lite2: store current validator set (#4472)

Before we were storing trustedHeader (height=1) and trustedNextVals
(height=2).

After this change, we will be storing trustedHeader (height=1) and
trustedVals (height=1). This a) simplifies the code b) fixes #4399
inconsistent pairing issue c) gives a relayer access to the current
validator set #4470.

The only downside is more jumps during bisection. If validator set
changes between trustedHeader and the next header (by 2/3 or more), the
light client will be forced to download the next header and check that
2/3+ signed the transition. But we don't expect validator set change too
much and too often, so it's an acceptable compromise.

Closes #4470 and #4399

lite2/store/db/db.go

@@ -31,9 +31,9 @@ func New(db dbm.DB, prefix string) store.Store {
 	return &dbs{db: db, prefix: prefix, cdc: cdc}
 }
 
-// SaveSignedHeaderAndNextValidatorSet persists SignedHeader and ValidatorSet
-// to the db.
-func (s *dbs) SaveSignedHeaderAndNextValidatorSet(sh *types.SignedHeader, valSet *types.ValidatorSet) error {
+// SaveSignedHeaderAndValidatorSet persists SignedHeader and ValidatorSet to
+// the db.
+func (s *dbs) SaveSignedHeaderAndValidatorSet(sh *types.SignedHeader, valSet *types.ValidatorSet) error {
 	if sh.Height <= 0 {
 		panic("negative or zero height")
 	}
@@ -42,6 +42,7 @@ func (s *dbs) SaveSignedHeaderAndNextValidatorSet(sh *types.SignedHeader, valSet
 	if err != nil {
 		return errors.Wrap(err, "marshalling header")
 	}
+
 	valSetBz, err := s.cdc.MarshalBinaryLengthPrefixed(valSet)
 	if err != nil {
 		return errors.Wrap(err, "marshalling validator set")
@@ -49,22 +50,22 @@ func (s *dbs) SaveSignedHeaderAndNextValidatorSet(sh *types.SignedHeader, valSet
 
 	b := s.db.NewBatch()
 	b.Set(s.shKey(sh.Height), shBz)
-	b.Set(s.vsKey(sh.Height+1), valSetBz)
+	b.Set(s.vsKey(sh.Height), valSetBz)
 	err = b.WriteSync()
 	b.Close()
 	return err
 }
 
-// DeleteSignedHeaderAndNextValidatorSet deletes SignedHeader and ValidatorSet
-// from the db.
-func (s *dbs) DeleteSignedHeaderAndNextValidatorSet(height int64) error {
+// DeleteSignedHeaderAndValidatorSet deletes SignedHeader and ValidatorSet from
+// the db.
+func (s *dbs) DeleteSignedHeaderAndValidatorSet(height int64) error {
 	if height <= 0 {
 		panic("negative or zero height")
 	}
 
 	b := s.db.NewBatch()
 	b.Delete(s.shKey(height))
-	b.Delete(s.vsKey(height + 1))
+	b.Delete(s.vsKey(height))
 	err := b.WriteSync()
 	b.Close()
 	return err

lite2/store/db/db_test.go

@@ -24,7 +24,7 @@ func TestLast_FirstSignedHeaderHeight(t *testing.T) {
 	assert.EqualValues(t, -1, height)
 
 	// 1 key
-	err = dbStore.SaveSignedHeaderAndNextValidatorSet(
+	err = dbStore.SaveSignedHeaderAndValidatorSet(
 		&types.SignedHeader{Header: &types.Header{Height: 1}}, &types.ValidatorSet{})
 	require.NoError(t, err)
 
@@ -37,20 +37,20 @@ func TestLast_FirstSignedHeaderHeight(t *testing.T) {
 	assert.EqualValues(t, 1, height)
 }
 
-func Test_SaveSignedHeaderAndNextValidatorSet(t *testing.T) {
-	dbStore := New(dbm.NewMemDB(), "Test_SaveSignedHeaderAndNextValidatorSet")
+func Test_SaveSignedHeaderAndValidatorSet(t *testing.T) {
+	dbStore := New(dbm.NewMemDB(), "Test_SaveSignedHeaderAndValidatorSet")
 
