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package lite
import (
"bytes"
"fmt"
"math/rand"
"sync"
"time"
"github.com/pkg/errors"
"github.com/tendermint/tendermint/libs/log"
tmmath "github.com/tendermint/tendermint/libs/math"
"github.com/tendermint/tendermint/lite2/provider"
"github.com/tendermint/tendermint/lite2/store"
"github.com/tendermint/tendermint/types"
)
type mode byte
const (
sequential mode = iota + 1
skipping
defaultUpdatePeriod = 5 * time.Second
defaultRemoveNoLongerTrustedHeadersPeriod = 24 * time.Hour
defaultMaxRetryAttempts = 10
)
// Option sets a parameter for the light client.
type Option func(*Client)
// SequentialVerification option configures the light client to sequentially
// 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
}
}
// SkippingVerification option configures the light client to skip headers as
// long as {trustLevel} of the old validator set signed the new header. The
// bisection algorithm from the specification is used for finding the minimal
// "trust path".
//
// 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-adjacent headers. For adjacent headers, sequential
// verification is used.
func SkippingVerification(trustLevel tmmath.Fraction) Option {
return func(c *Client) {
c.verificationMode = skipping
c.trustLevel = trustLevel
}
}
// UpdatePeriod option can be used to change default polling period (5s).
func UpdatePeriod(d time.Duration) Option {
return func(c *Client) {
c.updatePeriod = d
}
}
// 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
}
}
// Logger option can be used to set a logger for the client.
func Logger(l log.Logger) Option {
return func(c *Client) {
c.logger = l
}
}
// MaxRetryAttempts option can be used to set max attempts before replacing
// primary with a witness.
func MaxRetryAttempts(max uint16) Option {
return func(c *Client) {
c.maxRetryAttempts = max
}
}
// 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).
//
// By default, the client will poll the primary provider for new headers every
// 5s (UpdatePeriod). If there are any, it will try to advance the state.
//
// Default verification: SkippingVerification(DefaultTrustLevel)
type Client struct {
chainID string
trustingPeriod time.Duration // see TrustOptions.Period
verificationMode mode
trustLevel tmmath.Fraction
maxRetryAttempts uint16 // see MaxRetryAttempts option
// Mutex for locking during changes of the lite clients providers
providerMutex sync.Mutex
// Primary provider of new headers.
primary provider.Provider
// See Witnesses option
witnesses []provider.Provider
// Where trusted headers are stored.
trustedStore store.Store
// Highest trusted header from the store (height=H).
latestTrustedHeader *types.SignedHeader
// Highest next validator set from the store (height=H+1).
latestTrustedNextVals *types.ValidatorSet
// See UpdatePeriod option
updatePeriod time.Duration
// See RemoveNoLongerTrustedHeadersPeriod option
removeNoLongerTrustedHeadersPeriod time.Duration
// See ConfirmationFunction option
confirmationFn func(action string) bool
routinesWaitGroup sync.WaitGroup
quit chan struct{}
logger log.Logger
}
// NewClient returns a new light client. It returns an error if it fails to
// obtain the header & vals from the primary or they are invalid (e.g. trust
// hash does not match with the one from the header).
//
// Witnesses are providers, which will be used for cross-checking the primary
// provider. At least one witness must be given. A witness can become a primary
// iff the current primary is unavailable.
//
// See all Option(s) for the additional configuration.
func NewClient(
chainID string,
trustOptions TrustOptions,
primary provider.Provider,
witnesses []provider.Provider,
trustedStore store.Store,
options ...Option) (*Client, error) {
if err := trustOptions.ValidateBasic(); err != nil {
return nil, errors.Wrap(err, "invalid TrustOptions")
}
c, err := NewClientFromTrustedStore(chainID, trustOptions.Period, primary, witnesses, trustedStore, options...)
if err != nil {
return nil, err
}
if c.latestTrustedHeader != nil {
if err := c.checkTrustedHeaderUsingOptions(trustOptions); err != nil {
return nil, err
}
}
if c.latestTrustedHeader == nil || c.latestTrustedHeader.Height < trustOptions.Height {
if err := c.initializeWithTrustOptions(trustOptions); err != nil {
return nil, err
}
}
return c, err
}
// NewClientFromTrustedStore initializes existing client from the trusted store.
