multi: remove GetTxFee(), improve fee logging

In this commit, we add extra logging of fee rates to the minter, and
also remove a reimplementation of psbt.GetTxFee(). We also deduplicate
some dummy PkScript generation.

Author: jharveyb

tapfreighter/wallet.go

@@ -1437,7 +1437,7 @@ func (f *AssetWallet) AnchorVirtualTransactions(ctx context.Context,
 
 	// Before we finalize, we need to calculate the actual, final fees that
 	// we pay.
-	chainFees, err := tapgarden.GetTxFee(signedPsbt)
+	chainFees, err := signedPsbt.GetTxFee()
 	if err != nil {
 		return nil, fmt.Errorf("unable to get on-chain fees for psbt: "+
 			"%w", err)
@@ -1466,7 +1466,7 @@ func (f *AssetWallet) AnchorVirtualTransactions(ctx context.Context,
 		FundedPsbt:        &anchorPkt,
 		FinalTx:           finalTx,
 		TargetFeeRate:     params.FeeRate,
-		ChainFees:         chainFees,
+		ChainFees:         int64(chainFees),
 		OutputCommitments: mergedCommitments,
 	}, nil
 }
@@ -1717,10 +1717,15 @@ func addAnchorPsbtInputs(btcPkt *psbt.Packet, vPkt *tappsbt.VPacket,
 	// Earlier in adjustFundedPsbt we set wallet's change output to be the
 	// very last output in the transaction.
 	lastIdx := len(btcPkt.UnsignedTx.TxOut) - 1
-	currentFee := inputAmt - outputAmt
-	feeDelta := int64(requiredFee) - currentFee
+	currentFee, err := btcPkt.GetTxFee()
+	if err != nil {
+		return err
+	}
+
+	feeDelta := int64(requiredFee) - int64(currentFee)
 	changeValue := btcPkt.UnsignedTx.TxOut[lastIdx].Value
 
+	log.Infof("Current fee: %d, fee delta: %d", currentFee, feeDelta)
 	// The fee may exceed the total value of the change output, which means
 	// this spend is impossible with the given inputs and fee rate.
 	if changeValue-feeDelta < 0 {
@@ -1730,8 +1735,8 @@ func addAnchorPsbtInputs(btcPkt *psbt.Packet, vPkt *tappsbt.VPacket,
 
 	btcPkt.UnsignedTx.TxOut[lastIdx].Value -= feeDelta
 
-	log.Infof("Adjusting send pkt by delta of %v from %d sats to %d sats",
-		feeDelta, currentFee, requiredFee)
+	log.Infof("Adjusting send pkt fee by delta of %d from %d sats to %d "+
+		"sats", feeDelta, currentFee, requiredFee)
 
 	return nil
 }

tapgarden/caretaker.go

@@ -30,14 +30,6 @@ import (
 )
 
 var (
-
-	// DummyGenesisTxOut is the dummy TxOut we'll place in the PSBt funding
-	// request to make sure we leave enough room for change and fees.
-	DummyGenesisTxOut = wire.TxOut{
-		PkScript: tapscript.GenesisDummyScript[:],
-		Value:    int64(GenesisAmtSats),
-	}
-
 	// ErrGroupKeyUnknown is an error returned if an asset has a group key
 	// attached that has not been previously verified.
 	ErrGroupKeyUnknown = errors.New("group key not known")
@@ -402,7 +394,7 @@ func (b *BatchCaretaker) fundGenesisPsbt(ctx context.Context) (*FundedPsbt, erro
 		b.batchKey[:])
 
 	txTemplate := wire.NewMsgTx(2)
-	txTemplate.AddTxOut(&DummyGenesisTxOut)
+	txTemplate.AddTxOut(tapscript.CreateDummyOutput())
 	genesisPkt, err := psbt.NewFromUnsignedTx(txTemplate)
 	if err != nil {
 		return nil, fmt.Errorf("unable to make psbt packet: %w", err)
@@ -411,26 +403,28 @@ func (b *BatchCaretaker) fundGenesisPsbt(ctx context.Context) (*FundedPsbt, erro
 	log.Infof("BatchCaretaker(%x): creating skeleton PSBT", b.batchKey[:])
 	log.Tracef("PSBT: %v", spew.Sdump(genesisPkt))
 
