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package light
import (
"bytes"
"errors"
"fmt"
"time"
"github.com/tendermint/tendermint/libs/log"
tmmath "github.com/tendermint/tendermint/libs/math"
tmsync "github.com/tendermint/tendermint/libs/sync"
"github.com/tendermint/tendermint/light/provider"
"github.com/tendermint/tendermint/light/store"
"github.com/tendermint/tendermint/types"
)
type mode byte
const (
sequential mode = iota + 1
skipping
defaultPruningSize = 1000
defaultMaxRetryAttempts = 10
// For verifySkipping, when using the cache of headers from the previous batch,
// they will always be at a height greater than 1/2 (normal verifySkipping) so to
// find something in between the range, 9/16 is used.
verifySkippingNumerator = 9
verifySkippingDenominator = 16
// 10s should cover most of the clients.
// References:
// - http://vancouver-webpages.com/time/web.html
// - https://blog.codinghorror.com/keeping-time-on-the-pc/
defaultMaxClockDrift = 10 * time.Second
)
// Option sets a parameter for the light client.
type Option func(*Client)
// SequentialVerification option configures the light client to sequentially
// check the blocks (every block, 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 blocks as
// long as {trustLevel} of the old validator set signed the new header. The
// verifySkipping 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
}
}
// PruningSize option sets the maximum amount of light blocks that the light
// client stores. When Prune() is run, all light blocks that are earlier than
// the h amount of light blocks will be removed from the store.
// Default: 1000. A pruning size of 0 will not prune the light client at all.
func PruningSize(h uint16) Option {
return func(c *Client) {
c.pruningSize = h
}
}
// 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
}
}
// MaxClockDrift defines how much new header's time can drift into
// the future. Default: 10s.
func MaxClockDrift(d time.Duration) Option {
return func(c *Client) {
c.maxClockDrift = d
}
}
// Client represents a light client, connected to a single chain, which gets
// light blocks from a primary provider, verifies them either sequentially or by
// skipping some and stores them in a trusted store (usually, a local FS).
//
// 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
maxClockDrift time.Duration
// Mutex for locking during changes of the light clients providers
providerMutex tmsync.Mutex
// Primary provider of new headers.
primary provider.Provider
// See Witnesses option
witnesses []provider.Provider
// Where trusted light blocks are stored.
trustedStore store.Store
// Highest trusted light block from the store (height=H).
latestTrustedBlock *types.LightBlock
// See RemoveNoLongerTrustedHeadersPeriod option
pruningSize uint16
// See ConfirmationFunction option
confirmationFn func(action string) bool
quit chan struct{}
logger log.Logger
}
// NewClient returns a new light client. It returns an error if it fails to
// obtain the light block from the primary or they are invalid (e.g. trust
// hash does not match with the one from the headers).
//
// Witnesses are providers, which will be used for cross-checking the primary
// provider. At least one witness must be given when skipping verification is
// used (default). 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, fmt.Errorf("invalid TrustOptions: %w", err)
}
c, err := NewClientFromTrustedStore(chainID, trustOptions.Period, primary, witnesses, trustedStore, options...)
if err != nil {
return nil, err
}
if c.latestTrustedBlock != nil {
c.logger.Info("Checking trusted light block using options")
if err := c.checkTrustedHeaderUsingOptions(trustOptions); err != nil {
return nil, err
}
}
if c.latestTrustedBlock == nil || c.latestTrustedBlock.Height < trustOptions.Height {
c.logger.Info("Downloading trusted light block using options")
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,
maxClockDrift: defaultMaxClockDrift,
primary: primary,
witnesses: witnesses,
trustedStore: trustedStore,
pruningSize: defaultPruningSize,
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 && c.verificationMode == skipping {
return nil, errNoWitnesses{}
}
// Verify witnesses are all on the same chain.