//
// See NewClient
func NewClientFromTrustedStore(
chainID string,
trustingPeriod time.Duration,
primary provider.Provider,
witnesses []provider.Provider,
trustedStore store.Store,
options ...Option) (*Client, error) {
c := &Client{
chainID: chainID,
trustingPeriod: trustingPeriod,
verificationMode: skipping,
trustLevel: DefaultTrustLevel,
maxRetryAttempts: defaultMaxRetryAttempts,
primary: primary,
witnesses: witnesses,
trustedStore: trustedStore,
updatePeriod: defaultUpdatePeriod,
removeNoLongerTrustedHeadersPeriod: defaultRemoveNoLongerTrustedHeadersPeriod,
confirmationFn: func(action string) bool { return true },
quit: make(chan struct{}),
logger: log.NewNopLogger(),
}
for _, o := range options {
o(c)
}
// Validate the number of witnesses.
if len(c.witnesses) < 1 {
return nil, errors.New("expected at least one witness")
}
// Verify witnesses are all on the same chain.
for i, w := range witnesses {
if w.ChainID() != chainID {
return nil, errors.Errorf("witness #%d: %v is on another chain %s, expected %s",
i, w, w.ChainID(), chainID)
}
}
// Validate trust level.
if err := ValidateTrustLevel(c.trustLevel); err != nil {
return nil, err
}
if err := c.restoreTrustedHeaderAndNextVals(); err != nil {
return nil, err
}
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.latestTrustedHeader = trustedHeader
c.latestTrustedNextVals = trustedNextVals
c.logger.Debug("Restored trusted header and next vals", lastHeight)
}
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.latestTrustedHeader.Height:
h, err := c.signedHeaderFromPrimary(c.latestTrustedHeader.Height)
if err != nil {
return err
}
primaryHash = h.Hash()
case options.Height == c.latestTrustedHeader.Height:
primaryHash = options.Hash
case options.Height < c.latestTrustedHeader.Height:
c.logger.Info("Client initialized with old header (trusted is more recent)",
"old", options.Height,
"trustedHeight", c.latestTrustedHeader.Height,
"trustedHash", hash2str(c.latestTrustedHeader.Hash()))
action := fmt.Sprintf(
"Rollback to %d (%X)? Note this will remove newer headers up to %d (%X)",
options.Height, options.Hash,
c.latestTrustedHeader.Height, c.latestTrustedHeader.Hash())
if c.confirmationFn(action) {
// remove all the headers (options.Height, trustedHeader.Height]
c.cleanup(options.Height + 1)
c.logger.Info("Rolled back to older header (newer headers were removed)",
"old", options.Height)
} else {
return nil
}
primaryHash = options.Hash
}
if !bytes.Equal(primaryHash, c.latestTrustedHeader.Hash()) {
c.logger.Info("Prev. trusted header's hash (h1) doesn't match hash from primary provider (h2)",
"h1", hash2str(c.latestTrustedHeader.Hash()), "h2", hash2str(primaryHash))
action := fmt.Sprintf(
"Prev. trusted header's hash %X doesn't match hash %X from primary provider. Remove all the stored headers?",
c.latestTrustedHeader.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.signedHeaderFromPrimary(options.Height)
if err != nil {
return err
}
// NOTE: - Verify func will check if it's expired or not.
// - h.Time is not being checked against time.Now() because we don't
// want to add yet another argument to NewClient* functions.
if err := h.ValidateBasic(c.chainID); err != nil {
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 vals.
vals, err := c.validatorSetFromPrimary(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
// updateTrustedHeaderAndNextVals).
nextVals, err := c.validatorSetFromPrimary(options.Height + 1)
if err != nil {
return err
}
// 4) Persist both of them and continue.
return c.updateTrustedHeaderAndNextVals(h, nextVals)
}
// Start starts two processes: 1) auto updating 2) removing outdated headers.
func (c *Client) Start() error {
c.logger.Info("Starting light client")
if c.removeNoLongerTrustedHeadersPeriod > 0 {
c.routinesWaitGroup.Add(1)
go c.removeNoLongerTrustedHeadersRoutine()
}
if c.updatePeriod > 0 {
c.routinesWaitGroup.Add(1)
go c.autoUpdateRoutine()
}
return nil
}
// Stop stops two processes: 1) auto updating 2) removing outdated headers.
