feat: bitcoin depositor fee V2 to achieve better dev experience (#2765)

* implementation of bitcoin depositor fee V2

* add changelog entry

* attached tracking issue# for TODO; formatted comments to be go idiomatic

* disable live test in CI

* group transaction size related constants to make comments more concise

* reorder bitcoin fee related constants

* replace GetRecentBlockhash with GetLatestBlockhash; add check on Vsize; misc

changelog.md

@@ -71,6 +71,7 @@
 * [2524](https://github.com/zeta-chain/node/pull/2524) - add inscription envelop parsing 
 * [2560](https://github.com/zeta-chain/node/pull/2560) - add support for Solana SOL token withdraw
 * [2533](https://github.com/zeta-chain/node/pull/2533) - parse memo from both OP_RETURN and inscription
+* [2765](https://github.com/zeta-chain/node/pull/2765) - bitcoin depositor fee improvement
 
 ### Refactor
 

e2e/runner/solana.go

@@ -65,7 +65,7 @@ func (r *E2ERunner) CreateSignedTransaction(
 	privateKey solana.PrivateKey,
 ) *solana.Transaction {
 	// get a recent blockhash
-	recent, err := r.SolanaClient.GetRecentBlockhash(r.Ctx, rpc.CommitmentFinalized)
+	recent, err := r.SolanaClient.GetLatestBlockhash(r.Ctx, rpc.CommitmentFinalized)
 	require.NoError(r, err)
 
 	// create the initialize transaction

zetaclient/chains/bitcoin/fee.go

@@ -15,27 +15,42 @@ import (
 	"github.com/rs/zerolog"
 
 	"github.com/zeta-chain/zetacore/pkg/chains"
+	"github.com/zeta-chain/zetacore/zetaclient/chains/bitcoin/rpc"
+	"github.com/zeta-chain/zetacore/zetaclient/chains/interfaces"
 	clientcommon "github.com/zeta-chain/zetacore/zetaclient/common"
 )
 
 const (
-	bytesPerKB              = 1000
-	bytesPerInput           = 41  // each input is 41 bytes
-	bytesPerOutputP2TR      = 43  // each P2TR output is 43 bytes
-	bytesPerOutputP2WSH     = 43  // each P2WSH output is 43 bytes
-	bytesPerOutputP2WPKH    = 31  // each P2WPKH output is 31 bytes
-	bytesPerOutputP2SH      = 32  // each P2SH output is 32 bytes
-	bytesPerOutputP2PKH     = 34  // each P2PKH output is 34 bytes
-	bytesPerOutputAvg       = 37  // average size of all above types of outputs (36.6 bytes)
-	bytes1stWitness         = 110 // the 1st witness incurs about 110 bytes and it may vary
-	bytesPerWitness         = 108 // each additional witness incurs about 108 bytes and it may vary
-	defaultDepositorFeeRate = 20  // 20 sat/byte is the default depositor fee rate
-
-	OutboundBytesMin = uint64(239)  // 239vB == EstimateSegWitTxSize(2, 2, toP2WPKH)
-	OutboundBytesMax = uint64(1543) // 1543v == EstimateSegWitTxSize(21, 2, toP2TR)
-	OutboundBytesAvg = uint64(245)  // 245vB is a suggested gas limit for zetacore
-
-	DynamicDepositorFeeHeight = 834500 // DynamicDepositorFeeHeight contains the starting height (Bitcoin mainnet) from which dynamic depositor fee will take effect
+	// constants related to transaction size calculations
+	bytesPerKB           = 1000
+	bytesPerInput        = 41           // each input is 41 bytes
+	bytesPerOutputP2TR   = 43           // each P2TR output is 43 bytes
+	bytesPerOutputP2WSH  = 43           // each P2WSH output is 43 bytes
+	bytesPerOutputP2WPKH = 31           // each P2WPKH output is 31 bytes
+	bytesPerOutputP2SH   = 32           // each P2SH output is 32 bytes
+	bytesPerOutputP2PKH  = 34           // each P2PKH output is 34 bytes
+	bytesPerOutputAvg    = 37           // average size of all above types of outputs (36.6 bytes)
+	bytes1stWitness      = 110          // the 1st witness incurs about 110 bytes and it may vary
+	bytesPerWitness      = 108          // each additional witness incurs about 108 bytes and it may vary
+	OutboundBytesMin     = uint64(239)  // 239vB == EstimateSegWitTxSize(2, 2, toP2WPKH)
+	OutboundBytesMax     = uint64(1543) // 1543v == EstimateSegWitTxSize(21, 2, toP2TR)
+	OutboundBytesAvg     = uint64(245)  // 245vB is a suggested gas limit for zetacore
+
+	// defaultDepositorFeeRate is the default fee rate for depositor fee, 20 sat/vB
+	defaultDepositorFeeRate = 20
+
+	// defaultTestnetFeeRate is the default fee rate for testnet, 10 sat/vB
+	defaultTestnetFeeRate = 10
+
+	// feeRateCountBackBlocks is the default number of blocks to look back for fee rate estimation
+	feeRateCountBackBlocks = 2
+
+	// DynamicDepositorFeeHeight is the mainnet height from which dynamic depositor fee V1 is applied
+	DynamicDepositorFeeHeight = 834500
+
+	// DynamicDepositorFeeHeightV2 is the mainnet height from which dynamic depositor fee V2 is applied
+	// Height 863400 is approximately a month away (2024-09-28) from the time of writing, allowing enough time for the upgrade
+	DynamicDepositorFeeHeightV2 = 863400
 )
 