-	// If a fee rate was manually assigned for this batch, use that instead
-	// of a fee rate estimate.
 	var feeRate chainfee.SatPerKWeight
 	switch {
+	// If a fee rate was manually assigned for this batch, use that instead
+	// of a fee rate estimate.
 	case b.cfg.BatchFeeRate != nil:
 		feeRate = *b.cfg.BatchFeeRate
-		log.Infof("BatchCaretaker(%x): using manual fee rate",
-			b.batchKey[:])
+		log.Infof("BatchCaretaker(%x): using manual fee rate: %s, %d "+
+			"sat/vB", b.batchKey[:], feeRate.String(),
+			feeRate.FeePerKVByte()/1000)
 
 	default:
 		feeRate, err = b.cfg.ChainBridge.EstimateFee(
 			ctx, GenesisConfTarget,
 		)
 		if err != nil {
-			return nil, fmt.Errorf("unable to estimate fee: %w", err)
+			return nil, fmt.Errorf("unable to estimate fee: %w",
+				err)
 		}
-	}
 
-	log.Infof("BatchCaretaker(%x): using fee rate: %v",
-		b.batchKey[:], feeRate.FeePerKVByte().String())
+		log.Infof("BatchCaretaker(%x): estimated fee rate: %s",
+			b.batchKey[:], feeRate.FeePerKVByte().String())
+	}
 
 	fundedGenesisPkt, err := b.cfg.Wallet.FundPsbt(
 		ctx, genesisPkt, 1, feeRate,
@@ -755,17 +749,15 @@ func (b *BatchCaretaker) stateStep(currentState BatchState) (BatchState, error)
 		b.cfg.Batch.GenesisPacket.Pkt = signedPkt
 
 		// Populate how much this tx paid in on-chain fees.
-		chainFees, err := GetTxFee(signedPkt)
+		chainFees, err := signedPkt.GetTxFee()
 		if err != nil {
 			return 0, fmt.Errorf("unable to get on-chain fees "+
 				"for psbt: %w", err)
 		}
-		b.cfg.Batch.GenesisPacket.ChainFees = chainFees
+		b.cfg.Batch.GenesisPacket.ChainFees = int64(chainFees)
 
-		log.Infof("BatchCaretaker(%x): GenesisPacket absolute fee: "+
-			"%d sats", b.batchKey[:], chainFees)
-		log.Infof("BatchCaretaker(%x): GenesisPacket finalized",
-			b.batchKey[:])
+		log.Infof("BatchCaretaker(%x): GenesisPacket finalized "+
+			"(absolute_fee_sats: %d)", b.batchKey[:], chainFees)
 		log.Tracef("GenesisPacket: %v", spew.Sdump(signedPkt))
 
 		// At this point we have a fully signed PSBT packet which'll
@@ -1344,21 +1336,6 @@ func SortAssets(fullAssets []*asset.Asset,
 	return anchorAssets, nonAnchorAssets, nil
 }
 
-// GetTxFee returns the value of the on-chain fees paid by a finalized PSBT.
-func GetTxFee(pkt *psbt.Packet) (int64, error) {
-	inputValue, err := psbt.SumUtxoInputValues(pkt)
-	if err != nil {
-		return 0, fmt.Errorf("unable to sum input values: %v", err)
-	}
-
-	outputValue := int64(0)
-	for _, out := range pkt.UnsignedTx.TxOut {
-		outputValue += out.Value
-	}
-
-	return inputValue - outputValue, nil
-}
-
 // GenHeaderVerifier generates a block header on-chain verification callback
 // function given a chain bridge.
 func GenHeaderVerifier(ctx context.Context,

tapscript/send.go

@@ -115,14 +115,14 @@ var (
 	)
 )
 
-// createDummyOutput creates a new Bitcoin transaction output that is later
+// CreateDummyOutput creates a new Bitcoin transaction output that is later
 // used to embed a Taproot Asset commitment.
-func createDummyOutput() *wire.TxOut {
+func CreateDummyOutput() *wire.TxOut {
 	// The dummy PkScript is the same size as an encoded P2TR output and has
 	// a valid P2TR prefix.
 	newOutput := wire.TxOut{
 		Value:    int64(DummyAmtSats),
-		PkScript: GenesisDummyScript,
+		PkScript: bytes.Clone(GenesisDummyScript),
 	}
 	return &newOutput
 }
@@ -1029,7 +1029,7 @@ func CreateAnchorTx(outputs []*tappsbt.VOutput) (*psbt.Packet, error) {
 
 	txTemplate := wire.NewMsgTx(2)
 	for i := uint32(0); i < maxOutputIndex; i++ {
-		txTemplate.AddTxOut(createDummyOutput())
+		txTemplate.AddTxOut(CreateDummyOutput())
 	}
 
 	spendPkt, err := psbt.NewFromUnsignedTx(txTemplate)