// Stop only returns after both of them are finished running. If you wish to
// remove all the data, call Cleanup.
func (c *Client) Stop() {
c.logger.Info("Stopping light client")
close(c.quit)
c.routinesWaitGroup.Wait()
}
// TrustedHeader returns a trusted header at the given height (0 - the latest).
// If a header is missing in trustedStore (e.g. it was skipped during
// bisection), it will be downloaded from primary.
//
// Headers along with validator sets, 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:
// - 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;
// - header has not been verified yet
//
// Safe for concurrent use by multiple goroutines.
func (c *Client) TrustedHeader(height int64, now time.Time) (*types.SignedHeader, error) {
if height < 0 {
return nil, errors.New("negative height")
}
// 1) Get latest height.
latestHeight, err := c.LastTrustedHeight()
if err != nil {
return nil, err
}
if latestHeight == -1 {
return nil, errors.New("no headers exist")
}
if height > latestHeight {
return nil, errors.Errorf("unverified header requested (latest: %d)", latestHeight)
}
if height == 0 {
height = latestHeight
}
// 2) Get header from store.
h, err := c.trustedStore.SignedHeader(height)
if err != nil {
return nil, err
}
// 3) Ensure header can still be trusted.
if HeaderExpired(h, c.trustingPeriod, now) {
return nil, ErrOldHeaderExpired{h.Time.Add(c.trustingPeriod), now}
}
return h, nil
}
// TrustedValidatorSet returns a trusted validator set at the given height. If
// a validator set is missing in trustedStore (e.g. the associated header was
// skipped during bisection), it will be downloaded from primary. The second
// return parameter is height validator set corresponds to (useful when you
// pass 0).
//
// height must be >= 0.
//
// Headers along with validator sets, which can't be trusted anymore, are
// removed once a day (can be changed with RemoveNoLongerTrustedHeadersPeriod
// option).
//
// It returns an error if:
// - header signed by that validator set expired (ErrOldHeaderExpired)
// - there are some issues with the trusted store, although that should not
// happen normally;
// - negative height is passed;
// - header signed by that validator set has not been verified yet
//
// Safe for concurrent use by multiple goroutines.
func (c *Client) TrustedValidatorSet(height int64, now time.Time) (*types.ValidatorSet, error) {
// Checks height is positive and header (note: height - 1) is not expired.
// Additionally, it fetches validator set from primary if it's missing in
// store.
_, err := c.TrustedHeader(height-1, now)
if err != nil {
return nil, err
}
return c.trustedStore.ValidatorSet(height)
}
// LastTrustedHeight returns a last trusted height. -1 and nil are returned if
// there are no trusted headers.
//
// Safe for concurrent use by multiple goroutines.
func (c *Client) LastTrustedHeight() (int64, error) {
return c.trustedStore.LastSignedHeaderHeight()
}
// FirstTrustedHeight returns a first trusted height. -1 and nil are returned if
// there are no trusted headers.
//
// Safe for concurrent use by multiple goroutines.
func (c *Client) FirstTrustedHeight() (int64, error) {
return c.trustedStore.FirstSignedHeaderHeight()
}
// ChainID returns the chain ID the light client was configured with.
//
// Safe for concurrent use by multiple goroutines.
func (c *Client) ChainID() string {
return c.chainID
}
// VerifyHeaderAtHeight fetches header and validators at the given height
// and calls VerifyHeader. It returns header immediately if such exists in
// trustedStore (no verification is needed).
//
// It returns provider.ErrSignedHeaderNotFound if header is not found by
// primary.
// It returns ErrOldHeaderExpired if header expired.
func (c *Client) VerifyHeaderAtHeight(height int64, now time.Time) (*types.SignedHeader, error) {
if height <= 0 {
return nil, errors.New("negative or zero height")
}
h, err := c.TrustedHeader(height, now)
switch err.(type) {
case nil: // Return already trusted header
c.logger.Info("Header has already been verified", "height", height, "hash", hash2str(h.Hash()))
return h, nil
case ErrOldHeaderExpired:
return nil, err
}
// Request the header and the vals.
newHeader, newVals, err := c.fetchHeaderAndValsAtHeight(height)
if err != nil {
return nil, err
}
return newHeader, c.verifyHeader(newHeader, newVals, now)
}
// VerifyHeader verifies new header against the trusted state. It returns
// immediately if newHeader exists in trustedStore (no verification is
// needed).
