client/eth: Add send tx fee estiamte buffer

This adds a 20% buffer to the send tx fee estimate in order to not return
an error from the send function when the base fee rises between the time
the estimate is done and the ETH is sent.

client/asset/eth/eth.go

@@ -2768,15 +2768,19 @@ func isValidSend(addr string, value uint64, subtract bool) error {
 // canSend ensures that the wallet has enough to cover send value and returns
 // the fee rate and max fee required for the send tx. If isPreEstimate is false,
 // wallet balance must be enough to cover total spend.
-func (w *ETHWallet) canSend(value uint64, isPreEstimate bool) (uint64, *big.Int, error) {
+func (w *ETHWallet) canSend(value uint64, verifyBalance, isPreEstimate bool) (uint64, *big.Int, error) {
 	maxFeeRate, err := w.recommendedMaxFeeRate(w.ctx)
 	if err != nil {
 		return 0, nil, fmt.Errorf("error getting max fee rate: %w", err)
 	}
 
 	maxFee := defaultSendGasLimit * dexeth.WeiToGwei(maxFeeRate)
 
-	if !isPreEstimate {
+	if isPreEstimate {
+		maxFee = maxFee * 12 / 10 // 20% buffer
+	}
+
+	if verifyBalance {
 		bal, err := w.Balance()
 		if err != nil {
 			return 0, nil, err
@@ -2795,7 +2799,7 @@ func (w *ETHWallet) canSend(value uint64, isPreEstimate bool) (uint64, *big.Int,
 
 // canSend ensures that the wallet has enough to cover send value and returns
 // the fee rate and max fee required for the send tx.
-func (w *TokenWallet) canSend(value uint64, isPreEstimate bool) (uint64, *big.Int, error) {
+func (w *TokenWallet) canSend(value uint64, verifyBalance, isPreEstimate bool) (uint64, *big.Int, error) {
 	maxFeeRate, err := w.recommendedMaxFeeRate(w.ctx)
 	if err != nil {
 		return 0, nil, fmt.Errorf("error getting max fee rate: %w", err)
@@ -2808,7 +2812,11 @@ func (w *TokenWallet) canSend(value uint64, isPreEstimate bool) (uint64, *big.In
 
 	maxFee := dexeth.WeiToGwei(maxFeeRate) * g.Transfer
 
-	if !isPreEstimate {
+	if isPreEstimate {
+		maxFee = maxFee * 12 / 10 // 20% buffer
+	}
+
+	if verifyBalance {
 		bal, err := w.Balance()
 		if err != nil {
 			return 0, nil, err
@@ -2839,7 +2847,7 @@ func (w *ETHWallet) EstimateSendTxFee(addr string, value, _ uint64, subtract boo
 	if err := isValidSend(addr, value, subtract); err != nil && addr != "" { // fee estimate for a send tx.
 		return 0, false, err
 	}
-	maxFee, _, err := w.canSend(value, addr == "")
+	maxFee, _, err := w.canSend(value, addr != "", true)
 	if err != nil {
 		return 0, false, err
 	}
@@ -2854,7 +2862,7 @@ func (w *TokenWallet) EstimateSendTxFee(addr string, value, _ uint64, subtract b
 	if err := isValidSend(addr, value, subtract); err != nil && addr != "" { // fee estimate for a send tx.
 		return 0, false, err
 	}
-	maxFee, _, err := w.canSend(value, addr == "")
+	maxFee, _, err := w.canSend(value, addr != "", true)
 	if err != nil {
 		return 0, false, err
 	}
@@ -2935,7 +2943,7 @@ func (w *ETHWallet) Send(addr string, value, _ uint64) (asset.Coin, error) {
 		return nil, err
 	}
 
-	maxFee, maxFeeRate, err := w.canSend(value, false)
+	maxFee, maxFeeRate, err := w.canSend(value, true, false)
 	if err != nil {
 		return nil, err
 	}
@@ -2961,7 +2969,7 @@ func (w *TokenWallet) Send(addr string, value, _ uint64) (asset.Coin, error) {
 		return nil, err
 	}
 
-	maxFee, maxFeeRate, err := w.canSend(value, false)
+	maxFee, maxFeeRate, err := w.canSend(value, true, false)
 	if err != nil {
 		return nil, err
 	}

client/asset/eth/eth_test.go

@@ -4620,6 +4620,55 @@ func TestMarshalMonitoredTx(t *testing.T) {
 	}
 }
 
+// Ensures that a small rise in the base fee between estimation
+// and sending will not cause a failure.
+func TestEstimateVsActualSendFees(t *testing.T) {
+	t.Run("eth", func(t *testing.T) { testEstimateVsActualSendFees(t, BipID) })
+	t.Run("token", func(t *testing.T) { testEstimateVsActualSendFees(t, simnetTokenID) })
+}
+
+func testEstimateVsActualSendFees(t *testing.T, assetID uint32) {
+	w, _, node, shutdown := tassetWallet(assetID)
+	defer shutdown()
+
+	tx := tTx(0, 0, 0, &testAddressA, nil)
+	node.sendTxTx = tx
+	node.tokenContractor.transferTx = tx
+
+	const testAddr = "dd93b447f7eBCA361805eBe056259853F3912E04"
+
+	txFeeEstimator := w.(asset.TxFeeEstimator)
+	fee, _, err := txFeeEstimator.EstimateSendTxFee("", 0, 0, false)
+	if err != nil {
+		t.Fatalf("error estimating fee: %v", err)
+	}
+
+	// Increase the base fee by 10%.
+	node.baseFee = node.baseFee.Mul(node.baseFee, big.NewInt(11))
+	node.baseFee = node.baseFee.Div(node.baseFee, big.NewInt(10))
+
+	if assetID == BipID {
+		node.bal = dexeth.GweiToWei(11e9)
+		canSend := new(big.Int).Sub(node.bal, dexeth.GweiToWei(fee))
+		canSendGwei, err := dexeth.WeiToGweiUint64(canSend)
+		if err != nil {
+			t.Fatalf("error converting canSend to gwei: %v", err)
+		}
+		_, err = w.Send(testAddr, canSendGwei, 0)
+		if err != nil {
+			t.Fatalf("error sending: %v", err)
+		}
+	} else {
+		tokenVal := uint64(10e9)
+		node.tokenContractor.bal = dexeth.GweiToWei(tokenVal)
+		node.bal = dexeth.GweiToWei(fee)
+		_, err = w.Send(testAddr, tokenVal, 0)
+		if err != nil {
+			t.Fatalf("error sending: %v", err)
+		}
+	}
+}
+
 func TestEstimateSendTxFee(t *testing.T) {
 	t.Run("eth", func(t *testing.T) { testEstimateSendTxFee(t, BipID) })
 	t.Run("token", func(t *testing.T) { testEstimateSendTxFee(t, simnetTokenID) })
@@ -4633,6 +4682,9 @@ func testEstimateSendTxFee(t *testing.T, assetID uint32) {
 	ethFees := dexeth.WeiToGwei(maxFeeRate) * defaultSendGasLimit
 	tokenFees := dexeth.WeiToGwei(maxFeeRate) * tokenGases.Transfer
 
+	ethFees = ethFees * 12 / 10
+	tokenFees = tokenFees * 12 / 10
+
 	const testAddr = "dd93b447f7eBCA361805eBe056259853F3912E04"
 
 	const val = 10e9