sweepbatcher: add method DryRun

sweepbatcher/sweep_batcher.go

@@ -517,6 +517,37 @@ func NewBatcher(wallet lndclient.WalletKitClient,
 	}
 }
 
+// DryRun tests if the batcher can start, but does not start it.
+// This method is useful to check if dependency databases are ready.
+func (b *Batcher) DryRun(ctx context.Context) error {
+	// First we fetch all the batches that are not in a confirmed state from
+	// the database. We will then load their sweeps to make sure it works.
+	batches, err := b.FetchUnconfirmedBatches(ctx)
+	if err != nil {
+		return fmt.Errorf("b.FetchUnconfirmedBatches failed: %w", err)
+	}
+
+	for _, batch := range batches {
+		dbSweeps, err := b.store.FetchBatchSweeps(ctx, batch.id)
+		if err != nil {
+			return fmt.Errorf("store.FetchBatchSweeps failed: %w",
+				err)
+		}
+
+		for _, dbSweep := range dbSweeps {
+			swapHash := dbSweep.SwapHash
+			_, err = b.sweepStore.FetchSweep(ctx, swapHash)
+			if err != nil {
+				return fmt.Errorf("failed to fetch sweep "+
+					"data for %x: %w", swapHash[:6], err)
+			}
+		}
+	}
+
+	// Everything was loaded successfully.
+	return nil
+}
+
 // Run starts the batcher and processes incoming sweep requests.
 func (b *Batcher) Run(ctx context.Context) error {
 	runCtx, cancel := context.WithCancel(ctx)

sweepbatcher/sweep_batcher_test.go

@@ -2810,11 +2810,16 @@ func testRestoringPreservesConfTarget(t *testing.T, store testStore,
 
 type sweepFetcherMock struct {
 	store map[lntypes.Hash]*SweepInfo
+	err   error
 }
 
 func (f *sweepFetcherMock) FetchSweep(ctx context.Context, hash lntypes.Hash) (
 	*SweepInfo, error) {
 
+	if f.err != nil {
+		return nil, f.err
+	}
+
 	return f.store[hash], nil
 }
 
@@ -2972,6 +2977,17 @@ func testSweepFetcher(t *testing.T, store testStore,
 
 	// Make sure the batcher exited without an error.
 	checkBatcherError(t, runErr)
+
+	// Check DryRun method.
+	batcher2 := NewBatcher(lnd.WalletKit, lnd.ChainNotifier, lnd.Signer,
+		nil, testVerifySchnorrSig, lnd.ChainParams,
+		batcherStore, sweepFetcher, WithCustomFeeRate(customFeeRate),
+		WithCustomSignMuSig2(testSignMuSig2func))
+	ctx = context.Background()
+	sweepFetcher.err = errors.New("test FetchSweep error")
+	require.ErrorIs(t, batcher2.DryRun(ctx), sweepFetcher.err)
+	sweepFetcher.err = nil
+	require.NoError(t, batcher2.DryRun(ctx))
 }
 
 // testSweepBatcherCloseDuringAdding tests that sweep batcher works correctly