//
// SequentialVerification: verifies that 2/3 of the trusted validator set has
// signed the new header. If the headers are not adjacent, **all** intermediate
// headers will be requested.
//
// 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 details.
// https://github.com/tendermint/spec/blob/master/spec/consensus/light-client.md
//
// It returns ErrOldHeaderExpired if newHeader expired.
//
// If, at any moment, SignedHeader or ValidatorSet are not found by the primary
// provider, provider.ErrSignedHeaderNotFound /
// provider.ErrValidatorSetNotFound error is returned.
//
// NOTE: although newVals is entered as input, trustedStore will only store the
// validator set at height newHeader.Height+1 (i.e.
// newHeader.NextValidatorsHash).
func (c *Client) VerifyHeader(newHeader *types.SignedHeader, newVals *types.ValidatorSet, now time.Time) error {
h, err := c.TrustedHeader(newHeader.Height, now)
switch err.(type) {
case nil: // Return already trusted header
// Make sure it's the same header.
if !bytes.Equal(h.Hash(), newHeader.Hash()) {
return errors.Errorf("existing trusted header %X does not match newHeader %X", h.Hash(), newHeader.Hash())
}
c.logger.Info("Header has already been verified",
"height", newHeader.Height, "hash", hash2str(newHeader.Hash()))
return nil
case ErrOldHeaderExpired:
return err
}
return c.verifyHeader(newHeader, newVals, now)
}
func (c *Client) verifyHeader(newHeader *types.SignedHeader, newVals *types.ValidatorSet, now time.Time) error {
c.logger.Info("VerifyHeader", "height", newHeader.Height, "hash", hash2str(newHeader.Hash()),
"vals", hash2str(newVals.Hash()))
var err error
// 1) If going forward, perform either bisection or sequential verification
if newHeader.Height >= c.latestTrustedHeader.Height {
switch c.verificationMode {
case sequential:
err = c.sequence(c.latestTrustedHeader, c.latestTrustedNextVals, newHeader, newVals, now)
case skipping:
err = c.bisection(c.latestTrustedHeader, c.latestTrustedNextVals, newHeader, newVals, now)
default:
panic(fmt.Sprintf("Unknown verification mode: %b", c.verificationMode))
}
} else {
// 2) Otherwise, perform backwards verification
// Find the closest trusted header after newHeader.Height
var closestHeader *types.SignedHeader
closestHeader, err = c.trustedStore.SignedHeaderAfter(newHeader.Height)
if err != nil {
return errors.Wrapf(err, "can't get signed header after height %d", newHeader.Height)
}
err = c.backwards(closestHeader, newHeader, now)
}
if err != nil {
c.logger.Error("Can't verify", "err", err)
return err
}
if err := c.compareNewHeaderWithWitnesses(newHeader); err != nil {
c.logger.Error("Error when comparing new header with witnesses", "err", err)
return err
}
// Update trusted header and vals.
nextVals, err := c.validatorSetFromPrimary(newHeader.Height + 1)
if err != nil {
return err
}
return c.updateTrustedHeaderAndNextVals(newHeader, nextVals)
}
// Primary returns the primary provider.
//
// NOTE: provider may be not safe for concurrent access.
func (c *Client) Primary() provider.Provider {
c.providerMutex.Lock()
defer c.providerMutex.Unlock()
return c.primary
}
// Witnesses returns the witness providers.
//
// NOTE: providers may be not safe for concurrent access.
func (c *Client) Witnesses() []provider.Provider {
c.providerMutex.Lock()
defer c.providerMutex.Unlock()
return c.witnesses
}
// Cleanup removes all the data (headers and validator sets) stored. Note: the
// client must be stopped at this point.
func (c *Client) Cleanup() error {
c.logger.Info("Removing all the data")
return c.cleanup(0)
}
// cleanup deletes all headers & validator sets between +stopHeight+ and latest
// height included. It also sets trustedHeader (vals) to the latest header
// (vals) if such exists.