for i, w := range witnesses {
if w.ChainID() != chainID {
return nil, fmt.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.restoreTrustedLightBlock(); err != nil {
return nil, err
}
return c, nil
}
// restoreTrustedLightBlock loads the latest trusted light block from the store
func (c *Client) restoreTrustedLightBlock() error {
lastHeight, err := c.trustedStore.LastLightBlockHeight()
if err != nil {
return fmt.Errorf("can't get last trusted light block height: %w", err)
}
if lastHeight > 0 {
trustedBlock, err := c.trustedStore.LightBlock(lastHeight)
if err != nil {
return fmt.Errorf("can't get last trusted light block: %w", err)
}
c.latestTrustedBlock = trustedBlock
c.logger.Info("Restored trusted light block", "height", lastHeight)
}
return nil
}
// if options.Height:
//
// 1) ahead of trustedLightBlock.Height => fetch light blocks (same height as
// trustedLightBlock) from primary provider and check it's hash matches the
// trustedLightBlock's hash (if not, remove trustedLightBlock and all the light blocks
// before)
//
// 2) equals trustedLightBlock.Height => check options.Hash matches the
// trustedLightBlock's hash (if not, remove trustedLightBlock and all the light blocks
// before)
//
// 3) behind trustedLightBlock.Height => remove all the light blocks between
// options.Height and trustedLightBlock.Height, update trustedLightBlock, then
// check options.Hash matches the trustedLightBlock's hash (if not, remove
// trustedLightBlock and all the light blocks 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.latestTrustedBlock.Height:
h, err := c.lightBlockFromPrimary(c.latestTrustedBlock.Height)
if err != nil {
return err
}
primaryHash = h.Hash()
case options.Height == c.latestTrustedBlock.Height:
primaryHash = options.Hash
case options.Height < c.latestTrustedBlock.Height:
c.logger.Info("Client initialized with old header (trusted is more recent)",
"old", options.Height,
"trustedHeight", c.latestTrustedBlock.Height,
"trustedHash", hash2str(c.latestTrustedBlock.Hash()))
action := fmt.Sprintf(
"Rollback to %d (%X)? Note this will remove newer light blocks up to %d (%X)",
options.Height, options.Hash,
c.latestTrustedBlock.Height, c.latestTrustedBlock.Hash())
if c.confirmationFn(action) {
// remove all the headers (options.Height, trustedHeader.Height]
err := c.cleanupAfter(options.Height)
if err != nil {
return fmt.Errorf("cleanupAfter(%d): %w", options.Height, err)
}
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.latestTrustedBlock.Hash()) {
c.logger.Info("Prev. trusted header's hash (h1) doesn't match hash from primary provider (h2)",
"h1", hash2str(c.latestTrustedBlock.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 light blocks?",
c.latestTrustedBlock.Hash(), primaryHash)
if c.confirmationFn(action) {
err := c.Cleanup()
if err != nil {
return fmt.Errorf("failed to cleanup: %w", err)
}
} else {
return errors.New("refused to remove the stored light blocks despite hashes mismatch")
}
}
return nil
}
// initializeWithTrustOptions fetches the weakly-trusted light block from
// primary provider.
func (c *Client) initializeWithTrustOptions(options TrustOptions) error {
// 1) Fetch and verify the light block.
l, err := c.lightBlockFromPrimary(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 := l.ValidateBasic(c.chainID); err != nil {
return err
}
if !bytes.Equal(l.Hash(), options.Hash) {
return fmt.Errorf("expected header's hash %X, but got %X", options.Hash, l.Hash())
}
// Ensure that +2/3 of validators signed correctly.
err = l.ValidatorSet.VerifyCommitLight(c.chainID, l.Commit.BlockID, l.Height, l.Commit)
if err != nil {
return fmt.Errorf("invalid commit: %w", err)
}
// 3) Persist both of them and continue.
return c.updateTrustedLightBlock(l)
}
// TrustedLightBlock returns a trusted light block at the given height (0 - the latest).
