Merge pull request #764 from bhandras/costs-cleanup-migration

loop: add migration to fix stored loop out costs

cost_migration.go

@@ -0,0 +1,177 @@
+package loop
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/lightninglabs/lndclient"
+	"github.com/lightninglabs/loop/loopdb"
+	"github.com/lightninglabs/loop/swap"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+const (
+	costMigrationID = "cost_migration"
+)
+
+// CalculateLoopOutCost calculates the total cost of a loop out swap. It will
+// correctly account for the on-chain and off-chain fees that were paid and
+// make sure that all costs are positive.
+func CalculateLoopOutCost(params *chaincfg.Params, loopOutSwap *loopdb.LoopOut,
+	paymentFees map[lntypes.Hash]lnwire.MilliSatoshi) (loopdb.SwapCost,
+	error) {
+
+	// First make sure that this swap is actually finished.
+	if loopOutSwap.State().State.IsPending() {
+		return loopdb.SwapCost{}, fmt.Errorf("swap is not yet finished")
+	}
+
+	// We first need to decode the prepay invoice to get the prepay hash and
+	// the prepay amount.
+	_, _, hash, prepayAmount, err := swap.DecodeInvoice(
+		params, loopOutSwap.Contract.PrepayInvoice,
+	)
+	if err != nil {
+		return loopdb.SwapCost{}, fmt.Errorf("unable to decode the "+
+			"prepay invoice: %v", err)
+	}
+
+	// The swap hash is given and we don't need to get it from the
+	// swap invoice, however we'll decode it anyway to get the invoice amount
+	// that was paid in case we don't have the payment anymore.
+	_, _, swapHash, swapPaymentAmount, err := swap.DecodeInvoice(
+		params, loopOutSwap.Contract.SwapInvoice,
+	)
+	if err != nil {
+		return loopdb.SwapCost{}, fmt.Errorf("unable to decode the "+
+			"swap invoice: %v", err)
+	}
+
+	var (
+		cost                 loopdb.SwapCost
+		swapPaid, prepayPaid bool
+	)
+
+	// Now that we have the prepay and swap amount, we can calculate the
+	// total cost of the swap. Note that we only need to account for the
+	// server cost in case the swap was successful or if the sweep timed
+	// out. Otherwise the server didn't pull the off-chain htlc nor the
+	// prepay.
+	switch loopOutSwap.State().State {
+	case loopdb.StateSuccess:
+		cost.Server = swapPaymentAmount + prepayAmount -
+			loopOutSwap.Contract.AmountRequested
+
+		swapPaid = true
+		prepayPaid = true
+
+	case loopdb.StateFailSweepTimeout:
+		cost.Server = prepayAmount
+
+		prepayPaid = true
+
+	default:
+		cost.Server = 0
+	}
+
+	// Now attempt to look up the actual payments so we can calculate the
+	// total routing costs.
+	prepayPaymentFee, ok := paymentFees[hash]
+	if prepayPaid && ok {
+		cost.Offchain += prepayPaymentFee.ToSatoshis()
+	} else {
+		log.Debugf("Prepay payment %s is missing, won't account for "+
+			"routing fees", hash)
+	}
+
+	swapPaymentFee, ok := paymentFees[swapHash]
+	if swapPaid && ok {
+		cost.Offchain += swapPaymentFee.ToSatoshis()
+	} else {
+		log.Debugf("Swap payment %s is missing, won't account for "+
+			"routing fees", swapHash)
+	}
+
+	// For the on-chain cost, just make sure that the cost is positive.
+	cost.Onchain = loopOutSwap.State().Cost.Onchain
+	if cost.Onchain < 0 {
+		cost.Onchain *= -1
+	}
+
+	return cost, nil
+}
+
+// MigrateLoopOutCosts will calculate the correct cost for all loop out swaps
+// and override the cost values of the last update in the database.
+func MigrateLoopOutCosts(ctx context.Context, lnd lndclient.LndServices,
+	db loopdb.SwapStore) error {
+
+	migrationDone, err := db.HasMigration(ctx, costMigrationID)
+	if err != nil {
+		return err
+	}
+	if migrationDone {
+		log.Infof("Cost cleanup migration already done, skipping")
+
+		return nil
+	}
+
+	log.Infof("Starting cost cleanup migration")
+	startTs := time.Now()
+	defer func() {
+		log.Infof("Finished cost cleanup migration in %v",
+			time.Since(startTs))
+	}()
+
+	// First we'll fetch all loop out swaps from the database.
+	loopOutSwaps, err := db.FetchLoopOutSwaps(ctx)
+	if err != nil {
+		return err
+	}
+
+	// Next we fetch all payments from LND.
+	payments, err := lnd.Client.ListPayments(
+		ctx, lndclient.ListPaymentsRequest{},
+	)
+	if err != nil {
+		return err
+	}
+
+	// Gather payment fees to a map for easier lookup.
+	paymentFees := make(map[lntypes.Hash]lnwire.MilliSatoshi)
+	for _, payment := range payments.Payments {
+		paymentFees[payment.Hash] = payment.Fee
+	}
+
+	// Now we'll calculate the cost for each swap and finally update the
+	// costs in the database.
+	updatedCosts := make(map[lntypes.Hash]loopdb.SwapCost)
+	for _, loopOutSwap := range loopOutSwaps {
+		cost, err := CalculateLoopOutCost(
+			lnd.ChainParams, loopOutSwap, paymentFees,
+		)
+		if err != nil {
+			return err
+		}
+
+		_, ok := updatedCosts[loopOutSwap.Hash]
+		if ok {
+			return fmt.Errorf("found a duplicate swap %v while "+
+				"updating costs", loopOutSwap.Hash)
+		}
+
+		updatedCosts[loopOutSwap.Hash] = cost
+	}
+
+	log.Infof("Updating costs for %d loop out swaps", len(updatedCosts))
+	err = db.BatchUpdateLoopOutSwapCosts(ctx, updatedCosts)
+	if err != nil {
+		return err
+	}
+
+	// Finally mark the migration as done.
+	return db.SetMigration(ctx, costMigrationID)
+}

