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1317 lines
42 KiB
1317 lines
42 KiB
package light
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import (
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"bytes"
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"errors"
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"fmt"
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"math/rand"
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"time"
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"github.com/tendermint/tendermint/libs/log"
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tmmath "github.com/tendermint/tendermint/libs/math"
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tmsync "github.com/tendermint/tendermint/libs/sync"
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"github.com/tendermint/tendermint/light/provider"
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"github.com/tendermint/tendermint/light/store"
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"github.com/tendermint/tendermint/types"
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)
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type mode byte
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const (
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sequential mode = iota + 1
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skipping
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defaultPruningSize = 1000
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defaultMaxRetryAttempts = 10
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// For bisection, when using the cache of headers from the previous batch,
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// they will always be at a height greater than 1/2 (normal bisection) so to
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// find something in between the range, 9/16 is used.
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bisectionNumerator = 9
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bisectionDenominator = 16
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// 10s should cover most of the clients.
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// References:
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// - http://vancouver-webpages.com/time/web.html
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// - https://blog.codinghorror.com/keeping-time-on-the-pc/
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defaultMaxClockDrift = 10 * time.Second
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)
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// Option sets a parameter for the light client.
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type Option func(*Client)
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// SequentialVerification option configures the light client to sequentially
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// check the headers (every header, in ascending height order). Note this is
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// much slower than SkippingVerification, albeit more secure.
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func SequentialVerification() Option {
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return func(c *Client) {
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c.verificationMode = sequential
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}
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}
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// SkippingVerification option configures the light client to skip headers as
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// long as {trustLevel} of the old validator set signed the new header. The
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// bisection algorithm from the specification is used for finding the minimal
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// "trust path".
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//
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// trustLevel - fraction of the old validator set (in terms of voting power),
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// which must sign the new header in order for us to trust it. NOTE this only
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// applies to non-adjacent headers. For adjacent headers, sequential
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// verification is used.
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func SkippingVerification(trustLevel tmmath.Fraction) Option {
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return func(c *Client) {
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c.verificationMode = skipping
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c.trustLevel = trustLevel
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}
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}
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// PruningSize option sets the maximum amount of headers & validator set pairs
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// that the light client stores. When Prune() is run, all headers (along with
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// the associated validator sets) that are earlier than the h amount of headers
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// will be removed from the store. Default: 1000. A pruning size of 0 will not
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// prune the light client at all.
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func PruningSize(h uint16) Option {
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return func(c *Client) {
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c.pruningSize = h
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}
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}
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// ConfirmationFunction option can be used to prompt to confirm an action. For
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// example, remove newer headers if the light client is being reset with an
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// older header. No confirmation is required by default!
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func ConfirmationFunction(fn func(action string) bool) Option {
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return func(c *Client) {
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c.confirmationFn = fn
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}
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}
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// Logger option can be used to set a logger for the client.
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func Logger(l log.Logger) Option {
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return func(c *Client) {
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c.logger = l
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}
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}
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// MaxRetryAttempts option can be used to set max attempts before replacing
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// primary with a witness.
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func MaxRetryAttempts(max uint16) Option {
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return func(c *Client) {
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c.maxRetryAttempts = max
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}
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}
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// MaxClockDrift defines how much new (untrusted) header's Time can drift into
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// the future. Default: 10s.
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func MaxClockDrift(d time.Duration) Option {
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return func(c *Client) {
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c.maxClockDrift = d
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}
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}
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// Client represents a light client, connected to a single chain, which gets
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// headers from a primary provider, verifies them either sequentially or by
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// skipping some and stores them in a trusted store (usually, a local FS).
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//
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// Default verification: SkippingVerification(DefaultTrustLevel)
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type Client struct {
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chainID string
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trustingPeriod time.Duration // see TrustOptions.Period
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verificationMode mode
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trustLevel tmmath.Fraction
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maxRetryAttempts uint16 // see MaxRetryAttempts option
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maxClockDrift time.Duration
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// Mutex for locking during changes of the light clients providers
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providerMutex tmsync.Mutex
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// Primary provider of new headers.
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primary provider.Provider
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// See Witnesses option
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witnesses []provider.Provider
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// Where trusted headers are stored.
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trustedStore store.Store
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// Highest trusted header from the store (height=H).
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latestTrustedHeader *types.SignedHeader
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// Highest validator set from the store (height=H).
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latestTrustedVals *types.ValidatorSet
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// See RemoveNoLongerTrustedHeadersPeriod option
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pruningSize uint16
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// See ConfirmationFunction option
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confirmationFn func(action string) bool
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quit chan struct{}
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logger log.Logger
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}
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// NewClient returns a new light client. It returns an error if it fails to
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// obtain the header & vals from the primary or they are invalid (e.g. trust
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// hash does not match with the one from the header).
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//
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// Witnesses are providers, which will be used for cross-checking the primary
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// provider. At least one witness must be given when skipping verification is
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// used (default). A witness can become a primary iff the current primary is
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// unavailable.
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//
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// See all Option(s) for the additional configuration.
