accounts: implement sqlc DebitAccount

This commit introduces the `DebitAccount` function in the sqlc store, to
support decreasing the balance of an existing off-chain account by a
specified amount for sql backends.

We'll also add testing of the store functionality, as both stores now
support the `DebitAccount` operation.

Author: ViktorT-11

accounts/interface.go

@@ -257,6 +257,11 @@ type Store interface {
 	CreditAccount(ctx context.Context, id AccountID,
 		amount lnwire.MilliSatoshi) error
 
+	// DebitAccount decreases the balance of the account with the
+	// given ID by the given amount.
+	DebitAccount(ctx context.Context, id AccountID,
+		amount lnwire.MilliSatoshi) error
+
 	// UpsertAccountPayment updates or inserts a payment entry for the given
 	// account. Various functional options can be passed to modify the
 	// behavior of the method. The returned boolean is true if the payment

accounts/store_kvdb.go

@@ -246,6 +246,8 @@ func (s *BoltStore) CreditAccount(_ context.Context, id AccountID,
 
 // DebitAccount decreases the balance of the account with the given ID
 // by the given amount.
+//
+// NOTE: This is part of the Store interface.
 func (s *BoltStore) DebitAccount(_ context.Context, id AccountID,
 	amount lnwire.MilliSatoshi) error {
 

accounts/store_sql.go

@@ -34,6 +34,7 @@ const (
 //nolint:lll
 type SQLQueries interface {
 	AddAccountInvoice(ctx context.Context, arg sqlc.AddAccountInvoiceParams) error
+	DebitAccount(ctx context.Context, arg sqlc.DebitAccountParams) (int64, error)
 	DeleteAccount(ctx context.Context, id int64) error
 	DeleteAccountPayment(ctx context.Context, arg sqlc.DeleteAccountPaymentParams) error
 	GetAccount(ctx context.Context, id int64) (sqlc.Account, error)
@@ -417,6 +418,38 @@ func (s *SQLStore) CreditAccount(ctx context.Context, alias AccountID,
 	})
 }
 
+// DebitAccount decreases the balance of the account with the given alias by
+// the given amount.
+//
+// NOTE: This is part of the Store interface.
+func (s *SQLStore) DebitAccount(ctx context.Context, alias AccountID,
+	amount lnwire.MilliSatoshi) error {
+
+	var writeTxOpts db.QueriesTxOptions
+	return s.db.ExecTx(ctx, &writeTxOpts, func(db SQLQueries) error {
+		id, err := getAccountIDByAlias(ctx, db, alias)
+		if err != nil {
+			return err
+		}
+
+		id, err = db.DebitAccount(
+			ctx, sqlc.DebitAccountParams{
+				ID:     id,
+				Amount: int64(amount),
+			},
+		)
+		if errors.Is(err, sql.ErrNoRows) {
+			return fmt.Errorf("cannot debit %v from the account "+
+				"balance, as the resulting balance would be "+
+				"below 0", int64(amount/1000))
+		} else if err != nil {
+			return err
+		}
+
+		return s.markAccountUpdated(ctx, db, id)
+	})
+}
+
 // Account retrieves an account from the SQL store and un-marshals it. If the
 // account cannot be found, then ErrAccNotFound is returned.
 //

accounts/store_test.go

@@ -2,6 +2,7 @@ package accounts
 
 import (
 	"context"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"testing"
 	"time"
 
@@ -71,6 +72,14 @@ func TestAccountStore(t *testing.T) {
 	)
 	require.NoError(t, err)
 
+	// Adjust the account balance by first crediting 10000, and then
+	// debiting 5000.
+	err = store.CreditAccount(ctx, acct1.ID, lnwire.MilliSatoshi(10000))
+	require.NoError(t, err)
+
+	err = store.DebitAccount(ctx, acct1.ID, lnwire.MilliSatoshi(5000))
+	require.NoError(t, err)
+
 	// Update the in-memory account so that we can compare it with the
 	// account we get from the store.
 	acct1.CurrentBalance = -500
@@ -85,11 +94,30 @@ func TestAccountStore(t *testing.T) {
 	}
 	acct1.Invoices[lntypes.Hash{12, 34, 56, 78}] = struct{}{}
 	acct1.Invoices[lntypes.Hash{34, 56, 78, 90}] = struct{}{}
+	acct1.CurrentBalance += 10000
+	acct1.CurrentBalance -= 5000
 
 	dbAccount, err = store.Account(ctx, acct1.ID)
 	require.NoError(t, err)
 	assertEqualAccounts(t, acct1, dbAccount)
 
+	// Test that adjusting the balance to exactly 0 should work, while
+	// adjusting the balance to below 0 should fail.
+	err = store.DebitAccount(
+		ctx, acct1.ID, lnwire.MilliSatoshi(acct1.CurrentBalance),
+	)
+	require.NoError(t, err)
+
+	acct1.CurrentBalance = 0
+
+	dbAccount, err = store.Account(ctx, acct1.ID)
+	require.NoError(t, err)
+	assertEqualAccounts(t, acct1, dbAccount)
+
+	// Adjusting the value to below 0 should fail.
+	err = store.DebitAccount(ctx, acct1.ID, lnwire.MilliSatoshi(1))
+	require.ErrorContains(t, err, "balance would be below 0")
+
 	// Sleep just a tiny bit to make sure we are never too quick to measure
 	// the expiry, even though the time is nanosecond scale and writing to
 	// the store and reading again should take at least a couple of

db/sqlc/accounts.sql.go

@@ -9,6 +9,13 @@ SET current_balance_msat = $1
 WHERE id = $2
 RETURNING id;
 
+-- name: DebitAccount :one
+UPDATE accounts
+SET current_balance_msat = current_balance_msat - sqlc.arg(amount)
+WHERE id = sqlc.arg(id)
+AND current_balance_msat >= sqlc.arg(amount)
+RETURNING id;
+
 -- name: UpdateAccountExpiry :one
 UPDATE accounts
 SET expiration = $1