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444 lines
13 KiB
444 lines
13 KiB
package lite
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import (
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"bytes"
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"fmt"
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"time"
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"github.com/pkg/errors"
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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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tmrand "github.com/tendermint/tendermint/libs/rand"
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"github.com/tendermint/tendermint/lite2/provider"
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"github.com/tendermint/tendermint/lite2/store"
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"github.com/tendermint/tendermint/types"
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)
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// TrustOptions are the trust parameters needed when a new light client
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// connects to the network or when an existing light client that has been
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// offline for longer than the trusting period connects to the network.
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//
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// The expectation is the user will get this information from a trusted source
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// like a validator, a friend, or a secure website. A more user friendly
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// solution with trust tradeoffs is that we establish an https based protocol
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// with a default end point that populates this information. Also an on-chain
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// registry of roots-of-trust (e.g. on the Cosmos Hub) seems likely in the
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// future.
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type TrustOptions struct {
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// tp: trusting period.
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//
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// Should be significantly less than the unbonding period (e.g. unbonding
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// period = 3 weeks, trusting period = 2 weeks).
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//
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// More specifically, trusting period + time needed to check headers + time
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// needed to report and punish misbehavior should be less than the unbonding
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// period.
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Period time.Duration
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// Header's Height and Hash must both be provided to force the trusting of a
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// particular header.
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Height int64
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Hash []byte
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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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)
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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. Note this is much slower than SkippingVerification,
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// 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-adjusted headers. For adjusted headers, sequential
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// verification is used.
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func SkippingVerification(trustLevel tmmath.Fraction) Option {
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if err := ValidateTrustLevel(trustLevel); err != nil {
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panic(err)
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}
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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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// AlternativeSources option can be used to supply alternative providers, which
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// will be used for cross-checking the primary provider.
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func AlternativeSources(providers []provider.Provider) Option {
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return func(c *Client) {
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c.alternatives = providers
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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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// Primary provider of new headers.
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primary provider.Provider
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// Alternative providers for checking the primary for misbehavior by
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// comparing data.
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alternatives []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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trustedHeader *types.SignedHeader
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// Highest next validator set from the store (height=H+1).
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trustedNextVals *types.ValidatorSet
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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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// 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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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: trustOptions.Period,
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verificationMode: skipping,
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trustLevel: DefaultTrustLevel,
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primary: primary,
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trustedStore: trustedStore,
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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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if err := c.initializeWithTrustOptions(trustOptions); 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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func (c *Client) initializeWithTrustOptions(options TrustOptions) error {
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// 1) Fetch and verify the header.
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h, err := c.primary.SignedHeader(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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if err := h.ValidateBasic(c.chainID); err != nil {
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return errors.Wrap(err, "ValidateBasic failed")
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}
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if !bytes.Equal(h.Hash(), options.Hash) {
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return errors.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 next vals.
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vals, err := c.primary.ValidatorSet(options.Height + 1)
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if err != nil {
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return 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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// SetLogger sets a logger.
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func (c *Client) SetLogger(l log.Logger) {
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c.logger = l
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}
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// TrustedHeader returns a trusted header at the given height (0 - the latest)
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// or nil if no such header exist.
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// TODO: mention how many headers will be kept by the light client.
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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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// - the header expired (ErrOldHeaderExpired). In that case, update your
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// client to more recent height;
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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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func (c *Client) TrustedHeader(height int64, now time.Time) (*types.SignedHeader, error) {
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if height < 0 {
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return nil, errors.New("negative height")
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}
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if height == 0 {
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var err error
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height, err = c.LastTrustedHeight()
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if err != nil {
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return nil, err
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}
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}
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h, err := c.trustedStore.SignedHeader(height)
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if err != nil {
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return nil, err
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}
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// Ensure header can still be trusted.
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expirationTime := h.Time.Add(c.trustingPeriod)
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if !expirationTime.After(now) {
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return nil, ErrOldHeaderExpired{expirationTime, now}
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}
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return h, nil
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}
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// LastTrustedHeight returns a last trusted height.
