voter.go

// Copyright (C) 2019-2021, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package snowman

import (
	"github.com/MetalBlockchain/metalgo/ids"
)

// Voter records chits received from [vdr] once its dependencies are met.
type voter struct {
	t         *Transitive
	vdr       ids.ShortID
	requestID uint32
	response  ids.ID
	deps      ids.Set
}

func (v *voter) Dependencies() ids.Set { return v.deps }

// Mark that a dependency has been met.
func (v *voter) Fulfill(id ids.ID) {
	v.deps.Remove(id)
	v.Update()
}

// Abandon this attempt to record chits.
func (v *voter) Abandon(id ids.ID) { v.Fulfill(id) }

func (v *voter) Update() {
	if v.deps.Len() != 0 || v.t.errs.Errored() {
		return
	}

	var results []ids.Bag
	if v.response == ids.Empty {
		results = v.t.polls.Drop(v.requestID, v.vdr)
	} else {
		results = v.t.polls.Vote(v.requestID, v.vdr, v.response)
	}

	if len(results) == 0 {
		return
	}

	// To prevent any potential deadlocks with un-disclosed dependencies, votes
	// must be bubbled to the nearest valid block
	for i, result := range results {
		results[i] = v.bubbleVotes(result)
	}

	for _, result := range results {
		result := result

		v.t.Ctx.Log.Debug("Finishing poll with:\n%s", &result)
		if err := v.t.Consensus.RecordPoll(result); err != nil {
			v.t.errs.Add(err)
		}
	}

	if v.t.errs.Errored() {
		return
	}

	if err := v.t.VM.SetPreference(v.t.Consensus.Preference()); err != nil {
		v.t.errs.Add(err)
		return
	}

	if v.t.Consensus.Finalized() {
		v.t.Ctx.Log.Debug("Snowman engine can quiesce")
		return
	}

	v.t.Ctx.Log.Debug("Snowman engine can't quiesce")
	v.t.repoll()
}

// bubbleVotes bubbles the [votes] a set of the number of votes for specific
// blkIDs that received votes in consensus, to their most recent ancestor that
// has been issued to consensus.
//
// Note: bubbleVotes does not bubbleVotes to all of the ancestors in consensus,
// just the most recent one. bubbling to the rest of the ancestors, which may
// also be in consensus is handled in RecordPoll.
func (v *voter) bubbleVotes(votes ids.Bag) ids.Bag {
	bubbledVotes := ids.Bag{}

votesLoop:
	for _, vote := range votes.List() {
		count := votes.Count(vote)
		// use rootID in case of this is a non-verified block ID
		rootID := v.t.nonVerifieds.GetRoot(vote)
		v.t.Ctx.Log.Verbo("Bubbling %d vote(s) for %s to %s through unverified blocks", count, vote, rootID)

		blk, err := v.t.GetBlock(rootID)
		// If we cannot retrieve the block, drop [vote]
		if err != nil {
			v.t.Ctx.Log.Debug("Dropping %d vote(s) for %s because %s couldn't be fetched", count, vote, rootID)
			continue
		}

		status := blk.Status()
		blkID := blk.ID()
		// If we have not fetched [blkID] break from the loop. We will drop the
		// vote below and move on to the next vote.
		//
		// If [blk] has already been decided, break from the loop, we will drop
		// the vote below since there is no need to count the votes for a [blk]
		// we've already finalized.
		//
		// If [blk] is currently in consensus, break from the loop, we have
		// reached the first ancestor of the original [vote] that has been
		// issued consensus. In this case, the votes will be bubbled further
		// from [blk] to any of its ancestors that are also in consensus.
		for status.Fetched() && !(v.t.Consensus.Decided(blk) || v.t.Consensus.Processing(blkID)) {
			parentID := blk.Parent()
			v.t.Ctx.Log.Verbo("Pushing %d vote(s) from %s (%s) to %s", count, blkID, status, parentID)

			blkID = parentID
			blk, err = v.t.GetBlock(blkID)
			// If we cannot retrieve the block, drop [vote]
			if err != nil {
				v.t.Ctx.Log.Debug("Dropping %d vote(s) for %s because %s couldn't be fetched",
					count, vote, blkID)
				continue votesLoop
			}
			status = blk.Status()
		}

		// If [blkID] is currently in consensus, count the votes
		if v.t.Consensus.Processing(blkID) {
			v.t.Ctx.Log.Verbo("Applying %d vote(s) to %s (%s)", count, blkID, status)
			bubbledVotes.AddCount(blkID, count)
		} else {
			v.t.Ctx.Log.Verbo("Dropping %d vote(s) to %s (%s)", count, blkID, status)
		}
	}
	return bubbledVotes
}