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tendermint/light/client.go

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package light
import (
"bytes"
"context"
"errors"
"fmt"
"sort"
"sync"
"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
// 10s is sufficient for most networks.
defaultMaxBlockLag = 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 relative to the light clients local time. Default: 10s.
func MaxClockDrift(d time.Duration) Option {
return func(c *Client) {
c.maxClockDrift = d
}
}
// MaxBlockLag represents the maximum time difference between the realtime
// that a block is received and the timestamp of that block.
// One can approximate it to the maximum block production time
//
// As an example, say the light client received block B at a time
// 12:05 (this is the real time) and the time on the block
// was 12:00. Then the lag here is 5 minutes.
// Default: 10s
func MaxBlockLag(d time.Duration) Option {
return func(c *Client) {
c.maxBlockLag = 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
maxBlockLag time.Duration
// Mutex for locking during changes of the light clients providers
providerMutex tmsync.Mutex
// Primary provider of new headers.
primary provider.Provider
// Providers used to "witness" new headers.
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(
ctx context.Context,
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(ctx, 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(ctx, 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,
maxBlockLag: defaultMaxBlockLag,
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) == 0 {
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(ctx context.Context, options TrustOptions) error {
var primaryHash []byte
switch {
case options.Height > c.latestTrustedBlock.Height:
h, err := c.lightBlockFromPrimary(ctx, 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", 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", c.latestTrustedBlock.Hash(), "h2", 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(ctx context.Context, options TrustOptions) error {
// 1) Fetch and verify the light block.
l, err := c.lightBlockFromPrimary(ctx, 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())
}
// 2) 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) Cross-verify with witnesses to ensure everybody has the same state.
if err := c.compareFirstHeaderWithWitnesses(ctx, l.SignedHeader); err != nil {
return err
}
// 4) 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
}
// 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(ctx context.Context, 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(ctx, 0)
if err != nil {
return nil, err
}
if latestBlock.Height > lastTrustedHeight {
err = c.verifyLightBlock(ctx, latestBlock, now)
if err != nil {
return nil, err
}
c.logger.Info("Advanced to new state", "height", latestBlock.Height, "hash", latestBlock.Hash())
return latestBlock, nil
}
return nil, nil
}
// VerifyLightBlockAtHeight fetches the light block at the given height
// and verifies it. 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(ctx context.Context, 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", h.Hash())
// Return already trusted light block
return h, nil
}
// Request the light block from primary
l, err := c.lightBlockFromPrimary(ctx, height)
if err != nil {
return nil, err
}
return l, c.verifyLightBlock(ctx, 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(ctx context.Context, 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", newHeader.Hash())
return nil
}
// Request the header and the vals.
l, err = c.lightBlockFromPrimary(ctx, 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(ctx, l, now)
}
func (c *Client) verifyLightBlock(ctx context.Context, newLightBlock *types.LightBlock, now time.Time) error {
c.logger.Info("VerifyHeader", "height", newLightBlock.Height, "hash", newLightBlock.Hash())
var (
verifyFunc func(ctx context.Context, 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(ctx, 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(ctx, 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(ctx, 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(
ctx context.Context,
trustedBlock *types.LightBlock,
newLightBlock *types.LightBlock,
now time.Time) error {
var (
verifiedBlock = trustedBlock
interimBlock *types.LightBlock
err error
trace = []*types.LightBlock{trustedBlock}
)
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(ctx, 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", verifiedBlock.Hash(),
"newHeight", interimBlock.Height,
"newHash", interimBlock.Hash())
err = VerifyAdjacent(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)
replacementBlock, removeErr := c.findNewPrimary(ctx, newLightBlock.Height, true)
if removeErr != nil {
c.logger.Debug("failed to replace primary. Returning original error", "err", removeErr)
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
// 4) Add verifiedBlock to trace
trace = append(trace, verifiedBlock)
}
// 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).