//
// It returns an error if:
// - there are some issues with the trusted store, although that should not
// happen normally;
// - negative height is passed;
// - header has not been verified yet and is therefore not in the store
//
// Safe for concurrent use by multiple goroutines.
func (c *Client) TrustedLightBlock(height int64) (*types.LightBlock, error) {
height, err := c.compareWithLatestHeight(height)
if err != nil {
return nil, err
}
return c.trustedStore.LightBlock(height)
}
func (c *Client) compareWithLatestHeight(height int64) (int64, error) {
latestHeight, err := c.LastTrustedHeight()
if err != nil {
return 0, fmt.Errorf("can't get last trusted height: %w", err)
}
if latestHeight == -1 {
return 0, errors.New("no headers exist")
}
switch {
case height > latestHeight:
return 0, fmt.Errorf("unverified header/valset requested (latest: %d)", latestHeight)
case height == 0:
return latestHeight, nil
case height < 0:
return 0, errors.New("negative height")
}
return height, nil
}
// VerifyLightBlockAtHeight fetches the light block at the given height
// and calls verifyLightBlock. It returns the block immediately if it exists in
// the trustedStore (no verification is needed).
//
// height must be > 0.
//
// It returns provider.ErrlightBlockNotFound if light block is not found by
// primary.
//
// It will replace the primary provider if an error from a request to the provider occurs
func (c *Client) VerifyLightBlockAtHeight(height int64, now time.Time) (*types.LightBlock, error) {
if height <= 0 {
return nil, errors.New("negative or zero height")
}
// Check if the light block already verified.
h, err := c.TrustedLightBlock(height)
if err == nil {
c.logger.Info("Header has already been verified", "height", height, "hash", hash2str(h.Hash()))
// Return already trusted light block
return h, nil
}
// Request the light block from primary
l, err := c.lightBlockFromPrimary(height)
if err != nil {
return nil, err
}
return l, c.verifyLightBlock(l, now)
}
// VerifyHeader verifies a new header against the trusted state. It returns
// immediately if newHeader exists in trustedStore (no verification is
// needed). Else it performs one of the two types of verification:
//
// 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. Intermediate headers are not saved to database.
//
// 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, verifySkipping is performed and necessary (not all)
// intermediate headers will be requested. See the specification for details.
// Intermediate headers are not saved to database.
// https://github.com/tendermint/spec/blob/master/spec/consensus/light-client.md
//
// If the header, which is older than the currently trusted header, is
// requested and the light client does not have it, VerifyHeader will perform:
// a) verifySkipping verification if nearest trusted header is found & not expired
// b) backwards verification in all other cases
//
// It returns ErrOldHeaderExpired if the latest trusted header expired.
//
// If the primary provides an invalid header (ErrInvalidHeader), it is rejected
// and replaced by another provider until all are exhausted.
//
// If, at any moment, a LightBlock is not found by the primary provider as part of
// verification then the provider will be replaced by another and the process will
// restart.
func (c *Client) VerifyHeader(newHeader *types.Header, now time.Time) error {
if newHeader == nil {
return errors.New("nil header")
}
if newHeader.Height <= 0 {
return errors.New("negative or zero height")
}
// Check if newHeader already verified.
l, err := c.TrustedLightBlock(newHeader.Height)
if err == nil {
// Make sure it's the same header.
if !bytes.Equal(l.Hash(), newHeader.Hash()) {
return fmt.Errorf("existing trusted header %X does not match newHeader %X", l.Hash(), newHeader.Hash())
}
c.logger.Info("Header has already been verified",
"height", newHeader.Height, "hash", hash2str(newHeader.Hash()))
return nil
}
// Request the header and the vals.