cost_migration_test.go

@@ -0,0 +1,184 @@
+package loop
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/lightninglabs/lndclient"
+	"github.com/lightninglabs/loop/loopdb"
+	"github.com/lightninglabs/loop/test"
+	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/stretchr/testify/require"
+)
+
+// TestCalculateLoopOutCost tests the CalculateLoopOutCost function.
+func TestCalculateLoopOutCost(t *testing.T) {
+	// Set up test context objects.
+	lnd := test.NewMockLnd()
+	server := newServerMock(lnd)
+	store := loopdb.NewStoreMock(t)
+
+	cfg := &swapConfig{
+		lnd:    &lnd.LndServices,
+		store:  store,
+		server: server,
+	}
+
+	height := int32(600)
+	req := *testRequest
+	initResult, err := newLoopOutSwap(
+		context.Background(), cfg, height, &req,
+	)
+	require.NoError(t, err)
+	swap, err := store.FetchLoopOutSwap(
+		context.Background(), initResult.swap.hash,
+	)
+	require.NoError(t, err)
+
+	// Override the chain cost so it's negative.
+	const expectedChainCost = btcutil.Amount(1000)
+
+	// Now we have the swap and prepay invoices so let's calculate the
+	// costs without providing the payments first, so we don't account for
+	// any routing fees.
+	paymentFees := make(map[lntypes.Hash]lnwire.MilliSatoshi)
+	_, err = CalculateLoopOutCost(lnd.ChainParams, swap, paymentFees)
+
+	// We expect that the call fails as the swap isn't finished yet.
+	require.Error(t, err)
+
+	// Override the swap state to make it look like the swap is finished
+	// and make the chain cost negative too, so we can test that it'll be
+	// corrected to be positive in the cost calculation.
+	swap.Events = append(
+		swap.Events, &loopdb.LoopEvent{
+			SwapStateData: loopdb.SwapStateData{
+				State: loopdb.StateSuccess,
+				Cost: loopdb.SwapCost{
+					Onchain: -expectedChainCost,
+				},
+			},
+		},
+	)
+	costs, err := CalculateLoopOutCost(lnd.ChainParams, swap, paymentFees)
+	require.NoError(t, err)
+
+	expectedServerCost := server.swapInvoiceAmt + server.prepayInvoiceAmt -
+		swap.Contract.AmountRequested
+	require.Equal(t, expectedServerCost, costs.Server)
+	require.Equal(t, btcutil.Amount(0), costs.Offchain)
+	require.Equal(t, expectedChainCost, costs.Onchain)
+
+	// Now add the two payments to the payments map and calculate the costs
+	// again. We expect that the routng fees are now accounted for.
+	paymentFees[server.swapHash] = lnwire.NewMSatFromSatoshis(44)
+	paymentFees[server.prepayHash] = lnwire.NewMSatFromSatoshis(11)
+
+	costs, err = CalculateLoopOutCost(lnd.ChainParams, swap, paymentFees)
+	require.NoError(t, err)
+
+	expectedOffchainCost := btcutil.Amount(44 + 11)
+	require.Equal(t, expectedServerCost, costs.Server)
+	require.Equal(t, expectedOffchainCost, costs.Offchain)
+	require.Equal(t, expectedChainCost, costs.Onchain)
+
+	// Now override the last update to make the swap timed out at the HTLC
+	// sweep. We expect that the chain cost won't change, and only the
+	// prepay will be accounted for.
+	swap.Events[0] = &loopdb.LoopEvent{
+		SwapStateData: loopdb.SwapStateData{
+			State: loopdb.StateFailSweepTimeout,
+			Cost: loopdb.SwapCost{
