lite: follow up from #3989 (#4209)

* rename adjusted to adjacent

Refs https://github.com/tendermint/tendermint/pull/3989#discussion_r352140829

* rename ErrTooMuchChange to ErrNotEnoughVotingPowerSigned

Refs https://github.com/tendermint/tendermint/pull/3989#discussion_r352142785

* verify commit is properly signed

* remove no longer trusted headers

* restore trustedHeader and trustedNextVals

* check trustedHeader using options

Refs https://github.com/tendermint/tendermint/pull/4209#issuecomment-562462165

* use correct var when checking if headers are adjacent

in bisection func
+ replace TODO with a comment

https://github.com/tendermint/tendermint/pull/3989#discussion_r352125455

* return header in VerifyHeaderAtHeight

because that way we avoid DB call

+ add godoc comments
+ check if there are no headers yet in AutoClient

https://github.com/tendermint/tendermint/pull/3989#pullrequestreview-315454506

* TestVerifyAdjacentHeaders: add 2 more test-cases

+ add TestVerifyReturnsErrorIfTrustLevelIsInvalid

* lite: avoid overflow when parsing key in db store!

* lite: rename AutoClient#Err to Errs

* lite: add a test for AutoClient

* lite: fix keyPattern and call itr.Next in db store

* lite: add two tests for db store

* lite: add TestClientRemovesNoLongerTrustedHeaders

* lite: test Client#Cleanup

* lite: test restoring trustedHeader

https://github.com/tendermint/tendermint/pull/4209#issuecomment-562462165

* lite: comment out unused code in test_helpers

* fix TestVerifyReturnsErrorIfTrustLevelIsInvalid after merge

* change defaultRemoveNoLongerTrustedHeadersPeriod

and add docs

* write more doc

* lite: uncomment testable examples

* use stdlog.Fatal to stop AutoClient tests

* make lll linter happy

* separate errors for 2 cases

- the validator set of a skipped header cannot be trusted, i.e. <1/3rd
  of h1 validator set has signed (new error, something like
  ErrNewValSetCantBeTrusted)
- the validator set is trusted but < 2/3rds has signed
  (ErrNewHeaderCantBeTrusted)

https://github.com/tendermint/tendermint/pull/4209#discussion_r360331253

* remove all headers (even the last one) that are outside

of the trusting period. By doing this, we avoid checking the
trustedHeader's hash in checkTrustedHeaderUsingOptions (case #1).

https://github.com/tendermint/tendermint/pull/4209#discussion_r360332460

* explain restoreTrustedHeaderAndNextVals better

https://github.com/tendermint/tendermint/pull/4209#discussion_r360602328

* add ConfirmationFunction option

for optionally prompting for user input Y/n before removing headers

Refs https://github.com/tendermint/tendermint/pull/4209#discussion_r360602945

* make cleaning optional

https://github.com/tendermint/tendermint/pull/4209#discussion_r364838189

* return error when user refused to remove headers

* check for double votes in VerifyCommitTrusting

* leave only ErrNewValSetCantBeTrusted error

to differenciate between h2Vals.VerifyCommit and
h1NextVals.VerifyCommitTrusting

* fix example tests

* remove unnecessary if condition

https://github.com/tendermint/tendermint/pull/4209#discussion_r365171847

It will be handled by the above switch.

* verifyCommitBasic does not depend on vals

Co-authored-by: Marko <marbar3778@yahoo.com>

lite/dynamic_verifier.go

@@ -185,7 +185,7 @@ func (dv *DynamicVerifier) Verify(shdr types.SignedHeader) error {
 
 // verifyAndSave will verify if this is a valid source full commit given the
 // best match trusted full commit, and if good, persist to dv.trusted.
-// Returns ErrTooMuchChange when >2/3 of trustedFC did not sign sourceFC.
+// Returns ErrNotEnoughVotingPowerSigned when >2/3 of trustedFC did not sign sourceFC.
 // Panics if trustedFC.Height() >= sourceFC.Height().
 func (dv *DynamicVerifier) verifyAndSave(trustedFC, sourceFC FullCommit) error {
 	if trustedFC.Height() >= sourceFC.Height() {
@@ -247,8 +247,8 @@ FOR_LOOP:
 			return sourceFC, nil
 		}
 
-		// Handle special case when err is ErrTooMuchChange.
-		if types.IsErrTooMuchChange(err) {
+		// Handle special case when err is ErrNotEnoughVotingPowerSigned.
+		if types.IsErrNotEnoughVotingPowerSigned(err) {
 			// Divide and conquer.
 			start, end := trustedFC.Height(), sourceFC.Height()
 			if !(start < end) {

lite2/auto_client.go

@@ -13,7 +13,7 @@ type AutoClient struct {
 	quit         chan struct{}
 
 	trustedHeaders chan *types.SignedHeader
-	err            chan error
+	errs           chan error
 }
 
 // NewAutoClient creates a new client and starts a polling goroutine.
@@ -23,7 +23,7 @@ func NewAutoClient(base *Client, updatePeriod time.Duration) *AutoClient {
 		updatePeriod:   updatePeriod,
 		quit:           make(chan struct{}),
 		trustedHeaders: make(chan *types.SignedHeader),
-		err:            make(chan error),
+		errs:           make(chan error),
 	}
 	go c.autoUpdate()
 	return c
@@ -35,8 +35,8 @@ func (c *AutoClient) TrustedHeaders() <-chan *types.SignedHeader {
 }
 
 // Err returns a channel onto which errors are posted.
-func (c *AutoClient) Err() <-chan error {
-	return c.err
+func (c *AutoClient) Errs() <-chan error {
+	return c.errs
 }
 
 // Stop stops the client.
@@ -45,30 +45,30 @@ func (c *AutoClient) Stop() {
 }
 
 func (c *AutoClient) autoUpdate() {
-	lastTrustedHeight, err := c.base.LastTrustedHeight()
-	if err != nil {
-		c.err <- err
-		return
-	}
-
 	ticker := time.NewTicker(c.updatePeriod)
 	defer ticker.Stop()
 
 	for {
 		select {
 		case <-ticker.C:
-			err := c.base.VerifyHeaderAtHeight(lastTrustedHeight+1, time.Now())
+			lastTrustedHeight, err := c.base.LastTrustedHeight()
 			if err != nil {
-				c.err <- err
+				c.errs <- err
+				continue
+			}
+
+			if lastTrustedHeight == -1 {
+				// no headers yet => wait
 				continue
 			}
-			h, err := c.base.TrustedHeader(lastTrustedHeight+1, time.Now())
+
+			h, err := c.base.VerifyHeaderAtHeight(lastTrustedHeight+1, time.Now())
 			if err != nil {
-				c.err <- err
+				// no header yet or verification error => try again after updatePeriod
+				c.errs <- err
 				continue
 			}
 			c.trustedHeaders <- h
-			lastTrustedHeight = h.Height
 		case <-c.quit:
 			return
 		}

lite2/auto_client_test.go

@@ -0,0 +1,76 @@
+package lite
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	dbm "github.com/tendermint/tm-db"
+
+	"github.com/tendermint/tendermint/libs/log"
+	mockp "github.com/tendermint/tendermint/lite2/provider/mock"
+	dbs "github.com/tendermint/tendermint/lite2/store/db"
+	"github.com/tendermint/tendermint/types"
+)
+
+func TestAutoClient(t *testing.T) {
+	const (
+		chainID = "TestAutoClient"
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals   = keys.ToValidators(20, 10)
+		bTime  = time.Now().Add(-1 * time.Hour)
+		header = keys.GenSignedHeader(chainID, 1, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+	)
+
+	base, err := NewClient(
+		chainID,
+		TrustOptions{
+			Period: 4 * time.Hour,
+			Height: 1,
+			Hash:   header.Hash(),
+		},
+		mockp.New(
+			chainID,
+			map[int64]*types.SignedHeader{
+				// trusted header
+				1: header,
+				// interim header (3/3 signed)
+				2: keys.GenSignedHeader(chainID, 2, bTime.Add(30*time.Minute), nil, vals, vals,
+					[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
+				// last header (3/3 signed)
+				3: keys.GenSignedHeader(chainID, 3, bTime.Add(1*time.Hour), nil, vals, vals,
+					[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
+			},
+			map[int64]*types.ValidatorSet{
+				1: vals,
+				2: vals,
+				3: vals,
+				4: vals,
+			},
+		),
+		dbs.New(dbm.NewMemDB(), chainID),
+	)
+	require.NoError(t, err)
+	base.SetLogger(log.TestingLogger())
+
+	c := NewAutoClient(base, 1*time.Second)
+	defer c.Stop()
+
+	for i := 2; i <= 3; i++ {
+		select {
+		case h := <-c.TrustedHeaders():
+			assert.EqualValues(t, i, h.Height)
+		case err := <-c.Errs():
+			require.NoError(t, err)
+		case <-time.After(2 * time.Second):
+			t.Fatal("no headers/errors received in 2 sec")
+		}
+	}
+}

lite2/client.go

@@ -47,14 +47,16 @@ type mode byte
 const (
 	sequential mode = iota + 1
 	skipping
+
+	defaultRemoveNoLongerTrustedHeadersPeriod = 24 * time.Hour
 )
 
 // Option sets a parameter for the light client.
 type Option func(*Client)
 
 // SequentialVerification option configures the light client to sequentially
-// check the headers. Note this is much slower than SkippingVerification,
-// albeit more secure.
+// check the headers (every header, in ascending height order). Note this is
+// much slower than SkippingVerification, albeit more secure.
 func SequentialVerification() Option {
 	return func(c *Client) {
 		c.verificationMode = sequential
@@ -68,7 +70,7 @@ func SequentialVerification() Option {
 //
 // trustLevel - fraction of the old validator set (in terms of voting power),
 // which must sign the new header in order for us to trust it. NOTE this only
-// applies to non-adjusted headers. For adjusted headers, sequential
+// applies to non-adjacent headers. For adjacent headers, sequential
 // verification is used.
 func SkippingVerification(trustLevel tmmath.Fraction) Option {
 	if err := ValidateTrustLevel(trustLevel); err != nil {
@@ -88,6 +90,25 @@ func AlternativeSources(providers []provider.Provider) Option {
 	}
 }
 
+// RemoveNoLongerTrustedHeadersPeriod option can be used to define how often
+// the routine, which cleans up no longer trusted headers (outside of trusting
+// period), is run. Default: once a day. When set to zero, the routine won't be
+// started.
+func RemoveNoLongerTrustedHeadersPeriod(d time.Duration) Option {
+	return func(c *Client) {
+		c.removeNoLongerTrustedHeadersPeriod = d
+	}
+}
+
+// ConfirmationFunction option can be used to prompt to confirm an action. For
+// example, remove newer headers if the light client is being reset with an
+// older header. No confirmation is required by default!
+func ConfirmationFunction(fn func(action string) bool) Option {
+	return func(c *Client) {
+		c.confirmationFn = fn
+	}
+}
+
 // Client represents a light client, connected to a single chain, which gets
 // headers from a primary provider, verifies them either sequentially or by
 // skipping some and stores them in a trusted store (usually, a local FS).
@@ -113,6 +134,12 @@ type Client struct {
 	// Highest next validator set from the store (height=H+1).
 	trustedNextVals *types.ValidatorSet
 