l, err = c.lightBlockFromPrimary(newHeader.Height)
if err != nil {
return fmt.Errorf("failed to retrieve light block from primary to verify against: %w", err)
}
if !bytes.Equal(l.Hash(), newHeader.Hash()) {
return fmt.Errorf("light block header %X does not match newHeader %X", l.Hash(), newHeader.Hash())
}
return c.verifyLightBlock(l, now)
}
func (c *Client) verifyLightBlock(newLightBlock *types.LightBlock, now time.Time) error {
c.logger.Info("VerifyHeader", "height", newLightBlock.Height, "hash", hash2str(newLightBlock.Hash()))
var (
verifyFunc func(trusted *types.LightBlock, new *types.LightBlock, now time.Time) error
err error
)
switch c.verificationMode {
case sequential:
verifyFunc = c.verifySequential
case skipping:
verifyFunc = c.verifySkippingAgainstPrimary
default:
panic(fmt.Sprintf("Unknown verification mode: %b", c.verificationMode))
}
firstBlockHeight, err := c.FirstTrustedHeight()
if err != nil {
return fmt.Errorf("can't get first light block height: %w", err)
}
switch {
// Verifying forwards
case newLightBlock.Height >= c.latestTrustedBlock.Height:
err = verifyFunc(c.latestTrustedBlock, newLightBlock, now)
// Verifying backwards
case newLightBlock.Height < firstBlockHeight:
var firstBlock *types.LightBlock
firstBlock, err = c.trustedStore.LightBlock(firstBlockHeight)
if err != nil {
return fmt.Errorf("can't get first light block: %w", err)
}
err = c.backwards(firstBlock.Header, newLightBlock.Header)
// Verifying between first and last trusted light block
default:
var closestBlock *types.LightBlock
closestBlock, err = c.trustedStore.LightBlockBefore(newLightBlock.Height)
if err != nil {
return fmt.Errorf("can't get signed header before height %d: %w", newLightBlock.Height, err)
}
err = verifyFunc(closestBlock, newLightBlock, now)
}
if err != nil {
c.logger.Error("Can't verify", "err", err)
return err
}
// Once verified, save and return
return c.updateTrustedLightBlock(newLightBlock)
}
// see VerifyHeader
func (c *Client) verifySequential(
trustedBlock *types.LightBlock,
newLightBlock *types.LightBlock,
now time.Time) error {
var (
verifiedBlock = trustedBlock
interimBlock *types.LightBlock
err error
)
for height := trustedBlock.Height + 1; height <= newLightBlock.Height; height++ {
// 1) Fetch interim light block if needed.
if height == newLightBlock.Height { // last light block
interimBlock = newLightBlock
} else { // intermediate light blocks
interimBlock, err = c.lightBlockFromPrimary(height)
if err != nil {
return ErrVerificationFailed{From: verifiedBlock.Height, To: height, Reason: err}
}
}
// 2) Verify them
c.logger.Debug("Verify adjacent newLightBlock against verifiedBlock",
"trustedHeight", verifiedBlock.Height,
"trustedHash", hash2str(verifiedBlock.Hash()),
"newHeight", interimBlock.Height,
"newHash", hash2str(interimBlock.Hash()))
err = VerifyAdjacent(c.chainID, verifiedBlock.SignedHeader, interimBlock.SignedHeader, interimBlock.ValidatorSet,
c.trustingPeriod, now, c.maxClockDrift)
if err != nil {
err := ErrVerificationFailed{From: verifiedBlock.Height, To: interimBlock.Height, Reason: err}
switch errors.Unwrap(err).(type) {
case ErrInvalidHeader:
// If the target header is invalid, return immediately.
if err.To == newLightBlock.Height {
c.logger.Debug("Target header is invalid", "err", err)
return err
}
// If some intermediate header is invalid, replace the primary and try
// again.