+				Onchain: 0,
+			},
+		},
+	}
+
+	costs, err = CalculateLoopOutCost(lnd.ChainParams, swap, paymentFees)
+	require.NoError(t, err)
+
+	expectedServerCost = server.prepayInvoiceAmt
+	expectedOffchainCost = btcutil.Amount(11)
+	require.Equal(t, expectedServerCost, costs.Server)
+	require.Equal(t, expectedOffchainCost, costs.Offchain)
+	require.Equal(t, btcutil.Amount(0), costs.Onchain)
+}
+
+// TestCostMigration tests the cost migration for loop out swaps.
+func TestCostMigration(t *testing.T) {
+	// Set up test context objects.
+	lnd := test.NewMockLnd()
+	server := newServerMock(lnd)
+	store := loopdb.NewStoreMock(t)
+
+	cfg := &swapConfig{
+		lnd:    &lnd.LndServices,
+		store:  store,
+		server: server,
+	}
+
+	height := int32(600)
+	req := *testRequest
+	initResult, err := newLoopOutSwap(
+		context.Background(), cfg, height, &req,
+	)
+	require.NoError(t, err)
+
+	// Override the chain cost so it's negative.
+	const expectedChainCost = btcutil.Amount(1000)
+
+	// Override the swap state to make it look like the swap is finished
+	// and make the chain cost negative too, so we can test that it'll be
+	// corrected to be positive in the cost calculation.
+	err = store.UpdateLoopOut(
+		context.Background(), initResult.swap.hash, time.Now(),
+		loopdb.SwapStateData{
+			State: loopdb.StateSuccess,
+			Cost: loopdb.SwapCost{
+				Onchain: -expectedChainCost,
+			},
+		},
+	)
+	require.NoError(t, err)
+
+	// Add the two mocked payment to LND. Note that we only care about the
+	// fees here, so we don't need to provide the full payment details.
+	lnd.Payments = []lndclient.Payment{
+		{
+			Hash: server.swapHash,
+			Fee:  lnwire.NewMSatFromSatoshis(44),
+		},
+		{
+			Hash: server.prepayHash,
+			Fee:  lnwire.NewMSatFromSatoshis(11),
+		},
+	}
+
+	// Now we can run the migration.
+	err = MigrateLoopOutCosts(context.Background(), lnd.LndServices, store)
+	require.NoError(t, err)
+
+	// Finally check that the swap cost has been updated correctly.
+	swap, err := store.FetchLoopOutSwap(
+		context.Background(), initResult.swap.hash,
+	)
+	require.NoError(t, err)
+
+	expectedServerCost := server.swapInvoiceAmt + server.prepayInvoiceAmt -
+		swap.Contract.AmountRequested
+
+	costs := swap.Events[0].Cost
+	expectedOffchainCost := btcutil.Amount(44 + 11)
+	require.Equal(t, expectedServerCost, costs.Server)
+	require.Equal(t, expectedOffchainCost, costs.Offchain)
+	require.Equal(t, expectedChainCost, costs.Onchain)
+
+	// Now run the migration again to make sure it doesn't fail. This also
+	// indicates that the migration did not run the second time as
+	// otherwise the store mocks SetMigration function would fail.
+	err = MigrateLoopOutCosts(context.Background(), lnd.LndServices, store)
+	require.NoError(t, err)
+}

loopd/daemon.go

@@ -409,6 +409,12 @@ func (d *Daemon) initialize(withMacaroonService bool) error {
 		return err
 	}
 
+	// Run the costs migration.
+	err = loop.MigrateLoopOutCosts(d.mainCtx, d.lnd.LndServices, swapDb)
+	if err != nil {
+		return err
+	}
+
 	sweeperDb := sweepbatcher.NewSQLStore(baseDb, chainParams)
 
