loopout: extend htlc expiry based on conf target

Author: joostjager

client.go

@@ -3,6 +3,7 @@ package loop
 import (
 	"context"
 	"errors"
+	"fmt"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -33,20 +34,10 @@ var (
 	// more than the server maximum.
 	ErrSwapAmountTooHigh = errors.New("swap amount too high")
 
-	// ErrExpiryTooSoon is returned when the server proposes an expiry that
-	// is too soon for us.
-	ErrExpiryTooSoon = errors.New("swap expiry too soon")
-
 	// ErrExpiryTooFar is returned when the server proposes an expiry that
 	// is too soon for us.
 	ErrExpiryTooFar = errors.New("swap expiry too far")
 
-	// ErrSweepConfTargetTooFar is returned when the client proposes a
-	// confirmation target to sweep the on-chain HTLC of a Loop Out that is
-	// beyond the expiration height proposed by the server.
-	ErrSweepConfTargetTooFar = errors.New("sweep confirmation target is " +
-		"beyond swap expiration height")
-
 	// serverRPCTimeout is the maximum time a gRPC request to the server
 	// should be allowed to take.
 	serverRPCTimeout = 30 * time.Second
@@ -363,8 +354,21 @@ func (s *Client) LoopOut(globalCtx context.Context,
 		return nil, err
 	}
 
-	// Create a new swap object for this swap.
+	// Calculate htlc expiry height.
+	terms, err := s.Server.GetLoopOutTerms(globalCtx)
+	if err != nil {
+		return nil, err
+	}
+
 	initiationHeight := s.executor.height()
+	request.Expiry, err = s.getExpiry(
+		initiationHeight, terms, request.SweepConfTarget,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	// Create a new swap object for this swap.
 	swapCfg := newSwapConfig(s.lndServices, s.Store, s.Server)
 	initResult, err := newLoopOutSwap(
 		globalCtx, swapCfg, initiationHeight, request,
@@ -386,6 +390,24 @@ func (s *Client) LoopOut(globalCtx context.Context,
 	}, nil
 }
 
+// getExpiry returns an absolute expiry height based on the sweep confirmation
+// target, constrained by the server terms.
+func (s *Client) getExpiry(height int32, terms *LoopOutTerms,
+	confTarget int32) (int32, error) {
+
+	switch {
+	case confTarget < terms.MinCltvDelta:
+		return height + terms.MinCltvDelta, nil
+
+	case confTarget > terms.MaxCltvDelta:
+		return 0, fmt.Errorf("confirmation target %v exceeds maximum "+
+			"server cltv delta of %v", confTarget,
+			terms.MaxCltvDelta)
+	}
+
+	return height + confTarget, nil
+}
+
 // LoopOutQuote takes a LoopOut amount and returns a break down of estimated
 // costs for the client. Both the swap server and the on-chain fee estimator
 // are queried to get to build the quote response.
@@ -405,8 +427,14 @@ func (s *Client) LoopOutQuote(ctx context.Context,
 		return nil, ErrSwapAmountTooHigh
 	}
 
+	height := s.executor.height()
+	expiry, err := s.getExpiry(height, terms, request.SweepConfTarget)
+	if err != nil {
+		return nil, err
+	}
+
 	quote, err := s.Server.GetLoopOutQuote(
-		ctx, request.Amount, request.SwapPublicationDeadline,
+		ctx, request.Amount, expiry, request.SwapPublicationDeadline,
 	)
 	if err != nil {
 		return nil, err
@@ -440,7 +468,6 @@ func (s *Client) LoopOutQuote(ctx context.Context,
 		MinerFee:        minerFee,
 		PrepayAmount:    quote.PrepayAmount,
 		SwapPaymentDest: quote.SwapPaymentDest,
-		CltvDelta:       quote.CltvDelta,
 	}, nil
 }
 

interface.go

@@ -71,6 +71,9 @@ type OutRequest struct {
 	// SwapPublicationDeadline can be set by the client to allow the server
 	// delaying publication of the swap HTLC to save on chain fees.
 	SwapPublicationDeadline time.Time
+
+	// Expiry is the absolute expiry height of the on-chain htlc.
+	Expiry int32
 }
 