c.logger.Error("primary sent invalid header -> replacing", "err", err)
replaceErr := c.replacePrimaryProvider()
if replaceErr != nil {
c.logger.Error("Can't replace primary", "err", replaceErr)
// return original error
return err
}
replacementBlock, fErr := c.lightBlockFromPrimary(newLightBlock.Height)
if fErr != nil {
c.logger.Error("Can't fetch light block from primary", "err", fErr)
// return original error
return err
}
if !bytes.Equal(replacementBlock.Hash(), newLightBlock.Hash()) {
c.logger.Error("Replacement provider has a different light block",
"newHash", newLightBlock.Hash(),
"replHash", replacementBlock.Hash())
// return original error
return err
}
// attempt to verify header again
height--
continue
default:
return err
}
}
// 3) Update verifiedBlock
verifiedBlock = interimBlock
}
return nil
}
// see VerifyHeader
//
// verifySkipping finds the middle light block between a trusted and new light block,
// reiterating the action until it verifies a light block. A cache of light blocks
// requested from source is kept such that when a verification is made, and the
// light client tries again to verify the new light block in the middle, the light
// client does not need to ask for all the same light blocks again.
func (c *Client) verifySkipping(
source provider.Provider,
trustedBlock *types.LightBlock,
newLightBlock *types.LightBlock,
now time.Time) error {
var (
blockCache = []*types.LightBlock{newLightBlock}
depth = 0
verifiedBlock = trustedBlock
)
for {
c.logger.Debug("Verify non-adjacent newHeader against verifiedBlock",
"trustedHeight", verifiedBlock.Height,
"trustedHash", hash2str(verifiedBlock.Hash()),
"newHeight", blockCache[depth].Height,
"newHash", hash2str(blockCache[depth].Hash()))
err := Verify(c.chainID, verifiedBlock.SignedHeader, verifiedBlock.ValidatorSet, blockCache[depth].SignedHeader,
blockCache[depth].ValidatorSet, c.trustingPeriod, now, c.maxClockDrift, c.trustLevel)
switch err.(type) {
case nil:
// Have we verified the last header
if depth == 0 {
return nil
}
// If not, update the lower bound to the previous upper bound
verifiedBlock = blockCache[depth]
// Remove the light block at the lower bound in the header cache - it will no longer be needed
blockCache = blockCache[:depth]
// Reset the cache depth so that we start from the upper bound again
depth = 0
case ErrNewValSetCantBeTrusted:
// do add another header to the end of the cache
if depth == len(blockCache)-1 {
pivotHeight := verifiedBlock.Height + (blockCache[depth].Height-verifiedBlock.
Height)*verifySkippingNumerator/verifySkippingDenominator
interimBlock, err := source.LightBlock(pivotHeight)
if err != nil {
return ErrVerificationFailed{From: verifiedBlock.Height, To: pivotHeight, Reason: err}
}
blockCache = append(blockCache, interimBlock)
}
depth++
default:
return ErrVerificationFailed{From: verifiedBlock.Height, To: blockCache[depth].Height, Reason: err}
}
}
}
// verifySkippingAgainstPrimary does verifySkipping plus it compares new header with
// witnesses and replaces primary if it does not respond after
// MaxRetryAttempts.
func (c *Client) verifySkippingAgainstPrimary(
trustedBlock *types.LightBlock,
newLightBlock *types.LightBlock,
now time.Time) error {
err := c.verifySkipping(c.primary, trustedBlock, newLightBlock, now)
switch errors.Unwrap(err).(type) {
case ErrInvalidHeader:
// If the target header is invalid, return immediately.
invalidHeaderHeight := err.(ErrVerificationFailed).To
if invalidHeaderHeight == newLightBlock.Height {
c.logger.Debug("Target header is invalid", "err", err)
return err
}
// If some intermediate header is invalid, replace the primary and try
// again.
c.logger.Error("primary sent invalid header -> replacing", "err", err)
replaceErr := c.replacePrimaryProvider()
if replaceErr != nil {
c.logger.Error("Can't replace primary", "err", replaceErr)
// return original error
return err
}
replacementBlock, fErr := c.lightBlockFromPrimary(newLightBlock.Height)
if fErr != nil {
c.logger.Error("Can't fetch light block from primary", "err", fErr)
// return original error
return err
}
if !bytes.Equal(replacementBlock.Hash(), newLightBlock.Hash()) {
c.logger.Error("Replacement provider has a different light block",
"newHash", newLightBlock.Hash(),
"replHash", replacementBlock.Hash())
// return original error
return err
}
// attempt to verify the header again
return c.verifySkippingAgainstPrimary(trustedBlock, replacementBlock, now)
case nil:
// Compare header with the witnesses to ensure it's not a fork.