 	// Create an instance of the loop client library.

loopdb/interface.go

@@ -65,6 +65,18 @@ type SwapStore interface {
 	// it's decoding using the proto package's `Unmarshal` method.
 	FetchLiquidityParams(ctx context.Context) ([]byte, error)
 
+	// BatchUpdateLoopOutSwapCosts updates the swap costs for a batch of
+	// loop out swaps.
+	BatchUpdateLoopOutSwapCosts(ctx context.Context,
+		swaps map[lntypes.Hash]SwapCost) error
+
+	// HasMigration returns true if the migration with the given ID has
+	// been done.
+	HasMigration(ctx context.Context, migrationID string) (bool, error)
+
+	// SetMigration marks the migration with the given ID as done.
+	SetMigration(ctx context.Context, migrationID string) error
+
 	// Close closes the underlying database.
 	Close() error
 }

loopdb/sql_store.go

@@ -407,6 +407,61 @@ func (s *BaseDB) BatchInsertUpdate(ctx context.Context,
 	})
 }
 
+// BatchUpdateLoopOutSwapCosts updates the swap costs for a batch of loop out
+// swaps.
+func (b *BaseDB) BatchUpdateLoopOutSwapCosts(ctx context.Context,
+	costs map[lntypes.Hash]SwapCost) error {
+
+	writeOpts := &SqliteTxOptions{}
+	return b.ExecTx(ctx, writeOpts, func(tx *sqlc.Queries) error {
+		for swapHash, cost := range costs {
+			lastUpdateID, err := tx.GetLastUpdateID(
+				ctx, swapHash[:],
+			)
+			if err != nil {
+				return err
+			}
+
+			err = tx.OverrideSwapCosts(
+				ctx, sqlc.OverrideSwapCostsParams{
+					ID:           lastUpdateID,
+					ServerCost:   int64(cost.Server),
+					OnchainCost:  int64(cost.Onchain),
+					OffchainCost: int64(cost.Offchain),
+				},
+			)
+			if err != nil {
+				return err
+			}
+		}
+
+		return nil
+	})
+}
+
+// HasMigration returns true if the migration with the given ID has been done.
+func (b *BaseDB) HasMigration(ctx context.Context, migrationID string) (
+	bool, error) {
+
+	migration, err := b.GetMigration(ctx, migrationID)
+	if err != nil && !errors.Is(err, sql.ErrNoRows) {
+		return false, err
+	}
+
+	return migration.MigrationTs.Valid, nil
+}
+
+// SetMigration marks the migration with the given ID as done.
+func (b *BaseDB) SetMigration(ctx context.Context, migrationID string) error {
+	return b.InsertMigration(ctx, sqlc.InsertMigrationParams{
+		MigrationID: migrationID,
+		MigrationTs: sql.NullTime{
+			Time:  time.Now().UTC(),
+			Valid: true,
+		},
+	})
+}
+
 // loopToInsertArgs converts a SwapContract struct to the arguments needed to
 // insert it into the database.
 func loopToInsertArgs(hash lntypes.Hash,

loopdb/sql_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/lightninglabs/loop/loopdb/sqlc"
 	"github.com/lightninglabs/loop/test"
 	"github.com/lightningnetwork/lnd/keychain"
+	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/stretchr/testify/require"
 )
@@ -396,6 +397,140 @@ func TestIssue615(t *testing.T) {
 	require.NoError(t, err)
 }
 