+	removeNoLongerTrustedHeadersPeriod time.Duration
+
+	confirmationFn func(action string) bool
+
+	quit chan struct{}
+
 	logger log.Logger
 }
 
@@ -129,26 +156,136 @@ func NewClient(
 	options ...Option) (*Client, error) {
 
 	c := &Client{
-		chainID:          chainID,
-		trustingPeriod:   trustOptions.Period,
-		verificationMode: skipping,
-		trustLevel:       DefaultTrustLevel,
-		primary:          primary,
-		trustedStore:     trustedStore,
-		logger:           log.NewNopLogger(),
+		chainID:                            chainID,
+		trustingPeriod:                     trustOptions.Period,
+		verificationMode:                   skipping,
+		trustLevel:                         DefaultTrustLevel,
+		primary:                            primary,
+		trustedStore:                       trustedStore,
+		removeNoLongerTrustedHeadersPeriod: defaultRemoveNoLongerTrustedHeadersPeriod,
+		confirmationFn:                     func(action string) bool { return true },
+		quit:                               make(chan struct{}),
+		logger:                             log.NewNopLogger(),
 	}
 
 	for _, o := range options {
 		o(c)
 	}
 
-	if err := c.initializeWithTrustOptions(trustOptions); err != nil {
+	if err := c.restoreTrustedHeaderAndNextVals(); err != nil {
 		return nil, err
 	}
+	if c.trustedHeader != nil {
+		if err := c.checkTrustedHeaderUsingOptions(trustOptions); err != nil {
+			return nil, err
+		}
+	}
+
+	if c.trustedHeader == nil || c.trustedHeader.Height != trustOptions.Height {
+		if err := c.initializeWithTrustOptions(trustOptions); err != nil {
+			return nil, err
+		}
+	}
+
+	if c.removeNoLongerTrustedHeadersPeriod > 0 {
+		go c.removeNoLongerTrustedHeadersRoutine()
+	}
 
 	return c, nil
 }
 
+// Load trustedHeader and trustedNextVals from trustedStore.
+func (c *Client) restoreTrustedHeaderAndNextVals() error {
+	lastHeight, err := c.trustedStore.LastSignedHeaderHeight()
+	if err != nil {
+		return errors.Wrap(err, "can't get last trusted header height")
+	}
+
+	if lastHeight > 0 {
+		trustedHeader, err := c.trustedStore.SignedHeader(lastHeight)
+		if err != nil {
+			return errors.Wrap(err, "can't get last trusted header")
+		}
+
+		trustedNextVals, err := c.trustedStore.ValidatorSet(lastHeight + 1)
+		if err != nil {
+			return errors.Wrap(err, "can't get last trusted next validators")
+		}
+
+		c.trustedHeader = trustedHeader
+		c.trustedNextVals = trustedNextVals
+	}
+
+	return nil
+}
+
+// if options.Height:
+//
+//     1) ahead of trustedHeader.Height => fetch header (same height as
+//     trustedHeader) from primary provider and check it's hash matches the
+//     trustedHeader's hash (if not, remove trustedHeader and all the headers
+//     before)
+//
+//     2) equals trustedHeader.Height => check options.Hash matches the
+//     trustedHeader's hash (if not, remove trustedHeader and all the headers
+//     before)
+//
+//     3) behind trustedHeader.Height => remove all the headers between
+//     options.Height and trustedHeader.Height, update trustedHeader, then
+//     check options.Hash matches the trustedHeader's hash (if not, remove
+//     trustedHeader and all the headers before)
+//
+// The intuition here is the user is always right. I.e. if she decides to reset
+// the light client with an older header, there must be a reason for it.
+func (c *Client) checkTrustedHeaderUsingOptions(options TrustOptions) error {
+	var primaryHash []byte
+	switch {
+	case options.Height > c.trustedHeader.Height:
+		h, err := c.primary.SignedHeader(c.trustedHeader.Height)
+		if err != nil {
+			return err
+		}
+		primaryHash = h.Hash()
+	case options.Height == c.trustedHeader.Height:
+		primaryHash = options.Hash
+	case options.Height < c.trustedHeader.Height:
+		action := fmt.Sprintf(
+			"Rollback to %d (%X)? Note this will remove newer headers up to %d (%X)",
+			options.Height, options.Hash,
+			c.trustedHeader.Height, c.trustedHeader.Hash())
+		if c.confirmationFn(action) {
+			// remove all the headers ( options.Height, trustedHeader.Height ]
+			c.cleanup(options.Height + 1)
+			// set c.trustedHeader to one at options.Height
+			c.restoreTrustedHeaderAndNextVals()
+		} else {
+			return errors.New("rollback aborted")
+		}
+
+		primaryHash = options.Hash
+	}
+
+	if !bytes.Equal(primaryHash, c.trustedHeader.Hash()) {
+		c.logger.Info("Prev. trusted header's hash %X doesn't match hash %X from primary provider",
+			c.trustedHeader.Hash(), primaryHash)
+
+		action := fmt.Sprintf(
+			"Prev. trusted header's hash %X doesn't match hash %X from primary provider. Remove all the stored headers?",
+			c.trustedHeader.Hash(), primaryHash)
+		if c.confirmationFn(action) {
+			err := c.Cleanup()
+			if err != nil {
+				return errors.Wrap(err, "failed to cleanup")
+			}
+		} else {
+			return errors.New("refused to remove the stored headers despite hashes mismatch")
+		}
+	}
+
+	return nil
+}
+
+// Fetch trustedHeader and trustedNextVals from primary provider.
 func (c *Client) initializeWithTrustOptions(options TrustOptions) error {
 	// 1) Fetch and verify the header.
 	h, err := c.primary.SignedHeader(options.Height)
@@ -158,21 +295,44 @@ func (c *Client) initializeWithTrustOptions(options TrustOptions) error {
 
 	// NOTE: Verify func will check if it's expired or not.
 	if err := h.ValidateBasic(c.chainID); err != nil {
-		return errors.Wrap(err, "ValidateBasic failed")
+		return err
 	}
 
 	if !bytes.Equal(h.Hash(), options.Hash) {
 		return errors.Errorf("expected header's hash %X, but got %X", options.Hash, h.Hash())
 	}
 
-	// 2) Fetch and verify the next vals.
-	vals, err := c.primary.ValidatorSet(options.Height + 1)
+	// 2) Fetch and verify the vals.
+	vals, err := c.primary.ValidatorSet(options.Height)
+	if err != nil {
+		return err
+	}
+	if !bytes.Equal(h.ValidatorsHash, vals.Hash()) {
+		return errors.Errorf("expected header's validators (%X) to match those that were supplied (%X)",
+			h.ValidatorsHash,
+			vals.Hash(),
+		)
+	}
+	// Ensure that +2/3 of validators signed correctly.
+	err = vals.VerifyCommit(c.chainID, h.Commit.BlockID, h.Height, h.Commit)
+	if err != nil {
+		return errors.Wrap(err, "invalid commit")
+	}
+
+	// 3) Fetch and verify the next vals (verification happens in
+	// updateTrustedHeaderAndVals).
+	nextVals, err := c.primary.ValidatorSet(options.Height + 1)
 	if err != nil {
 		return err
 	}
 
-	// 3) Persist both of them and continue.
-	return c.updateTrustedHeaderAndVals(h, vals)
+	// 4) Persist both of them and continue.
+	return c.updateTrustedHeaderAndVals(h, nextVals)
+}
+
+// Stop stops the light client.
+func (c *Client) Stop() {
+	close(c.quit)
 }
 
 // SetLogger sets a logger.
@@ -182,15 +342,17 @@ func (c *Client) SetLogger(l log.Logger) {
 
 // TrustedHeader returns a trusted header at the given height (0 - the latest)
 // or nil if no such header exist.
-// TODO: mention how many headers will be kept by the light client.
+//
+// Headers, which can't be trusted anymore, are removed once a day (can be
+// changed with RemoveNoLongerTrustedHeadersPeriod option).
 // .
 // height must be >= 0.
 //
 // It returns an error if:
-//		- the header expired (ErrOldHeaderExpired). In that case, update your
-//		client to more recent height;
-//		- there are some issues with the trusted store, although that should not
-//		happen normally.
+//  - header expired, therefore can't be trusted (ErrOldHeaderExpired);
+//  - there are some issues with the trusted store, although that should not
+//  happen normally;
+//  - negative height is passed.
 func (c *Client) TrustedHeader(height int64, now time.Time) (*types.SignedHeader, error) {
 	if height < 0 {
 		return nil, errors.New("negative height")
@@ -208,22 +370,25 @@ func (c *Client) TrustedHeader(height int64, now time.Time) (*types.SignedHeader
 	if err != nil {
 		return nil, err
 	}
+	if h == nil {
+		return nil, nil
+	}
 
 	// Ensure header can still be trusted.
-	expirationTime := h.Time.Add(c.trustingPeriod)
-	if !expirationTime.After(now) {
-		return nil, ErrOldHeaderExpired{expirationTime, now}
+	if HeaderExpired(h, c.trustingPeriod, now) {
+		return nil, ErrOldHeaderExpired{h.Time.Add(c.trustingPeriod), now}
 	}
 
 	return h, nil
 }
 
-// LastTrustedHeight returns a last trusted height.
+// LastTrustedHeight returns a last trusted height. -1 and nil are returned if
+// there are no trusted headers.
 func (c *Client) LastTrustedHeight() (int64, error) {
 	return c.trustedStore.LastSignedHeaderHeight()
 }
 
-// ChainID returns the chain ID.
+// ChainID returns the chain ID the light client was configured with.
 func (c *Client) ChainID() string {
 	return c.chainID
 }
@@ -232,18 +397,18 @@ func (c *Client) ChainID() string {
 // and calls VerifyHeader.
 //
 // If the trusted header is more recent than one here, an error is returned.
-func (c *Client) VerifyHeaderAtHeight(height int64, now time.Time) error {
+func (c *Client) VerifyHeaderAtHeight(height int64, now time.Time) (*types.SignedHeader, error) {
 	if c.trustedHeader.Height >= height {
-		return errors.Errorf("height #%d is already trusted (last: #%d)", height, c.trustedHeader.Height)
+		return nil, errors.Errorf("header at more recent height #%d exists", c.trustedHeader.Height)
 	}
 