return c.detectDivergence(ctx, trace, now)
}
// 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(
ctx context.Context,
source provider.Provider,
trustedBlock *types.LightBlock,
newLightBlock *types.LightBlock,
now time.Time) ([]*types.LightBlock, error) {
var (
blockCache = []*types.LightBlock{newLightBlock}
depth = 0
verifiedBlock = trustedBlock
trace = []*types.LightBlock{trustedBlock}
)
for {
c.logger.Debug("Verify non-adjacent newHeader against verifiedBlock",
"trustedHeight", verifiedBlock.Height,
"trustedHash", verifiedBlock.Hash(),
"newHeight", blockCache[depth].Height,
"newHash", blockCache[depth].Hash())
err := Verify(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 {
trace = append(trace, newLightBlock)
return trace, 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
// add verifiedBlock to the trace
trace = append(trace, verifiedBlock)
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, providerErr := source.LightBlock(ctx, pivotHeight)
switch providerErr {
case nil:
blockCache = append(blockCache, interimBlock)
// if the error is benign, the client does not need to replace the primary
case provider.ErrLightBlockNotFound, provider.ErrNoResponse, provider.ErrHeightTooHigh:
return nil, err
// all other errors such as ErrBadLightBlock or ErrUnreliableProvider are seen as malevolent and the
// provider is removed
default:
return nil, ErrVerificationFailed{From: verifiedBlock.Height, To: pivotHeight, Reason: providerErr}
}
blockCache = append(blockCache, interimBlock)
}
depth++
default:
return nil, 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 sends the light client an invalid header
func (c *Client) verifySkippingAgainstPrimary(
ctx context.Context,
trustedBlock *types.LightBlock,
newLightBlock *types.LightBlock,
now time.Time) error {
trace, err := c.verifySkipping(ctx, 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)
replacementBlock, removeErr := c.findNewPrimary(ctx, newLightBlock.Height, true)
if removeErr != nil {
c.logger.Error("failed to replace primary. Returning original error", "err", removeErr)
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(ctx, 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.detectDivergence(ctx, trace, 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 {
c.logger.Debug("updating trusted light block", "light_block", l)
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(
ctx context.Context,
trustedHeader *types.Header,
newHeader *types.Header) error {
var (
verifiedHeader = trustedHeader
interimHeader *types.Header
)
for verifiedHeader.Height > newHeader.Height {
interimBlock, err := c.lightBlockFromPrimary(ctx, 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", verifiedHeader.Hash(),
"newHeight", interimHeader.Height,
"newHash", interimHeader.Hash())
if err := VerifyBackwards(interimHeader, verifiedHeader); err != nil {
// verification has failed
c.logger.Error("backwards verification failed, replacing primary...", "err", err, "primary", c.primary)
// the client tries to see if it can get a witness to continue with the request
newPrimarysBlock, replaceErr := c.findNewPrimary(ctx, newHeader.Height, true)
if replaceErr != nil {
c.logger.Debug("failed to replace primary. Returning original error", "err", replaceErr)
return err
}
// before continuing we must check that they have the same target header to validate
if !bytes.Equal(newPrimarysBlock.Hash(), newHeader.Hash()) {
c.logger.Debug("replaced primary but new primary has a different block to the initial one")
// return the original error
return err
}
// try again with the new primary
return c.backwards(ctx, verifiedHeader, newPrimarysBlock.Header)
}
verifiedHeader = interimHeader
}
return nil
}
// lightBlockFromPrimary retrieves the lightBlock from the primary provider
// at the specified height. This method also handles provider behavior as follows:
//
// 1. If the provider does not respond or does not have the block, it tries again
// with a different provider
// 2. If all providers return the same error, the light client forwards the error to
// where the initial request came from
// 3. If the provider provides an invalid light block, is deemed unreliable or returns
// any other error, the primary is permanently dropped and is replaced by a witness.
func (c *Client) lightBlockFromPrimary(ctx context.Context, height int64) (*types.LightBlock, error) {
c.providerMutex.Lock()
l, err := c.primary.LightBlock(ctx, height)
c.providerMutex.Unlock()
switch err {
case nil:
// Everything went smoothly. We reset the lightBlockRequests and return the light block
return l, nil
case context.Canceled, context.DeadlineExceeded:
return l, err
case provider.ErrNoResponse, provider.ErrLightBlockNotFound, provider.ErrHeightTooHigh:
// we find a new witness to replace the primary
c.logger.Info("error from light block request from primary, replacing...",
"error", err, "height", height, "primary", c.primary)
return c.findNewPrimary(ctx, height, false)
default:
// The light client has most likely received either provider.ErrUnreliableProvider or provider.ErrBadLightBlock
// These errors mean that the light client should drop the primary and try with another provider instead
c.logger.Info("error from light block request from primary, removing...",
"error", err, "height", height, "primary", c.primary)
return c.findNewPrimary(ctx, height, true)
}
}
// NOTE: requires a providerMutex lock
func (c *Client) removeWitnesses(indexes []int) error {
// check that we will still have witnesses remaining
if len(c.witnesses) <= len(indexes) {
return ErrNoWitnesses
}
// we need to make sure that we remove witnesses by index in the reverse
// order so as to not affect the indexes themselves
sort.Ints(indexes)
for i := len(indexes) - 1; i >= 0; i-- {
c.witnesses[indexes[i]] = c.witnesses[len(c.witnesses)-1]
c.witnesses = c.witnesses[:len(c.witnesses)-1]
}
return nil
}
type witnessResponse struct {
lb *types.LightBlock
witnessIndex int
err error
}
// findNewPrimary concurrently sends a light block request, promoting the first witness to return
// a valid light block as the new primary. The remove option indicates whether the primary should be
// entire removed or just appended to the back of the witnesses list. This method also handles witness
// errors. If no witness is available, it returns the last error of the witness.
