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snapshot.go
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snapshot.go
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// (c) 2019 Dapper Labs - ALL RIGHTS RESERVED
package badger
import (
"errors"
"fmt"
"github.com/onflow/flow-go/model/flow"
"github.com/onflow/flow-go/model/flow/filter"
"github.com/onflow/flow-go/model/flow/mapfunc"
"github.com/onflow/flow-go/model/flow/order"
"github.com/onflow/flow-go/state"
"github.com/onflow/flow-go/state/fork"
"github.com/onflow/flow-go/state/protocol"
"github.com/onflow/flow-go/state/protocol/inmem"
"github.com/onflow/flow-go/state/protocol/invalid"
"github.com/onflow/flow-go/state/protocol/seed"
"github.com/onflow/flow-go/storage"
"github.com/onflow/flow-go/storage/badger/operation"
"github.com/onflow/flow-go/storage/badger/procedure"
)
// Snapshot implements the protocol.Snapshot interface.
// It represents a read-only immutable snapshot of the protocol state at the
// block it is constructed with. It allows efficient access to data associated directly
// with blocks at a given state (finalized, sealed), such as the related header, commit,
// seed or descending blocks. A block snapshot can lazily convert to an epoch snapshot in
// order to make data associated directly with epochs accessible through its API.
type Snapshot struct {
state *State
blockID flow.Identifier // reference block for this snapshot
}
func NewSnapshot(state *State, blockID flow.Identifier) *Snapshot {
return &Snapshot{
state: state,
blockID: blockID,
}
}
func (s *Snapshot) Head() (*flow.Header, error) {
head, err := s.state.headers.ByBlockID(s.blockID)
return head, err
}
// QuorumCertificate (QC) returns a valid quorum certificate pointing to the
// header at this snapshot. With the exception of the root block, a valid child
// block must be which contains the desired QC. The sentinel error
// state.NoValidChildBlockError is returned if the the QC is unknown.
//
// For root block snapshots, returns the root quorum certificate. For all other
// blocks, generates a quorum certificate from a valid child, if one exists.
func (s *Snapshot) QuorumCertificate() (*flow.QuorumCertificate, error) {
// CASE 1: for the root block, return the root QC
root, err := s.state.Params().Root()
if err != nil {
return nil, fmt.Errorf("could not get root: %w", err)
}
if s.blockID == root.ID() {
var rootQC flow.QuorumCertificate
err := s.state.db.View(operation.RetrieveRootQuorumCertificate(&rootQC))
if err != nil {
return nil, fmt.Errorf("could not retrieve root qc: %w", err)
}
return &rootQC, nil
}
// CASE 2: for any other block, generate the root QC from a valid child
child, err := s.validChild()
if err != nil {
return nil, fmt.Errorf("could not get valid child of block %x: %w", s.blockID, err)
}
// sanity check: ensure the child has the snapshot block as parent
if child.ParentID != s.blockID {
return nil, fmt.Errorf("child parent id (%x) does not match snapshot id (%x)", child.ParentID, s.blockID)
}
// retrieve the full header as we need the view for the quorum certificate
head, err := s.Head()
if err != nil {
return nil, fmt.Errorf("could not get head: %w", err)
}
qc := &flow.QuorumCertificate{
View: head.View,
BlockID: s.blockID,
SignerIndices: child.ParentVoterIndices,
SigData: child.ParentVoterSigData,
}
return qc, nil
}
// validChild returns a child of the snapshot head that has been validated
// by HotStuff. Returns state.NoValidChildBlockError if no valid child exists.
//
// Any valid child may be returned. Subsequent calls are not guaranteed to
// return the same child.
