mirror of
https://gitlab.com/pulsechaincom/prysm-pulse.git
synced 2024-12-29 14:48:28 +00:00
315 lines
11 KiB
Go
315 lines
11 KiB
Go
package blockchain
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import (
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"context"
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"fmt"
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"github.com/prysmaticlabs/prysm/beacon-chain/blockchain/stategenerator"
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"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
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"github.com/prysmaticlabs/prysm/beacon-chain/db"
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pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
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"github.com/prysmaticlabs/prysm/shared/bytesutil"
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"github.com/prysmaticlabs/prysm/shared/hashutil"
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"go.opencensus.io/trace"
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)
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// ForkChoice interface defines the methods for applying fork choice rule
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// operations to the blockchain.
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type ForkChoice interface {
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ApplyForkChoiceRule(ctx context.Context, block *pb.BeaconBlock, computedState *pb.BeaconState) error
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}
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// updateFFGCheckPts checks whether the existing FFG check points saved in DB
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// are not older than the ones just processed in state. If it's older, we update
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// the db with the latest FFG check points, both justification and finalization.
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func (c *ChainService) updateFFGCheckPts(state *pb.BeaconState) error {
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lastJustifiedSlot := helpers.StartSlot(state.JustifiedEpoch)
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savedJustifiedBlock, err := c.beaconDB.JustifiedBlock()
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if err != nil {
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return err
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}
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// If the last processed justification slot in state is greater than
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// the slot of justified block saved in DB.
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if lastJustifiedSlot > savedJustifiedBlock.Slot {
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// Retrieve the new justified block from DB using the new justified slot and save it.
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newJustifiedBlock, err := c.beaconDB.BlockBySlot(lastJustifiedSlot)
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if err != nil {
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return err
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}
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// If the new justified slot is a skip slot in db then we keep getting it's ancestors
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// until we can get a block.
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for newJustifiedBlock == nil {
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log.Debugf("Saving new justified block, no block with slot %d in db, trying slot %d",
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lastJustifiedSlot, lastJustifiedSlot-1)
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lastJustifiedSlot--
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newJustifiedBlock, err = c.beaconDB.BlockBySlot(lastJustifiedSlot)
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if err != nil {
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return err
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}
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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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if err := c.beaconDB.SaveJustifiedBlock(newJustifiedBlock); err != nil {
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return err
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}
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// Generate the new justified state with using new justified block and save it.
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newJustifiedState, err := stategenerator.GenerateStateFromBlock(c.ctx, c.beaconDB, newJustifiedBlock)
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if err != nil {
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return err
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}
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if err := c.beaconDB.SaveJustifiedState(newJustifiedState); err != nil {
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return err
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}
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}
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lastFinalizedSlot := helpers.StartSlot(state.FinalizedEpoch)
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savedFinalizedBlock, err := c.beaconDB.FinalizedBlock()
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// If the last processed finalized slot in state is greater than
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// the slot of finalized block saved in DB.
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if err != nil {
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return err
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}
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if lastFinalizedSlot > savedFinalizedBlock.Slot {
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// Retrieve the new finalized block from DB using the new finalized slot and save it.
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newFinalizedBlock, err := c.beaconDB.BlockBySlot(lastFinalizedSlot)
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if err != nil {
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return err
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}
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// If the new finalized slot is a skip slot in db then we keep getting it's ancestors
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// until we can get a block.
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for newFinalizedBlock == nil {
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log.Debugf("Saving new finalized block, no block with slot %d in db, trying slot %d",
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lastFinalizedSlot, lastFinalizedSlot-1)
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lastFinalizedSlot--
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newFinalizedBlock, err = c.beaconDB.BlockBySlot(lastFinalizedSlot)
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if err != nil {
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return err
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}
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}
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if err := c.beaconDB.SaveFinalizedBlock(newFinalizedBlock); err != nil {
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return err
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}
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// Generate the new finalized state with using new finalized block and save it.