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func NewClient(
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chainID string,
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trustOptions TrustOptions,
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primary provider.Provider,
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witnesses []provider.Provider,
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trustedStore store.Store,
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options ...Option) (*Client, error) {
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if err := trustOptions.ValidateBasic(); err != nil {
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return nil, fmt.Errorf("invalid TrustOptions: %w", err)
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}
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c, err := NewClientFromTrustedStore(chainID, trustOptions.Period, primary, witnesses, trustedStore, options...)
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if err != nil {
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return nil, err
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}
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if c.latestTrustedHeader != nil {
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c.logger.Info("Checking trusted header using options")
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if err := c.checkTrustedHeaderUsingOptions(trustOptions); err != nil {
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return nil, err
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}
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}
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if c.latestTrustedHeader == nil || c.latestTrustedHeader.Height < trustOptions.Height {
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c.logger.Info("Downloading trusted header using options")
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if err := c.initializeWithTrustOptions(trustOptions); err != nil {
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return nil, err
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}
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}
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return c, err
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}
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// NewClientFromTrustedStore initializes existing client from the trusted store.
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//
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// See NewClient
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func NewClientFromTrustedStore(
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chainID string,
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trustingPeriod time.Duration,
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primary provider.Provider,
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witnesses []provider.Provider,
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trustedStore store.Store,
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options ...Option) (*Client, error) {
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c := &Client{
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chainID: chainID,
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trustingPeriod: trustingPeriod,
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verificationMode: skipping,
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trustLevel: DefaultTrustLevel,
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maxRetryAttempts: defaultMaxRetryAttempts,
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maxClockDrift: defaultMaxClockDrift,
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primary: primary,
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witnesses: witnesses,
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trustedStore: trustedStore,
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pruningSize: defaultPruningSize,
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confirmationFn: func(action string) bool { return true },
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quit: make(chan struct{}),
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logger: log.NewNopLogger(),
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}
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for _, o := range options {
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o(c)
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}
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// Validate the number of witnesses.
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if len(c.witnesses) < 1 && c.verificationMode == skipping {
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return nil, errNoWitnesses{}
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}
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// Verify witnesses are all on the same chain.
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for i, w := range witnesses {
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if w.ChainID() != chainID {
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return nil, fmt.Errorf("witness #%d: %v is on another chain %s, expected %s",
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i, w, w.ChainID(), chainID)
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}
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}
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// Validate trust level.
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if err := ValidateTrustLevel(c.trustLevel); err != nil {
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return nil, err
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}
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if err := c.restoreTrustedHeaderAndVals(); err != nil {
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return nil, err
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}
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return c, nil
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}
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// restoreTrustedHeaderAndVals loads trustedHeader and trustedVals from
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// trustedStore.
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func (c *Client) restoreTrustedHeaderAndVals() error {
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lastHeight, err := c.trustedStore.LastSignedHeaderHeight()
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if err != nil {
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return fmt.Errorf("can't get last trusted header height: %w", err)
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}
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if lastHeight > 0 {
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trustedHeader, err := c.trustedStore.SignedHeader(lastHeight)
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if err != nil {
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return fmt.Errorf("can't get last trusted header: %w", err)
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}
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trustedVals, err := c.trustedStore.ValidatorSet(lastHeight)
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if err != nil {
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return fmt.Errorf("can't get last trusted validators: %w", err)
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}
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c.latestTrustedHeader = trustedHeader
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c.latestTrustedVals = trustedVals
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c.logger.Info("Restored trusted header and vals", "height", lastHeight)
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}
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return nil
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}
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// if options.Height:
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//
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// 1) ahead of trustedHeader.Height => fetch header (same height as
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// trustedHeader) from primary provider and check it's hash matches the
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// trustedHeader's hash (if not, remove trustedHeader and all the headers
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// before)
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//
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// 2) equals trustedHeader.Height => check options.Hash matches the
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// trustedHeader's hash (if not, remove trustedHeader and all the headers
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// before)
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//
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// 3) behind trustedHeader.Height => remove all the headers between
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// options.Height and trustedHeader.Height, update trustedHeader, then
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// check options.Hash matches the trustedHeader's hash (if not, remove
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// trustedHeader and all the headers before)
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//
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// The intuition here is the user is always right. I.e. if she decides to reset
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// the light client with an older header, there must be a reason for it.
