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traversal.go
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traversal.go
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package chain
import (
"context"
"errors"
"github.com/filecoin-project/venus/pkg/types"
"github.com/filecoin-project/go-state-types/abi"
"github.com/ipfs/go-cid"
)
// TipSetProvider provides tipsets for traversal.
type TipSetProvider interface {
GetTipSet(tsKey types.TipSetKey) (*types.TipSet, error)
}
// IterAncestors returns an iterator over tipset ancestors, yielding first the start tipset and
// then its parent tipsets until (and including) the genesis tipset.
func IterAncestors(ctx context.Context, store TipSetProvider, start *types.TipSet) *TipsetIterator {
return &TipsetIterator{ctx, store, start}
}
// TipsetIterator is an iterator over tipsets.
type TipsetIterator struct {
ctx context.Context
store TipSetProvider
value *types.TipSet
}
// Value returns the iterator's current value, if not Complete().
func (it *TipsetIterator) Value() *types.TipSet {
return it.value
}
// Complete tests whether the iterator is exhausted.
func (it *TipsetIterator) Complete() bool {
return !it.value.Defined()
}
// Next advances the iterator to the next value.
func (it *TipsetIterator) Next() error {
select {
case <-it.ctx.Done():
return it.ctx.Err()
default:
if it.value.Height() == 0 {
it.value = &types.TipSet{}
} else {
var err error
parentKey := it.value.Parents()
it.value, err = it.store.GetTipSet(parentKey)
return err
}
return nil
}
}
// BlockProvider provides blocks.
type BlockProvider interface {
GetBlock(ctx context.Context, cid cid.Cid) (*types.BlockHeader, error)
}
// LoadTipSetBlocks loads all the blocks for a tipset from the store.
func LoadTipSetBlocks(ctx context.Context, store BlockProvider, key types.TipSetKey) (*types.TipSet, error) {
var blocks []*types.BlockHeader
for _, bid := range key.Cids() {
blk, err := store.GetBlock(ctx, bid)
if err != nil {
return nil, err
}
blocks = append(blocks, blk)
}
return types.NewTipSet(blocks...)
}
type tipsetFromBlockProvider struct {
ctx context.Context // Context to use when loading blocks
blocks BlockProvider // Provides blocks
}
// TipSetProviderFromBlocks builds a tipset provider backed by a block provider.
// Blocks will be loaded with the provided context, since GetTipSet does not accept a
// context parameter. This can and should be removed when GetTipSet does take a context.
func TipSetProviderFromBlocks(ctx context.Context, blocks BlockProvider) TipSetProvider {
return &tipsetFromBlockProvider{ctx, blocks}
}
// GetTipSet loads the blocks for a tipset.
func (p *tipsetFromBlockProvider) GetTipSet(tsKey types.TipSetKey) (*types.TipSet, error) {
return LoadTipSetBlocks(p.ctx, p.blocks, tsKey)
}
// CollectTipsToCommonAncestor traverses chains from two tipsets (called old and new) until their common
// ancestor, collecting all tipsets that are in one chain but not the other.
// The resulting lists of tipsets are ordered by decreasing height.
func CollectTipsToCommonAncestor(ctx context.Context, store TipSetProvider, oldHead, newHead *types.TipSet) (oldTips, newTips []*types.TipSet, err error) {
oldIter := IterAncestors(ctx, store, oldHead)
newIter := IterAncestors(ctx, store, newHead)
commonAncestor, err := FindCommonAncestor(oldIter, newIter)
if err != nil {
return
}
commonHeight := commonAncestor.Height()
// Refresh iterators modified by FindCommonAncestors
oldIter = IterAncestors(ctx, store, oldHead)
newIter = IterAncestors(ctx, store, newHead)
// Add 1 to the height argument so that the common ancestor is not
// included in the outputs.
oldTips, err = CollectTipSetsOfHeightAtLeast(ctx, oldIter, commonHeight+1)
if err != nil {
return
}
newTips, err = CollectTipSetsOfHeightAtLeast(ctx, newIter, commonHeight+1)
return
}
// ErrNoCommonAncestor is returned when two chains assumed to have a common ancestor do not.
var ErrNoCommonAncestor = errors.New("no common ancestor")
// FindCommonAncestor returns the common ancestor of the two tipsets pointed to
// by the input iterators. If they share no common ancestor ErrNoCommonAncestor
// will be returned.
func FindCommonAncestor(leftIter, rightIter *TipsetIterator) (*types.TipSet, error) {
for !rightIter.Complete() && !leftIter.Complete() {
left := leftIter.Value()
right := rightIter.Value()
leftHeight := left.Height()
rightHeight := right.Height()
// Found common ancestor.
if left.Equals(right) {
return left, nil
}
// Update the pointers. Pointers move back one tipset if they
// point to a tipset at the same height or higher than the
// other pointer's tipset.
if rightHeight >= leftHeight {
if err := rightIter.Next(); err != nil {
return nil, err
}
}
if leftHeight >= rightHeight {
if err := leftIter.Next(); err != nil {
return nil, err
}
}
}
return nil, ErrNoCommonAncestor
}
// CollectTipSetsOfHeightAtLeast collects all tipsets with a height greater
// than or equal to minHeight from the input tipset.
func CollectTipSetsOfHeightAtLeast(ctx context.Context, iterator *TipsetIterator, minHeight abi.ChainEpoch) ([]*types.TipSet, error) {
var ret []*types.TipSet
var err error
var h abi.ChainEpoch
for ; !iterator.Complete(); err = iterator.Next() {
if err != nil {
return nil, err
}
h = iterator.Value().Height()
if h < minHeight {
return ret, nil
}
ret = append(ret, iterator.Value())
}
return ret, nil
}
// FindLatestDRAND returns the latest DRAND entry in the chain beginning at start
func FindLatestDRAND(ctx context.Context, start *types.TipSet, reader TipSetProvider) (*types.BeaconEntry, error) {
iterator := IterAncestors(ctx, reader, start)
var err error
for ; !iterator.Complete(); err = iterator.Next() {
if err != nil {
return nil, err
}
ts := iterator.Value()
// DRAND entries must be the same for all blocks on the tipset as
// an invariant of the tipset provider
entries := ts.At(0).BeaconEntries
if len(entries) > 0 {
return entries[len(entries)-1], nil
}
// No entries, simply move on to the next ancestor
}
return nil, errors.New("no DRAND entries in chain")
}