func (s *Snapshot) validChild() (*flow.Header, error) {
var childIDs []flow.Identifier
err := s.state.db.View(procedure.LookupBlockChildren(s.blockID, &childIDs))
if err != nil {
return nil, fmt.Errorf("could not look up children: %w", err)
}
// find the first child that has been validated
validChildID := flow.ZeroID
for _, childID := range childIDs {
var valid bool
err = s.state.db.View(operation.RetrieveBlockValidity(childID, &valid))
// skip blocks whose validity hasn't been checked yet
if errors.Is(err, storage.ErrNotFound) {
continue
}
if err != nil {
return nil, fmt.Errorf("failed to determine validity of child block %v: %w", childID, err)
}
if valid {
validChildID = childID
break
}
}
if validChildID == flow.ZeroID {
return nil, state.NewNoValidChildBlockErrorf("block has no valid children (total children: %d)", len(childIDs))
}
// get the header of the first child
child, err := s.state.headers.ByBlockID(validChildID)
return child, err
}
func (s *Snapshot) Phase() (flow.EpochPhase, error) {
status, err := s.state.epoch.statuses.ByBlockID(s.blockID)
if err != nil {
return flow.EpochPhaseUndefined, fmt.Errorf("could not retrieve epoch status: %w", err)
}
phase, err := status.Phase()
return phase, err
}
func (s *Snapshot) Identities(selector flow.IdentityFilter) (flow.IdentityList, error) {
// TODO: CAUTION SHORTCUT
// we retrieve identities based on the initial identity table from the EpochSetup
// event here -- this will need revision to support mid-epoch identity changes
// once slashing is implemented
status, err := s.state.epoch.statuses.ByBlockID(s.blockID)
if err != nil {
return nil, err
}
setup, err := s.state.epoch.setups.ByID(status.CurrentEpoch.SetupID)
if err != nil {
return nil, err
}
// sort the identities so the 'Exists' binary search works
identities := setup.Participants.Sort(order.Canonical)
// get identities that are in either last/next epoch but NOT in the current epoch
var otherEpochIdentities flow.IdentityList
phase, err := status.Phase()
if err != nil {
return nil, fmt.Errorf("could not get phase: %w", err)
}
switch phase {
// during staking phase (the beginning of the epoch) we include identities
// from the previous epoch that are now un-staking
case flow.EpochPhaseStaking:
if !status.HasPrevious() {
break
}
previousSetup, err := s.state.epoch.setups.ByID(status.PreviousEpoch.SetupID)
if err != nil {
return nil, fmt.Errorf("could not get previous epoch setup event: %w", err)
}
for _, identity := range previousSetup.Participants {
exists := identities.Exists(identity)
// add identity from previous epoch that is not in current epoch
if !exists {
otherEpochIdentities = append(otherEpochIdentities, identity)
}
}
// during setup and committed phases (the end of the epoch) we include
// identities that will join in the next epoch
case flow.EpochPhaseSetup, flow.EpochPhaseCommitted:
nextSetup, err := s.state.epoch.setups.ByID(status.NextEpoch.SetupID)
if err != nil {
return nil, fmt.Errorf("could not get next epoch setup: %w", err)
}
for _, identity := range nextSetup.Participants {
exists := identities.Exists(identity)
// add identity from next epoch that is not in current epoch
if !exists {
otherEpochIdentities = append(otherEpochIdentities, identity)
}
}
default:
return nil, fmt.Errorf("invalid epoch phase: %s", phase)
}
// add the identities from next/last epoch, with weight set to 0
identities = append(
identities,
otherEpochIdentities.Map(mapfunc.WithWeight(0))...,
)
// apply the filter to the participants
identities = identities.Filter(selector)
// apply a deterministic sort to the participants
identities = identities.Sort(order.Canonical)
return identities, nil
}
func (s *Snapshot) Identity(nodeID flow.Identifier) (*flow.Identity, error) {
// filter identities at snapshot for node ID
identities, err := s.Identities(filter.HasNodeID(nodeID))
if err != nil {
return nil, fmt.Errorf("could not get identities: %w", err)
}
// check if node ID is part of identities
if len(identities) == 0 {
return nil, protocol.IdentityNotFoundError{NodeID: nodeID}
}
return identities[0], nil
}
// Commit retrieves the latest execution state commitment at the current block snapshot. This
// commitment represents the execution state as currently finalized.
func (s *Snapshot) Commit() (flow.StateCommitment, error) {
// get the ID of the sealed block
seal, err := s.state.seals.HighestInFork(s.blockID)
if err != nil {
return flow.DummyStateCommitment, fmt.Errorf("could not retrieve sealed state commit: %w", err)
}
return seal.FinalState, nil
}
func (s *Snapshot) SealedResult() (*flow.ExecutionResult, *flow.Seal, error) {
seal, err := s.state.seals.HighestInFork(s.blockID)
if err != nil {
return nil, nil, fmt.Errorf("could not look up latest seal: %w", err)
}
result, err := s.state.results.ByID(seal.ResultID)
if err != nil {
return nil, nil, fmt.Errorf("could not get latest result: %w", err)
}
return result, seal, nil
}
// SealingSegment will walk through the chain backward until we reach the block referenced
// by the latest seal and build a SealingSegment. As we visit each block we check each execution
// receipt in the block's payload to make sure we have a corresponding execution result, any execution
// results missing from blocks are stored in the SealingSegment.ExecutionResults field.