 // Out contains the full details of a loop out request. This includes things
@@ -146,10 +149,6 @@ type LoopOutQuote struct {
 	// sweep the htlc.
 	MinerFee btcutil.Amount
 
-	// Time lock delta relative to current block height that swap server
-	// will accept on the swap initiation call.
-	CltvDelta int32
-
 	// SwapPaymentDest is the node pubkey where to swap payment needs to be
 	// sent to.
 	SwapPaymentDest [33]byte

loopd/swapclient_server.go

@@ -373,7 +373,6 @@ func (s *swapClientServer) LoopOutQuote(ctx context.Context,
 		PrepayAmtSat:    int64(quote.PrepayAmount),
 		SwapFeeSat:      int64(quote.SwapFee),
 		SwapPaymentDest: quote.SwapPaymentDest[:],
-		CltvDelta:       quote.CltvDelta,
 	}, nil
 }
 

loopout.go

@@ -106,13 +106,14 @@ func newLoopOutSwap(globalCtx context.Context, cfg *swapConfig,
 
 	// Post the swap parameters to the swap server. The response contains
 	// the server revocation key and the swap and prepay invoices.
-	log.Infof("Initiating swap request at height %v", currentHeight)
+	log.Infof("Initiating swap request at height %v: amt=%v, expiry=%v",
+		currentHeight, request.Amount, request.Expiry)
 
 	// The swap deadline will be given to the server for it to use as the
 	// latest swap publication time.
 	swapResp, err := cfg.server.NewLoopOutSwap(
-		globalCtx, swapHash, request.Amount, receiverKey,
-		request.SwapPublicationDeadline,
+		globalCtx, swapHash, request.Amount, request.Expiry,
+		receiverKey, request.SwapPublicationDeadline,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("cannot initiate swap: %v", err)
@@ -150,7 +151,7 @@ func newLoopOutSwap(globalCtx context.Context, cfg *swapConfig,
 			SenderKey:        swapResp.senderKey,
 			Preimage:         swapPreimage,
 			AmountRequested:  request.Amount,
-			CltvExpiry:       swapResp.expiry,
+			CltvExpiry:       request.Expiry,
 			MaxMinerFee:      request.MaxMinerFee,
 			MaxSwapFee:       request.MaxSwapFee,
 		},
@@ -994,18 +995,5 @@ func validateLoopOutContract(lnd *lndclient.LndServices,
 		return ErrPrepayAmountTooHigh
 	}
 
-	if response.expiry-height < MinLoopOutPreimageRevealDelta {
-		log.Warnf("Proposed expiry %v (delta %v) too soon",
-			response.expiry, response.expiry-height)
-
-		return ErrExpiryTooSoon
-	}
-
-	// Ensure the client has provided a sweep confirmation target that does
-	// not exceed the height at which we revert back to using the default.
-	if height+request.SweepConfTarget >= response.expiry-DefaultSweepConfTargetDelta {
-		return ErrSweepConfTargetTooFar
-	}
-
 	return nil
 }

loopout_test.go

@@ -151,6 +151,8 @@ func TestLateHtlcPublish(t *testing.T) {
 
 	cfg := newSwapConfig(&lnd.LndServices, store, server)
 
+	testRequest.Expiry = height + testLoopOutMinOnChainCltvDelta
+
 	initResult, err := newLoopOutSwap(
 		context.Background(), cfg, height, testRequest,
 	)
@@ -227,7 +229,7 @@ func TestCustomSweepConfTarget(t *testing.T) {
 	// the default.
 	testReq := *testRequest
 
-	testReq.SweepConfTarget = testLoopOutOnChainCltvDelta -
+	testReq.SweepConfTarget = testLoopOutMinOnChainCltvDelta -
 		DefaultSweepConfTargetDelta - 1
 
 	// Set up custom fee estimates such that the lower confirmation target
@@ -376,8 +378,8 @@ func TestCustomSweepConfTarget(t *testing.T) {
 
 	// We'll then notify the height at which we begin using the default
 	// confirmation target.
-	defaultConfTargetHeight := ctx.Lnd.Height + testLoopOutOnChainCltvDelta -
-		DefaultSweepConfTargetDelta
+	defaultConfTargetHeight := ctx.Lnd.Height +
+		testLoopOutMinOnChainCltvDelta - DefaultSweepConfTargetDelta
 	blockEpochChan <- int32(defaultConfTargetHeight)
 	expiryChan <- time.Now()
 