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func (c *Client) checkTrustedHeaderUsingOptions(options TrustOptions) error {
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var primaryHash []byte
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switch {
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case options.Height > c.latestTrustedHeader.Height:
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h, err := c.signedHeaderFromPrimary(c.latestTrustedHeader.Height)
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if err != nil {
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return err
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}
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primaryHash = h.Hash()
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case options.Height == c.latestTrustedHeader.Height:
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primaryHash = options.Hash
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case options.Height < c.latestTrustedHeader.Height:
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c.logger.Info("Client initialized with old header (trusted is more recent)",
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"old", options.Height,
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"trustedHeight", c.latestTrustedHeader.Height,
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"trustedHash", hash2str(c.latestTrustedHeader.Hash()))
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action := fmt.Sprintf(
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"Rollback to %d (%X)? Note this will remove newer headers up to %d (%X)",
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options.Height, options.Hash,
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c.latestTrustedHeader.Height, c.latestTrustedHeader.Hash())
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if c.confirmationFn(action) {
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// remove all the headers (options.Height, trustedHeader.Height]
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err := c.cleanupAfter(options.Height)
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if err != nil {
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return fmt.Errorf("cleanupAfter(%d): %w", options.Height, err)
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}
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c.logger.Info("Rolled back to older header (newer headers were removed)",
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"old", options.Height)
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} else {
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return nil
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}
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primaryHash = options.Hash
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}
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if !bytes.Equal(primaryHash, c.latestTrustedHeader.Hash()) {
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c.logger.Info("Prev. trusted header's hash (h1) doesn't match hash from primary provider (h2)",
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"h1", hash2str(c.latestTrustedHeader.Hash()), "h2", hash2str(primaryHash))
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action := fmt.Sprintf(
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"Prev. trusted header's hash %X doesn't match hash %X from primary provider. Remove all the stored headers?",
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c.latestTrustedHeader.Hash(), primaryHash)
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if c.confirmationFn(action) {
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err := c.Cleanup()
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if err != nil {
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return fmt.Errorf("failed to cleanup: %w", err)
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}
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} else {
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return errors.New("refused to remove the stored headers despite hashes mismatch")
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}
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}
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return nil
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}
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// initializeWithTrustOptions fetches the weakly-trusted header and vals from
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// primary provider.
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func (c *Client) initializeWithTrustOptions(options TrustOptions) error {
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// 1) Fetch and verify the header.
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h, err := c.signedHeaderFromPrimary(options.Height)
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if err != nil {
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return err
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}
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// NOTE: - Verify func will check if it's expired or not.
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// - h.Time is not being checked against time.Now() because we don't
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// want to add yet another argument to NewClient* functions.
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if err := h.ValidateBasic(c.chainID); err != nil {
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return err
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}
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if !bytes.Equal(h.Hash(), options.Hash) {
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return fmt.Errorf("expected header's hash %X, but got %X", options.Hash, h.Hash())
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}
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// 2) Fetch and verify the vals.
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vals, err := c.validatorSetFromPrimary(options.Height)
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if err != nil {
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return err
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}
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if !bytes.Equal(h.ValidatorsHash, vals.Hash()) {
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return fmt.Errorf("expected header's validators (%X) to match those that were supplied (%X)",
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h.ValidatorsHash,
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vals.Hash(),
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)
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}
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// Ensure that +2/3 of validators signed correctly.
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err = vals.VerifyCommitLight(c.chainID, h.Commit.BlockID, h.Height, h.Commit)
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if err != nil {
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return fmt.Errorf("invalid commit: %w", err)
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}
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// 3) Persist both of them and continue.
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return c.updateTrustedHeaderAndVals(h, vals)
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}
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// TrustedHeader returns a trusted header at the given height (0 - the latest).
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//
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// Headers along with validator sets, which can't be trusted anymore, are
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// removed once a day (can be changed with RemoveNoLongerTrustedHeadersPeriod
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// option).
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// .
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// height must be >= 0.
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//
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// It returns an error if:
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// - there are some issues with the trusted store, although that should not
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// happen normally;
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// - negative height is passed;
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// - header has not been verified yet and is therefore not in the store
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//
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// Safe for concurrent use by multiple goroutines.
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func (c *Client) TrustedHeader(height int64) (*types.SignedHeader, error) {
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height, err := c.compareWithLatestHeight(height)
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if err != nil {
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return nil, err
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}
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return c.trustedStore.SignedHeader(height)
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}
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// TrustedValidatorSet returns a trusted validator set at the given height (0 -
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// latest). The second return parameter is the height used (useful if 0 was
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// passed; otherwise can be ignored).
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//
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// height must be >= 0.
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//
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// Headers along with validator sets are
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// removed once a day (can be changed with RemoveNoLongerTrustedHeadersPeriod
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// option).
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//
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// Function returns an error if:
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// - there are some issues with the trusted store, although that should not
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// happen normally;
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// - negative height is passed;
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// - header signed by that validator set has not been verified yet
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//
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// Safe for concurrent use by multiple goroutines.
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func (c *Client) TrustedValidatorSet(height int64) (valSet *types.ValidatorSet, heightUsed int64, err error) {
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heightUsed, err = c.compareWithLatestHeight(height)
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if err != nil {
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return nil, heightUsed, err
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}
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valSet, err = c.trustedStore.ValidatorSet(heightUsed)
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if err != nil {
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return nil, heightUsed, err
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}
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return valSet, heightUsed, err
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}
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|
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func (c *Client) compareWithLatestHeight(height int64) (int64, error) {
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latestHeight, err := c.LastTrustedHeight()
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if err != nil {
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return 0, fmt.Errorf("can't get last trusted height: %w", err)
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}
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if latestHeight == -1 {
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return 0, errors.New("no headers exist")
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}
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|
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switch {
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case height > latestHeight:
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return 0, fmt.Errorf("unverified header/valset requested (latest: %d)", latestHeight)
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case height == 0:
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return latestHeight, nil
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case height < 0:
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return 0, errors.New("negative height")
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}
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return height, nil
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}
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|
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// VerifyHeaderAtHeight fetches header and validators at the given height
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// and calls VerifyHeader. It returns header immediately if such exists in
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// trustedStore (no verification is needed).