func (s *Snapshot) SealingSegment() (*flow.SealingSegment, error) {
var rootHeight uint64
err := s.state.db.View(operation.RetrieveRootHeight(&rootHeight))
if err != nil {
return nil, fmt.Errorf("could not get root height: %w", err)
}
head, err := s.Head()
if err != nil {
return nil, fmt.Errorf("could not get snapshot reference block: %w", err)
}
if head.Height < rootHeight {
return nil, protocol.ErrSealingSegmentBelowRootBlock
}
seal, err := s.state.seals.HighestInFork(s.blockID)
if err != nil {
return nil, fmt.Errorf("could not get seal for sealing segment: %w", err)
}
// walk through the chain backward until we reach the block referenced by
// the latest seal - the returned segment includes this block
builder := flow.NewSealingSegmentBuilder(s.state.results.ByID, s.state.seals.HighestInFork)
scraper := func(header *flow.Header) error {
blockID := header.ID()
block, err := s.state.blocks.ByID(blockID)
if err != nil {
return fmt.Errorf("could not get block: %w", err)
}
err = builder.AddBlock(block)
if err != nil {
return fmt.Errorf("could not add block to sealing segment: %w", err)
}
return nil
}
err = fork.TraverseForward(s.state.headers, s.blockID, scraper, fork.IncludingBlock(seal.BlockID))
if err != nil {
return nil, fmt.Errorf("could not traverse sealing segment: %w", err)
}
segment, err := builder.SealingSegment()
if err != nil {
return nil, fmt.Errorf("could not build sealing segment: %w", err)
}
return segment, nil
}
func (s *Snapshot) Descendants() ([]flow.Identifier, error) {
descendants, err := s.descendants(s.blockID)
if err != nil {
return nil, fmt.Errorf("failed to traverse the descendants tree of block %v: %w", s.blockID, err)
}
return descendants, nil
}
func (s *Snapshot) ValidDescendants() ([]flow.Identifier, error) {
valid, err := s.lookupValidity(s.blockID)
if err != nil {
return nil, fmt.Errorf("could not determine validity of block %v: %w", s.blockID, err)
}
if !valid {
return []flow.Identifier{}, nil
}
descendants, err := s.validDescendants(s.blockID)
if err != nil {
return nil, fmt.Errorf("failed to traverse the descendants tree of block %v: %w", s.blockID, err)
}
return descendants, nil
}
func (s *Snapshot) lookupChildren(blockID flow.Identifier) ([]flow.Identifier, error) {
var children []flow.Identifier
err := s.state.db.View(procedure.LookupBlockChildren(blockID, &children))
if err != nil {
return nil, fmt.Errorf("could not get children of block %v: %w", blockID, err)
}
return children, nil
}
func (s *Snapshot) lookupValidity(blockID flow.Identifier) (bool, error) {
valid := false
err := s.state.db.View(operation.RetrieveBlockValidity(blockID, &valid))
if err != nil {
// We only store the validity flag for blocks that have been marked valid.
// For blocks that haven't been marked valid (yet), the flag is simply absent.
if !errors.Is(err, storage.ErrNotFound) {
return false, fmt.Errorf("could not retrieve validity of block %v: %w", blockID, err)
}
}
return valid, nil
}
func (s *Snapshot) validDescendants(blockID flow.Identifier) ([]flow.Identifier, error) {
var descendantIDs []flow.Identifier
children, err := s.lookupChildren(blockID)
if err != nil {
return nil, err
}
for _, descendantID := range children {
valid, err := s.lookupValidity(descendantID)
if err != nil {
return nil, err
}
if valid {
descendantIDs = append(descendantIDs, descendantID)
additionalIDs, err := s.validDescendants(descendantID)
if err != nil {
return nil, err
}
descendantIDs = append(descendantIDs, additionalIDs...)
}
}
return descendantIDs, nil
}
func (s *Snapshot) descendants(blockID flow.Identifier) ([]flow.Identifier, error) {
descendantIDs, err := s.lookupChildren(blockID)
if err != nil {
return nil, err
}
for _, descendantID := range descendantIDs {
additionalIDs, err := s.descendants(descendantID)
if err != nil {
return nil, err
}
descendantIDs = append(descendantIDs, additionalIDs...)
}
return descendantIDs, nil
}
// RandomSource returns the seed for the current block snapshot.
