feat(ledger): add append-only double-entry engine
The Lightning bridge is modelled as the boundary with the outside world and is the one account permitted to go negative; its negative balance is exactly what is owed to players inside the system. All other accounts are floored at zero by both the application and a database trigger. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
drjones
229
pkg/ledger/ledger_test.go
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229
pkg/ledger/ledger_test.go
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@@ -0,0 +1,229 @@
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package ledger_test
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import (
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"context"
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"errors"
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"fmt"
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"math/rand"
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"os"
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"sync"
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"testing"
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"time"
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"github.com/drjones/quantum-arcade/pkg/ledger"
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"github.com/jackc/pgx/v5/pgxpool"
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)
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func testPool(t *testing.T) *pgxpool.Pool {
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t.Helper()
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dsn := os.Getenv("ARCADE_TEST_DSN")
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if dsn == "" {
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dsn = "postgres://arcade:arcade_dev@localhost:5432/arcade"
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}
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pool, err := pgxpool.New(context.Background(), dsn)
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if err != nil {
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t.Skipf("no database available: %v", err)
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}
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if err := pool.Ping(context.Background()); err != nil {
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t.Skipf("no database available: %v", err)
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}
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return pool
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}
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// runID is fresh for each execution of the test binary. The ledger is
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// append-only and never truncated, so accounts must not be shared between runs
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// or balances would accumulate across them.
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var runID = fmt.Sprintf("%d-%d", time.Now().UnixNano(), rand.Int63())
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// uniqueKey produces an account key unique to this test and this run.
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func uniqueKey(t *testing.T, label string) []byte {
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t.Helper()
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return []byte(fmt.Sprintf("%s-%s-%s", runID, t.Name(), label))
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}
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func TestPostRejectsUnbalanced(t *testing.T) {
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l := ledger.New(testPool(t))
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ctx := context.Background()
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a, err := l.EnsurePlayer(ctx, uniqueKey(t, "a"))
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if err != nil {
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t.Fatal(err)
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}
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b, err := l.EnsurePlayer(ctx, uniqueKey(t, "b"))
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if err != nil {
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t.Fatal(err)
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}
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_, err = l.Post(ctx, "test", nil, []ledger.Posting{
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{AccountID: a, AmountMsat: -100},
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{AccountID: b, AmountMsat: 50},
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})
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if !errors.Is(err, ledger.ErrUnbalanced) {
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t.Fatalf("got %v, want ErrUnbalanced", err)
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}
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}
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func TestPostRejectsOverdraft(t *testing.T) {
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l := ledger.New(testPool(t))
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ctx := context.Background()
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a, _ := l.EnsurePlayer(ctx, uniqueKey(t, "a"))
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b, _ := l.EnsurePlayer(ctx, uniqueKey(t, "b"))
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_, err := l.Post(ctx, "test", nil, []ledger.Posting{
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{AccountID: a, AmountMsat: -1_000_000},
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{AccountID: b, AmountMsat: 1_000_000},
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})
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if !errors.Is(err, ledger.ErrInsufficientFunds) {
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t.Fatalf("got %v, want ErrInsufficientFunds", err)
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}
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}
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func TestRejectedTransactionLeavesNoTrace(t *testing.T) {
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l := ledger.New(testPool(t))
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ctx := context.Background()
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a, _ := l.EnsurePlayer(ctx, uniqueKey(t, "a"))
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b, _ := l.EnsurePlayer(ctx, uniqueKey(t, "b"))
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before, err := l.Balance(ctx, a)
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if err != nil {
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t.Fatal(err)
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}
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_, _ = l.Post(ctx, "test", nil, []ledger.Posting{
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{AccountID: a, AmountMsat: -500},
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{AccountID: b, AmountMsat: 500},
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})
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after, err := l.Balance(ctx, a)
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if err != nil {
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t.Fatal(err)
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}
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if before != after {
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t.Fatalf("failed transaction changed balance: %d -> %d", before, after)
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}
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}
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func TestConservationOfValue(t *testing.T) {
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l := ledger.New(testPool(t))
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ctx := context.Background()
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bridge, err := l.AccountByName(ctx, "lightning_bridge")
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if err != nil {
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t.Fatal(err)
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}
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p, _ := l.EnsurePlayer(ctx, uniqueKey(t, "player"))
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before, err := l.TotalIssued(ctx)
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if err != nil {
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t.Fatal(err)
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}
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if _, err := l.Deposit(ctx, p, 5000); err != nil {
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t.Fatal(err)
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}
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if _, err := l.Withdraw(ctx, p, 5000); err != nil {
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t.Fatal(err)
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}
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after, err := l.TotalIssued(ctx)
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if err != nil {
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t.Fatal(err)
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}
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if before != after {
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t.Fatalf("total value changed: %d -> %d", before, after)
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}
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_ = bridge
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}
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func TestBalanceTracksPostings(t *testing.T) {
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l := ledger.New(testPool(t))
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ctx := context.Background()
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p, _ := l.EnsurePlayer(ctx, uniqueKey(t, "p"))
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if _, err := l.Deposit(ctx, p, 12_345); err != nil {
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t.Fatal(err)
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}
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bal, err := l.Balance(ctx, p)
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if err != nil {
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t.Fatal(err)
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}
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if bal != 12_345 {
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t.Fatalf("balance = %d, want 12345", bal)
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}
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}
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// Two concurrent spends of the same funds must not both succeed. The account
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// row lock is what prevents a double-spend under load.