// More witnesses we have, more chance to notice one.
//
// CORRECTNESS ASSUMPTION: there's at least 1 correct full node
// (primary or one of the witnesses).
if cmpErr := c.compareNewHeaderWithWitnesses(newLightBlock, now); cmpErr != nil {
return cmpErr
}
default:
return err
}
return nil
}
// 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.LastLightBlockHeight()
}
// 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.FirstLightBlockHeight()
}
// 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
}
// 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")
c.latestTrustedBlock = nil
return c.trustedStore.Prune(0)
}
// cleanupAfter deletes all headers & validator sets after +height+. It also
// resets latestTrustedBlock to the latest header.
func (c *Client) cleanupAfter(height int64) error {
prevHeight := c.latestTrustedBlock.Height
for {
h, err := c.trustedStore.LightBlockBefore(prevHeight)
if err == store.ErrLightBlockNotFound || (h != nil && h.Height <= height) {
break
} else if err != nil {
return fmt.Errorf("failed to get header before %d: %w", prevHeight, err)
}
err = c.trustedStore.DeleteLightBlock(h.Height)
if err != nil {
c.logger.Error("can't remove a trusted header & validator set", "err", err,
"height", h.Height)
}
prevHeight = h.Height
}
c.latestTrustedBlock = nil
err := c.restoreTrustedLightBlock()
if err != nil {
return err
}
return nil
}
func (c *Client) updateTrustedLightBlock(l *types.LightBlock) error {
if err := c.trustedStore.SaveLightBlock(l); err != nil {
return fmt.Errorf("failed to save trusted header: %w", err)
}
if c.pruningSize > 0 {
if err := c.trustedStore.Prune(c.pruningSize); err != nil {
return fmt.Errorf("prune: %w", err)
}
}
if c.latestTrustedBlock == nil || l.Height > c.latestTrustedBlock.Height {
c.latestTrustedBlock = l
}
return nil
}
// backwards verification (see VerifyHeaderBackwards func in the spec) verifies
// headers before a trusted header. If a sent header is invalid the primary is
// replaced with another provider and the operation is repeated.
func (c *Client) backwards(
trustedHeader *types.Header,
newHeader *types.Header) error {
var (
verifiedHeader = trustedHeader
interimHeader *types.Header
)
for verifiedHeader.Height > newHeader.Height {
interimBlock, err := c.lightBlockFromPrimary(verifiedHeader.Height - 1)
if err != nil {
return fmt.Errorf("failed to obtain the header at height #%d: %w", verifiedHeader.Height-1, err)
}
interimHeader = interimBlock.Header
c.logger.Debug("Verify newHeader against verifiedHeader",
"trustedHeight", verifiedHeader.Height,
"trustedHash", hash2str(verifiedHeader.Hash()),
"newHeight", interimHeader.Height,
"newHash", hash2str(interimHeader.Hash()))
if err := VerifyBackwards(interimHeader, verifiedHeader); err != nil {
c.logger.Error("primary sent invalid header -> replacing", "err", err)
if replaceErr := c.replacePrimaryProvider(); replaceErr != nil {
c.logger.Error("Can't replace primary", "err", replaceErr)
// return original error
return fmt.Errorf("verify backwards from %d to %d failed: %w",
verifiedHeader.Height, interimHeader.Height, err)
}
// we need to verify the header at the same height again
continue
}
verifiedHeader = interimHeader
}
return nil
}
// compare header with all witnesses provided.
func (c *Client) compareNewHeaderWithWitnesses(l *types.LightBlock, now time.Time) error {
c.providerMutex.Lock()
defer c.providerMutex.Unlock()
// 1. Make sure AT LEAST ONE witness returns the same header.