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//
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// height must be > 0.
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//
|
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// It returns provider.ErrSignedHeaderNotFound if header is not found by
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// primary.
|
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//
|
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// It will replace the primary provider if an error from a request to the provider occurs
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func (c *Client) VerifyHeaderAtHeight(height int64, now time.Time) (*types.SignedHeader, error) {
|
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if height <= 0 {
|
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return nil, errors.New("negative or zero height")
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}
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|
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// Check if header already verified.
|
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h, err := c.TrustedHeader(height)
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if err == nil {
|
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c.logger.Info("Header has already been verified", "height", height, "hash", hash2str(h.Hash()))
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// Return already trusted header
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return h, nil
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}
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|
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// Request the header and the vals.
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newHeader, newVals, err := c.signedHeaderAndValSetFromPrimary(height)
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if err != nil {
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return nil, err
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}
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return newHeader, c.verifyHeader(newHeader, newVals, now)
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}
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|
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// VerifyHeader verifies new header against the trusted state. It returns
|
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// immediately if newHeader exists in trustedStore (no verification is
|
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// needed). Else it performs one of the two types of verification:
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//
|
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// SequentialVerification: verifies that 2/3 of the trusted validator set has
|
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// 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
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// headers are not adjacent, bisection 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) bisection 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, SignedHeader or ValidatorSet are not found by the primary
|
|
// provider, provider.ErrSignedHeaderNotFound /
|
|
// provider.ErrValidatorSetNotFound error is returned.
|
|
func (c *Client) VerifyHeader(newHeader *types.SignedHeader, newVals *types.ValidatorSet, now time.Time) error {
|
|
if newHeader.Height <= 0 {
|
|
return errors.New("negative or zero height")
|
|
}
|
|
|
|
// Check if newHeader already verified.
|
|
h, err := c.TrustedHeader(newHeader.Height)
|
|
if err == nil {
|
|
// Make sure it's the same header.
|
|
if !bytes.Equal(h.Hash(), newHeader.Hash()) {
|
|
return fmt.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
|
|
}
|
|
|
|
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, newHeader, newVals, now)
|
|
case skipping:
|
|
err = c.bisectionAgainstPrimary(c.latestTrustedHeader, c.latestTrustedVals, newHeader, newVals, now)
|
|
default:
|
|
panic(fmt.Sprintf("Unknown verification mode: %b", c.verificationMode))
|
|
}
|
|
} else {
|
|
// 2) If verifying before the first trusted header, perform backwards
|
|
// verification.
|
|
var (
|
|
closestHeader *types.SignedHeader
|
|
firstHeaderHeight int64
|
|
)
|
|
firstHeaderHeight, err = c.FirstTrustedHeight()
|
|
if err != nil {
|
|
return fmt.Errorf("can't get first header height: %w", err)
|
|
}
|
|
if newHeader.Height < firstHeaderHeight {
|
|
closestHeader, err = c.TrustedHeader(firstHeaderHeight)
|
|
if err != nil {
|
|
return fmt.Errorf("can't get first signed header: %w", err)
|
|
}
|
|
if HeaderExpired(closestHeader, c.trustingPeriod, now) {
|
|
closestHeader = c.latestTrustedHeader
|
|
}
|
|
err = c.backwards(closestHeader, newHeader, now)
|
|
} else {
|
|
// 3) OR if between trusted headers where the nearest has not expired,
|
|
// perform bisection verification, else backwards.
|
|
closestHeader, err = c.trustedStore.SignedHeaderBefore(newHeader.Height)
|
|
if err != nil {
|
|
return fmt.Errorf("can't get signed header before height %d: %w", newHeader.Height, err)
|
|
}
|
|
var closestValidatorSet *types.ValidatorSet
|
|
if c.verificationMode == sequential || HeaderExpired(closestHeader, c.trustingPeriod, now) {
|
|
err = c.backwards(c.latestTrustedHeader, newHeader, now)
|
|
} else {
|
|
closestValidatorSet, _, err = c.TrustedValidatorSet(closestHeader.Height)
|
|
if err != nil {
|
|
return fmt.Errorf("can't get validator set at height %d: %w", closestHeader.Height, err)
|
|
}
|
|
err = c.bisectionAgainstPrimary(closestHeader, closestValidatorSet, newHeader, newVals, now)
|
|
}
|
|
}
|
|
}
|
|
if err != nil {
|
|
c.logger.Error("Can't verify", "err", err)
|
|
return err
|
|
}
|
|
|
|
// 4) Once verified, save and return
|
|
return c.updateTrustedHeaderAndVals(newHeader, newVals)
|
|
}
|
|
|
|
// see VerifyHeader
|
|
func (c *Client) sequence(
|
|
initiallyTrustedHeader *types.SignedHeader,
|
|
newHeader *types.SignedHeader,
|
|
newVals *types.ValidatorSet,
|
|
now time.Time) error {
|
|
|
|
var (
|
|
trustedHeader = initiallyTrustedHeader
|
|
|
|
interimHeader *types.SignedHeader
|
|
interimVals *types.ValidatorSet
|
|
|
|
err error
|
|
)
|
|
|
|
for height := initiallyTrustedHeader.Height + 1; height <= newHeader.Height; height++ {
|
|
// 1) Fetch interim headers and vals if needed.