 	// Request the header and the vals.
 	newHeader, newVals, err := c.fetchHeaderAndValsAtHeight(height)
 	if err != nil {
-		return err
+		return nil, err
 	}
 
-	return c.VerifyHeader(newHeader, newVals, now)
+	return newHeader, c.VerifyHeader(newHeader, newVals, now)
 }
 
 // VerifyHeader verifies new header against the trusted state.
@@ -255,13 +420,13 @@ func (c *Client) VerifyHeaderAtHeight(height int64, now time.Time) error {
 // SkippingVerification(trustLevel): verifies that {trustLevel} of the trusted
 // validator set has signed the new header. If it's not the case and the
 // headers are not adjacent, bisection is performed and necessary (not all)
-// intermediate headers will be requested. See the specification for the
-// algorithm.
+// intermediate headers will be requested. See the specification for details.
+// https://github.com/tendermint/spec/blob/master/spec/consensus/light-client.md
 //
 // If the trusted header is more recent than one here, an error is returned.
 func (c *Client) VerifyHeader(newHeader *types.SignedHeader, newVals *types.ValidatorSet, now time.Time) error {
 	if c.trustedHeader.Height >= newHeader.Height {
-		return errors.Errorf("height #%d is already trusted (last: #%d)", newHeader.Height, c.trustedHeader.Height)
+		return errors.Errorf("header at more recent height #%d exists", c.trustedHeader.Height)
 	}
 
 	if len(c.alternatives) > 0 {
@@ -291,6 +456,44 @@ func (c *Client) VerifyHeader(newHeader *types.SignedHeader, newVals *types.Vali
 	return c.updateTrustedHeaderAndVals(newHeader, nextVals)
 }
 
+// Cleanup removes all the data (headers and validator sets) stored.
+func (c *Client) Cleanup() error {
+	return c.cleanup(0)
+}
+
+// stopHeight=0 -> remove all data
+func (c *Client) cleanup(stopHeight int64) error {
+	// 1) Get the oldest height.
+	oldestHeight, err := c.trustedStore.FirstSignedHeaderHeight()
+	if err != nil {
+		return errors.Wrap(err, "can't get first trusted height")
+	}
+
+	// 2) Get the latest height.
+	latestHeight, err := c.trustedStore.LastSignedHeaderHeight()
+	if err != nil {
+		return errors.Wrap(err, "can't get last trusted height")
+	}
+
+	// 3) Remove all headers and validator sets.
+	if stopHeight == 0 {
+		stopHeight = oldestHeight
+	}
+	for height := stopHeight; height <= latestHeight; height++ {
+		err = c.trustedStore.DeleteSignedHeaderAndNextValidatorSet(height)
+		if err != nil {
+			c.logger.Error("can't remove a trusted header & validator set", "err", err, "height", height)
+			continue
+		}
+	}
+
+	c.trustedHeader = nil
+	c.trustedNextVals = nil
+
+	return nil
+}
+
+// see VerifyHeader
 func (c *Client) sequence(newHeader *types.SignedHeader, newVals *types.ValidatorSet, now time.Time) error {
 	// 1) Verify any intermediate headers.
 	var (
@@ -329,6 +532,7 @@ func (c *Client) sequence(newHeader *types.SignedHeader, newVals *types.Validato
 	return Verify(c.chainID, c.trustedHeader, c.trustedNextVals, newHeader, newVals, c.trustingPeriod, now, c.trustLevel)
 }
 
+// see VerifyHeader
 func (c *Client) bisection(
 	lastHeader *types.SignedHeader,
 	lastVals *types.ValidatorSet,
@@ -340,15 +544,10 @@ func (c *Client) bisection(
 	switch err.(type) {
 	case nil:
 		return nil
-	case types.ErrTooMuchChange:
+	case ErrNewValSetCantBeTrusted:
 		// continue bisection
 	default:
-		return errors.Wrapf(err, "failed to verify the header #%d ", newHeader.Height)
-	}
-
-	if newHeader.Height == c.trustedHeader.Height+1 {
-		// TODO: submit evidence here
-		return errors.Errorf("adjacent headers (#%d and #%d) that are not matching", lastHeader.Height, newHeader.Height)
+		return errors.Wrapf(err, "failed to verify the header #%d", newHeader.Height)
 	}
 
 	pivot := (c.trustedHeader.Height + newHeader.Header.Height) / 2
@@ -392,22 +591,23 @@ func (c *Client) bisection(
 	return nil
 }
 
-func (c *Client) updateTrustedHeaderAndVals(h *types.SignedHeader, vals *types.ValidatorSet) error {
-	if !bytes.Equal(h.NextValidatorsHash, vals.Hash()) {
-		return errors.Errorf("expected next validator's hash %X, but got %X", h.NextValidatorsHash, vals.Hash())
+// persist header and next validators to trustedStore.
+func (c *Client) updateTrustedHeaderAndVals(h *types.SignedHeader, nextVals *types.ValidatorSet) error {
+	if !bytes.Equal(h.NextValidatorsHash, nextVals.Hash()) {
+		return errors.Errorf("expected next validator's hash %X, but got %X", h.NextValidatorsHash, nextVals.Hash())
 	}
 
-	if err := c.trustedStore.SaveSignedHeader(h); err != nil {
+	if err := c.trustedStore.SaveSignedHeaderAndNextValidatorSet(h, nextVals); err != nil {
 		return errors.Wrap(err, "failed to save trusted header")
 	}
-	if err := c.trustedStore.SaveValidatorSet(vals, h.Height+1); err != nil {
-		return errors.Wrap(err, "failed to save trusted vals")
-	}
+
 	c.trustedHeader = h
-	c.trustedNextVals = vals
+	c.trustedNextVals = nextVals
+
 	return nil
 }
 
+// fetch header and validators for the given height from primary provider.
 func (c *Client) fetchHeaderAndValsAtHeight(height int64) (*types.SignedHeader, *types.ValidatorSet, error) {
 	h, err := c.primary.SignedHeader(height)
 	if err != nil {
@@ -420,6 +620,7 @@ func (c *Client) fetchHeaderAndValsAtHeight(height int64) (*types.SignedHeader,
 	return h, vals, nil
 }
 
+// compare header with one from a random alternative provider.
 func (c *Client) compareNewHeaderWithRandomAlternative(h *types.SignedHeader) error {
 	// 1. Pick an alternative provider.
 	p := c.alternatives[tmrand.Intn(len(c.alternatives))]
@@ -442,3 +643,61 @@ func (c *Client) compareNewHeaderWithRandomAlternative(h *types.SignedHeader) er
 
 	return nil
 }
+
+func (c *Client) removeNoLongerTrustedHeadersRoutine() {
+	ticker := time.NewTicker(c.removeNoLongerTrustedHeadersPeriod)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			c.RemoveNoLongerTrustedHeaders(time.Now())
+		case <-c.quit:
+			return
+		}
+	}
+}
+
+// RemoveNoLongerTrustedHeaders removes no longer trusted headers (due to
+// expiration).
+//
+// Exposed for testing.
+func (c *Client) RemoveNoLongerTrustedHeaders(now time.Time) {
+	// 1) Get the oldest height.
+	oldestHeight, err := c.trustedStore.FirstSignedHeaderHeight()
+	if err != nil {
+		c.logger.Error("can't get first trusted height", "err", err)
+		return
+	}
+
+	// 2) Get the latest height.
+	latestHeight, err := c.LastTrustedHeight()
+	if err != nil {
+		c.logger.Error("can't get last trusted height", "err", err)
+		return
+	}
+
+	// 3) Remove all headers that are outside of the trusting period.
+	for height := oldestHeight; height <= latestHeight; height++ {
+		h, err := c.trustedStore.SignedHeader(height)
+		if err != nil {
+			c.logger.Error("can't get a trusted header", "err", err, "height", height)
+			continue
+		}
+		if h == nil {
+			c.logger.Debug("attempted to remove non-existing header", "height", height)
+			continue
+		}
+
+		// Stop if the header is within the trusting period.
+		if !HeaderExpired(h, c.trustingPeriod, now) {
+			break
+		}
+
+		err = c.trustedStore.DeleteSignedHeaderAndNextValidatorSet(height)
+		if err != nil {
+			c.logger.Error("can't remove a trusted header & validator set", "err", err, "height", height)
+			continue
+		}
+	}
+}

lite2/client_test.go

@@ -9,6 +9,7 @@ import (
 
 	dbm "github.com/tendermint/tm-db"
 
+	"github.com/tendermint/tendermint/libs/log"
 	mockp "github.com/tendermint/tendermint/lite2/provider/mock"
 	dbs "github.com/tendermint/tendermint/lite2/store/db"
 	"github.com/tendermint/tendermint/types"
@@ -135,8 +136,9 @@ func TestClient_SequentialVerification(t *testing.T) {
 		} else {
 			require.NoError(t, err)
 		}
+		defer c.Stop()
 
-		err = c.VerifyHeaderAtHeight(3, bTime.Add(3*time.Hour))
+		_, err = c.VerifyHeaderAtHeight(3, bTime.Add(3*time.Hour))
 		if tc.verifyErr {
 			assert.Error(t, err)
 		} else {
@@ -232,8 +234,9 @@ func TestClient_SkippingVerification(t *testing.T) {
 		} else {
 			require.NoError(t, err)
 		}
+		defer c.Stop()
 