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newFinalizedState, err := stategenerator.GenerateStateFromBlock(c.ctx, c.beaconDB, newFinalizedBlock)
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if err != nil {
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return err
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}
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if err := c.beaconDB.SaveFinalizedState(newFinalizedState); err != nil {
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return err
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}
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}
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return nil
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}
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// ApplyForkChoiceRule determines the current beacon chain head using LMD GHOST as a block-vote
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// weighted function to select a canonical head in Ethereum Serenity.
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func (c *ChainService) ApplyForkChoiceRule(ctx context.Context, block *pb.BeaconBlock, computedState *pb.BeaconState) error {
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ctx, span := trace.StartSpan(ctx, "beacon-chain.blockchain.ApplyForkChoiceRule")
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defer span.End()
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h, err := hashutil.HashBeaconBlock(block)
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if err != nil {
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return fmt.Errorf("could not tree hash incoming block: %v", err)
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}
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// TODO(#1307): Use LMD GHOST as the fork-choice rule for Ethereum Serenity.
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// TODO(#674): Handle chain reorgs.
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if err := c.beaconDB.UpdateChainHead(block, computedState); err != nil {
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return fmt.Errorf("failed to update chain: %v", err)
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}
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log.WithField("blockRoot", fmt.Sprintf("0x%x", h)).Info("Chain head block and state updated")
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if err := c.saveHistoricalState(computedState); err != nil {
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log.Errorf("Could not save new historical state: %v", err)
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}
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return nil
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}
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// lmdGhost applies the Latest Message Driven, Greediest Heaviest Observed Sub-Tree
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// fork-choice rule defined in the Ethereum Serenity specification for the beacon chain.
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//
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// Spec pseudocode definition:
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// def lmd_ghost(store: Store, start_state: BeaconState, start_block: BeaconBlock) -> BeaconBlock:
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// """
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// Execute the LMD-GHOST algorithm to find the head ``BeaconBlock``.
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// """
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// validators = start_state.validator_registry
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// active_validator_indices = get_active_validator_indices(validators, slot_to_epoch(start_state.slot))
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// attestation_targets = [
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// (validator_index, get_latest_attestation_target(store, validator_index))
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// for validator_index in active_validator_indices
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// ]
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//
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// def get_vote_count(block: BeaconBlock) -> int:
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// return sum(
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// get_effective_balance(start_state.validator_balances[validator_index]) // FORK_CHOICE_BALANCE_INCREMENT
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// for validator_index, target in attestation_targets
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// if get_ancestor(store, target, block.slot) == block
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// )
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//
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// head = start_block
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// while 1:
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// children = get_children(store, head)
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// if len(children) == 0:
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// return head
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// head = max(children, key=get_vote_count)
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func (c *ChainService) lmdGhost(
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block *pb.BeaconBlock,
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state *pb.BeaconState,
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voteTargets map[uint64]*pb.BeaconBlock,
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) (*pb.BeaconBlock, error) {
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head := block
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for {
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children, err := c.blockChildren(head, state)
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if err != nil {
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return nil, fmt.Errorf("could not fetch block children: %v", err)
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}
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if len(children) == 0 {
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return head, nil
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}
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maxChild := children[0]
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maxChildVotes, err := VoteCount(maxChild, state, voteTargets, c.beaconDB)
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if err != nil {
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return nil, fmt.Errorf("unable to determine vote count for block: %v", err)
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}
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for i := 0; i < len(children); i++ {
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candidateChildVotes, err := VoteCount(children[i], state, voteTargets, c.beaconDB)
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if err != nil {
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return nil, fmt.Errorf("unable to determine vote count for block: %v", err)
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}
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if candidateChildVotes > maxChildVotes {
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maxChild = children[i]
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}
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}
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head = maxChild
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}
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}
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// blockChildren returns the child blocks of the given block.
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// ex:
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// /- C - E
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// A - B - D - F
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// \- G
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// Input: B. Output: [C, D, G]
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//
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// Spec pseudocode definition:
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// get_children(store: Store, block: BeaconBlock) -> List[BeaconBlock]
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// returns the child blocks of the given block.