 var (
@@ -239,3 +254,73 @@ func CalcDepositorFee(
 
 	return DepositorFee(feeRate)
 }
+
+// CalcDepositorFeeV2 calculates the depositor fee for a given tx result
+func CalcDepositorFeeV2(
+	rpcClient interfaces.BTCRPCClient,
+	rawResult *btcjson.TxRawResult,
+	netParams *chaincfg.Params,
+) (float64, error) {
+	// use default fee for regnet
+	if netParams.Name == chaincfg.RegressionNetParams.Name {
+		return DefaultDepositorFee, nil
+	}
+
+	// get fee rate of the transaction
+	_, feeRate, err := rpc.GetTransactionFeeAndRate(rpcClient, rawResult)
+	if err != nil {
+		return 0, errors.Wrapf(err, "error getting fee rate for tx %s", rawResult.Txid)
+	}
+
+	// apply gas price multiplier
+	// #nosec G115 always in range
+	feeRate = int64(float64(feeRate) * clientcommon.BTCOutboundGasPriceMultiplier)
+
+	return DepositorFee(feeRate), nil
+}
+
+// GetRecentFeeRate gets the highest fee rate from recent blocks
+// Note: this method should be used for testnet ONLY
+func GetRecentFeeRate(rpcClient interfaces.BTCRPCClient, netParams *chaincfg.Params) (uint64, error) {
+	// should avoid using this method for mainnet
+	if netParams.Name == chaincfg.MainNetParams.Name {
+		return 0, errors.New("GetRecentFeeRate should not be used for mainnet")
+	}
+
+	// get the current block number
+	blockNumber, err := rpcClient.GetBlockCount()
+	if err != nil {
+		return 0, err
+	}
+
+	// get the highest fee rate among recent 'countBack' blocks to avoid underestimation
+	highestRate := int64(0)
+	for i := int64(0); i < feeRateCountBackBlocks; i++ {
+		// get the block
+		hash, err := rpcClient.GetBlockHash(blockNumber - i)
+		if err != nil {
+			return 0, err
+		}
+		block, err := rpcClient.GetBlockVerboseTx(hash)
+		if err != nil {
+			return 0, err
+		}
+
+		// computes the average fee rate of the block and take the higher rate
+		avgFeeRate, err := CalcBlockAvgFeeRate(block, netParams)
+		if err != nil {
+			return 0, err
+		}
+		if avgFeeRate > highestRate {
+			highestRate = avgFeeRate
+		}
+	}
+
+	// use 10 sat/byte as default estimation if recent fee rate drops to 0
+	if highestRate == 0 {
+		highestRate = defaultTestnetFeeRate
+	}
+
+	// #nosec G115 always in range
+	return uint64(highestRate), nil
+}