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func (c *Client) LastTrustedHeight() (int64, error) {
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return c.trustedStore.LastSignedHeaderHeight()
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}
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// ChainID returns the chain ID.
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func (c *Client) ChainID() string {
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return c.chainID
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}
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// VerifyHeaderAtHeight fetches the header and validators at the given height
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// and calls VerifyHeader.
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//
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// If the trusted header is more recent than one here, an error is returned.
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func (c *Client) VerifyHeaderAtHeight(height int64, now time.Time) error {
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if c.trustedHeader.Height >= height {
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return errors.Errorf("height #%d is already trusted (last: #%d)", height, c.trustedHeader.Height)
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}
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// Request the header and the vals.
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newHeader, newVals, err := c.fetchHeaderAndValsAtHeight(height)
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if err != nil {
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return err
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}
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return c.VerifyHeader(newHeader, newVals, now)
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}
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// VerifyHeader verifies new header against the trusted state.
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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
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// headers will be requested.
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//
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// SkippingVerification(trustLevel): verifies that {trustLevel} of the trusted
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// 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)
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// intermediate headers will be requested. See the specification for the
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// algorithm.
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//
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// If the trusted header is more recent than one here, an error is returned.
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func (c *Client) VerifyHeader(newHeader *types.SignedHeader, newVals *types.ValidatorSet, now time.Time) error {
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if c.trustedHeader.Height >= newHeader.Height {
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return errors.Errorf("height #%d is already trusted (last: #%d)", newHeader.Height, c.trustedHeader.Height)
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}
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if len(c.alternatives) > 0 {
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if err := c.compareNewHeaderWithRandomAlternative(newHeader); err != nil {
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return err
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}
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}
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var err error
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switch c.verificationMode {
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case sequential:
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err = c.sequence(newHeader, newVals, now)
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case skipping:
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err = c.bisection(c.trustedHeader, c.trustedNextVals, newHeader, newVals, now)
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default:
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panic(fmt.Sprintf("Unknown verification mode: %b", c.verificationMode))
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}
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if err != nil {
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return err
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}
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// Update trusted header and vals.
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nextVals, err := c.primary.ValidatorSet(newHeader.Height + 1)
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if err != nil {
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return err
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}
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return c.updateTrustedHeaderAndVals(newHeader, nextVals)
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}
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func (c *Client) sequence(newHeader *types.SignedHeader, newVals *types.ValidatorSet, now time.Time) error {
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// 1) Verify any intermediate headers.
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var (
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interimHeader *types.SignedHeader
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nextVals *types.ValidatorSet
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err error
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)
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for height := c.trustedHeader.Height + 1; height < newHeader.Height; height++ {
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interimHeader, err = c.primary.SignedHeader(height)
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if err != nil {
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return errors.Wrapf(err, "failed to obtain the header #%d", height)
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}
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err = Verify(c.chainID, c.trustedHeader, c.trustedNextVals, interimHeader, c.trustedNextVals,
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c.trustingPeriod, now, c.trustLevel)
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if err != nil {
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return errors.Wrapf(err, "failed to verify the header #%d", height)
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}
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// Update trusted header and vals.
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if height == newHeader.Height-1 {
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nextVals = newVals
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} else {
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nextVals, err = c.primary.ValidatorSet(height + 1)
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if err != nil {
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return errors.Wrapf(err, "failed to obtain the vals #%d", height+1)
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}
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}
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err = c.updateTrustedHeaderAndVals(interimHeader, nextVals)
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if err != nil {
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return errors.Wrapf(err, "failed to update trusted state #%d", height)
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}
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}
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// 2) Verify the new header.
