Taker: provided amount out of range checks (#386)

protocol/xmrtaker/errors.go

@@ -48,3 +48,27 @@ func errContractAddrMismatch(addr string) error {
 	//nolint:lll
 	return fmt.Errorf("cannot recover from swap where contract address is not the one loaded at start-up; please restart with --contract-address=%s", addr)
 }
+
+type errAmountProvidedTooLow struct {
+	providedAmount *apd.Decimal
+	minAmount      *apd.Decimal
+}
+
+func (e errAmountProvidedTooLow) Error() string {
+	return fmt.Sprintf("%s ETH provided is under offer minimum of %s XMR",
+		e.providedAmount.String(),
+		e.minAmount.String(),
+	)
+}
+
+type errAmountProvidedTooHigh struct {
+	providedAmount *apd.Decimal
+	maxAmount      *apd.Decimal
+}
+
+func (e errAmountProvidedTooHigh) Error() string {
+	return fmt.Sprintf("%s ETH provided is over offer maximum of %s XMR",
+		e.providedAmount.String(),
+		e.maxAmount.String(),
+	)
+}

protocol/xmrtaker/net.go

@@ -27,10 +27,24 @@ func (inst *Instance) InitiateProtocol(
 	providesAmount *apd.Decimal,
 	offer *types.Offer,
 ) (common.SwapState, error) {
+	err := coins.ValidatePositive("providesAmount", coins.NumEtherDecimals, providesAmount)
+	if err != nil {
+		return nil, err
+	}
+
 	expectedAmount, err := offer.ExchangeRate.ToXMR(providesAmount)
 	if err != nil {
 		return nil, err
 	}
+
+	if expectedAmount.Cmp(offer.MinAmount) < 0 {
+		return nil, errAmountProvidedTooLow{providesAmount, offer.MinAmount}
+	}
+
+	if expectedAmount.Cmp(offer.MaxAmount) > 0 {
+		return nil, errAmountProvidedTooHigh{providesAmount, offer.MaxAmount}
+	}
+
 	providedAmount, err := pcommon.GetEthAssetAmount(
 		inst.backend.Ctx(),
 		inst.backend.ETHClient(),

protocol/xmrtaker/net_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/athanorlabs/atomic-swap/coins"
+	"github.com/athanorlabs/atomic-swap/common"
 	"github.com/athanorlabs/atomic-swap/common/types"
 )
 
@@ -26,13 +27,50 @@ func newTestXMRTaker(t *testing.T) *Instance {
 	return xmrtaker
 }
 
+func initiate(
+	xmrtaker *Instance,
+	providesAmount *apd.Decimal,
+	minAmount *apd.Decimal,
+	maxAmount *apd.Decimal,
+) (*types.Offer, common.SwapState, error) {
+	offer := types.NewOffer(
+		coins.ProvidesETH,
+		minAmount,
+		maxAmount,
+		coins.ToExchangeRate(apd.New(1, 0)),
+		types.EthAssetETH,
+	)
+	s, err := xmrtaker.InitiateProtocol(testPeerID, providesAmount, offer)
+	return offer, s, err
+}
+
 func TestXMRTaker_InitiateProtocol(t *testing.T) {
 	a := newTestXMRTaker(t)
 	zero := new(apd.Decimal)
 	one := apd.New(1, 0)
-	offer := types.NewOffer(coins.ProvidesETH, zero, zero, coins.ToExchangeRate(one), types.EthAssetETH)
-	providesAmount := apd.New(333, -2) // 3.33
-	s, err := a.InitiateProtocol(testPeerID, providesAmount, offer)
+
+	// Provided between minAmount and maxAmount
+	offer, s, err := initiate(a, apd.New(1, -1), zero, one) // 0.1
 	require.NoError(t, err)
 	require.Equal(t, a.swapStates[offer.ID], s)
+
+	// Provided with too many decimals
+	_, s, err = initiate(a, apd.New(1, -50), zero, one) // 10^-50
+	require.Error(t, err)
+	require.Equal(t, nil, s)
+
+	// Provided with a negative number
+	_, s, err = initiate(a, apd.New(-1, 0), zero, one) // -1
+	require.Error(t, err)
+	require.Equal(t, nil, s)
+
+	// Provided over maxAmount
+	_, s, err = initiate(a, apd.New(2, 0), one, one) // 2
+	require.Error(t, err)
+	require.Equal(t, nil, s)
+
+	// Provided under minAmount
+	_, s, err = initiate(a, apd.New(1, -1), one, one) // 0.1
+	require.Error(t, err)
+	require.Equal(t, nil, s)
 }