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 < oldestHeight {
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.latestTrustedHeader = nil
c.latestTrustedNextVals = nil
err = c.restoreTrustedHeaderAndNextVals()
if err != nil {
return err
}
return nil
}
// see VerifyHeader
func (c *Client) sequence(
trustedHeader *types.SignedHeader,
trustedNextVals *types.ValidatorSet,
newHeader *types.SignedHeader,
newVals *types.ValidatorSet,
now time.Time) error {
// 1) Verify any intermediate headers.
var (
interimHeader *types.SignedHeader
interimNextVals *types.ValidatorSet
err error
)
for height := trustedHeader.Height + 1; height < newHeader.Height; height++ {
interimHeader, err = c.signedHeaderFromPrimary(height)
if err != nil {
return errors.Wrapf(err, "failed to obtain the header #%d", height)
}
c.logger.Debug("Verify newHeader against trustedHeader",
"trustedHeight", c.latestTrustedHeader.Height,
"trustedHash", hash2str(c.latestTrustedHeader.Hash()),
"newHeight", interimHeader.Height,
"newHash", hash2str(interimHeader.Hash()))
err = VerifyAdjacent(c.chainID, trustedHeader, interimHeader, trustedNextVals,
c.trustingPeriod, now)
if err != nil {
return errors.Wrapf(err, "failed to verify the header #%d", height)
}
// Update trusted header and vals.
if height == newHeader.Height-1 {
interimNextVals = newVals
} else {
interimNextVals, err = c.validatorSetFromPrimary(height + 1)
if err != nil {
return errors.Wrapf(err, "failed to obtain the vals #%d", height+1)
}
}
err = c.updateTrustedHeaderAndNextVals(interimHeader, interimNextVals)
if err != nil {
return errors.Wrapf(err, "failed to update trusted state #%d", height)
}
trustedHeader, trustedNextVals = interimHeader, interimNextVals
}
// 2) Verify the new header.
return VerifyAdjacent(c.chainID, c.latestTrustedHeader, newHeader, newVals, c.trustingPeriod, now)
}
// see VerifyHeader
func (c *Client) bisection(
trustedHeader *types.SignedHeader, // height h
trustedNextVals *types.ValidatorSet, // height h + 1
newHeader *types.SignedHeader, // height g
newVals *types.ValidatorSet, // height g
now time.Time) error {
interimVals := newVals
interimHeader := newHeader
for trustedHeader.Height < newHeader.Height {
c.logger.Debug("Verify newHeader against trustedHeader",
"trustedHeight", trustedHeader.Height,
"trustedHash", hash2str(trustedHeader.Hash()),
"newHeight", newHeader.Height,
"newHash", hash2str(newHeader.Hash()))
err := Verify(c.chainID, trustedHeader, trustedNextVals, interimHeader, interimVals, c.trustingPeriod, now,
c.trustLevel)
switch err.(type) {
case nil:
// Update the lower bound to the previous upper bound
trustedHeader = interimHeader
trustedNextVals, err = c.validatorSetFromPrimary(interimHeader.Height + 1)
if err != nil {
return err
}
if !bytes.Equal(trustedHeader.NextValidatorsHash, trustedNextVals.Hash()) {
return errors.Errorf("expected next validator's hash %X, but got %X (height #%d)",
trustedHeader.NextValidatorsHash,
trustedNextVals.Hash(),
trustedHeader.Height)
}
err = c.updateTrustedHeaderAndNextVals(trustedHeader, trustedNextVals)
if err != nil {
return err
}
// Update the upper bound to the untrustedHeader
interimHeader, interimVals = newHeader, newVals
case ErrNewValSetCantBeTrusted:
pivotHeight := (interimHeader.Height + trustedHeader.Height) / 2
interimHeader, interimVals, err = c.fetchHeaderAndValsAtHeight(pivotHeight)
if err != nil {
return err
}
default:
return errors.Wrapf(err, "failed to verify the header #%d", newHeader.Height)
}
}
return nil
}
// persist header and next validators to trustedStore.
func (c *Client) updateTrustedHeaderAndNextVals(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.SaveSignedHeaderAndNextValidatorSet(h, nextVals); err != nil {
return errors.Wrap(err, "failed to save trusted header")
}
c.latestTrustedHeader = h
c.latestTrustedNextVals = nextVals
return nil
}
// fetch header and validators for the given height (0 - latest) from primary
// provider.