|
|
if height == newHeader.Height { // last header
|
|
interimHeader, interimVals = newHeader, newVals
|
|
} else { // intermediate headers
|
|
interimHeader, interimVals, err = c.signedHeaderAndValSetFromPrimary(height)
|
|
if err != nil {
|
|
return ErrVerificationFailed{From: trustedHeader.Height, To: height, Reason: err}
|
|
}
|
|
}
|
|
|
|
// 2) Verify them
|
|
c.logger.Debug("Verify adjacent newHeader against trustedHeader",
|
|
"trustedHeight", trustedHeader.Height,
|
|
"trustedHash", hash2str(trustedHeader.Hash()),
|
|
"newHeight", interimHeader.Height,
|
|
"newHash", hash2str(interimHeader.Hash()))
|
|
|
|
err = VerifyAdjacent(c.chainID, trustedHeader, interimHeader, interimVals,
|
|
c.trustingPeriod, now, c.maxClockDrift)
|
|
if err != nil {
|
|
err := ErrVerificationFailed{From: trustedHeader.Height, To: interimHeader.Height, Reason: err}
|
|
|
|
switch errors.Unwrap(err).(type) {
|
|
case ErrInvalidHeader:
|
|
// If the target header is invalid, return immediately.
|
|
if err.To == newHeader.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
|
|
}
|
|
|
|
replacementHeader, replacementVals, fErr := c.signedHeaderAndValSetFromPrimary(newHeader.Height)
|
|
if fErr != nil {
|
|
c.logger.Error("Can't fetch header/vals from primary", "err", fErr)
|
|
// return original error
|
|
return err
|
|
}
|
|
|
|
if !bytes.Equal(replacementHeader.Hash(), newHeader.Hash()) ||
|
|
!bytes.Equal(replacementVals.Hash(), newVals.Hash()) {
|
|
c.logger.Error("Replacement provider has a different header/vals",
|
|
"newHash", newHeader.Hash(),
|
|
"newVals", newVals.Hash(),
|
|
"replHash", replacementHeader.Hash(),
|
|
"replVals", replacementVals.Hash())
|
|
// return original error
|
|
return err
|
|
}
|
|
|
|
// attempt to verify header again
|
|
height--
|
|
|
|
continue
|
|
default:
|
|
return err
|
|
}
|
|
}
|
|
|
|
// 3) Update trustedHeader
|
|
trustedHeader = interimHeader
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// see VerifyHeader
|
|
//
|
|
// Bisection finds the middle header between a trusted and new header,
|
|
// reiterating the action until it verifies a header. A cache of headers
|
|
// requested from source is kept such that when a verification is made, and the
|
|
// light client tries again to verify the new header in the middle, the light
|
|
// client does not need to ask for all the same headers again.
|
|
func (c *Client) bisection(
|
|
source provider.Provider,
|
|
initiallyTrustedHeader *types.SignedHeader,
|
|
initiallyTrustedVals *types.ValidatorSet,
|
|
newHeader *types.SignedHeader,
|
|
newVals *types.ValidatorSet,
|
|
now time.Time) error {
|
|
|
|
type headerSet struct {
|
|
sh *types.SignedHeader
|
|
valSet *types.ValidatorSet
|
|
}
|
|
|
|
var (
|
|
headerCache = []headerSet{{newHeader, newVals}}
|
|
depth = 0
|
|
|
|
trustedHeader = initiallyTrustedHeader
|
|
trustedVals = initiallyTrustedVals
|
|
)
|
|
|
|
for {
|
|
c.logger.Debug("Verify non-adjacent newHeader against trustedHeader",
|
|
"trustedHeight", trustedHeader.Height,
|
|
"trustedHash", hash2str(trustedHeader.Hash()),
|
|
"newHeight", headerCache[depth].sh.Height,
|
|
"newHash", hash2str(headerCache[depth].sh.Hash()))
|
|
|
|
err := Verify(c.chainID, trustedHeader, trustedVals, headerCache[depth].sh, headerCache[depth].valSet,
|
|
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
|
|
trustedHeader, trustedVals = headerCache[depth].sh, headerCache[depth].valSet
|
|
// Remove the untrusted header at the lower bound in the header cache - it's no longer useful
|
|
headerCache = headerCache[: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(headerCache)-1 {
|
|
pivotHeight := trustedHeader.Height + (headerCache[depth].sh.Height-trustedHeader.
|
|
Height)*bisectionNumerator/bisectionDenominator
|
|
interimHeader, interimVals, err := c.signedHeaderAndValSetFrom(pivotHeight, source)
|
|
if err != nil {
|
|
return ErrVerificationFailed{From: trustedHeader.Height, To: pivotHeight, Reason: err}
|
|
}
|
|
headerCache = append(headerCache, headerSet{interimHeader, interimVals})
|
|
}
|
|
depth++
|
|
|
|
default:
|
|
return ErrVerificationFailed{From: trustedHeader.Height, To: headerCache[depth].sh.Height, Reason: err}
|
|
}
|
|
}
|
|
}
|
|
|
|
// bisectionAgainstPrimary does bisection plus it compares new header with
|
|
// witnesses and replaces primary if it does not respond after
|
|
// MaxRetryAttempts.
