htlcswitch: add cleanStore method

That let us clean up handed off payment results, as they will never be
queried again.

htlcswitch/payment_result.go

@@ -258,3 +258,48 @@ func fetchResult(tx kvdb.RTx, pid uint64) (*networkResult, error) {
 
 	return deserializeNetworkResult(r)
 }
+
+// cleanStore removes all entries from the store, except the payment IDs given.
+// NOTE: Since every result not listed in the keep map will be deleted, care
+// should be taken to ensure no new payment attempts are being made
+// concurrently while this process is ongoing, as its result might end up being
+// deleted.
+func (store *networkResultStore) cleanStore(keep map[uint64]struct{}) error {
+	return kvdb.Update(store.db.Backend, func(tx kvdb.RwTx) error {
+		networkResults, err := tx.CreateTopLevelBucket(
+			networkResultStoreBucketKey,
+		)
+		if err != nil {
+			return err
+		}
+
+		// Iterate through the bucket, deleting all items not in the
+		// keep map.
+		var toClean [][]byte
+		if err := networkResults.ForEach(func(k, _ []byte) error {
+			pid := binary.BigEndian.Uint64(k)
+			if _, ok := keep[pid]; ok {
+				return nil
+			}
+
+			toClean = append(toClean, k)
+			return nil
+		}); err != nil {
+			return err
+		}
+
+		for _, k := range toClean {
+			err := networkResults.Delete(k)
+			if err != nil {
+				return err
+			}
+		}
+
+		if len(toClean) > 0 {
+			log.Infof("Removed %d stale entries from network "+
+				"result store", len(toClean))
+		}
+
+		return nil
+	})
+}

htlcswitch/payment_result_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/stretchr/testify/require"
 )
 
 // TestNetworkResultSerialization checks that NetworkResults are properly
@@ -180,7 +181,6 @@ func TestNetworkResultStore(t *testing.T) {
 
 	// Since we don't delete results from the store (yet), make sure we
 	// will get subscriptions for all of them.
-	// TODO(halseth): check deletion when we have reliable handoff.
 	for i := uint64(0); i < numResults; i++ {
 		sub, err := store.subscribeResult(i)
 		if err != nil {
@@ -193,4 +193,25 @@ func TestNetworkResultStore(t *testing.T) {
 			t.Fatalf("no result received")
 		}
 	}
+
+	// Clean the store keeping the first two results.
+	toKeep := map[uint64]struct{}{
+		0: {},
+		1: {},
+	}
+	// Finally, delete the result.
+	err = store.cleanStore(toKeep)
+	require.NoError(t, err)
+
+	// Payment IDs 0 and 1 should be found, 2 and 3 should be deleted.
+	for i := uint64(0); i < numResults; i++ {
+		_, err = store.getResult(i)
+		if i <= 1 {
+			require.NoError(t, err, "unable to get result")
+		}
+		if i >= 2 && err != ErrPaymentIDNotFound {
+			t.Fatalf("expected ErrPaymentIDNotFound, got %v", err)
+		}
+
+	}
 }