-		err = c.VerifyHeaderAtHeight(3, bTime.Add(3*time.Hour))
+		_, err = c.VerifyHeaderAtHeight(3, bTime.Add(3*time.Hour))
 		if tc.verifyErr {
 			assert.Error(t, err)
 		} else {
@@ -241,3 +244,418 @@ func TestClient_SkippingVerification(t *testing.T) {
 		}
 	}
 }
+
+func TestClientRemovesNoLongerTrustedHeaders(t *testing.T) {
+	const (
+		chainID = "TestClientRemovesNoLongerTrustedHeaders"
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals     = keys.ToValidators(20, 10)
+		bTime, _ = time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+		header   = keys.GenSignedHeader(chainID, 1, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+	)
+
+	c, err := NewClient(
+		chainID,
+		TrustOptions{
+			Period: 4 * time.Hour,
+			Height: 1,
+			Hash:   header.Hash(),
+		},
+		mockp.New(
+			chainID,
+			map[int64]*types.SignedHeader{
+				// trusted header
+				1: header,
+				// interim header (3/3 signed)
+				2: keys.GenSignedHeader(chainID, 2, bTime.Add(2*time.Hour), nil, vals, vals,
+					[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
+				// last header (3/3 signed)
+				3: keys.GenSignedHeader(chainID, 3, bTime.Add(4*time.Hour), nil, vals, vals,
+					[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
+			},
+			map[int64]*types.ValidatorSet{
+				1: vals,
+				2: vals,
+				3: vals,
+				4: vals,
+			},
+		),
+		dbs.New(dbm.NewMemDB(), chainID),
+	)
+	require.NoError(t, err)
+	defer c.Stop()
+	c.SetLogger(log.TestingLogger())
+
+	// Verify new headers.
+	_, err = c.VerifyHeaderAtHeight(2, bTime.Add(2*time.Hour).Add(1*time.Second))
+	require.NoError(t, err)
+	now := bTime.Add(4 * time.Hour).Add(1 * time.Second)
+	_, err = c.VerifyHeaderAtHeight(3, now)
+	require.NoError(t, err)
+
+	// Remove expired headers.
+	c.RemoveNoLongerTrustedHeaders(now)
+
+	// Check expired headers are no longer available.
+	h, err := c.TrustedHeader(1, now)
+	assert.NoError(t, err)
+	assert.Nil(t, h)
+
+	// Check not expired headers are available.
+	h, err = c.TrustedHeader(2, now)
+	assert.NoError(t, err)
+	assert.NotNil(t, h)
+}
+
+func TestClient_Cleanup(t *testing.T) {
+	const (
+		chainID = "TestClient_Cleanup"
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals     = keys.ToValidators(20, 10)
+		bTime, _ = time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+		header   = keys.GenSignedHeader(chainID, 1, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+	)
+
+	c, err := NewClient(
+		chainID,
+		TrustOptions{
+			Period: 4 * time.Hour,
+			Height: 1,
+			Hash:   header.Hash(),
+		},
+		mockp.New(
+			chainID,
+			map[int64]*types.SignedHeader{
+				// trusted header
+				1: header,
+			},
+			map[int64]*types.ValidatorSet{
+				1: vals,
+				2: vals,
+			},
+		),
+		dbs.New(dbm.NewMemDB(), chainID),
+	)
+	require.NoError(t, err)
+	c.SetLogger(log.TestingLogger())
+
+	c.Cleanup()
+
+	// Check no headers exist after Cleanup.
+	h, err := c.TrustedHeader(1, bTime.Add(1*time.Second))
+	assert.NoError(t, err)
+	assert.Nil(t, h)
+}
+
+// trustedHeader.Height == options.Height
+func TestClientRestoreTrustedHeaderAfterStartup1(t *testing.T) {
+	const (
+		chainID = "TestClientRestoreTrustedHeaderAfterStartup1"
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals     = keys.ToValidators(20, 10)
+		bTime, _ = time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+		header   = keys.GenSignedHeader(chainID, 1, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+	)
+
+	// 1. options.Hash == trustedHeader.Hash
+	{
+		trustedStore := dbs.New(dbm.NewMemDB(), chainID)
+		err := trustedStore.SaveSignedHeaderAndNextValidatorSet(header, vals)
+		require.NoError(t, err)
+
+		c, err := NewClient(
+			chainID,
+			TrustOptions{
+				Period: 4 * time.Hour,
+				Height: 1,
+				Hash:   header.Hash(),
+			},
+			mockp.New(
+				chainID,
+				map[int64]*types.SignedHeader{
+					// trusted header
+					1: header,
+				},
+				map[int64]*types.ValidatorSet{
+					1: vals,
+					2: vals,
+				},
+			),
+			trustedStore,
+		)
+		require.NoError(t, err)
+		c.SetLogger(log.TestingLogger())
+
+		h, err := c.TrustedHeader(1, bTime.Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.NotNil(t, h)
+		assert.Equal(t, h.Hash(), header.Hash())
+	}
+
+	// 2. options.Hash != trustedHeader.Hash
+	{
+		trustedStore := dbs.New(dbm.NewMemDB(), chainID)
+		err := trustedStore.SaveSignedHeaderAndNextValidatorSet(header, vals)
+		require.NoError(t, err)
+
+		// header1 != header
+		header1 := keys.GenSignedHeader(chainID, 1, bTime.Add(1*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+
+		c, err := NewClient(
+			chainID,
+			TrustOptions{
+				Period: 4 * time.Hour,
+				Height: 1,
+				Hash:   header1.Hash(),
+			},
+			mockp.New(
+				chainID,
+				map[int64]*types.SignedHeader{
+					// trusted header
+					1: header1,
+				},
+				map[int64]*types.ValidatorSet{
+					1: vals,
+					2: vals,
+				},
+			),
+			trustedStore,
+		)
+		require.NoError(t, err)
+		c.SetLogger(log.TestingLogger())
+
+		h, err := c.TrustedHeader(1, bTime.Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.NotNil(t, h)
+		assert.Equal(t, h.Hash(), header1.Hash())
+	}
+}
+
+// trustedHeader.Height < options.Height
+func TestClientRestoreTrustedHeaderAfterStartup2(t *testing.T) {
+	const (
+		chainID = "TestClientRestoreTrustedHeaderAfterStartup2"
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals     = keys.ToValidators(20, 10)
+		bTime, _ = time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+		header   = keys.GenSignedHeader(chainID, 1, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+	)
+
+	// 1. options.Hash == trustedHeader.Hash
+	{
+		trustedStore := dbs.New(dbm.NewMemDB(), chainID)
+		err := trustedStore.SaveSignedHeaderAndNextValidatorSet(header, vals)
+		require.NoError(t, err)
+
+		header2 := keys.GenSignedHeader(chainID, 2, bTime.Add(2*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+
+		c, err := NewClient(
+			chainID,
+			TrustOptions{
+				Period: 4 * time.Hour,
+				Height: 2,
+				Hash:   header2.Hash(),
+			},
+			mockp.New(
+				chainID,
+				map[int64]*types.SignedHeader{
+					1: header,
+					2: header2,
+				},
+				map[int64]*types.ValidatorSet{
+					1: vals,
+					2: vals,
+					3: vals,
+				},
+			),
+			trustedStore,
+		)
+		require.NoError(t, err)
+		c.SetLogger(log.TestingLogger())
+
+		// Check we still have the 1st header (+header+).
+		h, err := c.TrustedHeader(1, bTime.Add(2*time.Hour).Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.NotNil(t, h)
+		assert.Equal(t, h.Hash(), header.Hash())
+	}
+
+	// 2. options.Hash != trustedHeader.Hash
+	// This could happen if previous provider was lying to us.
+	{
+		trustedStore := dbs.New(dbm.NewMemDB(), chainID)
+		err := trustedStore.SaveSignedHeaderAndNextValidatorSet(header, vals)
+		require.NoError(t, err)
+
+		// header1 != header
+		header1 := keys.GenSignedHeader(chainID, 1, bTime.Add(1*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+
+		header2 := keys.GenSignedHeader(chainID, 2, bTime.Add(2*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+
+		c, err := NewClient(
+			chainID,
+			TrustOptions{
+				Period: 4 * time.Hour,
+				Height: 2,
+				Hash:   header2.Hash(),
+			},
+			mockp.New(
+				chainID,
+				map[int64]*types.SignedHeader{
+					1: header1,
+					2: header2,
+				},
+				map[int64]*types.ValidatorSet{
+					1: vals,
+					2: vals,
+					3: vals,
+				},
+			),
+			trustedStore,
+		)
+		require.NoError(t, err)
+		c.SetLogger(log.TestingLogger())
+
+		// Check we no longer have the invalid 1st header (+header+).
+		h, err := c.TrustedHeader(1, bTime.Add(2*time.Hour).Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.Nil(t, h)
+	}
+}
+
+// trustedHeader.Height > options.Height
+func TestClientRestoreTrustedHeaderAfterStartup3(t *testing.T) {
+	const (
+		chainID = "TestClientRestoreTrustedHeaderAfterStartup3"
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals     = keys.ToValidators(20, 10)
+		bTime, _ = time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+		header   = keys.GenSignedHeader(chainID, 1, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+	)
+
+	// 1. options.Hash == trustedHeader.Hash
+	{
+		trustedStore := dbs.New(dbm.NewMemDB(), chainID)
+		err := trustedStore.SaveSignedHeaderAndNextValidatorSet(header, vals)
+		require.NoError(t, err)
+
+		header2 := keys.GenSignedHeader(chainID, 2, bTime.Add(2*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+		err = trustedStore.SaveSignedHeaderAndNextValidatorSet(header2, vals)
+		require.NoError(t, err)
+
+		c, err := NewClient(
+			chainID,
+			TrustOptions{
+				Period: 4 * time.Hour,
+				Height: 1,
+				Hash:   header.Hash(),
+			},
+			mockp.New(
+				chainID,
+				map[int64]*types.SignedHeader{
+					1: header,
+					2: header2,
+				},
+				map[int64]*types.ValidatorSet{
+					1: vals,
+					2: vals,
+					3: vals,
+				},
+			),
+			trustedStore,
+		)
+		require.NoError(t, err)
+		c.SetLogger(log.TestingLogger())
+
+		// Check we still have the 1st header (+header+).
+		h, err := c.TrustedHeader(1, bTime.Add(2*time.Hour).Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.NotNil(t, h)
+		assert.Equal(t, h.Hash(), header.Hash())
+
+		// Check we no longer have 2nd header (+header2+).
+		h, err = c.TrustedHeader(2, bTime.Add(2*time.Hour).Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.Nil(t, h)
+	}
+
+	// 2. options.Hash != trustedHeader.Hash
+	// This could happen if previous provider was lying to us.
+	{
+		trustedStore := dbs.New(dbm.NewMemDB(), chainID)
+		err := trustedStore.SaveSignedHeaderAndNextValidatorSet(header, vals)
+		require.NoError(t, err)
+
+		// header1 != header
+		header1 := keys.GenSignedHeader(chainID, 1, bTime.Add(1*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+
+		header2 := keys.GenSignedHeader(chainID, 2, bTime.Add(2*time.Hour), nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+		err = trustedStore.SaveSignedHeaderAndNextValidatorSet(header2, vals)
+		require.NoError(t, err)
+
+		c, err := NewClient(
+			chainID,
+			TrustOptions{
+				Period: 4 * time.Hour,
+				Height: 1,
+				Hash:   header1.Hash(),
+			},
+			mockp.New(
+				chainID,
+				map[int64]*types.SignedHeader{
+					1: header1,
+				},
+				map[int64]*types.ValidatorSet{
+					1: vals,
+					2: vals,
+				},
+			),
+			trustedStore,
+		)
+		require.NoError(t, err)
+		c.SetLogger(log.TestingLogger())
+
+		// Check we have swapped invalid 1st header (+header+) with correct one (+header1+).
+		h, err := c.TrustedHeader(1, bTime.Add(2*time.Hour).Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.NotNil(t, h)
+		assert.Equal(t, h.Hash(), header1.Hash())
+
+		// Check we no longer have invalid 2nd header (+header2+).
+		h, err = c.TrustedHeader(2, bTime.Add(2*time.Hour).Add(1*time.Second))
+		assert.NoError(t, err)
+		assert.Nil(t, h)
+	}
+}