// Expected error returns:
// * state.NoValidChildBlockError if no valid child is known
func (s *Snapshot) RandomSource() ([]byte, error) {
// CASE 1: for the root block, generate the seed from the root qc
root, err := s.state.Params().Root()
if err != nil {
return nil, fmt.Errorf("could not get root: %w", err)
}
if s.blockID == root.ID() {
var rootQC flow.QuorumCertificate
err := s.state.db.View(operation.RetrieveRootQuorumCertificate(&rootQC))
if err != nil {
return nil, fmt.Errorf("could not retrieve root qc: %w", err)
}
seed, err := seed.FromParentQCSignature(rootQC.SigData)
if err != nil {
return nil, fmt.Errorf("could not create seed from root qc: %w", err)
}
return seed, nil
}
// CASE 2: for any other block, use any valid child
child, err := s.validChild()
if err != nil {
return nil, fmt.Errorf("failed to get valid child of block %x: %w", s.blockID, err)
}
seed, err := seed.FromParentQCSignature(child.ParentVoterSigData)
if err != nil {
return nil, fmt.Errorf("could not create seed from header's signature: %w", err)
}
return seed, nil
}
func (s *Snapshot) Epochs() protocol.EpochQuery {
return &EpochQuery{
snap: s,
}
}
func (s *Snapshot) Params() protocol.GlobalParams {
return s.state.Params()
}
// EpochQuery encapsulates querying epochs w.r.t. a snapshot.
type EpochQuery struct {
snap *Snapshot
}
// Current returns the current epoch.
func (q *EpochQuery) Current() protocol.Epoch {
status, err := q.snap.state.epoch.statuses.ByBlockID(q.snap.blockID)
if err != nil {
return invalid.NewEpoch(err)
}
setup, err := q.snap.state.epoch.setups.ByID(status.CurrentEpoch.SetupID)
if err != nil {
return invalid.NewEpoch(err)
}
commit, err := q.snap.state.epoch.commits.ByID(status.CurrentEpoch.CommitID)
if err != nil {
return invalid.NewEpoch(err)
}
epoch, err := inmem.NewCommittedEpoch(setup, commit)
if err != nil {
return invalid.NewEpoch(err)
}
return epoch
}
// Next returns the next epoch, if it is available.
func (q *EpochQuery) Next() protocol.Epoch {
status, err := q.snap.state.epoch.statuses.ByBlockID(q.snap.blockID)
if err != nil {
return invalid.NewEpoch(err)
}
phase, err := status.Phase()
if err != nil {
return invalid.NewEpoch(err)
}
// if we are in the staking phase, the next epoch is not setup yet
if phase == flow.EpochPhaseStaking {
return invalid.NewEpoch(protocol.ErrNextEpochNotSetup)
}
// if we are in setup phase, return a SetupEpoch
nextSetup, err := q.snap.state.epoch.setups.ByID(status.NextEpoch.SetupID)
if err != nil {
return invalid.NewEpoch(fmt.Errorf("failed to retrieve setup event for next epoch: %w", err))
}
if phase == flow.EpochPhaseSetup {
epoch, err := inmem.NewSetupEpoch(nextSetup)
if err != nil {
return invalid.NewEpoch(err)
}
return epoch
}
// if we are in committed phase, return a CommittedEpoch
nextCommit, err := q.snap.state.epoch.commits.ByID(status.NextEpoch.CommitID)
if err != nil {
return invalid.NewEpoch(fmt.Errorf("failed to retrieve commit event for next epoch: %w", err))
}
epoch, err := inmem.NewCommittedEpoch(nextSetup, nextCommit)
if err != nil {
return invalid.NewEpoch(err)
}
return epoch
}
// Previous returns the previous epoch. During the first epoch after the root
// block, this returns a sentinel error (since there is no previous epoch).
// For all other epochs, returns the previous epoch.
func (q *EpochQuery) Previous() protocol.Epoch {
status, err := q.snap.state.epoch.statuses.ByBlockID(q.snap.blockID)
if err != nil {
return invalid.NewEpoch(err)
}
// CASE 1: there is no previous epoch - this indicates we are in the first
// epoch after a spork root or genesis block
if !status.HasPrevious() {
return invalid.NewEpoch(protocol.ErrNoPreviousEpoch)
}
// CASE 2: we are in any other epoch - retrieve the setup and commit events
// for the previous epoch
setup, err := q.snap.state.epoch.setups.ByID(status.PreviousEpoch.SetupID)
if err != nil {
return invalid.NewEpoch(err)
}
commit, err := q.snap.state.epoch.commits.ByID(status.PreviousEpoch.CommitID)
if err != nil {
return invalid.NewEpoch(err)
}
epoch, err := inmem.NewCommittedEpoch(setup, commit)
if err != nil {
return invalid.NewEpoch(err)
}
return epoch
}