 	// Empty store
 	h, err := dbStore.SignedHeader(1)
 	require.Error(t, err)
 	assert.Nil(t, h)
 
-	valSet, err := dbStore.ValidatorSet(2)
+	valSet, err := dbStore.ValidatorSet(1)
 	require.Error(t, err)
 	assert.Nil(t, valSet)
 
 	// 1 key
-	err = dbStore.SaveSignedHeaderAndNextValidatorSet(
+	err = dbStore.SaveSignedHeaderAndValidatorSet(
 		&types.SignedHeader{Header: &types.Header{Height: 1}}, &types.ValidatorSet{})
 	require.NoError(t, err)
 
@@ -58,19 +58,19 @@ func Test_SaveSignedHeaderAndNextValidatorSet(t *testing.T) {
 	require.NoError(t, err)
 	assert.NotNil(t, h)
 
-	valSet, err = dbStore.ValidatorSet(2)
+	valSet, err = dbStore.ValidatorSet(1)
 	require.NoError(t, err)
 	assert.NotNil(t, valSet)
 
 	// Empty store
-	err = dbStore.DeleteSignedHeaderAndNextValidatorSet(1)
+	err = dbStore.DeleteSignedHeaderAndValidatorSet(1)
 	require.NoError(t, err)
 
 	h, err = dbStore.SignedHeader(1)
 	require.Error(t, err)
 	assert.Nil(t, h)
 
-	valSet, err = dbStore.ValidatorSet(2)
+	valSet, err = dbStore.ValidatorSet(1)
 	require.Error(t, err)
 	assert.Nil(t, valSet)
 }
@@ -83,7 +83,7 @@ func Test_SignedHeaderAfter(t *testing.T) {
 		dbStore.SignedHeaderAfter(100)
 	})
 
-	err := dbStore.SaveSignedHeaderAndNextValidatorSet(
+	err := dbStore.SaveSignedHeaderAndValidatorSet(
 		&types.SignedHeader{Header: &types.Header{Height: 2}}, &types.ValidatorSet{})
 	require.NoError(t, err)
 

lite2/store/errors.go

@@ -6,6 +6,7 @@ var (
 	// ErrSignedHeaderNotFound is returned when a store does not have the
 	// requested header.
 	ErrSignedHeaderNotFound = errors.New("signed header not found")
+
 	// ErrValidatorSetNotFound is returned when a store does not have the
 	// requested validator set.
 	ErrValidatorSetNotFound = errors.New("validator set not found")

lite2/store/store.go

@@ -4,17 +4,17 @@ import "github.com/tendermint/tendermint/types"
 
 // Store is anything that can persistenly store headers.
 type Store interface {
-	// SaveSignedHeaderAndNextValidatorSet saves a SignedHeader (h: sh.Height)
-	// and a ValidatorSet (h: sh.Height+1).
+	// SaveSignedHeaderAndValidatorSet saves a SignedHeader (h: sh.Height) and a
+	// ValidatorSet (h: sh.Height).
 	//
 	// height must be > 0.
-	SaveSignedHeaderAndNextValidatorSet(sh *types.SignedHeader, valSet *types.ValidatorSet) error
+	SaveSignedHeaderAndValidatorSet(sh *types.SignedHeader, valSet *types.ValidatorSet) error
 
-	// DeleteSignedHeaderAndNextValidatorSet deletes SignedHeader (h: height) and
-	// ValidatorSet (h: height+1).
+	// DeleteSignedHeaderAndValidatorSet deletes SignedHeader (h: height) and
+	// ValidatorSet (h: height).
 	//
 	// height must be > 0.
-	DeleteSignedHeaderAndNextValidatorSet(height int64) error
+	DeleteSignedHeaderAndValidatorSet(height int64) error
 
 	// SignedHeader returns the SignedHeader that corresponds to the given
 	// height.