@@ -427,8 +429,9 @@ func TestPreimagePush(t *testing.T) {
 	// Start with a high confirmation delta which will have a very high fee
 	// attached to it.
 	testReq := *testRequest
-	testReq.SweepConfTarget = testLoopOutOnChainCltvDelta -
+	testReq.SweepConfTarget = testLoopOutMinOnChainCltvDelta -
 		DefaultSweepConfTargetDelta - 1
+	testReq.Expiry = ctx.Lnd.Height + testLoopOutMinOnChainCltvDelta
 
 	// We set our mock fee estimate for our target sweep confs to be our
 	// max miner fee *2, so that our fee will definitely be above what we
@@ -520,7 +523,7 @@ func TestPreimagePush(t *testing.T) {
 	// Now, we notify the height at which the client will start using the
 	// default confirmation target. This has the effect of lowering our fees
 	// so that the client still start sweeping.
-	defaultConfTargetHeight := ctx.Lnd.Height + testLoopOutOnChainCltvDelta -
+	defaultConfTargetHeight := ctx.Lnd.Height + testLoopOutMinOnChainCltvDelta -
 		DefaultSweepConfTargetDelta
 	blockEpochChan <- defaultConfTargetHeight
 

server_mock_test.go

@@ -18,12 +18,13 @@ import (
 var (
 	testTime = time.Date(2018, time.January, 9, 14, 00, 00, 0, time.UTC)
 
-	testLoopOutOnChainCltvDelta = int32(30)
-	testChargeOnChainCltvDelta  = int32(100)
-	testSwapFee                 = btcutil.Amount(210)
-	testFixedPrepayAmount       = btcutil.Amount(100)
-	testMinSwapAmount           = btcutil.Amount(10000)
-	testMaxSwapAmount           = btcutil.Amount(1000000)
+	testLoopOutMinOnChainCltvDelta = int32(30)
+	testLoopOutMaxOnChainCltvDelta = int32(40)
+	testChargeOnChainCltvDelta     = int32(100)
+	testSwapFee                    = btcutil.Amount(210)
+	testFixedPrepayAmount          = btcutil.Amount(100)
+	testMinSwapAmount              = btcutil.Amount(10000)
+	testMaxSwapAmount              = btcutil.Amount(1000000)
 )
 
 // serverMock is used in client unit tests to simulate swap server behaviour.
@@ -58,7 +59,7 @@ func newServerMock() *serverMock {
 }
 
 func (s *serverMock) NewLoopOutSwap(ctx context.Context,
-	swapHash lntypes.Hash, amount btcutil.Amount,
+	swapHash lntypes.Hash, amount btcutil.Amount, expiry int32,
 	receiverKey [33]byte, _ time.Time) (
 	*newLoopOutResponse, error) {
 
@@ -87,7 +88,6 @@ func (s *serverMock) NewLoopOutSwap(ctx context.Context,
 		senderKey:     senderKeyArray,
 		swapInvoice:   swapPayReqString,
 		prepayInvoice: prePayReqString,
-		expiry:        s.height + testLoopOutOnChainCltvDelta,
 	}, nil
 }
 
@@ -97,18 +97,19 @@ func (s *serverMock) GetLoopOutTerms(ctx context.Context) (
 	return &LoopOutTerms{
 		MinSwapAmount: testMinSwapAmount,
 		MaxSwapAmount: testMaxSwapAmount,
+		MinCltvDelta:  testLoopOutMinOnChainCltvDelta,
+		MaxCltvDelta:  testLoopOutMaxOnChainCltvDelta,
 	}, nil
 }
 
 func (s *serverMock) GetLoopOutQuote(ctx context.Context, amt btcutil.Amount,
-	_ time.Time) (*LoopOutQuote, error) {
+	expiry int32, _ time.Time) (*LoopOutQuote, error) {
 
 	dest := [33]byte{1, 2, 3}
 
 	return &LoopOutQuote{
 		SwapFee:         testSwapFee,
 		SwapPaymentDest: dest,
-		CltvDelta:       testLoopOutOnChainCltvDelta,
 		PrepayAmount:    testFixedPrepayAmount,
 	}, nil
 }