|
|
func (c *Client) bisectionAgainstPrimary(
|
|
initiallyTrustedHeader *types.SignedHeader,
|
|
initiallyTrustedVals *types.ValidatorSet,
|
|
newHeader *types.SignedHeader,
|
|
newVals *types.ValidatorSet,
|
|
now time.Time) error {
|
|
|
|
err := c.bisection(c.primary, initiallyTrustedHeader, initiallyTrustedVals, newHeader, newVals, now)
|
|
|
|
switch errors.Unwrap(err).(type) {
|
|
case ErrInvalidHeader:
|
|
// If the target header is invalid, return immediately.
|
|
invalidHeaderHeight := err.(ErrVerificationFailed).To
|
|
if invalidHeaderHeight == newHeader.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
|
|
}
|
|
|
|
replacementHeader, replacementVals, fErr := c.signedHeaderAndValSetFromPrimary(newHeader.Height)
|
|
if fErr != nil {
|
|
c.logger.Error("Can't fetch header/vals from primary", "err", fErr)
|
|
// return original error
|
|
return err
|
|
}
|
|
|
|
if !bytes.Equal(replacementHeader.Hash(), newHeader.Hash()) ||
|
|
!bytes.Equal(replacementVals.Hash(), newVals.Hash()) {
|
|
c.logger.Error("Replacement provider has a different header/vals",
|
|
"newHash", newHeader.Hash(),
|
|
"newVals", newVals.Hash(),
|
|
"replHash", replacementHeader.Hash(),
|
|
"replVals", replacementVals.Hash())
|
|
// return original error
|
|
return err
|
|
}
|
|
|
|
// attempt to verify the header again
|
|
return c.bisectionAgainstPrimary(
|
|
initiallyTrustedHeader,
|
|
initiallyTrustedVals,
|
|
replacementHeader,
|
|
replacementVals,
|
|
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(newHeader, 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.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
|
|
}
|
|
|
|
// 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.latestTrustedHeader = nil
|
|
c.latestTrustedVals = nil
|
|
return c.trustedStore.Prune(0)
|
|
}
|
|
|
|
// cleanupAfter deletes all headers & validator sets after +height+. It also
|
|
// resets latestTrustedHeader to the latest header.
|
|
func (c *Client) cleanupAfter(height int64) error {
|
|
prevHeight := c.latestTrustedHeader.Height
|
|
|
|
for {
|
|
h, err := c.trustedStore.SignedHeaderBefore(prevHeight)
|
|
if err == store.ErrSignedHeaderNotFound || (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.DeleteSignedHeaderAndValidatorSet(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.latestTrustedHeader = nil
|
|
c.latestTrustedVals = nil
|
|
err := c.restoreTrustedHeaderAndVals()
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
func (c *Client) updateTrustedHeaderAndVals(h *types.SignedHeader, vals *types.ValidatorSet) error {
|
|
if !bytes.Equal(h.ValidatorsHash, vals.Hash()) {
|
|
return fmt.Errorf("expected validator's hash %X, but got %X", h.ValidatorsHash, vals.Hash())
|
|
}
|
|
|
|
if err := c.trustedStore.SaveSignedHeaderAndValidatorSet(h, vals); 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.latestTrustedHeader == nil || h.Height > c.latestTrustedHeader.Height {
|
|
c.latestTrustedHeader = h
|
|
c.latestTrustedVals = vals
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// 0 - latest header
|
|
// Note it swaps the primary with a witness if primary is not responding after
|
|
// MaxRetryAttempts.
|
|
func (c *Client) signedHeaderAndValSetFromPrimary(height int64) (*types.SignedHeader, *types.ValidatorSet, error) {
|
|
h, err := c.signedHeaderFromPrimary(height)
|
|
if err != nil {
|
|
return nil, nil, fmt.Errorf("can't fetch header: %w", err)
|
|
}
|
|
vals, err := c.validatorSetFromPrimary(height)
|
|
if err != nil {
|
|
return nil, nil, fmt.Errorf("can't fetch vals: %w", err)
|
|
}
|
|
return h, vals, nil
|
|
}
|
|
|
|
// 0 - latest header
|
|
// Note it does not do retries nor swapping.