lite2/doc.go

@@ -31,5 +31,81 @@ Subjectivity](https://blog.ethereum.org/2014/11/25/proof-stake-learned-love-weak
 NOTE: Tendermint provides a somewhat different (stronger) light client model
 than Bitcoin under eclipse, since the eclipsing node(s) can only fool the light
 client if they have two-thirds of the private keys from the last root-of-trust.
+
+# Common structures
+
+* SignedHeader
+
+SignedHeader is a block header along with a commit -- enough validator
+precommit-vote signatures to prove its validity (> 2/3 of the voting power)
+given the validator set responsible for signing that header.
+
+The hash of the next validator set is included and signed in the SignedHeader.
+This lets the lite client keep track of arbitrary changes to the validator set,
+as every change to the validator set must be approved by inclusion in the
+header and signed in the commit.
+
+In the worst case, with every block changing the validators around completely,
+a lite client can sync up with every block header to verify each validator set
+change on the chain. In practice, most applications will not have frequent
+drastic updates to the validator set, so the logic defined in this package for
+lite client syncing is optimized to use intelligent bisection.
+
+# What this package provides
+
+This package provides three major things:
+
+1. Client implementation (see client.go)
+2. Pure functions to verify a new header (see verifier.go)
+3. Secure RPC proxy
+
+## 1. Client implementation (see client.go)
+
+Example usage:
+
+		db, err := dbm.NewGoLevelDB("lite-client-db", dbDir)
+		if err != nil {
+			// return err
+			t.Fatal(err)
+		}
+		c, err := NewClient(
+			chainID,
+			TrustOptions{
+				Period: 504 * time.Hour, // 21 days
+				Height: 100,
+				Hash:   header.Hash(),
+			},
+			httpp.New(chainID, "tcp://localhost:26657"),
+			dbs.New(db, chainID),
+		)
+
+		err = c.VerifyHeaderAtHeight(101, time.Now())
+		if err != nil {
+			fmt.Println("retry?")
+		}
+
+		h, err := c.TrustedHeader(101)
+		if err != nil {
+			fmt.Println("retry?")
+		}
+		fmt.Println("got header", h)
+
+## 2. Pure functions to verify a new header (see verifier.go)
+
+Verify function verifies a new header against some trusted header. See
+https://github.com/tendermint/spec/blob/master/spec/consensus/light-client.md
+for details.
+
+## 3. Secure RPC proxy
+
+Tendermint RPC exposes a lot of info, but a malicious node could return any
+data it wants to queries, or even to block headers, even making up fake
+signatures from non-existent validators to justify it. Secure RPC proxy serves
+as a wrapper, which verifies all the headers, using a light client connected to
+some other node.
+
+See
+https://github.com/tendermint/tendermint/blob/master/cmd/tendermint/commands/lite.go
+for usage example.
 */
 package lite

lite2/errors.go

@@ -3,6 +3,8 @@ package lite
 import (
 	"fmt"
 	"time"
+
+	"github.com/tendermint/tendermint/types"
 )
 
 // ErrOldHeaderExpired means the old (trusted) header has expired according to
@@ -16,3 +18,13 @@ type ErrOldHeaderExpired struct {
 func (e ErrOldHeaderExpired) Error() string {
 	return fmt.Sprintf("old header has expired at %v (now: %v)", e.At, e.Now)
 }
+
+// ErrNewValSetCantBeTrusted means the new validator set cannot be trusted
+// because < 1/3rd (+trustLevel+) of the old validator set has signed.
+type ErrNewValSetCantBeTrusted struct {
+	Reason types.ErrNotEnoughVotingPowerSigned
+}
+
+func (e ErrNewValSetCantBeTrusted) Error() string {
+	return fmt.Sprintf("cant trust new val set: %v", e.Reason)
+}

lite2/example_test.go

@@ -1,95 +1,155 @@
 package lite
 
-//func TestExample_Client(t *testing.T) {
-//	const (
-//		chainID = "my-awesome-chain"
-//	)
-//	dbDir, err := ioutil.TempDir("", "lite-client-example")
-//	if err != nil {
-//		t.Fatal(err)
-//	}
-//	defer os.RemoveAll(dbDir)
-
-//	// TODO: fetch the "trusted" header from a node
-//	header := (*types.SignedHeader)(nil)
-
-//	/////////////////////////////////////////////////////////////////////////////
-
-//	db, err := dbm.NewGoLevelDB("lite-client-db", dbDir)
-//	if err != nil {
-//		// return err
-//		t.Fatal(err)
-//	}
-//	c, err := NewClient(
-//		chainID,
-//		TrustOptions{
-//			Period: 504 * time.Hour, // 21 days
-//			Height: 100,
-//			Hash:   header.Hash(),
-//		},
-//		httpp.New(chainID, "tcp://localhost:26657"),
-//		dbs.New(db, chainID),
-//	)
-
-//	err = c.VerifyHeaderAtHeight(101, time.Now())
-//	if err != nil {
-//		fmt.Println("retry?")
-//	}
-
-//	h, err := c.TrustedHeader(101)
-//	if err != nil {
-//		fmt.Println("retry?")
-//	}
-//	fmt.Println("got header", h)
-//	// verify some data
-//}
-
-//func TestExample_AutoClient(t *testing.T) {
-//	const (
-//		chainID = "my-awesome-chain"
-//	)
-//	dbDir, err := ioutil.TempDir("", "lite-client-example")
-//	if err != nil {
-//		t.Fatal(err)
-//	}
-//	defer os.RemoveAll(dbDir)
-
-//	// TODO: fetch the "trusted" header from a node
-//	header := (*types.SignedHeader)(nil)
-
-//	/////////////////////////////////////////////////////////////////////////////
-
-//	db, err := dbm.NewGoLevelDB("lite-client-db", dbDir)
-//	if err != nil {
-//		// return err
-//		t.Fatal(err)
-//	}
-
-//	base, err := NewClient(
-//		chainID,
-//		TrustOptions{
-//			Period: 504 * time.Hour, // 21 days
-//			Height: 100,
-//			Hash:   header.Hash(),
-//		},
-//		httpp.New(chainID, "tcp://localhost:26657"),
-//		dbs.New(db, chainID),
-//	)
-
-//	c := NewAutoClient(base, 1*time.Second)
-//	defer c.Stop()
-
-//	select {
-//	case h := <-c.TrustedHeaders():
-//		fmt.Println("got header", h)
-//		// verify some data
-//	case err := <-c.Err():
-//		switch errors.Cause(err).(type) {
-//		case ErrOldHeaderExpired:
-//			// reobtain trust height and hash
-//		default:
-//			// try with another full node
-//			fmt.Println("got error", err)
-//		}
-//	}
-//}
+import (
+	"fmt"
+	"io/ioutil"
+	stdlog "log"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/pkg/errors"
+
+	dbm "github.com/tendermint/tm-db"
+
+	"github.com/tendermint/tendermint/abci/example/kvstore"
+	"github.com/tendermint/tendermint/libs/log"
+	httpp "github.com/tendermint/tendermint/lite2/provider/http"
+	dbs "github.com/tendermint/tendermint/lite2/store/db"
+	rpctest "github.com/tendermint/tendermint/rpc/test"
+)
+
+func TestExample_Client(t *testing.T) {
+	// give Tendermint time to generate some blocks
+	time.Sleep(5 * time.Second)
+
+	dbDir, err := ioutil.TempDir("", "lite-client-example")
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+	defer os.RemoveAll(dbDir)
+
+	var (
+		config  = rpctest.GetConfig()
+		chainID = config.ChainID()
+	)
+
+	provider, err := httpp.New(chainID, config.RPC.ListenAddress)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	header, err := provider.SignedHeader(2)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	db, err := dbm.NewGoLevelDB("lite-client-db", dbDir)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	c, err := NewClient(
+		chainID,
+		TrustOptions{
+			Period: 504 * time.Hour, // 21 days
+			Height: 2,
+			Hash:   header.Hash(),
+		},
+		provider,
+		dbs.New(db, chainID),
+	)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+	c.SetLogger(log.TestingLogger())
+
+	_, err = c.VerifyHeaderAtHeight(3, time.Now())
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	h, err := c.TrustedHeader(3, time.Now())
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	fmt.Println("got header", h.Height)
+	// Output: got header 3
+}
+
+func TestExample_AutoClient(t *testing.T) {
+	// give Tendermint time to generate some blocks
+	time.Sleep(5 * time.Second)
+
+	dbDir, err := ioutil.TempDir("", "lite-client-example")
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+	defer os.RemoveAll(dbDir)
+
+	var (
+		config  = rpctest.GetConfig()
+		chainID = config.ChainID()
+	)
+
+	provider, err := httpp.New(chainID, config.RPC.ListenAddress)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	header, err := provider.SignedHeader(2)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	db, err := dbm.NewGoLevelDB("lite-client-db", dbDir)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+
+	base, err := NewClient(
+		chainID,
+		TrustOptions{
+			Period: 504 * time.Hour, // 21 days
+			Height: 2,
+			Hash:   header.Hash(),
+		},
+		provider,
+		dbs.New(db, chainID),
+	)
+	if err != nil {
+		stdlog.Fatal(err)
+	}
+	base.SetLogger(log.TestingLogger())
+
+	c := NewAutoClient(base, 1*time.Second)
+	defer c.Stop()
+
+	select {
+	case h := <-c.TrustedHeaders():
+		fmt.Println("got header", h.Height)
+		// Output: got header 3
+	case err := <-c.Errs():
+		switch errors.Cause(err).(type) {
+		case ErrOldHeaderExpired:
+			// reobtain trust height and hash
+			stdlog.Fatal(err)
+		default:
+			// try with another full node
+			stdlog.Fatal(err)
+		}
+	}
+}
+
+func TestMain(m *testing.M) {
+	// start a tendermint node (and kvstore) in the background to test against
+	app := kvstore.NewApplication()
+	node := rpctest.StartTendermint(app)
+
+	code := m.Run()
+
+	// and shut down proper at the end
+	rpctest.StopTendermint(node)
+	os.Exit(code)
+}

lite2/provider/http/http.go

@@ -39,10 +39,13 @@ func NewWithClient(chainID string, client SignStatusClient) provider.Provider {
 	}
 }
 
+// ChainID returns a chainID this provider was configured with.
 func (p *http) ChainID() string {
 	return p.chainID
 }
 
+// SignedHeader fetches a SignedHeader at the given height and checks the
+// chainID matches.
 func (p *http) SignedHeader(height int64) (*types.SignedHeader, error) {
 	h, err := validateHeight(height)
 	if err != nil {
@@ -62,6 +65,8 @@ func (p *http) SignedHeader(height int64) (*types.SignedHeader, error) {
 	return &commit.SignedHeader, nil
 }
 