+// TestBatchUpdateCost tests that we can batch update the cost of multiple swaps
+// at once.
+func TestBatchUpdateCost(t *testing.T) {
+	// Create a new sqlite store for testing.
+	store := NewTestDB(t)
+
+	destAddr := test.GetDestAddr(t, 0)
+	initiationTime := time.Date(2018, 11, 1, 0, 0, 0, 0, time.UTC)
+
+	testContract := LoopOutContract{
+		SwapContract: SwapContract{
+			AmountRequested: 100,
+			CltvExpiry:      144,
+			HtlcKeys: HtlcKeys{
+				SenderScriptKey:        senderKey,
+				ReceiverScriptKey:      receiverKey,
+				SenderInternalPubKey:   senderInternalKey,
+				ReceiverInternalPubKey: receiverInternalKey,
+				ClientScriptKeyLocator: keychain.KeyLocator{
+					Family: 1,
+					Index:  2,
+				},
+			},
+			MaxMinerFee: 10,
+			MaxSwapFee:  20,
+
+			InitiationHeight: 99,
+
+			InitiationTime:  initiationTime,
+			ProtocolVersion: ProtocolVersionMuSig2,
+		},
+		MaxPrepayRoutingFee:     40,
+		PrepayInvoice:           "prepayinvoice",
+		DestAddr:                destAddr,
+		SwapInvoice:             "swapinvoice",
+		MaxSwapRoutingFee:       30,
+		SweepConfTarget:         2,
+		HtlcConfirmations:       2,
+		SwapPublicationDeadline: initiationTime,
+		PaymentTimeout:          time.Second * 11,
+	}
+
+	makeSwap := func(preimage lntypes.Preimage) *LoopOutContract {
+		contract := testContract
+		contract.Preimage = preimage
+
+		return &contract
+	}
+
+	// Next, we'll add two swaps to the database.
+	preimage1 := testPreimage
+	preimage2 := lntypes.Preimage{4, 4, 4}
+
+	ctxb := context.Background()
+	swap1 := makeSwap(preimage1)
+	swap2 := makeSwap(preimage2)
+
+	hash1 := swap1.Preimage.Hash()
+	err := store.CreateLoopOut(ctxb, hash1, swap1)
+	require.NoError(t, err)
+
+	hash2 := swap2.Preimage.Hash()
+	err = store.CreateLoopOut(ctxb, hash2, swap2)
+	require.NoError(t, err)
+
+	// Add an update to both swaps containing the cost.
+	err = store.UpdateLoopOut(
+		ctxb, hash1, testTime,
+		SwapStateData{
+			State: StateSuccess,
+			Cost: SwapCost{
+				Server:   1,
+				Onchain:  2,
+				Offchain: 3,
+			},
+		},
+	)
+	require.NoError(t, err)
+
+	err = store.UpdateLoopOut(
+		ctxb, hash2, testTime,
+		SwapStateData{
+			State: StateSuccess,
+			Cost: SwapCost{
+				Server:   4,
+				Onchain:  5,
+				Offchain: 6,
+			},
+		},
+	)
+	require.NoError(t, err)
+
+	updateMap := map[lntypes.Hash]SwapCost{
+		hash1: {
+			Server:   2,
+			Onchain:  3,
+			Offchain: 4,
+		},
+		hash2: {
+			Server:   6,
+			Onchain:  7,
+			Offchain: 8,
+		},
+	}
+	require.NoError(t, store.BatchUpdateLoopOutSwapCosts(ctxb, updateMap))
+
+	swaps, err := store.FetchLoopOutSwaps(ctxb)
+	require.NoError(t, err)
+	require.Len(t, swaps, 2)
+
+	swapsMap := make(map[lntypes.Hash]*LoopOut)
+	swapsMap[swaps[0].Hash] = swaps[0]
+	swapsMap[swaps[1].Hash] = swaps[1]
+
+	require.Equal(t, updateMap[hash1], swapsMap[hash1].State().Cost)
+	require.Equal(t, updateMap[hash2], swapsMap[hash2].State().Cost)
+}
+
+// TestMigrationTracker tests the migration tracker functionality.
+func TestMigrationTracker(t *testing.T) {
+	ctxb := context.Background()
+
+	// Create a new sqlite store for testing.
+	sqlDB := NewTestDB(t)
+	hasMigration, err := sqlDB.HasMigration(ctxb, "test")
+	require.NoError(t, err)
+	require.False(t, hasMigration)
+
+	require.NoError(t, sqlDB.SetMigration(ctxb, "test"))
+	hasMigration, err = sqlDB.HasMigration(ctxb, "test")
+	require.NoError(t, err)
+	require.True(t, hasMigration)
+}
+
 const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
 
 func randomString(length int) string {

loopdb/sqlc/migration_tracker.sql.go

@@ -0,0 +1,45 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.25.0
+// source: migration_tracker.sql
+
+package sqlc
+
+import (
+	"context"
+	"database/sql"
+)
+
+const getMigration = `-- name: GetMigration :one
+SELECT
+  migration_id,
+  migration_ts
+FROM
+  migration_tracker
+WHERE
+  migration_id = $1
+`
+
+func (q *Queries) GetMigration(ctx context.Context, migrationID string) (MigrationTracker, error) {
+	row := q.db.QueryRowContext(ctx, getMigration, migrationID)
+	var i MigrationTracker
+	err := row.Scan(&i.MigrationID, &i.MigrationTs)
+	return i, err
+}
+
+const insertMigration = `-- name: InsertMigration :exec
+INSERT INTO migration_tracker (
+  migration_id,
+  migration_ts
+) VALUES ($1, $2)
+`
+
+type InsertMigrationParams struct {
+	MigrationID string
+	MigrationTs sql.NullTime
+}
+
+func (q *Queries) InsertMigration(ctx context.Context, arg InsertMigrationParams) error {
+	_, err := q.db.ExecContext(ctx, insertMigration, arg.MigrationID, arg.MigrationTs)
+	return err
+}