var headerMatched bool
if len(c.witnesses) == 0 {
return errNoWitnesses{}
}
// launch one goroutine per witness
errc := make(chan error, len(c.witnesses))
for i, witness := range c.witnesses {
go c.compareNewHeaderWithWitness(errc, l, witness, i, now)
}
witnessesToRemove := make([]int, 0)
// handle errors as they come
for i := 0; i < cap(errc); i++ {
err := <-errc
switch e := err.(type) {
case nil: // at least one header matched
headerMatched = true
case errBadWitness:
c.logger.Info("Requested light block from bad witness", "witness", c.witnesses[e.WitnessIndex], "err", err)
// if witness sent us invalid header / vals, remove it
if e.Code == invalidLightBlock {
c.logger.Info("Witness sent us invalid header / vals -> removing it", "witness", c.witnesses[e.WitnessIndex])
witnessesToRemove = append(witnessesToRemove, e.WitnessIndex)
}
default:
c.logger.Info("Requested light block from witness but got error", "error", err)
}
}
for _, idx := range witnessesToRemove {
c.removeWitness(idx)
}
if headerMatched {
return nil
}
return errors.New("awaiting response from all witnesses exceeded dropout time")
}
func (c *Client) compareNewHeaderWithWitness(errc chan error, l *types.LightBlock,
witness provider.Provider, witnessIndex int, now time.Time) {
altBlock, err := witness.LightBlock(l.Height)
if err != nil {
if _, ok := err.(provider.ErrBadLightBlock); ok {
errc <- errBadWitness{Reason: err, Code: invalidLightBlock, WitnessIndex: witnessIndex}
} else {
errc <- err
}
// if not a bad light block, then the witness has either not responded or
// doesn't have the block -> we ignore
return
}
if !bytes.Equal(l.Hash(), altBlock.Hash()) {
if bsErr := c.verifySkipping(witness, c.latestTrustedBlock, altBlock, now); bsErr != nil {
errc <- errBadWitness{Reason: bsErr, Code: invalidLightBlock, WitnessIndex: witnessIndex}
return
}
}
errc <- nil
}
// 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]
}
}
// Update attempts to advance the state by downloading the latest light
// block and verifying it. It returns a new light block on a successful
// update. Otherwise, it returns nil (plus an error, if any).
func (c *Client) Update(now time.Time) (*types.LightBlock, error) {
lastTrustedHeight, err := c.LastTrustedHeight()
if err != nil {
return nil, fmt.Errorf("can't get last trusted height: %w", err)
}
if lastTrustedHeight == -1 {
// no light blocks yet => wait
return nil, nil
}
latestBlock, err := c.lightBlockFromPrimary(0)
if err != nil {
return nil, err
}
if latestBlock.Height > lastTrustedHeight {
err = c.verifyLightBlock(latestBlock, now)
if err != nil {
return nil, err
}
c.logger.Info("Advanced to new state", "height", latestBlock.Height, "hash", hash2str(latestBlock.Hash()))
return latestBlock, nil
}
return nil, 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 errNoWitnesses{}
}
c.primary = c.witnesses[0]
c.witnesses = c.witnesses[1:]
c.logger.Info("Replacing primary with the first witness", "new_primary", c.primary)
return nil
}
// lightBlockFromPrimary retrieves the lightBlock from the primary provider
// at the specified height. Handles dropout by the primary provider by swapping
// with an alternative provider.
func (c *Client) lightBlockFromPrimary(height int64) (*types.LightBlock, error) {
c.providerMutex.Lock()
l, err := c.primary.LightBlock(height)
c.providerMutex.Unlock()
if err != nil {
c.logger.Debug("Error on light block request from primary", "error", err)
replaceErr := c.replacePrimaryProvider()
if replaceErr != nil {
return nil, fmt.Errorf("%v. Tried to replace primary but: %w", err.Error(), replaceErr)
}
// replace primary and request a light block again
return c.lightBlockFromPrimary(height)
}
return l, err
}
func hash2str(hash []byte) string {
return fmt.Sprintf("%X", hash)
}