|
|
func (c *Client) signedHeaderAndValSetFromWitness(height int64,
|
|
witness provider.Provider) (*types.SignedHeader, *types.ValidatorSet, *errBadWitness) {
|
|
|
|
h, err := witness.SignedHeader(height)
|
|
if err != nil {
|
|
return nil, nil, &errBadWitness{err, noResponse, -1}
|
|
}
|
|
err = c.validateHeader(h, height)
|
|
if err != nil {
|
|
return nil, nil, &errBadWitness{err, invalidHeader, -1}
|
|
}
|
|
|
|
vals, err := witness.ValidatorSet(height)
|
|
if err != nil {
|
|
return nil, nil, &errBadWitness{err, noResponse, -1}
|
|
}
|
|
err = c.validateValidatorSet(vals)
|
|
if err != nil {
|
|
return nil, nil, &errBadWitness{err, invalidValidatorSet, -1}
|
|
}
|
|
|
|
return h, vals, nil
|
|
}
|
|
|
|
func (c *Client) signedHeaderAndValSetFrom(height int64,
|
|
source provider.Provider) (*types.SignedHeader, *types.ValidatorSet, error) {
|
|
|
|
c.providerMutex.Lock()
|
|
sourceIsPrimary := (c.primary == source)
|
|
c.providerMutex.Unlock()
|
|
|
|
if sourceIsPrimary {
|
|
return c.signedHeaderAndValSetFromPrimary(height)
|
|
}
|
|
return c.signedHeaderAndValSetFromWitness(height, source)
|
|
}
|
|
|
|
// 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(
|
|
initiallyTrustedHeader *types.SignedHeader,
|
|
newHeader *types.SignedHeader,
|
|
now time.Time) error {
|
|
|
|
if HeaderExpired(initiallyTrustedHeader, c.trustingPeriod, now) {
|
|
c.logger.Error("Header Expired")
|
|
return ErrOldHeaderExpired{initiallyTrustedHeader.Time.Add(c.trustingPeriod), now}
|
|
}
|
|
|
|
var (
|
|
trustedHeader = initiallyTrustedHeader
|
|
interimHeader *types.SignedHeader
|
|
err error
|
|
)
|
|
|
|
for trustedHeader.Height > newHeader.Height {
|
|
interimHeader, err = c.signedHeaderFromPrimary(trustedHeader.Height - 1)
|
|
if err != nil {
|
|
return fmt.Errorf("failed to obtain the header at height #%d: %w", trustedHeader.Height-1, err)
|
|
}
|
|
c.logger.Debug("Verify newHeader against trustedHeader",
|
|
"trustedHeight", trustedHeader.Height,
|
|
"trustedHash", hash2str(trustedHeader.Hash()),
|
|
"newHeight", interimHeader.Height,
|
|
"newHash", hash2str(interimHeader.Hash()))
|
|
if err := VerifyBackwards(c.chainID, interimHeader, trustedHeader); 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",
|
|
trustedHeader.Height, interimHeader.Height, err)
|
|
}
|
|
}
|
|
|
|
trustedHeader = interimHeader
|
|
}
|
|
|
|
// Initially trusted header might have expired at this point.
|
|
if HeaderExpired(initiallyTrustedHeader, c.trustingPeriod, now) {
|
|
return ErrOldHeaderExpired{initiallyTrustedHeader.Time.Add(c.trustingPeriod), now}
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// compare header with all witnesses provided.
|
|
func (c *Client) compareNewHeaderWithWitnesses(h *types.SignedHeader, 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
|
|
lastErrConfHeaders error
|
|
)
|
|
for attempt := uint16(1); attempt <= c.maxRetryAttempts; attempt++ {
|
|
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, h, 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 ErrConflictingHeaders: // fork detected
|
|
c.logger.Info("FORK DETECTED", "witness", e.Witness, "err", err)
|
|
c.sendConflictingHeadersEvidence(&types.ConflictingHeadersEvidence{H1: h, H2: e.H2})
|
|
lastErrConfHeaders = e
|
|
case errBadWitness:
|
|
c.logger.Info("Bad witness", "witness", c.witnesses[e.WitnessIndex], "err", err)
|
|
// if witness sent us invalid header / vals, remove it
|
|
if e.Code == invalidHeader || e.Code == invalidValidatorSet {
|
|
c.logger.Info("Witness sent us invalid header / vals -> removing it", "witness", c.witnesses[e.WitnessIndex])
|
|
witnessesToRemove = append(witnessesToRemove, e.WitnessIndex)
|
|
}
|
|
}
|
|
}
|
|
|
|
for _, idx := range witnessesToRemove {
|
|
c.removeWitness(idx)
|
|
}
|
|
|
|
if lastErrConfHeaders != nil {
|
|
// NOTE: all of the potential forks will be reported, but we only return
|
|
// the last ErrConflictingHeaders error here.
|
|
return lastErrConfHeaders
|
|
} else if headerMatched {
|
|
return nil
|
|
}
|
|
|
|
// 2. Otherwise, sleep
|
|
time.Sleep(backoffTimeout(attempt))
|
|
}
|
|
|
|
return errors.New("awaiting response from all witnesses exceeded dropout time")
|
|
}
|
|
|
|
func (c *Client) compareNewHeaderWithWitness(errc chan error, h *types.SignedHeader,
|
|
witness provider.Provider, witnessIndex int, now time.Time) {
|
|
|
|
altH, altVals, err := c.signedHeaderAndValSetFromWitness(h.Height, witness)
|
|
if err != nil {
|
|
err.WitnessIndex = witnessIndex
|
|
errc <- err
|
|
return
|
|
}
|
|
|
|
if !bytes.Equal(h.Hash(), altH.Hash()) {
|
|
if bsErr := c.bisection(witness, c.latestTrustedHeader, c.latestTrustedVals, altH, altVals, now); bsErr != nil {
|
|
errc <- errBadWitness{bsErr, invalidHeader, witnessIndex}
|
|
return
|
|
}
|
|
errc <- ErrConflictingHeaders{H1: h, Primary: c.primary, H2: altH, Witness: witness}
|
|
}
|
|
|
|
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 header and
|
|
// comparing it with the existing one. It returns a new header on a successful
|
|
// update. Otherwise, it returns nil (plus an error, if any).