+// ValidatorSet fetches a ValidatorSet at the given height. Multiple HTTP
+// requests might be required if the validator set size is over 100.
 func (p *http) ValidatorSet(height int64) (*types.ValidatorSet, error) {
 	h, err := validateHeight(height)
 	if err != nil {

lite2/rpc/client.go

@@ -90,14 +90,10 @@ func (c *Client) ABCIQueryWithOptions(path string, data tmbytes.HexBytes,
 	}
 
 	// Update the light client if we're behind.
-	if err := c.updateLiteClientIfNeededTo(resp.Height + 1); err != nil {
-		return nil, err
-	}
-
-	// AppHash for height H is in header H+1.
-	h, err := c.lc.TrustedHeader(resp.Height+1, time.Now())
+	// NOTE: AppHash for height H is in header H+1.
+	h, err := c.updateLiteClientIfNeededTo(resp.Height + 1)
 	if err != nil {
-		return nil, errors.Wrapf(err, "TrustedHeader(%d)", resp.Height+1)
+		return nil, err
 	}
 
 	// Validate the value proof against the trusted header.
@@ -188,7 +184,7 @@ func (c *Client) BlockchainInfo(minHeight, maxHeight int64) (*ctypes.ResultBlock
 	// Update the light client if we're behind.
 	if len(res.BlockMetas) > 0 {
 		lastHeight := res.BlockMetas[len(res.BlockMetas)-1].Header.Height
-		if err := c.updateLiteClientIfNeededTo(lastHeight); err != nil {
+		if _, err := c.updateLiteClientIfNeededTo(lastHeight); err != nil {
 			return nil, err
 		}
 	}
@@ -232,15 +228,12 @@ func (c *Client) Block(height *int64) (*ctypes.ResultBlock, error) {
 	}
 
 	// Update the light client if we're behind.
-	if err := c.updateLiteClientIfNeededTo(res.Block.Height); err != nil {
+	h, err := c.updateLiteClientIfNeededTo(res.Block.Height)
+	if err != nil {
 		return nil, err
 	}
 
 	// Verify block.
-	h, err := c.lc.TrustedHeader(res.Block.Height, time.Now())
-	if err != nil {
-		return nil, errors.Wrapf(err, "TrustedHeader(%d)", res.Block.Height)
-	}
 	if bH, tH := res.Block.Hash(), h.Hash(); !bytes.Equal(bH, tH) {
 		return nil, errors.Errorf("Block#Header %X does not match with trusted header %X",
 			bH, tH)
@@ -265,15 +258,12 @@ func (c *Client) Commit(height *int64) (*ctypes.ResultCommit, error) {
 	}
 
 	// Update the light client if we're behind.
-	if err := c.updateLiteClientIfNeededTo(res.Height); err != nil {
+	h, err := c.updateLiteClientIfNeededTo(res.Height)
+	if err != nil {
 		return nil, err
 	}
 
 	// Verify commit.
-	h, err := c.lc.TrustedHeader(res.Height, time.Now())
-	if err != nil {
-		return nil, errors.Wrapf(err, "TrustedHeader(%d)", res.Height)
-	}
 	if rH, tH := res.Hash(), h.Hash(); !bytes.Equal(rH, tH) {
 		return nil, errors.Errorf("header %X does not match with trusted header %X",
 			rH, tH)
@@ -296,15 +286,12 @@ func (c *Client) Tx(hash []byte, prove bool) (*ctypes.ResultTx, error) {
 	}
 
 	// Update the light client if we're behind.
-	if err := c.updateLiteClientIfNeededTo(res.Height); err != nil {
+	h, err := c.updateLiteClientIfNeededTo(res.Height)
+	if err != nil {
 		return nil, err
 	}
 
 	// Validate the proof.
-	h, err := c.lc.TrustedHeader(res.Height, time.Now())
-	if err != nil {
-		return res, errors.Wrapf(err, "TrustedHeader(%d)", res.Height)
-	}
 	return res, res.Proof.Validate(h.DataHash)
 }
 
@@ -333,17 +320,21 @@ func (c *Client) UnsubscribeAll(ctx context.Context, subscriber string) error {
 	return c.next.UnsubscribeAll(ctx, subscriber)
 }
 
-func (c *Client) updateLiteClientIfNeededTo(height int64) error {
+func (c *Client) updateLiteClientIfNeededTo(height int64) (*types.SignedHeader, error) {
 	lastTrustedHeight, err := c.lc.LastTrustedHeight()
 	if err != nil {
-		return errors.Wrap(err, "LastTrustedHeight")
+		return nil, errors.Wrap(err, "LastTrustedHeight")
 	}
+
 	if lastTrustedHeight < height {
-		if err := c.lc.VerifyHeaderAtHeight(height, time.Now()); err != nil {
-			return errors.Wrapf(err, "VerifyHeaderAtHeight(%d)", height)
-		}
+		return c.lc.VerifyHeaderAtHeight(height, time.Now())
 	}
-	return nil
+
+	h, err := c.lc.TrustedHeader(height, time.Now())
+	if err != nil {
+		return nil, errors.Wrapf(err, "TrustedHeader(#%d)", height)
+	}
+	return h, nil
 }
 
 func (c *Client) RegisterOpDecoder(typ string, dec merkle.OpDecoder) {

lite2/store/db/db.go

@@ -1,7 +1,6 @@
 package db
 
 import (
-	"errors"
 	"fmt"
 	"regexp"
 	"strconv"
@@ -23,39 +22,57 @@ type dbs struct {
 
 // New returns a Store that wraps any DB (with an optional prefix in case you
 // want to use one DB with many light clients).
+//
+// Objects are marshalled using amino (github.com/tendermint/go-amino)
 func New(db dbm.DB, prefix string) store.Store {
 	cdc := amino.NewCodec()
 	cryptoAmino.RegisterAmino(cdc)
 	return &dbs{db: db, prefix: prefix, cdc: cdc}
 }
 
-func (s *dbs) SaveSignedHeader(sh *types.SignedHeader) error {
+// SaveSignedHeaderAndNextValidatorSet persists SignedHeader and ValidatorSet
+// to the db.
+func (s *dbs) SaveSignedHeaderAndNextValidatorSet(sh *types.SignedHeader, valSet *types.ValidatorSet) error {
 	if sh.Height <= 0 {
 		panic("negative or zero height")
 	}
 
+	// TODO: batch
 	bz, err := s.cdc.MarshalBinaryLengthPrefixed(sh)
 	if err != nil {
 		return err
 	}
 	s.db.Set(s.shKey(sh.Height), bz)
+
+	bz, err = s.cdc.MarshalBinaryLengthPrefixed(valSet)
+	if err != nil {
+		return err
+	}
+	s.db.Set(s.vsKey(sh.Height+1), bz)
+
 	return nil
 }
 
-func (s *dbs) SaveValidatorSet(valSet *types.ValidatorSet, height int64) error {
+// DeleteSignedHeaderAndNextValidatorSet deletes SignedHeader and ValidatorSet
+// from the db.
+func (s *dbs) DeleteSignedHeaderAndNextValidatorSet(height int64) error {
 	if height <= 0 {
 		panic("negative or zero height")
 	}
 
-	bz, err := s.cdc.MarshalBinaryLengthPrefixed(valSet)
-	if err != nil {
-		return err
-	}
-	s.db.Set(s.vsKey(height), bz)
+	// TODO: batch
+	s.db.Delete(s.shKey(height))
+	s.db.Delete(s.vsKey(height + 1))
+
 	return nil
 }
 
+// SignedHeader loads SignedHeader at the given height.
 func (s *dbs) SignedHeader(height int64) (*types.SignedHeader, error) {
+	if height <= 0 {
+		panic("negative or zero height")
+	}
+
 	bz := s.db.Get(s.shKey(height))
 	if bz == nil {
 		return nil, nil
@@ -66,7 +83,12 @@ func (s *dbs) SignedHeader(height int64) (*types.SignedHeader, error) {
 	return signedHeader, err
 }
 
+// ValidatorSet loads ValidatorSet at the given height.
 func (s *dbs) ValidatorSet(height int64) (*types.ValidatorSet, error) {
+	if height <= 0 {
+		panic("negative or zero height")
+	}
+
 	bz := s.db.Get(s.vsKey(height))
 	if bz == nil {
 		return nil, nil
@@ -77,6 +99,7 @@ func (s *dbs) ValidatorSet(height int64) (*types.ValidatorSet, error) {
 	return valSet, err
 }
 
+// LastSignedHeaderHeight returns the last SignedHeader height stored.
 func (s *dbs) LastSignedHeaderHeight() (int64, error) {
 	itr := s.db.ReverseIterator(
 		s.shKey(1),
@@ -90,20 +113,41 @@ func (s *dbs) LastSignedHeaderHeight() (int64, error) {
 		if ok {
 			return height, nil
 		}
+		itr.Next()
+	}
+
+	return -1, nil
+}
+
+// FirstSignedHeaderHeight returns the first SignedHeader height stored.
+func (s *dbs) FirstSignedHeaderHeight() (int64, error) {
+	itr := s.db.Iterator(
+		s.shKey(1),
+		append(s.shKey(1<<63-1), byte(0x00)),
+	)
+	defer itr.Close()
+
+	for itr.Valid() {
+		key := itr.Key()
+		_, height, ok := parseShKey(key)
+		if ok {
+			return height, nil
+		}
+		itr.Next()
 	}
 
-	return -1, errors.New("no headers found")
+	return -1, nil
 }
 
 func (s *dbs) shKey(height int64) []byte {
-	return []byte(fmt.Sprintf("sh/%s/%010d", s.prefix, height))
+	return []byte(fmt.Sprintf("sh/%s/%020d", s.prefix, height))
 }
 
 func (s *dbs) vsKey(height int64) []byte {
-	return []byte(fmt.Sprintf("vs/%s/%010d", s.prefix, height))
+	return []byte(fmt.Sprintf("vs/%s/%020d", s.prefix, height))
 }
 