loopdb/sqlc/migrations/000008_migration_tracker.down.sql

@@ -0,0 +1,2 @@
+DROP TABLE migration_tracker;
+

loopdb/sqlc/migrations/000008_migration_tracker.up.sql

@@ -0,0 +1,9 @@
+CREATE TABLE migration_tracker (
+        -- migration_id is the id of the migration.
+        migration_id TEXT NOT NULL,
+
+        -- migration_ts is the timestamp at which the migration was run.
+        migration_ts TIMESTAMP,
+
+        PRIMARY KEY (migration_id)
+);

loopdb/sqlc/models.go

@@ -67,6 +67,11 @@ type LoopoutSwap struct {
 	PaymentTimeout      int32
 }
 
+type MigrationTracker struct {
+	MigrationID string
+	MigrationTs sql.NullTime
+}
+
 type Reservation struct {
 	ID                 int32
 	ReservationID      []byte

loopdb/sqlc/querier.go

@@ -18,10 +18,12 @@ type Querier interface {
 	GetInstantOutSwap(ctx context.Context, swapHash []byte) (GetInstantOutSwapRow, error)
 	GetInstantOutSwapUpdates(ctx context.Context, swapHash []byte) ([]InstantoutUpdate, error)
 	GetInstantOutSwaps(ctx context.Context) ([]GetInstantOutSwapsRow, error)
+	GetLastUpdateID(ctx context.Context, swapHash []byte) (int32, error)
 	GetLoopInSwap(ctx context.Context, swapHash []byte) (GetLoopInSwapRow, error)
 	GetLoopInSwaps(ctx context.Context) ([]GetLoopInSwapsRow, error)
 	GetLoopOutSwap(ctx context.Context, swapHash []byte) (GetLoopOutSwapRow, error)
 	GetLoopOutSwaps(ctx context.Context) ([]GetLoopOutSwapsRow, error)
+	GetMigration(ctx context.Context, migrationID string) (MigrationTracker, error)
 	GetParentBatch(ctx context.Context, swapHash []byte) (SweepBatch, error)
 	GetReservation(ctx context.Context, reservationID []byte) (Reservation, error)
 	GetReservationUpdates(ctx context.Context, reservationID []byte) ([]ReservationUpdate, error)
@@ -35,9 +37,11 @@ type Querier interface {
 	InsertInstantOutUpdate(ctx context.Context, arg InsertInstantOutUpdateParams) error
 	InsertLoopIn(ctx context.Context, arg InsertLoopInParams) error
 	InsertLoopOut(ctx context.Context, arg InsertLoopOutParams) error
+	InsertMigration(ctx context.Context, arg InsertMigrationParams) error
 	InsertReservationUpdate(ctx context.Context, arg InsertReservationUpdateParams) error
 	InsertSwap(ctx context.Context, arg InsertSwapParams) error
 	InsertSwapUpdate(ctx context.Context, arg InsertSwapUpdateParams) error
+	OverrideSwapCosts(ctx context.Context, arg OverrideSwapCostsParams) error
 	UpdateBatch(ctx context.Context, arg UpdateBatchParams) error
 	UpdateInstantOut(ctx context.Context, arg UpdateInstantOutParams) error
 	UpdateReservation(ctx context.Context, arg UpdateReservationParams) error

loopdb/sqlc/queries/migration_tracker.sql

@@ -0,0 +1,14 @@
+-- name: InsertMigration :exec
+INSERT INTO migration_tracker (
+  migration_id,
+  migration_ts
+) VALUES ($1, $2);
+
+-- name: GetMigration :one
+SELECT
+  migration_id,
+  migration_ts
+FROM
+  migration_tracker
+WHERE
+  migration_id = $1;

loopdb/sqlc/queries/swaps.sql

@@ -133,3 +133,19 @@ INSERT INTO htlc_keys(
 ) VALUES (
     $1, $2, $3, $4, $5, $6, $7
 );
+
+-- name: GetLastUpdateID :one
+SELECT id
+FROM swap_updates
+WHERE swap_hash = $1
+ORDER BY update_timestamp DESC
+LIMIT 1;
+
+-- name: OverrideSwapCosts :exec
+UPDATE swap_updates
+SET 
+    server_cost = $2,
+    onchain_cost = $3,
+    offchain_cost = $4
+WHERE id = $1;
+

loopdb/sqlc/swaps.sql.go

@@ -10,6 +10,21 @@ import (
 	"time"
 )
 