|
|
func (c *Client) Update(now time.Time) (*types.SignedHeader, error) {
|
|
lastTrustedHeight, err := c.LastTrustedHeight()
|
|
if err != nil {
|
|
return nil, fmt.Errorf("can't get last trusted height: %w", err)
|
|
}
|
|
|
|
if lastTrustedHeight == -1 {
|
|
// no headers yet => wait
|
|
return nil, nil
|
|
}
|
|
|
|
latestHeader, latestVals, err := c.signedHeaderAndValSetFromPrimary(0)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
if latestHeader.Height > lastTrustedHeight {
|
|
err = c.VerifyHeader(latestHeader, latestVals, now)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
c.logger.Info("Advanced to new state", "height", latestHeader.Height, "hash", hash2str(latestHeader.Hash()))
|
|
return latestHeader, 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()
|
|
|
|
c.logger.Info("Primary is unavailable. Replacing with the first witness")
|
|
if len(c.witnesses) <= 1 {
|
|
return errNoWitnesses{}
|
|
}
|
|
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, providerErr := c.primary.SignedHeader(height)
|
|
c.providerMutex.Unlock()
|
|
if providerErr == nil {
|
|
err := c.validateHeader(h, height)
|
|
if err != nil {
|
|
replaceErr := c.replacePrimaryProvider()
|
|
if replaceErr != nil {
|
|
return nil, fmt.Errorf("%v. Tried to replace primary but: %w", err.Error(), replaceErr)
|
|
}
|
|
// replace primary and request signed header again
|
|
return c.signedHeaderFromPrimary(height)
|
|
}
|
|
// valid header has been received
|
|
return h, nil
|
|
}
|
|
if providerErr == provider.ErrSignedHeaderNotFound {
|
|
return nil, providerErr
|
|
}
|
|
c.logger.Error("Failed to get signed header from primary", "attempt", attempt, "err", providerErr)
|
|
time.Sleep(backoffTimeout(attempt))
|
|
}
|
|
|
|
err := c.replacePrimaryProvider()
|
|
if err != nil {
|
|
return nil, fmt.Errorf("primary dropped out. Tried to replace but: %w", err)
|
|
}
|
|
|
|
return c.signedHeaderFromPrimary(height)
|
|
}
|
|
|
|
func (c *Client) validateHeader(h *types.SignedHeader, expectedHeight int64) error {
|
|
if h == nil {
|
|
return errors.New("nil header")
|
|
}
|
|
err := h.ValidateBasic(c.chainID)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if expectedHeight > 0 && h.Height != expectedHeight {
|
|
return errors.New("height mismatch")
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// 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, providerErr := c.primary.ValidatorSet(height)
|
|
c.providerMutex.Unlock()
|
|
if providerErr == nil {
|
|
err := c.validateValidatorSet(vals)
|
|
if err != nil {
|
|
replaceErr := c.replacePrimaryProvider()
|
|
if replaceErr != nil {
|
|
return nil, fmt.Errorf("%v. Tried to replace primary but: %w", err.Error(), replaceErr)
|
|
}
|
|
// replace primary and request signed header again
|
|
return c.validatorSetFromPrimary(height)
|
|
}
|
|
return vals, nil
|
|
}
|
|
|
|
if providerErr == provider.ErrValidatorSetNotFound {
|
|
return vals, providerErr
|
|
}
|
|
c.logger.Error("Failed to get validator set from primary", "attempt", attempt, "err", providerErr)
|
|
time.Sleep(backoffTimeout(attempt))
|
|
}
|
|
|
|
err := c.replacePrimaryProvider()
|
|
if err != nil {
|
|
return nil, fmt.Errorf("primary dropped out. Tried to replace but: %w", err)
|
|
}
|
|
|
|
return c.validatorSetFromPrimary(height)
|
|
}
|
|
|
|
func (c *Client) validateValidatorSet(vals *types.ValidatorSet) error {
|
|
if vals == nil {
|
|
return errors.New("validator set is nil")
|
|
}
|
|
return vals.ValidateBasic()
|
|
}
|
|
|
|
// sendConflictingHeadersEvidence sends evidence to all witnesses and primary
|
|
// on best effort basis.
|
|
//
|
|
// Evidence needs to be submitted to all full nodes since there's no way to
|
|
// determine which full node is correct (honest).
|
|
func (c *Client) sendConflictingHeadersEvidence(ev *types.ConflictingHeadersEvidence) {
|
|
err := c.primary.ReportEvidence(ev)
|
|
if err != nil {
|
|
c.logger.Error("Failed to report evidence to primary", "ev", ev, "primary", c.primary)
|
|
}
|
|
|
|
for _, w := range c.witnesses {
|
|
err := w.ReportEvidence(ev)
|
|
if err != nil {
|
|
c.logger.Error("Failed to report evidence to witness", "ev", ev, "witness", w)
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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)
|
|
}
|