zetaclient/chains/bitcoin/observer/inbound.go

@@ -421,6 +421,19 @@ func GetBtcEvent(
 				return nil, nil
 			}
 
+			// switch to depositor fee V2 if
+			// 1. it is bitcoin testnet, or
+			// 2. it is bitcoin mainnet and upgrade height is reached
+			// TODO: remove CalcDepositorFeeV1 and below conditions after the upgrade height
+			// https://github.com/zeta-chain/node/issues/2766
+			if netParams.Name == chaincfg.TestNet3Params.Name ||
+				(netParams.Name == chaincfg.MainNetParams.Name && blockNumber >= bitcoin.DynamicDepositorFeeHeightV2) {
+				depositorFee, err = bitcoin.CalcDepositorFeeV2(rpcClient, &tx, netParams)
+				if err != nil {
+					return nil, errors.Wrapf(err, "error calculating depositor fee V2 for inbound: %s", tx.Txid)
+				}
+			}
+
 			// deposit amount has to be no less than the minimum depositor fee
 			if vout0.Value < depositorFee {
 				logger.Info().

zetaclient/chains/bitcoin/observer/observer.go

@@ -23,7 +23,6 @@ import (
 	observertypes "github.com/zeta-chain/zetacore/x/observer/types"
 	"github.com/zeta-chain/zetacore/zetaclient/chains/base"
 	"github.com/zeta-chain/zetacore/zetaclient/chains/bitcoin"
-	"github.com/zeta-chain/zetacore/zetaclient/chains/bitcoin/rpc"
 	"github.com/zeta-chain/zetacore/zetaclient/chains/interfaces"
 	"github.com/zeta-chain/zetacore/zetaclient/db"
 	"github.com/zeta-chain/zetacore/zetaclient/metrics"
@@ -628,7 +627,7 @@ func (ob *Observer) specialHandleFeeRate() (uint64, error) {
 		// hardcode gas price for regnet
 		return 1, nil
 	case chains.NetworkType_testnet:
-		feeRateEstimated, err := rpc.GetRecentFeeRate(ob.btcClient, ob.netParams)
+		feeRateEstimated, err := bitcoin.GetRecentFeeRate(ob.btcClient, ob.netParams)
 		if err != nil {
 			return 0, errors.Wrapf(err, "error GetRecentFeeRate")
 		}

zetaclient/chains/bitcoin/rpc/rpc.go

@@ -4,24 +4,15 @@ import (
 	"fmt"
 
 	"github.com/btcsuite/btcd/btcjson"
-	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/rpcclient"
+	"github.com/btcsuite/btcutil"
 	"github.com/pkg/errors"
 
-	"github.com/zeta-chain/zetacore/zetaclient/chains/bitcoin"
 	"github.com/zeta-chain/zetacore/zetaclient/chains/interfaces"
 	"github.com/zeta-chain/zetacore/zetaclient/config"
 )
 
-const (
-	// feeRateCountBackBlocks is the default number of blocks to look back for fee rate estimation
-	feeRateCountBackBlocks = 2
-
-	// defaultTestnetFeeRate is the default fee rate for testnet, 10 sat/byte
-	defaultTestnetFeeRate = 10
-)
-
 // NewRPCClient creates a new RPC client by the given config.
 func NewRPCClient(btcConfig config.BTCConfig) (*rpcclient.Client, error) {
 	connCfg := &rpcclient.ConnConfig{
@@ -63,6 +54,20 @@ func GetTxResultByHash(
 	return hash, txResult, nil
 }
 