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return Verify(c.chainID, c.trustedHeader, c.trustedNextVals, newHeader, newVals, c.trustingPeriod, now, c.trustLevel)
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}
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func (c *Client) bisection(
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lastHeader *types.SignedHeader,
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lastVals *types.ValidatorSet,
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newHeader *types.SignedHeader,
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newVals *types.ValidatorSet,
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now time.Time) error {
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err := Verify(c.chainID, lastHeader, lastVals, newHeader, newVals, c.trustingPeriod, now, c.trustLevel)
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switch err.(type) {
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case nil:
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return nil
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case types.ErrTooMuchChange:
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// continue bisection
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default:
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return errors.Wrapf(err, "failed to verify the header #%d ", newHeader.Height)
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}
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if newHeader.Height == c.trustedHeader.Height+1 {
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// TODO: submit evidence here
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return errors.Errorf("adjacent headers (#%d and #%d) that are not matching", lastHeader.Height, newHeader.Height)
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}
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pivot := (c.trustedHeader.Height + newHeader.Header.Height) / 2
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pivotHeader, pivotVals, err := c.fetchHeaderAndValsAtHeight(pivot)
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if err != nil {
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return err
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}
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// left branch
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{
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err := c.bisection(lastHeader, lastVals, pivotHeader, pivotVals, now)
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if err != nil {
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return errors.Wrapf(err, "bisection of #%d and #%d", lastHeader.Height, pivot)
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}
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}
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// right branch
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{
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nextVals, err := c.primary.ValidatorSet(pivot + 1)
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if err != nil {
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return errors.Wrapf(err, "failed to obtain the vals #%d", pivot+1)
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}
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if !bytes.Equal(pivotHeader.NextValidatorsHash, nextVals.Hash()) {
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return errors.Errorf("expected next validator's hash %X, but got %X (height #%d)",
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pivotHeader.NextValidatorsHash,
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nextVals.Hash(),
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pivot)
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}
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err = c.updateTrustedHeaderAndVals(pivotHeader, nextVals)
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if err != nil {
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return errors.Wrapf(err, "failed to update trusted state #%d", pivot)
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}
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err = c.bisection(pivotHeader, nextVals, newHeader, newVals, now)
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if err != nil {
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return errors.Wrapf(err, "bisection of #%d and #%d", pivot, newHeader.Height)
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}
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}
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return nil
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}
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func (c *Client) updateTrustedHeaderAndVals(h *types.SignedHeader, vals *types.ValidatorSet) error {
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if !bytes.Equal(h.NextValidatorsHash, vals.Hash()) {
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return errors.Errorf("expected next validator's hash %X, but got %X", h.NextValidatorsHash, vals.Hash())
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}
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if err := c.trustedStore.SaveSignedHeader(h); err != nil {
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return errors.Wrap(err, "failed to save trusted header")
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}
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if err := c.trustedStore.SaveValidatorSet(vals, h.Height+1); err != nil {
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return errors.Wrap(err, "failed to save trusted vals")
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}
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c.trustedHeader = h
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c.trustedNextVals = vals
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return nil
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}
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func (c *Client) fetchHeaderAndValsAtHeight(height int64) (*types.SignedHeader, *types.ValidatorSet, error) {
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h, err := c.primary.SignedHeader(height)
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if err != nil {
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return nil, nil, errors.Wrapf(err, "failed to obtain the header #%d", height)
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}
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vals, err := c.primary.ValidatorSet(height)
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if err != nil {
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return nil, nil, errors.Wrapf(err, "failed to obtain the vals #%d", height)
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}
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return h, vals, nil
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}
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func (c *Client) compareNewHeaderWithRandomAlternative(h *types.SignedHeader) error {
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// 1. Pick an alternative provider.
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p := c.alternatives[tmrand.Intn(len(c.alternatives))]
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// 2. Fetch the header.
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altHeader, err := p.SignedHeader(h.Height)
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if err != nil {
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return errors.Wrapf(err,
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"failed to obtain header #%d from alternative provider %v", h.Height, p)
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}
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// 3. Compare hashes.
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if !bytes.Equal(h.Hash(), altHeader.Hash()) {
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// TODO: One of the providers is lying. Send the evidence to fork
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// accountability server.
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return errors.Errorf(
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"new header hash %X does not match one from alternative provider %X",
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h.Hash(), altHeader.Hash())
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}
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return nil
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}
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