+const getLastUpdateID = `-- name: GetLastUpdateID :one
+SELECT id
+FROM swap_updates
+WHERE swap_hash = $1
+ORDER BY update_timestamp DESC
+LIMIT 1
+`
+
+func (q *Queries) GetLastUpdateID(ctx context.Context, swapHash []byte) (int32, error) {
+	row := q.db.QueryRowContext(ctx, getLastUpdateID, swapHash)
+	var id int32
+	err := row.Scan(&id)
+	return id, err
+}
+
 const getLoopInSwap = `-- name: GetLoopInSwap :one
 SELECT
     swaps.id, swaps.swap_hash, swaps.preimage, swaps.initiation_time, swaps.amount_requested, swaps.cltv_expiry, swaps.max_miner_fee, swaps.max_swap_fee, swaps.initiation_height, swaps.protocol_version, swaps.label,
@@ -596,3 +611,29 @@ func (q *Queries) InsertSwapUpdate(ctx context.Context, arg InsertSwapUpdatePara
 	)
 	return err
 }
+
+const overrideSwapCosts = `-- name: OverrideSwapCosts :exec
+UPDATE swap_updates
+SET 
+    server_cost = $2,
+    onchain_cost = $3,
+    offchain_cost = $4
+WHERE id = $1
+`
+
+type OverrideSwapCostsParams struct {
+	ID           int32
+	ServerCost   int64
+	OnchainCost  int64
+	OffchainCost int64
+}
+
+func (q *Queries) OverrideSwapCosts(ctx context.Context, arg OverrideSwapCostsParams) error {
+	_, err := q.db.ExecContext(ctx, overrideSwapCosts,
+		arg.ID,
+		arg.ServerCost,
+		arg.OnchainCost,
+		arg.OffchainCost,
+	)
+	return err
+}

loopdb/store.go

@@ -1009,3 +1009,25 @@ func (b *boltSwapStore) BatchInsertUpdate(ctx context.Context,
 
 	return errUnimplemented
 }
+
+// BatchUpdateLoopOutSwapCosts updates the swap costs for a batch of loop out
+// swaps.
+func (b *boltSwapStore) BatchUpdateLoopOutSwapCosts(ctx context.Context,
+	costs map[lntypes.Hash]SwapCost) error {
+
+	return errUnimplemented
+}
+
+// HasMigration returns true if the migration with the given ID has been done.
+func (b *boltSwapStore) HasMigration(ctx context.Context, migrationID string) (
+	bool, error) {
+
+	return false, errUnimplemented
+}
+
+// SetMigration marks the migration with the given ID as done.
+func (b *boltSwapStore) SetMigration(ctx context.Context,
+	migrationID string) error {
+
+	return errUnimplemented
+}

loopdb/store_mock.go

@@ -3,6 +3,7 @@ package loopdb
 import (
 	"context"
 	"errors"
+	"fmt"
 	"testing"
 	"time"
 
@@ -23,6 +24,8 @@ type StoreMock struct {
 	loopInStoreChan  chan LoopInContract
 	loopInUpdateChan chan SwapStateData
 
+	migrations map[string]struct{}
+
 	t *testing.T
 }
 
@@ -38,6 +41,7 @@ func NewStoreMock(t *testing.T) *StoreMock {
 		loopInUpdateChan: make(chan SwapStateData, 1),
 		LoopInSwaps:      make(map[lntypes.Hash]*LoopInContract),
 		LoopInUpdates:    make(map[lntypes.Hash][]SwapStateData),
+		migrations:       make(map[string]struct{}),
 		t:                t,
 	}
 }
@@ -337,3 +341,46 @@ func (b *StoreMock) BatchInsertUpdate(ctx context.Context,
 