-var keyPattern = regexp.MustCompile(`^(sh|vs)/([^/]*)/([0-9]+)/$`)
+var keyPattern = regexp.MustCompile(`^(sh|vs)/([^/]*)/([0-9]+)$`)
 
 func parseKey(key []byte) (part string, prefix string, height int64, ok bool) {
 	submatch := keyPattern.FindSubmatch(key)
@@ -112,12 +156,10 @@ func parseKey(key []byte) (part string, prefix string, height int64, ok bool) {
 	}
 	part = string(submatch[1])
 	prefix = string(submatch[2])
-	heightStr := string(submatch[3])
-	heightInt, err := strconv.Atoi(heightStr)
+	height, err := strconv.ParseInt(string(submatch[3]), 10, 64)
 	if err != nil {
 		return "", "", 0, false
 	}
-	height = int64(heightInt)
 	ok = true // good!
 	return
 }

lite2/store/db/db_test.go

@@ -0,0 +1,76 @@
+package db
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	dbm "github.com/tendermint/tm-db"
+
+	"github.com/tendermint/tendermint/types"
+)
+
+func TestLast_FirstSignedHeaderHeight(t *testing.T) {
+	dbStore := New(dbm.NewMemDB(), "TestLast_FirstSignedHeaderHeight")
+
+	// Empty store
+	height, err := dbStore.LastSignedHeaderHeight()
+	require.NoError(t, err)
+	assert.EqualValues(t, -1, height)
+
+	height, err = dbStore.FirstSignedHeaderHeight()
+	require.NoError(t, err)
+	assert.EqualValues(t, -1, height)
+
+	// 1 key
+	err = dbStore.SaveSignedHeaderAndNextValidatorSet(
+		&types.SignedHeader{Header: &types.Header{Height: 1}}, &types.ValidatorSet{})
+	require.NoError(t, err)
+
+	height, err = dbStore.LastSignedHeaderHeight()
+	require.NoError(t, err)
+	assert.EqualValues(t, 1, height)
+
+	height, err = dbStore.FirstSignedHeaderHeight()
+	require.NoError(t, err)
+	assert.EqualValues(t, 1, height)
+}
+
+func Test_SaveSignedHeaderAndNextValidatorSet(t *testing.T) {
+	dbStore := New(dbm.NewMemDB(), "Test_SaveSignedHeaderAndNextValidatorSet")
+
+	// Empty store
+	h, err := dbStore.SignedHeader(1)
+	require.NoError(t, err)
+	assert.Nil(t, h)
+
+	valSet, err := dbStore.ValidatorSet(2)
+	require.NoError(t, err)
+	assert.Nil(t, valSet)
+
+	// 1 key
+	err = dbStore.SaveSignedHeaderAndNextValidatorSet(
+		&types.SignedHeader{Header: &types.Header{Height: 1}}, &types.ValidatorSet{})
+	require.NoError(t, err)
+
+	h, err = dbStore.SignedHeader(1)
+	require.NoError(t, err)
+	assert.NotNil(t, h)
+
+	valSet, err = dbStore.ValidatorSet(2)
+	require.NoError(t, err)
+	assert.NotNil(t, valSet)
+
+	// Empty store
+	err = dbStore.DeleteSignedHeaderAndNextValidatorSet(1)
+	require.NoError(t, err)
+
+	h, err = dbStore.SignedHeader(1)
+	require.NoError(t, err)
+	assert.Nil(t, h)
+
+	valSet, err = dbStore.ValidatorSet(2)
+	require.NoError(t, err)
+	assert.Nil(t, valSet)
+}

lite2/store/store.go

@@ -4,15 +4,17 @@ import "github.com/tendermint/tendermint/types"
 
 // Store is anything that can persistenly store headers.
 type Store interface {
-	// SaveSignedHeader saves a SignedHeader.
+	// SaveSignedHeaderAndNextValidatorSet saves a SignedHeader (h: sh.Height)
+	// and a ValidatorSet (h: sh.Height+1).
 	//
 	// height must be > 0.
-	SaveSignedHeader(sh *types.SignedHeader) error
+	SaveSignedHeaderAndNextValidatorSet(sh *types.SignedHeader, valSet *types.ValidatorSet) error
 
-	// SaveValidatorSet saves a ValidatorSet.
+	// DeleteSignedHeaderAndNextValidatorSet deletes SignedHeader (h: height) and
+	// ValidatorSet (h: height+1).
 	//
 	// height must be > 0.
-	SaveValidatorSet(valSet *types.ValidatorSet, height int64) error
+	DeleteSignedHeaderAndNextValidatorSet(height int64) error
 
 	// SignedHeader returns the SignedHeader that corresponds to the given
 	// height.
@@ -31,8 +33,13 @@ type Store interface {
 	// is returned.
 	ValidatorSet(height int64) (*types.ValidatorSet, error)
 
-	// LastSignedHeaderHeight returns the last SignedHeader height.
+	// LastSignedHeaderHeight returns the last (newest) SignedHeader height.
 	//
-	// If the store is empty, an error is returned.
+	// If the store is empty, -1 and nil error are returned.
 	LastSignedHeaderHeight() (int64, error)
+
+	// FirstSignedHeaderHeight returns the first (oldest) SignedHeader height.
+	//
+	// If the store is empty, -1 and nil error are returned.
+	FirstSignedHeaderHeight() (int64, error)
 }

lite2/test_helpers.go

@@ -5,7 +5,6 @@ import (
 
 	"github.com/tendermint/tendermint/crypto"
 	"github.com/tendermint/tendermint/crypto/ed25519"
-	"github.com/tendermint/tendermint/crypto/secp256k1"
 
 	"github.com/tendermint/tendermint/types"
 	tmtime "github.com/tendermint/tendermint/types/time"
@@ -29,34 +28,34 @@ func genPrivKeys(n int) privKeys {
 	return res
 }
 
-// Change replaces the key at index i.
-func (pkz privKeys) Change(i int) privKeys {
-	res := make(privKeys, len(pkz))
-	copy(res, pkz)
-	res[i] = ed25519.GenPrivKey()
-	return res
-}
-
-// Extend adds n more keys (to remove, just take a slice).
-func (pkz privKeys) Extend(n int) privKeys {
-	extra := genPrivKeys(n)
-	return append(pkz, extra...)
-}
-
-// GenSecpPrivKeys produces an array of secp256k1 private keys to generate commits.
-func GenSecpPrivKeys(n int) privKeys {
-	res := make(privKeys, n)
-	for i := range res {
-		res[i] = secp256k1.GenPrivKey()
-	}
-	return res
-}
-
-// ExtendSecp adds n more secp256k1 keys (to remove, just take a slice).
-func (pkz privKeys) ExtendSecp(n int) privKeys {
-	extra := GenSecpPrivKeys(n)
-	return append(pkz, extra...)
-}
+// // Change replaces the key at index i.
+// func (pkz privKeys) Change(i int) privKeys {
+// 	res := make(privKeys, len(pkz))
+// 	copy(res, pkz)
+// 	res[i] = ed25519.GenPrivKey()
+// 	return res
+// }
+
+// // Extend adds n more keys (to remove, just take a slice).
+// func (pkz privKeys) Extend(n int) privKeys {
+// 	extra := genPrivKeys(n)
+// 	return append(pkz, extra...)
+// }
+
+// // GenSecpPrivKeys produces an array of secp256k1 private keys to generate commits.
+// func GenSecpPrivKeys(n int) privKeys {
+// 	res := make(privKeys, n)
+// 	for i := range res {
+// 		res[i] = secp256k1.GenPrivKey()
+// 	}
+// 	return res
+// }
+
+// // ExtendSecp adds n more secp256k1 keys (to remove, just take a slice).
+// func (pkz privKeys) ExtendSecp(n int) privKeys {
+// 	extra := GenSecpPrivKeys(n)
+// 	return append(pkz, extra...)
+// }
 
 // ToValidators produces a valset from the set of keys.
 // The first key has weight `init` and it increases by `inc` every step

lite2/verifier.go

@@ -16,6 +16,15 @@ var (
 	DefaultTrustLevel = tmmath.Fraction{Numerator: 1, Denominator: 3}
 )
 
+// Verify verifies the new header (h2) against the old header (h1). It ensures that:
+//
+//	a) h1 can still be trusted (if not, ErrOldHeaderExpired is returned);
+//	b) h2 is valid (if not, ErrInvalidNewHeader is returned);
+//	c) either h2.ValidatorsHash equals h1NextVals.Hash()
+//		 OR trustLevel ([1/3, 1]) of last trusted validators (h1NextVals) signed
+//		 correctly  (if not, ErrNewValSetCantBeTrusted is returned);
+//	c) more than 2/3 of new validators (h2Vals) have signed h2 (if not,
+//	   ErrNotEnoughVotingPowerSigned is returned).
 func Verify(
 	chainID string,
 	h1 *types.SignedHeader,
@@ -31,9 +40,8 @@ func Verify(
 	}
 
 	// Ensure last header can still be trusted.
-	expirationTime := h1.Time.Add(trustingPeriod)
-	if !expirationTime.After(now) {
-		return ErrOldHeaderExpired{expirationTime, now}
+	if HeaderExpired(h1, trustingPeriod, now) {
+		return ErrOldHeaderExpired{h1.Time.Add(trustingPeriod), now}
 	}
 
 	if err := verifyNewHeaderAndVals(chainID, h2, h2Vals, h1, now); err != nil {
@@ -42,16 +50,22 @@ func Verify(
 
 	if h2.Height == h1.Height+1 {
 		if !bytes.Equal(h2.ValidatorsHash, h1NextVals.Hash()) {
-			return errors.Errorf("expected old header validators (%X) to match those from new header (%X)",
+			err := errors.Errorf("expected old header next validators (%X) to match those from new header (%X)",
 				h1NextVals.Hash(),
 				h2.ValidatorsHash,
 			)
+			return err
 		}
 	} else {
 		// Ensure that +`trustLevel` (default 1/3) or more of last trusted validators signed correctly.
 		err := h1NextVals.VerifyCommitTrusting(chainID, h2.Commit.BlockID, h2.Height, h2.Commit, trustLevel)
 		if err != nil {
-			return err
+			switch e := err.(type) {
+			case types.ErrNotEnoughVotingPowerSigned:
+				return ErrNewValSetCantBeTrusted{e}
+			default:
+				return e
+			}
 		}
 	}
 
@@ -95,8 +109,8 @@ func verifyNewHeaderAndVals(
 
 	if !bytes.Equal(h2.ValidatorsHash, h2Vals.Hash()) {
 		return errors.Errorf("expected new header validators (%X) to match those that were supplied (%X)",
+			h2.ValidatorsHash,
 			h2Vals.Hash(),
-			h2.NextValidatorsHash,
 		)
 	}
 
@@ -114,3 +128,9 @@ func ValidateTrustLevel(lvl tmmath.Fraction) error {
 	}
 	return nil
 }
+
+// HeaderExpired return true if the given header expired.
+func HeaderExpired(h *types.SignedHeader, trustingPeriod time.Duration, now time.Time) bool {
+	expirationTime := h.Time.Add(trustingPeriod)
+	return !expirationTime.After(now)
+}

lite2/verifier_test.go

@@ -11,9 +11,9 @@ import (
 	"github.com/tendermint/tendermint/types"
 )
 