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func TestConcurrentSpendsCannotOverdraw(t *testing.T) {
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l := ledger.New(testPool(t))
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ctx := context.Background()
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from, _ := l.EnsurePlayer(ctx, uniqueKey(t, "from"))
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to, _ := l.EnsurePlayer(ctx, uniqueKey(t, "to"))
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if _, err := l.Deposit(ctx, from, 1000); err != nil {
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t.Fatal(err)
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}
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const workers = 8
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var wg sync.WaitGroup
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succeeded := make([]bool, workers)
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for i := 0; i < workers; i++ {
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wg.Add(1)
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go func(i int) {
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defer wg.Done()
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_, err := l.Transfer(ctx, from, to, 1000)
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succeeded[i] = err == nil
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}(i)
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}
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wg.Wait()
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wins := 0
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for _, ok := range succeeded {
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if ok {
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wins++
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}
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}
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if wins != 1 {
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t.Fatalf("%d concurrent spends of the same 1000 msat succeeded, want 1", wins)
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}
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bal, _ := l.Balance(ctx, from)
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if bal != 0 {
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t.Fatalf("source balance = %d, want 0", bal)
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}
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}
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func TestAppendOnlyEnforcedByDatabase(t *testing.T) {
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pool := testPool(t)
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l := ledger.New(pool)
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ctx := context.Background()
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p, _ := l.EnsurePlayer(ctx, uniqueKey(t, "p"))
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if _, err := l.Deposit(ctx, p, 100); err != nil {
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t.Fatal(err)
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}
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_, err := pool.Exec(ctx, `UPDATE postings SET amount_msat = 999 WHERE account_id = $1`, p)
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if err == nil {
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t.Fatal("UPDATE on postings succeeded; append-only trigger is not working")
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}
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_, err = pool.Exec(ctx, `DELETE FROM postings WHERE account_id = $1`, p)
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if err == nil {
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t.Fatal("DELETE on postings succeeded; append-only trigger is not working")
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}
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}
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func TestHistoryExplainsEveryChange(t *testing.T) {
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l := ledger.New(testPool(t))
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ctx := context.Background()
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p, _ := l.EnsurePlayer(ctx, uniqueKey(t, "p"))
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if _, err := l.Deposit(ctx, p, 800); err != nil {
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t.Fatal(err)
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}
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if _, err := l.Withdraw(ctx, p, 300); err != nil {
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t.Fatal(err)
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}
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entries, err := l.History(ctx, p, 10)
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if err != nil {
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t.Fatal(err)
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}
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if len(entries) != 2 {
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t.Fatalf("got %d history entries, want 2", len(entries))
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}
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// History is newest-first.
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if entries[0].Kind != "withdraw" || entries[0].AmountMsat != -300 {
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t.Fatalf("unexpected newest entry: %+v", entries[0])
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}
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if entries[0].BalanceAfter != 500 {
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t.Fatalf("balance after withdraw = %d, want 500", entries[0].BalanceAfter)
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}
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}
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