 	return errors.New("not implemented")
 }
+
+// BatchUpdateLoopOutSwapCosts updates the swap costs for a batch of loop out
+// swaps.
+func (s *StoreMock) BatchUpdateLoopOutSwapCosts(ctx context.Context,
+	costs map[lntypes.Hash]SwapCost) error {
+
+	for hash, cost := range costs {
+		if _, ok := s.LoopOutUpdates[hash]; !ok {
+			return fmt.Errorf("swap has no updates: %v", hash)
+		}
+
+		updates, ok := s.LoopOutUpdates[hash]
+		if !ok {
+			return fmt.Errorf("swap has no updates: %v", hash)
+		}
+
+		updates[len(updates)-1].Cost = cost
+	}
+
+	return nil
+}
+
+// HasMigration returns true if the migration with the given ID has been done.
+func (s *StoreMock) HasMigration(ctx context.Context, migrationID string) (
+	bool, error) {
+
+	_, ok := s.migrations[migrationID]
+
+	return ok, nil
+}
+
+// SetMigration marks the migration with the given ID as done.
+func (s *StoreMock) SetMigration(ctx context.Context,
+	migrationID string) error {
+
+	if _, ok := s.migrations[migrationID]; ok {
+		return errors.New("migration already done")
+	}
+
+	s.migrations[migrationID] = struct{}{}
+
+	return nil
+}

loopout.go

@@ -77,6 +77,10 @@ type loopOutSwap struct {
 
 	swapInvoicePaymentAddr [32]byte
 
+	// prepayAmount holds the amount of the prepay invoice. We use this
+	// to calculate the total cost of the swap.
+	prepayAmount btcutil.Amount
+
 	swapPaymentChan chan paymentResult
 	prePaymentChan  chan paymentResult
 
@@ -466,16 +470,20 @@ func (s *loopOutSwap) handlePaymentResult(result paymentResult,
 		if swapPayment {
 			// The client pays for the swap with the swap invoice,
 			// so we can calculate the total cost of the swap by
-			// subtracting the amount requested from the amount we
-			// actually paid.
-			s.cost.Server += result.status.Value.ToSatoshis() -
+			// subtracting the amount requested from the total
+			// amount that we actually paid (which is the sum of
+			// the swap invoice amount and the prepay invoice
+			// amount).
+			s.cost.Server += s.prepayAmount +
+				result.status.Value.ToSatoshis() -
 				s.AmountRequested
-
-			// On top of the swap cost we also pay for routing which
-			// is reflected in the fee.
-			s.cost.Offchain += result.status.Fee.ToSatoshis()
 		}
 
+		// On top of the swap cost we also pay for routing which
+		// is reflected in the fee. We add the off-chain fee for both
+		// the swap payment and the prepay.
+		s.cost.Offchain += result.status.Fee.ToSatoshis()
+
 		return nil
 
 	case result.status.State == lnrpc.Payment_FAILED:
@@ -489,6 +497,16 @@ func (s *loopOutSwap) handlePaymentResult(result paymentResult,
 // executeSwap executes the swap, but returns as soon as the swap outcome is
 // final. At that point, there may still be pending off-chain payment(s).
 func (s *loopOutSwap) executeSwap(globalCtx context.Context) error {
+	// Decode the prepay invoice so we can ensure that we account for the
+	// prepay amount when calculating the final costs of the swap.
+	_, _, _, amt, err := swap.DecodeInvoice(
+		s.lnd.ChainParams, s.PrepayInvoice,
+	)
+	if err != nil {
+		return err
+	}
+	s.prepayAmount = amt
+
 	// We always pay both invoices (again). This is currently the only way
 	// to sort of resume payments.
 	//

server_mock_test.go

@@ -42,6 +42,7 @@ type serverMock struct {
 
 	swapInvoice string
 	swapHash    lntypes.Hash
+	prepayHash  lntypes.Hash
 
 	// preimagePush is a channel that preimage pushes are sent into.
 	preimagePush chan lntypes.Preimage
@@ -81,13 +82,17 @@ func (s *serverMock) NewLoopOutSwap(_ context.Context, swapHash lntypes.Hash,
 		return nil, errors.New("unexpected test swap amount")
 	}
 
+	s.swapHash = swapHash
 	swapPayReqString, err := getInvoice(swapHash, s.swapInvoiceAmt,
 		swapInvoiceDesc)
 	if err != nil {
 		return nil, err
 	}
 
-	prePayReqString, err := getInvoice(swapHash, s.prepayInvoiceAmt,
+	// Set the prepay hash to be different from the swap hash.
+	s.prepayHash = swapHash
+	s.prepayHash[0] ^= 1
+	prePayReqString, err := getInvoice(s.prepayHash, s.prepayInvoiceAmt,
 		prepayInvoiceDesc)
 	if err != nil {
 		return nil, err