+// GetTXRawResultByHash gets the raw transaction by hash
+func GetRawTxByHash(rpcClient interfaces.BTCRPCClient, txID string) (*btcutil.Tx, error) {
+	hash, err := chainhash.NewHashFromStr(txID)
+	if err != nil {
+		return nil, errors.Wrapf(err, "GetRawTxByHash: error NewHashFromStr: %s", txID)
+	}
+
+	tx, err := rpcClient.GetRawTransaction(hash)
+	if err != nil {
+		return nil, errors.Wrapf(err, "GetRawTxByHash: error GetRawTransaction %s", txID)
+	}
+	return tx, nil
+}
+
 // GetBlockHeightByHash gets the block height by block hash
 func GetBlockHeightByHash(
 	rpcClient interfaces.BTCRPCClient,
@@ -118,42 +123,53 @@ func GetRawTxResult(
 	return btcjson.TxRawResult{}, fmt.Errorf("GetRawTxResult: tx %s not included yet", hash)
 }
 
-// GetRecentFeeRate gets the highest fee rate from recent blocks
-// Note: this method is only used for testnet
-func GetRecentFeeRate(rpcClient interfaces.BTCRPCClient, netParams *chaincfg.Params) (uint64, error) {
-	blockNumber, err := rpcClient.GetBlockCount()
-	if err != nil {
-		return 0, err
+// GetTransactionFeeAndRate gets the transaction fee and rate for a given tx result
+func GetTransactionFeeAndRate(rpcClient interfaces.BTCRPCClient, rawResult *btcjson.TxRawResult) (int64, int64, error) {
+	var (
+		totalInputValue  int64
+		totalOutputValue int64
+	)
+
+	// make sure the tx Vsize is not zero (should not happen)
+	if rawResult.Vsize <= 0 {
+		return 0, 0, fmt.Errorf("tx %s has non-positive Vsize: %d", rawResult.Txid, rawResult.Vsize)
 	}
 
-	// get the highest fee rate among recent 'countBack' blocks to avoid underestimation
-	highestRate := int64(0)
-	for i := int64(0); i < feeRateCountBackBlocks; i++ {
-		// get the block
-		hash, err := rpcClient.GetBlockHash(blockNumber - i)
-		if err != nil {
-			return 0, err
-		}
-		block, err := rpcClient.GetBlockVerboseTx(hash)
+	// sum up total input value
+	for _, vin := range rawResult.Vin {
+		prevTx, err := GetRawTxByHash(rpcClient, vin.Txid)
 		if err != nil {
-			return 0, err
+			return 0, 0, errors.Wrapf(err, "failed to get previous tx: %s", vin.Txid)
 		}
+		totalInputValue += prevTx.MsgTx().TxOut[vin.Vout].Value
+	}
 
-		// computes the average fee rate of the block and take the higher rate
-		avgFeeRate, err := bitcoin.CalcBlockAvgFeeRate(block, netParams)
-		if err != nil {
-			return 0, err
-		}
-		if avgFeeRate > highestRate {
-			highestRate = avgFeeRate
-		}
+	// query the raw tx
+	tx, err := GetRawTxByHash(rpcClient, rawResult.Txid)
+	if err != nil {
+		return 0, 0, errors.Wrapf(err, "failed to get tx: %s", rawResult.Txid)
 	}
 
-	// use 10 sat/byte as default estimation if recent fee rate drops to 0
-	if highestRate == 0 {
-		highestRate = defaultTestnetFeeRate
+	// sum up total output value
+	for _, vout := range tx.MsgTx().TxOut {
+		totalOutputValue += vout.Value
 	}
 
+	// calculate the transaction fee in satoshis
+	fee := totalInputValue - totalOutputValue
+	if fee < 0 { // never happens
+		return 0, 0, fmt.Errorf("got negative fee: %d", fee)
+	}
+
+	// Note: the calculation uses 'Vsize' returned by RPC to simplify dev experience:
+	// 	- 1. the devs could use the same value returned by their RPC endpoints to estimate deposit fee.
+	// 	- 2. the devs don't have to bother 'Vsize' calculation, even though there is more accurate formula.
+	//		 Moreoever, the accurate 'Vsize' is usually an adjusted size (float value) by Bitcoin Core.
+	//	- 3. the 'Vsize' calculation could depend on program language and the library used.
+	//
+	// calculate the fee rate in satoshis/vByte
 	// #nosec G115 always in range
-	return uint64(highestRate), nil
+	feeRate := fee / int64(rawResult.Vsize)
+
+	return fee, feeRate, nil
 }