-func TestVerifyAdjustedHeaders(t *testing.T) {
+func TestVerifyAdjacentHeaders(t *testing.T) {
 	const (
-		chainID    = "TestVerifyAdjustedHeaders"
+		chainID    = "TestVerifyAdjacentHeaders"
 		lastHeight = 1
 		nextHeight = 2
 	)
@@ -52,10 +52,30 @@ func TestVerifyAdjustedHeaders(t *testing.T) {
 			3 * time.Hour,
 			bTime.Add(2 * time.Hour),
 			nil,
-			"h2.ValidateBasic failed: signedHeader belongs to another chain 'different-chainID' not 'TestVerifyAdjustedHeaders'",
+			"h2.ValidateBasic failed: signedHeader belongs to another chain 'different-chainID' not 'TestVerifyAdjacentHeaders'",
 		},
-		// 3/3 signed -> no error
+		// new header's time is before old header's time -> error
 		2: {
+			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(-1*time.Hour), nil, vals, vals,
+				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
+			vals,
+			3 * time.Hour,
+			bTime.Add(2 * time.Hour),
+			nil,
+			"to be after old header time",
+		},
+		// new header's time is from the future -> error
+		3: {
+			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(3*time.Hour), nil, vals, vals,
+				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
+			vals,
+			3 * time.Hour,
+			bTime.Add(2 * time.Hour),
+			nil,
+			"new header has a time from the future",
+		},
+		// 3/3 signed -> no error
+		4: {
 			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(1*time.Hour), nil, vals, vals,
 				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
 			vals,
@@ -65,7 +85,7 @@ func TestVerifyAdjustedHeaders(t *testing.T) {
 			"",
 		},
 		// 2/3 signed -> no error
-		3: {
+		5: {
 			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(1*time.Hour), nil, vals, vals,
 				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 1, len(keys)),
 			vals,
@@ -75,17 +95,17 @@ func TestVerifyAdjustedHeaders(t *testing.T) {
 			"",
 		},
 		// 1/3 signed -> error
-		4: {
+		6: {
 			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(1*time.Hour), nil, vals, vals,
 				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), len(keys)-1, len(keys)),
 			vals,
 			3 * time.Hour,
 			bTime.Add(2 * time.Hour),
-			types.ErrTooMuchChange{Got: 50, Needed: 93},
+			types.ErrNotEnoughVotingPowerSigned{Got: 50, Needed: 93},
 			"",
 		},
 		// vals does not match with what we have -> error
-		5: {
+		7: {
 			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(1*time.Hour), nil, keys.ToValidators(10, 1), vals,
 				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
 			keys.ToValidators(10, 1),
@@ -95,7 +115,7 @@ func TestVerifyAdjustedHeaders(t *testing.T) {
 			"to match those from new header",
 		},
 		// vals are inconsistent with newHeader -> error
-		6: {
+		8: {
 			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(1*time.Hour), nil, vals, vals,
 				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
 			keys.ToValidators(10, 1),
@@ -105,7 +125,7 @@ func TestVerifyAdjustedHeaders(t *testing.T) {
 			"to match those that were supplied",
 		},
 		// old header has expired -> error
-		7: {
+		9: {
 			keys.GenSignedHeader(chainID, nextHeight, bTime.Add(1*time.Hour), nil, vals, vals,
 				[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys)),
 			keys.ToValidators(10, 1),
@@ -131,11 +151,12 @@ func TestVerifyAdjustedHeaders(t *testing.T) {
 			}
 		})
 	}
+
 }
 
-func TestVerifyNonAdjustedHeaders(t *testing.T) {
+func TestVerifyNonAdjacentHeaders(t *testing.T) {
 	const (
-		chainID    = "TestVerifyNonAdjustedHeaders"
+		chainID    = "TestVerifyNonAdjacentHeaders"
 		lastHeight = 1
 	)
 
@@ -195,7 +216,7 @@ func TestVerifyNonAdjustedHeaders(t *testing.T) {
 			vals,
 			3 * time.Hour,
 			bTime.Add(2 * time.Hour),
-			types.ErrTooMuchChange{Got: 50, Needed: 93},
+			types.ErrNotEnoughVotingPowerSigned{Got: 50, Needed: 93},
 			"",
 		},
 		// 3/3 new vals signed, 2/3 old vals present -> no error
@@ -225,7 +246,7 @@ func TestVerifyNonAdjustedHeaders(t *testing.T) {
 			lessThanOneThirdVals,
 			3 * time.Hour,
 			bTime.Add(2 * time.Hour),
-			types.ErrTooMuchChange{Got: 20, Needed: 46},
+			ErrNewValSetCantBeTrusted{types.ErrNotEnoughVotingPowerSigned{Got: 20, Needed: 46}},
 			"",
 		},
 	}
@@ -247,6 +268,26 @@ func TestVerifyNonAdjustedHeaders(t *testing.T) {
 	}
 }
 
+func TestVerifyReturnsErrorIfTrustLevelIsInvalid(t *testing.T) {
+	const (
+		chainID    = "TestVerifyReturnsErrorIfTrustLevelIsInvalid"
+		lastHeight = 1
+	)
+
+	var (
+		keys = genPrivKeys(4)
+		// 20, 30, 40, 50 - the first 3 don't have 2/3, the last 3 do!
+		vals     = keys.ToValidators(20, 10)
+		bTime, _ = time.Parse(time.RFC3339, "2006-01-02T15:04:05Z")
+		header   = keys.GenSignedHeader(chainID, lastHeight, bTime, nil, vals, vals,
+			[]byte("app_hash"), []byte("cons_hash"), []byte("results_hash"), 0, len(keys))
+	)
+
+	err := Verify(chainID, header, vals, header, vals, 2*time.Hour, time.Now(),
+		tmmath.Fraction{Numerator: 2, Denominator: 1})
+	assert.Error(t, err)
+}
+
 func TestValidateTrustLevel(t *testing.T) {
 	testCases := []struct {
 		lvl   tmmath.Fraction

types/validator_set.go

@@ -631,7 +631,7 @@ func (vals *ValidatorSet) VerifyCommit(chainID string, blockID BlockID,
 	if vals.Size() != len(commit.Signatures) {
 		return NewErrInvalidCommitSignatures(vals.Size(), len(commit.Signatures))
 	}
-	if err := vals.verifyCommitBasic(commit, height, blockID); err != nil {
+	if err := verifyCommitBasic(commit, height, blockID); err != nil {
 		return err
 	}
 
@@ -661,7 +661,7 @@ func (vals *ValidatorSet) VerifyCommit(chainID string, blockID BlockID,
 	}
 
 	if got, needed := talliedVotingPower, vals.TotalVotingPower()*2/3; got <= needed {
-		return ErrTooMuchChange{Got: got, Needed: needed}
+		return ErrNotEnoughVotingPowerSigned{Got: got, Needed: needed}
 	}
 
 	return nil
@@ -738,7 +738,7 @@ func (vals *ValidatorSet) VerifyFutureCommit(newSet *ValidatorSet, chainID strin
 	}
 
 	if got, needed := oldVotingPower, oldVals.TotalVotingPower()*2/3; got <= needed {
-		return ErrTooMuchChange{Got: got, Needed: needed}
+		return ErrNotEnoughVotingPowerSigned{Got: got, Needed: needed}
 	}
 	return nil
 }
@@ -755,11 +755,15 @@ func (vals *ValidatorSet) VerifyCommitTrusting(chainID string, blockID BlockID,
 		panic(fmt.Sprintf("trustLevel must be within [1/3, 1], given %v", trustLevel))
 	}
 
-	if err := vals.verifyCommitBasic(commit, height, blockID); err != nil {
+	if err := verifyCommitBasic(commit, height, blockID); err != nil {
 		return err
 	}
 
-	talliedVotingPower := int64(0)
+	var (
+		talliedVotingPower int64
+		seenVals           = make(map[int]int, len(commit.Signatures)) // validator index -> commit index
+	)
+
 	for idx, commitSig := range commit.Signatures {
 		if commitSig.Absent() {
 			continue // OK, some signatures can be absent.
@@ -767,8 +771,16 @@ func (vals *ValidatorSet) VerifyCommitTrusting(chainID string, blockID BlockID,
 
 		// We don't know the validators that committed this block, so we have to
 		// check for each vote if its validator is already known.
-		_, val := vals.GetByAddress(commitSig.ValidatorAddress)
+		valIdx, val := vals.GetByAddress(commitSig.ValidatorAddress)
+
+		if firstIndex, ok := seenVals[valIdx]; ok { // double vote
+			secondIndex := idx
+			return errors.Errorf("double vote from %v (%d and %d)", val, firstIndex, secondIndex)
+		}
+
 		if val != nil {
+			seenVals[valIdx] = idx
+
 			// Validate signature.
 			voteSignBytes := commit.VoteSignBytes(chainID, idx)
 			if !val.PubKey.VerifyBytes(voteSignBytes, commitSig.Signature) {
@@ -789,13 +801,13 @@ func (vals *ValidatorSet) VerifyCommitTrusting(chainID string, blockID BlockID,
 	got := talliedVotingPower
 	needed := (vals.TotalVotingPower() * trustLevel.Numerator) / trustLevel.Denominator
 	if got <= needed {
-		return ErrTooMuchChange{Got: got, Needed: needed}
+		return ErrNotEnoughVotingPowerSigned{Got: got, Needed: needed}
 	}
 
 	return nil
 }
 
-func (vals *ValidatorSet) verifyCommitBasic(commit *Commit, height int64, blockID BlockID) error {
+func verifyCommitBasic(commit *Commit, height int64, blockID BlockID) error {
 	if err := commit.ValidateBasic(); err != nil {
 		return err
 	}
@@ -810,23 +822,23 @@ func (vals *ValidatorSet) verifyCommitBasic(commit *Commit, height int64, blockI
 }
 
 //-----------------
-// ErrTooMuchChange
 
-// IsErrTooMuchChange returns true if err is related to changes in validator
-// set exceeding max limit.
-func IsErrTooMuchChange(err error) bool {
-	_, ok := errors.Cause(err).(ErrTooMuchChange)
+// IsErrNotEnoughVotingPowerSigned returns true if err is
+// ErrNotEnoughVotingPowerSigned.
+func IsErrNotEnoughVotingPowerSigned(err error) bool {
+	_, ok := errors.Cause(err).(ErrNotEnoughVotingPowerSigned)
 	return ok
 }
 
-// ErrTooMuchChange indicates that changes in the validator set exceeded max limit.
-type ErrTooMuchChange struct {
+// ErrNotEnoughVotingPowerSigned is returned when not enough validators signed
+// a commit.
+type ErrNotEnoughVotingPowerSigned struct {
 	Got    int64
 	Needed int64
 }
 
-func (e ErrTooMuchChange) Error() string {
-	return fmt.Sprintf("invalid commit -- insufficient old voting power: got %d, needed more than %d", e.Got, e.Needed)
+func (e ErrNotEnoughVotingPowerSigned) Error() string {
+	return fmt.Sprintf("invalid commit -- insufficient voting power: got %d, needed more than %d", e.Got, e.Needed)
 }
 
 //----------------