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builder.go
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builder.go
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// Copyright (C) 2019-2023, Ava Labs, Inc. All rights reserved.
// See the file LICENSE for licensing terms.
package builder
import (
"context"
"errors"
"fmt"
"time"
"go.uber.org/zap"
"github.com/ava-labs/avalanchego/ids"
"github.com/ava-labs/avalanchego/snow/consensus/snowman"
"github.com/ava-labs/avalanchego/snow/engine/common"
"github.com/ava-labs/avalanchego/utils/timer"
"github.com/ava-labs/avalanchego/utils/timer/mockable"
"github.com/ava-labs/avalanchego/utils/units"
"github.com/ava-labs/avalanchego/vms/platformvm/blocks"
"github.com/ava-labs/avalanchego/vms/platformvm/state"
"github.com/ava-labs/avalanchego/vms/platformvm/txs"
"github.com/ava-labs/avalanchego/vms/platformvm/txs/mempool"
blockexecutor "github.com/ava-labs/avalanchego/vms/platformvm/blocks/executor"
txbuilder "github.com/ava-labs/avalanchego/vms/platformvm/txs/builder"
txexecutor "github.com/ava-labs/avalanchego/vms/platformvm/txs/executor"
)
// targetBlockSize is maximum number of transaction bytes to place into a
// StandardBlock
const targetBlockSize = 128 * units.KiB
var (
_ Builder = (*builder)(nil)
ErrEndOfTime = errors.New("program time is suspiciously far in the future")
ErrNoPendingBlocks = errors.New("no pending blocks")
ErrChainNotSynced = errors.New("chain not synced")
)
type Builder interface {
mempool.Mempool
mempool.BlockTimer
Network
// set preferred block on top of which we'll build next
SetPreference(blockID ids.ID)
// get preferred block on top of which we'll build next
Preferred() (snowman.Block, error)
// AddUnverifiedTx verifier the tx before adding it to mempool
AddUnverifiedTx(tx *txs.Tx) error
// BuildBlock is called on timer clock to attempt to create
// next block
BuildBlock(context.Context) (snowman.Block, error)
// Shutdown cleanly shuts Builder down
Shutdown()
}
// builder implements a simple builder to convert txs into valid blocks
type builder struct {
mempool.Mempool
Network
txBuilder txbuilder.Builder
txExecutorBackend *txexecutor.Backend
blkManager blockexecutor.Manager
// ID of the preferred block to build on top of
preferredBlockID ids.ID
// channel to send messages to the consensus engine
toEngine chan<- common.Message
// This timer goes off when it is time for the next validator to add/leave
// the validator set. When it goes off ResetTimer() is called, potentially
// triggering creation of a new block.
timer *timer.Timer
}
func New(
mempool mempool.Mempool,
txBuilder txbuilder.Builder,
txExecutorBackend *txexecutor.Backend,
blkManager blockexecutor.Manager,
toEngine chan<- common.Message,
appSender common.AppSender,
) Builder {
builder := &builder{
Mempool: mempool,
txBuilder: txBuilder,
txExecutorBackend: txExecutorBackend,
blkManager: blkManager,
toEngine: toEngine,
}
builder.timer = timer.NewTimer(builder.setNextBuildBlockTime)
builder.Network = NewNetwork(
txExecutorBackend.Ctx,
builder,
appSender,
)
go txExecutorBackend.Ctx.Log.RecoverAndPanic(builder.timer.Dispatch)
return builder
}
func (b *builder) SetPreference(blockID ids.ID) {
if blockID == b.preferredBlockID {
// If the preference didn't change, then this is a noop
return
}
b.preferredBlockID = blockID
b.ResetBlockTimer()
}
func (b *builder) Preferred() (snowman.Block, error) {
return b.blkManager.GetBlock(b.preferredBlockID)
}
// AddUnverifiedTx verifies a transaction and attempts to add it to the mempool
func (b *builder) AddUnverifiedTx(tx *txs.Tx) error {
if !b.txExecutorBackend.Bootstrapped.Get() {
return ErrChainNotSynced
}
txID := tx.ID()
if b.Mempool.Has(txID) {
// If the transaction is already in the mempool - then it looks the same
// as if it was successfully added
return nil
}
verifier := txexecutor.MempoolTxVerifier{
Backend: b.txExecutorBackend,
ParentID: b.preferredBlockID, // We want to build off of the preferred block
StateVersions: b.blkManager,
Tx: tx,
}
if err := tx.Unsigned.Visit(&verifier); err != nil {
b.MarkDropped(txID, err)
return err
}
if err := b.Mempool.Add(tx); err != nil {
return err
}
return b.GossipTx(tx)
}
// BuildBlock builds a block to be added to consensus.
// This method removes the transactions from the returned
// blocks from the mempool.
func (b *builder) BuildBlock(context.Context) (snowman.Block, error) {
b.Mempool.DisableAdding()
defer func() {
b.Mempool.EnableAdding()
b.ResetBlockTimer()
}()
ctx := b.txExecutorBackend.Ctx
ctx.Log.Debug("starting to attempt to build a block")
statelessBlk, err := b.buildBlock()
if err != nil {
return nil, err
}
// Remove selected txs from mempool now that we are returning the block to
// the consensus engine.
txs := statelessBlk.Txs()
b.Mempool.Remove(txs)
return b.blkManager.NewBlock(statelessBlk), nil
}
// Returns the block we want to build and issue.