func (c *Client) fetchHeaderAndValsAtHeight(height int64) (*types.SignedHeader, *types.ValidatorSet, error) {
h, err := c.signedHeaderFromPrimary(height)
if err != nil {
return nil, nil, errors.Wrapf(err, "failed to obtain the header #%d", height)
}
vals, err := c.validatorSetFromPrimary(height)
if err != nil {
return nil, nil, errors.Wrapf(err, "failed to obtain the vals #%d", height)
}
return h, vals, nil
}
// Backwards verification (see VerifyHeaderBackwards func in the spec)
func (c *Client) backwards(trustedHeader *types.SignedHeader, newHeader *types.SignedHeader,
now time.Time) error {
var (
interimHeader *types.SignedHeader
err error
)
for trustedHeader.Height > newHeader.Height {
interimHeader, err = c.signedHeaderFromPrimary(trustedHeader.Height - 1)
if err != nil {
return errors.Wrapf(err, "failed to obtain the header at height #%d", trustedHeader.Height-1)
}
if err := interimHeader.ValidateBasic(c.chainID); err != nil {
return errors.Wrap(err, "untrustedHeader.ValidateBasic failed")
}
if !interimHeader.Time.Before(trustedHeader.Time) {
return errors.Errorf("expected older header time %v to be before newer header time %v",
interimHeader.Time,
trustedHeader.Time)
}
if HeaderExpired(interimHeader, c.trustingPeriod, now) {
return ErrOldHeaderExpired{interimHeader.Time.Add(c.trustingPeriod), now}
}
if !bytes.Equal(interimHeader.Hash(), trustedHeader.LastBlockID.Hash) {
return errors.Errorf("older header hash %X does not match trusted header's last block %X",
interimHeader.Hash(),
trustedHeader.LastBlockID.Hash)
}
trustedHeader = interimHeader
}
return nil
}
// compare header with all witnesses provided.
func (c *Client) compareNewHeaderWithWitnesses(h *types.SignedHeader) error {
c.providerMutex.Lock()
defer c.providerMutex.Unlock()
// 1. Make sure AT LEAST ONE witness returns the same header.
headerMatched := false
witnessesToRemove := make([]int, 0)
for attempt := uint16(1); attempt <= c.maxRetryAttempts; attempt++ {
if len(c.witnesses) == 0 {
return errors.New("could not find any witnesses. please reset the light client")
}
for i, witness := range c.witnesses {
altH, err := witness.SignedHeader(h.Height)
if err != nil {
c.logger.Error("Failed to get a header from witness", "height", h.Height, "witness", witness)
continue
}
if err = altH.ValidateBasic(c.chainID); err != nil {
c.logger.Error("Witness sent us incorrect header", "err", err, "witness", witness)
witnessesToRemove = append(witnessesToRemove, i)
continue
}
if !bytes.Equal(h.Hash(), altH.Hash()) {
if err = c.latestTrustedNextVals.VerifyCommitTrusting(c.chainID, altH.Commit.BlockID,
altH.Height, altH.Commit, c.trustLevel); err != nil {
c.logger.Error("Witness sent us incorrect header", "err", err, "witness", witness)
witnessesToRemove = append(witnessesToRemove, i)
continue
}
// TODO: send the diverged headers to primary && all witnesses
return errors.Errorf(
"header hash %X does not match one %X from the witness %v",
h.Hash(), altH.Hash(), witness)
}
headerMatched = true
}
for _, idx := range witnessesToRemove {
c.removeWitness(idx)
}
witnessesToRemove = make([]int, 0)
if headerMatched {
return nil
}
// 2. Otherwise, sleep
time.Sleep(backoffTimeout(attempt))
}
return errors.New("awaiting response from all witnesses exceeded dropout time")
}
// NOTE: requires a providerMutex locked.
func (c *Client) removeWitness(idx int) {
switch len(c.witnesses) {
case 0:
panic(fmt.Sprintf("wanted to remove %d element from empty witnesses slice", idx))
case 1:
c.witnesses = make([]provider.Provider, 0)
default:
c.witnesses[idx] = c.witnesses[len(c.witnesses)-1]
c.witnesses = c.witnesses[:len(c.witnesses)-1]
}
}
func (c *Client) removeNoLongerTrustedHeadersRoutine() {
defer c.routinesWaitGroup.Done()
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.FirstTrustedHeight()
if err != nil {
c.logger.Error("can't get first trusted height", "err", err)
return
}
if oldestHeight == -1 { // no headers yet => wait
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
}
if latestHeight == -1 { // no headers yet => wait
return
}
// 3) Remove all headers that are outside of the trusting period.
