptionsFromConfig(bapp.TmpAppOptions())
-
 	stServ := runtime.NewKVStoreService(storeKey)
 	k := btclightclientk.NewKeeper(
 		cdc,
 		stServ,
 		testCfg,
+		&MockIncentiveKeeper{},
 		authtypes.NewModuleAddress(govtypes.ModuleName).String(),
 	)
 

testutil/keeper/btcstaking.go

@@ -28,6 +28,7 @@ func BTCStakingKeeper(
 	btclcKeeper types.BTCLightClientKeeper,
 	btccKeeper types.BtcCheckpointKeeper,
 	finalityKeeper types.FinalityKeeper,
+	iKeeper types.IncentiveKeeper,
 ) (*keeper.Keeper, sdk.Context) {
 	storeKey := storetypes.NewKVStoreKey(types.StoreKey)
 
@@ -45,6 +46,7 @@ func BTCStakingKeeper(
 		btclcKeeper,
 		btccKeeper,
 		finalityKeeper,
+		iKeeper,
 		&chaincfg.SimNetParams,
 		authtypes.NewModuleAddress(govtypes.ModuleName).String(),
 	)

x/btccheckpoint/keeper/msg_server.go

@@ -22,7 +22,7 @@ func NewMsgServerImpl(keeper Keeper) types.MsgServer {
 }
 
 // TODO at some point add proper logging of error
-// TODO emit some events for external consumers. Those should be probably emited
+// TODO emit some events for external consumers. Those should be probably emitted
 // at EndBlockerCallback
 func (ms msgServer) InsertBTCSpvProof(ctx context.Context, req *types.MsgInsertBTCSpvProof) (*types.MsgInsertBTCSpvProofResponse, error) {
 
@@ -92,6 +92,11 @@ func (ms msgServer) InsertBTCSpvProof(ctx context.Context, req *types.MsgInsertB
 		return nil, err
 	}
 
+	// At this point, the BTC checkpoint is considered the first valid submission
+	// for the epoch.
+	// Thus, we can safely consider this message as refundable
+	ms.k.incentiveKeeper.IndexRefundableMsg(sdkCtx, req)
+
 	return &types.MsgInsertBTCSpvProofResponse{}, nil
 }
 

x/btccheckpoint/types/expected_keepers.go

@@ -2,8 +2,10 @@ package types
 
 import (
 	"context"
+
 	txformat "github.com/babylonlabs-io/babylon/btctxformatter"
 	bbn "github.com/babylonlabs-io/babylon/types"
+	sdk "github.com/cosmos/cosmos-sdk/types"
 )
 
 type BTCLightClientKeeper interface {
@@ -40,4 +42,5 @@ type CheckpointingKeeper interface {
 
 type IncentiveKeeper interface {
 	RewardBTCTimestamping(ctx context.Context, epoch uint64, rewardDistInfo *RewardDistInfo)
+	IndexRefundableMsg(ctx context.Context, msg sdk.Msg)
 }