multi: Use common fee for split tx

Instead of relying on the wallet to specify the rate for split
transactions, this unifies buyers to using a single source for fee rate
determination, which prevents problems with wallets that have changed
their default fee rate.

pkg/buyer/wallet-client.go

@@ -237,7 +237,7 @@ func (wc *WalletClient) generateSplitTxInputs(ctx context.Context, session *Sess
 	}
 
 	req := &pb.ConstructTransactionRequest{
-		FeePerKb:              0, // whatever is the default wallet fee
+		FeePerKb:              int32(splitticket.TxFeeRate),
 		RequiredConfirmations: splitticket.MinimumSplitInputConfirms,
 		SourceAccount:         cfg.SourceAccount,
 		NonChangeOutputs:      outputs,
@@ -656,7 +656,7 @@ func (wc *WalletClient) testFunds(ctx context.Context, cfg *Config) error {
 	}
 
 	req := &pb.ConstructTransactionRequest{
-		FeePerKb:              0,
+		FeePerKb:              int32(splitticket.TxFeeRate),
 		RequiredConfirmations: splitticket.MinimumSplitInputConfirms,
 		SourceAccount:         cfg.SourceAccount,
 		NonChangeOutputs:      outputs,

pkg/splitticket/const.go

@@ -1,5 +1,7 @@
 package splitticket
 
+import "github.com/decred/dcrd/dcrutil"
+
 const (
 	// SplitTicketSrvService is the _service_ part of an SRV record that is
 	// looked up prior to connecting to the split ticket service
@@ -24,4 +26,10 @@ const (
 	// As of 2018-11-09 only ~3% of all mainnet txs used more than 20 inputs, so
 	// this should be reasonable.
 	MaximumSplitInputs = 20
+
+	// TxFeeRate is the expected transaction fee rate for the split and ticket
+	// transactions of participants of split tickets.
+	//
+	// Measured as Atoms/KB. 1e5 = 0.001 DCR
+	TxFeeRate dcrutil.Amount = 1e5
 )

pkg/splitticket/fees.go

@@ -24,10 +24,6 @@ const (
 		1 + 108 + // TxIn len(ScriptSig) + ScriptSig
 		8 + 2 + 1 + 32 + // Stake Commitment TxOut = amount + version + script
 		8 + 2 + 1 + 26 // Stake Change TxOut = amount + version + script
-
-	// TicketFeeEstimate is the fee rate estimate (in dcr/byte) of the fee in
-	// a ticket purchase
-	TicketFeeEstimate float64 = 0.001 / 1000
 )
 
 // TicketSizeEstimate returns the size estimate for the ticket transaction for
@@ -41,8 +37,9 @@ func TicketSizeEstimate(numParticipants int) int {
 // SessionParticipantFee returns the fee that a single participant of a ticket
 // split tx with the given number of participants should pay
 func SessionParticipantFee(numParticipants int) dcrutil.Amount {
+	feeRate := float64(TxFeeRate) / 1e11 // 1e11 = 1e8 * 1e3
 	txSize := TicketSizeEstimate(numParticipants)
-	ticketFee, _ := dcrutil.NewAmount(float64(txSize) * TicketFeeEstimate)
+	ticketFee, _ := dcrutil.NewAmount(float64(txSize) * feeRate)
 	partFee := dcrutil.Amount(math.Ceil(float64(ticketFee) / float64(numParticipants)))
 	return partFee
 }

pkg/splitticket/revocation.go

@@ -28,7 +28,7 @@ func RevocationFeeRate(params *chaincfg.Params) dcrutil.Amount {
 		return 1e4
 	}
 
-	return minRelayFeeRate
+	return TxFeeRate
 }
 
 // CheckRevocation checks whether the revocation for the given ticket respects

pkg/splitticket/revocation_test.go

@@ -68,7 +68,7 @@ func TestCreateUnsignedRevocation(t *testing.T) {
 
 		revocation.TxIn[0].SignatureScript = revocationSigScript
 		size := revocation.SerializeSize()
-		minFee := dcrutil.Amount((size * int(minRelayFeeRate)) / 1000)
+		minFee := dcrutil.Amount((size * int(TxFeeRate)) / 1000)
 
 		fee, err := FindRevocationTxFee(ticket, revocation)
 		if err != nil {

pkg/splitticket/splittx.go

@@ -122,7 +122,7 @@ func CheckSignedSplit(split *wire.MsgTx, utxos UtxoMap, params *chaincfg.Params)
 	txFee := totalAmountIn - int64(totalAmountOut)
 
 	serializedSize := int64(split.SerializeSize())
-	minFee := (serializedSize * int64(minRelayFeeRate)) / 1000
+	minFee := (serializedSize * int64(TxFeeRate)) / 1000
 	if txFee < minFee {
 		return errors.Errorf("split tx fee (%s) less than minimum required "+
 			"amount (%s)", dcrutil.Amount(txFee), dcrutil.Amount(minFee))

pkg/splitticket/ticket.go

@@ -246,7 +246,7 @@ func CheckSignedTicket(split, ticket *wire.MsgTx, params *chaincfg.Params) error
 	}
 	txFee := totalAmountIn - totalAmountOut
 	serializedSize := int64(ticket.SerializeSize())
-	minFee := (serializedSize * int64(minRelayFeeRate)) / 1000
+	minFee := (serializedSize * int64(TxFeeRate)) / 1000
 	if txFee < minFee {
 		return errors.Errorf("ticket fee (%s) less than minimum required amount (%s)",
 			dcrutil.Amount(txFee), dcrutil.Amount(minFee))

pkg/splitticket/util.go

@@ -25,10 +25,6 @@ var currentScriptFlags = txscript.ScriptDiscourageUpgradableNops |
 	txscript.ScriptVerifyCheckSequenceVerify |
 	txscript.ScriptVerifySHA256
 
-// minRelayFeeRate is the minimum tx fee rate for inclusion on the network.
-// Measured as Atoms/KB. 1e5 = 0.001 DCR
-const minRelayFeeRate dcrutil.Amount = 1e5
-
 // totalOutputAmount calculates the total amount of outputs for a transaction.
 // Only safe to be called on transactions which passed
 // blockchain.CheckTransactionSanity()