feat: add fee estimation util

pkg/btcutils/fee.go

@@ -0,0 +1,56 @@
+package btcutils
+
+import (
+	"github.com/btcsuite/btcd/blockchain"
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/cockroachdb/errors"
+	"github.com/gaze-network/indexer-network/common/errs"
+)
+
+// EstimateSignedTxNetworkFee estimates the network fee for the given transaction. "prevTxOuts" should be list of all outputs used as inputs in the transaction.
+// If the transaction has unsigned inputs, the fee will be calculated as if those inputs were signed.
+func EstimateSignedTxNetworkFee(tx *wire.MsgTx, prevTxOuts []*wire.TxOut, feeRate int64) (int64, error) {
+	if len(tx.TxIn) != len(prevTxOuts) {
+		return 0, errors.Wrapf(errs.InvalidArgument, "tx.TxIn length (%d) must match prevTxOuts length (%d)", len(tx.TxIn), len(prevTxOuts))
+	}
+	tx = tx.Copy()
+	mockPrivateKey, _ := btcec.NewPrivateKey()
+	for i := range tx.TxIn {
+		if len(tx.TxIn[i].SignatureScript) > 0 || (len(tx.TxIn[i].Witness) > 0 && len(tx.TxIn[i].Witness[0]) > 0) {
+			// already signed, skip
+			continue
+		}
+		address, err := ExtractAddressFromPkScript(prevTxOuts[i].PkScript)
+		if err != nil {
+			return 0, errors.Wrapf(err, "failed to extract address from pkScript %d", i)
+		}
+		// if the input is a taproot script-path spend, we need to sign it with the tapscript
+		if address.Type() == AddressTaproot && len(tx.TxIn[i].Witness) == 3 {
+			tx, err = SignTxInputTapScript(tx, mockPrivateKey, prevTxOuts[i], i)
+			if err != nil {
+				return 0, errors.Wrapf(err, "failed to sign tx input %d (tapscript)", i)
+			}
+		} else {
+			tx, err = SignTxInput(tx, mockPrivateKey, prevTxOuts[i], i)
+			if err != nil {
+				return 0, errors.Wrapf(err, "failed to sign tx input %d", i)
+			}
+		}
+	}
+	txWeight := blockchain.GetTransactionWeight(btcutil.NewTx(tx))
+	txVBytes := calVBytes(txWeight)
+
+	fee := txVBytes * feeRate
+	return fee, nil
+}
+
+func calVBytes(txWeight int64) int64 {
+	// VBytes = txWeight/4, a fraction of Vbyte uses 1 Vbyte.
+	txVBytes := txWeight / 4
+	if txWeight%4 > 0 {
+		txVBytes += 1
+	}
+	return txVBytes
+}