graph/db: migrate zombie index to SQL

This commit expands `MigrateGraphToSQL` to include migration of the
zombie index.

NOTE: we take this opportunity to clean up the zombie index a bit by
first checking for each channel in the zombie index if it has been
marked as closed in the closed-scid index. If it has, then there is no
need to include it in the zombie index. A special case test for this
is added too.

graph/db/sql_migration.go

@@ -70,6 +70,11 @@ func MigrateGraphToSQL(ctx context.Context, kvBackend kvdb.Backend,
 			err)
 	}
 
+	// 6) Migrate the zombie index.
+	if err := migrateZombieIndex(ctx, kvBackend, sqlDB); err != nil {
+		return fmt.Errorf("could not migrate zombie index: %w", err)
+	}
+
 	log.Infof("Finished migration of the graph store from KV to SQL in %v",
 		time.Since(t0))
 
@@ -741,6 +746,109 @@ func migrateClosedSCIDIndex(ctx context.Context, kvBackend kvdb.Backend,
 	return nil
 }
 
+// migrateZombieIndex migrates the zombie index from the KV backend to
+// the SQL database. It iterates over each zombie channel in the KV store,
+// inserts it into the SQL database, and then verifies that the channel is
+// indeed marked as a zombie channel in the SQL database.
+//
+// NOTE: before inserting an entry into the zombie index, the function checks
+// if the channel is already marked as closed in the SQL store. If it is,
+// the entry is skipped. This means that the resulting zombie index count in
+// the SQL store may well be less than the count of zombie channels in the KV
+// store.
+func migrateZombieIndex(ctx context.Context, kvBackend kvdb.Backend,
+	sqlDB SQLQueries) error {
+
+	var count uint64
+	err := forEachZombieEntry(kvBackend, func(chanID uint64, pubKey1,
+		pubKey2 [33]byte) error {
+
+		chanIDB := channelIDToBytes(chanID)
+
+		// If it is in the closed SCID index, we don't need to
+		// add it to the zombie index.
+		//
+		// NOTE: this means that the resulting zombie index count in
+		// the SQL store may well be less than the count of zombie
+		// channels in the KV store.
+		isClosed, err := sqlDB.IsClosedChannel(ctx, chanIDB)
+		if err != nil {
+			return fmt.Errorf("could not check closed "+
+				"channel: %w", err)
+		}
+		if isClosed {
+			return nil
+		}
+
+		count++
+
+		err = sqlDB.UpsertZombieChannel(
+			ctx, sqlc.UpsertZombieChannelParams{
+				Version:  int16(ProtocolV1),
+				Scid:     chanIDB,
+				NodeKey1: pubKey1[:],
+				NodeKey2: pubKey2[:],
+			},
+		)
+		if err != nil {
+			return fmt.Errorf("could not upsert zombie "+
+				"channel %d: %w", chanID, err)
+		}
+
+		// Finally, verify that the channel is indeed marked as a
+		// zombie channel.
+		isZombie, err := sqlDB.IsZombieChannel(
+			ctx, sqlc.IsZombieChannelParams{
+				Version: int16(ProtocolV1),
+				Scid:    chanIDB,
+			},
+		)
+		if err != nil {
+			return fmt.Errorf("could not check if "+
+				"channel %d is zombie: %w", chanID, err)
+		}
+
+		if !isZombie {
+			return fmt.Errorf("channel %d should be "+
+				"a zombie, but is not", chanID)
+		}
+
+		return nil
+	})
+	if err != nil {
+		return fmt.Errorf("could not migrate zombie index: %w", err)
+	}
+
+	log.Infof("Migrated %d zombie channels from KV to SQL", count)
+
+	return nil
+}
+
+// forEachZombieEntry iterates over each zombie channel entry in the
+// KV backend and calls the provided callback function for each entry.
+func forEachZombieEntry(db kvdb.Backend, cb func(chanID uint64, pubKey1,
+	pubKey2 [33]byte) error) error {
+
+	return kvdb.View(db, func(tx kvdb.RTx) error {
+		edges := tx.ReadBucket(edgeBucket)
+		if edges == nil {
+			return ErrGraphNoEdgesFound
+		}
+		zombieIndex := edges.NestedReadBucket(zombieBucket)
+		if zombieIndex == nil {
+			return nil
+		}
+
+		return zombieIndex.ForEach(func(k, v []byte) error {
+			var pubKey1, pubKey2 [33]byte
+			copy(pubKey1[:], v[:33])
+			copy(pubKey2[:], v[33:])
+
+			return cb(byteOrder.Uint64(k), pubKey1, pubKey2)
+		})
+	}, func() {})
+}
+
 // forEachClosedSCID iterates over each closed SCID in the KV backend and calls
 // the provided callback function for each SCID.
 func forEachClosedSCID(db kvdb.Backend,

graph/db/sql_migration_test.go

@@ -83,6 +83,12 @@ func TestMigrateGraphToSQL(t *testing.T) {
 		node2 = genPubKey(t)
 	)
 