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func (c *ChainService) blockChildren(block *pb.BeaconBlock, state *pb.BeaconState) ([]*pb.BeaconBlock, error) {
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var children []*pb.BeaconBlock
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currentRoot, err := hashutil.HashBeaconBlock(block)
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if err != nil {
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return nil, fmt.Errorf("could not tree hash incoming block: %v", err)
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}
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startSlot := block.Slot + 1
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currentSlot := state.Slot
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for i := startSlot; i <= currentSlot; i++ {
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block, err := c.beaconDB.BlockBySlot(i)
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if err != nil {
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return nil, fmt.Errorf("could not get block by slot: %v", err)
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}
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// Continue if there's a skip block.
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if block == nil {
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continue
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}
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parentRoot := bytesutil.ToBytes32(block.ParentRootHash32)
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if currentRoot == parentRoot {
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children = append(children, block)
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}
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}
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return children, nil
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}
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// attestationTargets retrieves the list of attestation targets since last finalized epoch,
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// each attestation target consists of validator index and its attestation target (i.e. the block
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// which the validator attested to)
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func (c *ChainService) attestationTargets(state *pb.BeaconState) ([]*attestationTarget, error) {
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indices := helpers.ActiveValidatorIndices(state.ValidatorRegistry, state.FinalizedEpoch)
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attestationTargets := make([]*attestationTarget, len(indices))
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for i, index := range indices {
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block, err := c.attsService.LatestAttestationTarget(c.ctx, index)
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if err != nil {
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return nil, fmt.Errorf("could not retrieve attestation target: %v", err)
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}
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attestationTargets[i] = &attestationTarget{
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validatorIndex: index,
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block: block,
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}
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}
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return attestationTargets, nil
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}
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// VoteCount determines the number of votes on a beacon block by counting the number
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// of target blocks that have such beacon block as a common ancestor.
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//
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// Spec pseudocode definition:
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// def get_vote_count(block: BeaconBlock) -> int:
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// return sum(
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// get_effective_balance(start_state.validator_balances[validator_index]) // FORK_CHOICE_BALANCE_INCREMENT
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// for validator_index, target in attestation_targets
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// if get_ancestor(store, target, block.slot) == block
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// )
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func VoteCount(block *pb.BeaconBlock, state *pb.BeaconState, targets map[uint64]*pb.BeaconBlock, beaconDB *db.BeaconDB) (int, error) {
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balances := 0
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for validatorIndex, targetBlock := range targets {
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ancestor, err := BlockAncestor(targetBlock, block.Slot, beaconDB)
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if err != nil {
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return 0, err
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}
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// This covers the following case, we start at B5, and want to process B6 and B7
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// B6 can be processed, B7 can not be processed because it's pointed to the
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// block older than current block 5.
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// B4 - B5 - B6
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// \ - - - - - B7
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if ancestor == nil {
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continue
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}
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ancestorRoot, err := hashutil.HashBeaconBlock(ancestor)
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if err != nil {
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return 0, err
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}
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blockRoot, err := hashutil.HashBeaconBlock(block)
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if err != nil {
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return 0, err
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}
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if blockRoot == ancestorRoot {
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balances += int(helpers.EffectiveBalance(state, validatorIndex))
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}
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}
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return balances, nil
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}
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// BlockAncestor obtains the ancestor at of a block at a certain slot.
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//
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// Spec pseudocode definition:
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// def get_ancestor(store: Store, block: BeaconBlock, slot: Slot) -> BeaconBlock:
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// """
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// Get the ancestor of ``block`` with slot number ``slot``; return ``None`` if not found.
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// """
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// if block.slot == slot:
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// return block
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// elif block.slot < slot:
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// return None
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// else:
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// return get_ancestor(store, store.get_parent(block), slot)
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func BlockAncestor(block *pb.BeaconBlock, slot uint64, beaconDB *db.BeaconDB) (*pb.BeaconBlock, error) {
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if block.Slot == slot {
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return block, nil
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}
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if block.Slot < slot {
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return nil, nil
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}
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parentHash := bytesutil.ToBytes32(block.ParentRootHash32)
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parent, err := beaconDB.Block(parentHash)
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if err != nil {
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return nil, fmt.Errorf("could not get parent block: %v", err)
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}
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if parent == nil {
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return nil, fmt.Errorf("parent block does not exist: %v", err)
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}
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return BlockAncestor(parent, slot, beaconDB)
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}
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