func (c *Client) findNewPrimary(ctx context.Context, height int64, remove bool) (*types.LightBlock, error) {
c.providerMutex.Lock()
defer c.providerMutex.Unlock()
if len(c.witnesses) == 0 {
return nil, ErrNoWitnesses
}
var (
witnessResponsesC = make(chan witnessResponse, len(c.witnesses))
witnessesToRemove []int
lastError error
wg sync.WaitGroup
)
// send out a light block request to all witnesses
subctx, cancel := context.WithCancel(ctx)
defer cancel()
for index := range c.witnesses {
wg.Add(1)
go func(witnessIndex int, witnessResponsesC chan witnessResponse) {
defer wg.Done()
lb, err := c.witnesses[witnessIndex].LightBlock(subctx, height)
witnessResponsesC <- witnessResponse{lb, witnessIndex, err}
}(index, witnessResponsesC)
}
// process all the responses as they come in
for i := 0; i < cap(witnessResponsesC); i++ {
response := <-witnessResponsesC
switch response.err {
// success! We have found a new primary
case nil:
cancel() // cancel all remaining requests to other witnesses
wg.Wait() // wait for all goroutines to finish
// if we are not intending on removing the primary then append the old primary to the end of the witness slice
if !remove {
c.witnesses = append(c.witnesses, c.primary)
}
// promote respondent as the new primary
c.logger.Debug("found new primary", "primary", c.witnesses[response.witnessIndex])
c.primary = c.witnesses[response.witnessIndex]
// add promoted witness to the list of witnesses to be removed
witnessesToRemove = append(witnessesToRemove, response.witnessIndex)
// remove witnesses marked as bad (the client must do this before we alter the witness slice and change the indexes
// of witnesses). Removal is done in descending order
if err := c.removeWitnesses(witnessesToRemove); err != nil {
return nil, err
}
// return the light block that new primary responded with
return response.lb, nil
// process benign errors by logging them only
case provider.ErrNoResponse, provider.ErrLightBlockNotFound, provider.ErrHeightTooHigh:
lastError = response.err
c.logger.Debug("error on light block request from witness",
"error", response.err, "primary", c.witnesses[response.witnessIndex])
continue
// process malevolent errors like ErrUnreliableProvider and ErrBadLightBlock by removing the witness
default:
lastError = response.err
c.logger.Error("error on light block request from witness, removing...",
"error", response.err, "primary", c.witnesses[response.witnessIndex])
witnessesToRemove = append(witnessesToRemove, response.witnessIndex)
}
}
// remove witnesses marked as bad. Removal is done in descending order
if err := c.removeWitnesses(witnessesToRemove); err != nil {
c.logger.Error("failed to remove witnesses", "err", err, "witnessesToRemove", witnessesToRemove)
}
return nil, lastError
}
// compareFirstHeaderWithWitnesses compares h with all witnesses. If any
// witness reports a different header than h, the function returns an error.
func (c *Client) compareFirstHeaderWithWitnesses(ctx context.Context, h *types.SignedHeader) error {
compareCtx, cancel := context.WithCancel(ctx)
defer cancel()
c.providerMutex.Lock()
defer c.providerMutex.Unlock()
if len(c.witnesses) == 0 {
return ErrNoWitnesses
}
errc := make(chan error, len(c.witnesses))
for i, witness := range c.witnesses {
go c.compareNewHeaderWithWitness(compareCtx, errc, h, witness, i)
}
witnessesToRemove := make([]int, 0, len(c.witnesses))
// handle errors from the header comparisons as they come in
for i := 0; i < cap(errc); i++ {
err := <-errc
switch e := err.(type) {
case nil:
continue
case errConflictingHeaders:
c.logger.Error(fmt.Sprintf(`Witness #%d has a different header. Please check primary is correct
and remove witness. Otherwise, use the different primary`, e.WitnessIndex), "witness", c.witnesses[e.WitnessIndex])
return err
case errBadWitness:
// If witness sent us an invalid header, then remove it
c.logger.Info("witness sent an invalid light block, removing...",
"witness", c.witnesses[e.WitnessIndex],
"err", err)
witnessesToRemove = append(witnessesToRemove, e.WitnessIndex)
default: // benign errors can be ignored with the exception of context errors
if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
return err
}
// the witness either didn't respond or didn't have the block. We ignore it.
c.logger.Info("error comparing first header with witness. You may want to consider removing the witness",
"err", err)
}
}
// remove witnesses that have misbehaved
if err := c.removeWitnesses(witnessesToRemove); err != nil {
c.logger.Error("failed to remove witnesses", "err", err, "witnessesToRemove", witnessesToRemove)
}
return nil
}