+	type zombieIndexObject struct {
+		scid    uint64
+		pubKey1 route.Vertex
+		pubKey2 route.Vertex
+	}
+
 	tests := []struct {
 		name          string
 		write         func(t *testing.T, db *KVStore, object any)
@@ -274,6 +280,35 @@ func TestMigrateGraphToSQL(t *testing.T) {
 				lnwire.NewShortChanIDFromInt(4),
 			},
 		},
+		{
+			name: "zombie index",
+			write: func(t *testing.T, db *KVStore, object any) {
+				obj, ok := object.(*zombieIndexObject)
+				require.True(t, ok)
+
+				err := db.MarkEdgeZombie(
+					obj.scid, obj.pubKey1, obj.pubKey2,
+				)
+				require.NoError(t, err)
+			},
+			objects: []any{
+				&zombieIndexObject{
+					scid:    prand.Uint64(),
+					pubKey1: genPubKey(t),
+					pubKey2: genPubKey(t),
+				},
+				&zombieIndexObject{
+					scid:    prand.Uint64(),
+					pubKey1: genPubKey(t),
+					pubKey2: genPubKey(t),
+				},
+				&zombieIndexObject{
+					scid:    prand.Uint64(),
+					pubKey1: genPubKey(t),
+					pubKey2: genPubKey(t),
+				},
+			},
+		},
 	}
 
 	for _, test := range tests {
@@ -345,6 +380,9 @@ func assertInSync(t *testing.T, kvDB *KVStore, sqlDB *SQLStore,
 	// log we iterate through the kvdb store and check that the entries
 	// match the entries in the SQL store.
 	checkClosedSCIDIndex(t, kvDB.db, sqlDB)
+
+	// 6) Finally, check that the zombie index is also in sync.
+	checkZombieIndex(t, kvDB.db, sqlDB)
 }
 
 // fetchAllNodes retrieves all nodes from the given store and returns them
@@ -501,6 +539,38 @@ func checkClosedSCIDIndex(t *testing.T, kv kvdb.Backend, sql *SQLStore) {
 	require.NoError(t, err)
 }
 
+// checkZombieIndex iterates through the zombie index in the
+// KVStore and checks that each SCID is marked as a zombie in the SQLStore.
+func checkZombieIndex(t *testing.T, kv kvdb.Backend, sql *SQLStore) {
+	err := forEachZombieEntry(kv, func(chanID uint64, pubKey1,
+		pubKey2 [33]byte) error {
+
+		scid := lnwire.NewShortChanIDFromInt(chanID)
+
+		// The migration logic skips zombie entries if they are already
+		// present in the closed SCID index in the SQL DB. We need to
+		// replicate that check here.
+		isClosed, err := sql.IsClosedScid(scid)
+		require.NoError(t, err)
+
+		isZombie, _, _, err := sql.IsZombieEdge(chanID)
+		require.NoError(t, err)
+
+		if isClosed {
+			// If it's in the closed index, it should NOT be in the
+			// zombie index.
+			require.False(t, isZombie)
+		} else {
+			// If it's not in the closed index, it SHOULD be in the
+			// zombie index.
+			require.True(t, isZombie)
+		}
+
+		return nil
+	})
+	require.NoError(t, err)
+}
+
 // setUpKVStore initializes a new KVStore for testing.
 func setUpKVStore(t *testing.T) *KVStore {
 	kvDB, cleanup, err := kvdb.GetTestBackend(t.TempDir(), "graph")
@@ -989,6 +1059,39 @@ func TestSQLMigrationEdgeCases(t *testing.T) {
 			}},
 		})
 	})
+
+	// This test covers the case where the KV store contains zombie entries
+	// that it also has entries for in the closed SCID index. In this case,
+	// the SQL store will only insert zombie entries for channels that
+	// are not yet closed.
+	t.Run("zombies and closed scids", func(t *testing.T) {
+		var (
+			n1, n2 route.Vertex
+			cID1   = uint64(1)
+			cID2   = uint64(2)
+		)
+
+		populateKV := func(t *testing.T, db *KVStore) {
+			// Mark both channels as zombies.
+			err := db.MarkEdgeZombie(cID1, n1, n2)
+			require.NoError(t, err)
+
+			err = db.MarkEdgeZombie(cID2, n1, n2)
+			require.NoError(t, err)
+
+			// Mark channel 1 as closed.
+			err = db.PutClosedScid(
+				lnwire.NewShortChanIDFromInt(cID1),
+			)
+			require.NoError(t, err)
+		}
+
+		runTestMigration(t, populateKV, dbState{
+			chans:   make(chanSet, 0),
+			closed:  []uint64{1},
+			zombies: []uint64{2},
+		})
+	})
 }
 
 // runTestMigration is a helper function that sets up the KVStore and SQLStore,
@@ -1020,8 +1123,10 @@ func runTestMigration(t *testing.T, populateKV func(t *testing.T, db *KVStore),
 
 // dbState describes the expected state of the SQLStore after a migration.
 type dbState struct {
-	nodes []*models.LightningNode
+	nodes   []*models.LightningNode
-	chans chanSet
+	chans   chanSet
+	closed  []uint64
+	zombies []uint64
 }
 
 // assertResultState asserts that the SQLStore contains the expected
@@ -1032,4 +1137,26 @@ func assertResultState(t *testing.T, sql *SQLStore, expState dbState) {
 	require.ElementsMatch(
 		t, expState.chans, fetchAllChannelsAndPolicies(t, sql),
 	)
+
+	for _, closed := range expState.closed {
+		isClosed, err := sql.IsClosedScid(
+			lnwire.NewShortChanIDFromInt(closed),
+		)
+		require.NoError(t, err)
+		require.True(t, isClosed)
+
+		// Any closed SCID should NOT be in the zombie
+		// index.
+		isZombie, _, _, err := sql.IsZombieEdge(closed)
+		require.NoError(t, err)
+		require.False(t, isZombie)
+	}
+
+	for _, zombie := range expState.zombies {
+		isZombie, _, _, err := sql.IsZombieEdge(
+			zombie,
+		)
+		require.NoError(t, err)
+		require.True(t, isZombie)
+	}
 }