//
// NOTE: even the latest header can be removed. it's okay because
// c.latestTrustedHeader will retain it in memory so other funcs like VerifyHeader
// don't crash.
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
}
// 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
}
}
}
func (c *Client) autoUpdateRoutine() {
defer c.routinesWaitGroup.Done()
ticker := time.NewTicker(c.updatePeriod)
defer ticker.Stop()
for {
select {
case <-ticker.C:
err := c.Update(time.Now())
if err != nil {
c.logger.Error("Error during auto update", "err", err)
}
case <-c.quit:
return
}
}
}
// Update attempts to advance the state making exponential steps (note:
// when SequentialVerification is being used, the client will still be
// downloading all intermediate headers).
//
// Exposed for testing.
func (c *Client) Update(now time.Time) error {
lastTrustedHeight, err := c.LastTrustedHeight()
if err != nil {
return errors.Wrap(err, "can't get last trusted height")
}
if lastTrustedHeight == -1 {
// no headers yet => wait
return nil
}
latestHeader, latestVals, err := c.fetchHeaderAndValsAtHeight(0)
if err != nil {
return errors.Wrapf(err, "can't get latest header and vals")
}
if latestHeader.Height > lastTrustedHeight {
err = c.VerifyHeader(latestHeader, latestVals, now)
if err != nil {
return err
}
c.logger.Info("Advanced to new state", "height", latestHeader.Height, "hash", hash2str(latestHeader.Hash()))
}
return nil
}
// replaceProvider takes the first alternative provider and promotes it as the
// primary provider.
func (c *Client) replacePrimaryProvider() error {
c.providerMutex.Lock()
defer c.providerMutex.Unlock()
if len(c.witnesses) <= 1 {
return errors.Errorf("only one witness left. please reset the light client")
}
c.primary = c.witnesses[0]
c.witnesses = c.witnesses[1:]
c.logger.Info("New primary", "p", c.primary)
return nil
}
// signedHeaderFromPrimary retrieves the SignedHeader from the primary provider
// at the specified height. Handles dropout by the primary provider by swapping
// with an alternative provider.
func (c *Client) signedHeaderFromPrimary(height int64) (*types.SignedHeader, error) {
for attempt := uint16(1); attempt <= c.maxRetryAttempts; attempt++ {
c.providerMutex.Lock()
h, err := c.primary.SignedHeader(height)
c.providerMutex.Unlock()
if err == nil {
// sanity check
if height > 0 && h.Height != height {
return nil, errors.Errorf("expected %d height, got %d", height, h.Height)
}
return h, nil
}
if err == provider.ErrSignedHeaderNotFound {
return nil, err
}
time.Sleep(backoffTimeout(attempt))
}
c.logger.Info("Primary is unavailable. Replacing with the first witness")
err := c.replacePrimaryProvider()
if err != nil {
return nil, err
}
return c.signedHeaderFromPrimary(height)
}
// validatorSetFromPrimary retrieves the ValidatorSet from the primary provider
// at the specified height. Handles dropout by the primary provider after 5
// attempts by replacing it with an alternative provider.
func (c *Client) validatorSetFromPrimary(height int64) (*types.ValidatorSet, error) {
for attempt := uint16(1); attempt <= c.maxRetryAttempts; attempt++ {
c.providerMutex.Lock()
vals, err := c.primary.ValidatorSet(height)
c.providerMutex.Unlock()
if err == nil || err == provider.ErrValidatorSetNotFound {
return vals, err
}
time.Sleep(backoffTimeout(attempt))
}
c.logger.Info("Primary is unavailable. Replacing with the first witness")
err := c.replacePrimaryProvider()
if err != nil {
return nil, err
}
return c.validatorSetFromPrimary(height)
}
// exponential backoff (with jitter)
// 0.5s -> 2s -> 4.5s -> 8s -> 12.5 with 1s variation
func backoffTimeout(attempt uint16) time.Duration {
return time.Duration(500*attempt*attempt)*time.Millisecond + time.Duration(rand.Intn(1000))*time.Millisecond
}
func hash2str(hash []byte) string {
return fmt.Sprintf("%X", hash)
}