swap_server_client.go

@@ -25,7 +25,7 @@ import (
 
 // protocolVersion defines the version of the protocol that is currently
 // supported by the loop client.
-const protocolVersion = looprpc.ProtocolVersion_PREIMAGE_PUSH_LOOP_OUT
+const protocolVersion = looprpc.ProtocolVersion_USER_EXPIRY_LOOP_OUT
 
 var (
 	// errServerSubscriptionComplete is returned when our subscription to
@@ -46,7 +46,7 @@ type swapServerClient interface {
 	GetLoopOutTerms(ctx context.Context) (
 		*LoopOutTerms, error)
 
-	GetLoopOutQuote(ctx context.Context, amt btcutil.Amount,
+	GetLoopOutQuote(ctx context.Context, amt btcutil.Amount, expiry int32,
 		swapPublicationDeadline time.Time) (
 		*LoopOutQuote, error)
 
@@ -57,7 +57,7 @@ type swapServerClient interface {
 		*LoopInQuote, error)
 
 	NewLoopOutSwap(ctx context.Context,
-		swapHash lntypes.Hash, amount btcutil.Amount,
+		swapHash lntypes.Hash, amount btcutil.Amount, expiry int32,
 		receiverKey [33]byte,
 		swapPublicationDeadline time.Time) (
 		*newLoopOutResponse, error)
@@ -146,7 +146,7 @@ func (s *grpcSwapServerClient) GetLoopOutTerms(ctx context.Context) (
 }
 
 func (s *grpcSwapServerClient) GetLoopOutQuote(ctx context.Context,
-	amt btcutil.Amount, swapPublicationDeadline time.Time) (
+	amt btcutil.Amount, expiry int32, swapPublicationDeadline time.Time) (
 	*LoopOutQuote, error) {
 
 	rpcCtx, rpcCancel := context.WithTimeout(ctx, globalCallTimeout)
@@ -156,6 +156,7 @@ func (s *grpcSwapServerClient) GetLoopOutQuote(ctx context.Context,
 			Amt:                     uint64(amt),
 			SwapPublicationDeadline: swapPublicationDeadline.Unix(),
 			ProtocolVersion:         protocolVersion,
+			Expiry:                  expiry,
 		},
 	)
 	if err != nil {
@@ -175,7 +176,6 @@ func (s *grpcSwapServerClient) GetLoopOutQuote(ctx context.Context,
 	return &LoopOutQuote{
 		PrepayAmount:    btcutil.Amount(quoteResp.PrepayAmt),
 		SwapFee:         btcutil.Amount(quoteResp.SwapFee),
-		CltvDelta:       quoteResp.CltvDelta,
 		SwapPaymentDest: destArray,
 	}, nil
 }
@@ -222,7 +222,7 @@ func (s *grpcSwapServerClient) GetLoopInQuote(ctx context.Context,
 }
 
 func (s *grpcSwapServerClient) NewLoopOutSwap(ctx context.Context,
-	swapHash lntypes.Hash, amount btcutil.Amount,
+	swapHash lntypes.Hash, amount btcutil.Amount, expiry int32,
 	receiverKey [33]byte, swapPublicationDeadline time.Time) (
 	*newLoopOutResponse, error) {
 
@@ -235,6 +235,7 @@ func (s *grpcSwapServerClient) NewLoopOutSwap(ctx context.Context,
 			ReceiverKey:             receiverKey[:],
 			SwapPublicationDeadline: swapPublicationDeadline.Unix(),
 			ProtocolVersion:         protocolVersion,
+			Expiry:                  expiry,
 		},
 	)
 	if err != nil {
@@ -254,7 +255,6 @@ func (s *grpcSwapServerClient) NewLoopOutSwap(ctx context.Context,
 		swapInvoice:   swapResp.SwapInvoice,
 		prepayInvoice: swapResp.PrepayInvoice,
 		senderKey:     senderKey,
-		expiry:        swapResp.Expiry,
 		serverMessage: swapResp.ServerMessage,
 	}, nil
 }
@@ -528,7 +528,6 @@ type newLoopOutResponse struct {
 	swapInvoice   string
 	prepayInvoice string
 	senderKey     [33]byte
-	expiry        int32
 	serverMessage string
 }