// Only modifies state to remove expired proposal txs.
func (b *builder) buildBlock() (blocks.Block, error) {
// Get the block to build on top of and retrieve the new block's context.
preferred, err := b.Preferred()
if err != nil {
return nil, err
}
preferredID := preferred.ID()
nextHeight := preferred.Height() + 1
preferredState, ok := b.blkManager.GetState(preferredID)
if !ok {
return nil, fmt.Errorf("%w: %s", state.ErrMissingParentState, preferredID)
}
timestamp := b.txExecutorBackend.Clk.Time()
if parentTime := preferred.Timestamp(); parentTime.After(timestamp) {
timestamp = parentTime
}
// [timestamp] = max(now, parentTime)
nextStakerChangeTime, err := txexecutor.GetNextStakerChangeTime(preferredState)
if err != nil {
return nil, fmt.Errorf("could not calculate next staker change time: %w", err)
}
// timeWasCapped means that [timestamp] was reduced to
// [nextStakerChangeTime]. It is used as a flag for [buildApricotBlock] to
// be willing to issue an advanceTimeTx. It is also used as a flag for
// [buildBanffBlock] to force the issuance of an empty block to advance
// the time forward; if there are no available transactions.
timeWasCapped := !timestamp.Before(nextStakerChangeTime)
if timeWasCapped {
timestamp = nextStakerChangeTime
}
// [timestamp] = min(max(now, parentTime), nextStakerChangeTime)
return buildBlock(
b,
preferredID,
nextHeight,
timestamp,
timeWasCapped,
preferredState,
)
}
func (b *builder) Shutdown() {
// There is a potential deadlock if the timer is about to execute a timeout.
// So, the lock must be released before stopping the timer.
ctx := b.txExecutorBackend.Ctx
ctx.Lock.Unlock()
b.timer.Stop()
ctx.Lock.Lock()
}
func (b *builder) ResetBlockTimer() {
// Next time the context lock is released, we can attempt to reset the block
// timer.
b.timer.SetTimeoutIn(0)
}
// dropExpiredStakerTxs drops add validator/delegator transactions in the
// mempool whose start time is not sufficiently far in the future
// (i.e. within local time plus [MaxFutureStartFrom]).
func (b *builder) dropExpiredStakerTxs(timestamp time.Time) {
minStartTime := timestamp.Add(txexecutor.SyncBound)
for b.Mempool.HasStakerTx() {
tx := b.Mempool.PeekStakerTx()
startTime := tx.Unsigned.(txs.Staker).StartTime()
if !startTime.Before(minStartTime) {
// The next proposal tx in the mempool starts sufficiently far in
// the future.
return
}
txID := tx.ID()
err := fmt.Errorf(
"synchrony bound (%s) is later than staker start time (%s)",
minStartTime,
startTime,
)
b.Mempool.Remove([]*txs.Tx{tx})
b.Mempool.MarkDropped(txID, err) // cache tx as dropped
b.txExecutorBackend.Ctx.Log.Debug("dropping tx",
zap.Stringer("txID", txID),
zap.Error(err),
)
}
}
func (b *builder) setNextBuildBlockTime() {
ctx := b.txExecutorBackend.Ctx
// Grabbing the lock here enforces that this function is not called mid-way
// through modifying of the state.
ctx.Lock.Lock()
defer ctx.Lock.Unlock()
if !b.txExecutorBackend.Bootstrapped.Get() {
ctx.Log.Verbo("skipping block timer reset",
zap.String("reason", "not bootstrapped"),
)
return
}
if _, err := b.buildBlock(); err == nil {
// We can build a block now
b.notifyBlockReady()
return
}
// Wake up when it's time to add/remove the next validator/delegator
preferredState, ok := b.blkManager.GetState(b.preferredBlockID)
if !ok {
// The preferred block should always be a decision block
ctx.Log.Error("couldn't get preferred block state",
zap.Stringer("preferredID", b.preferredBlockID),
zap.Stringer("lastAcceptedID", b.blkManager.LastAccepted()),
)
return
}
nextStakerChangeTime, err := txexecutor.GetNextStakerChangeTime(preferredState)
if err != nil {
ctx.Log.Error("couldn't get next staker change time",
zap.Stringer("preferredID", b.preferredBlockID),
zap.Stringer("lastAcceptedID", b.blkManager.LastAccepted()),
zap.Error(err),
)
return
}
now := b.txExecutorBackend.Clk.Time()
waitTime := nextStakerChangeTime.Sub(now)
ctx.Log.Debug("setting next scheduled event",
zap.Time("nextEventTime", nextStakerChangeTime),
zap.Duration("timeUntil", waitTime),
)
// Wake up when it's time to add/remove the next validator
b.timer.SetTimeoutIn(waitTime)
}
// notifyBlockReady tells the consensus engine that a new block is ready to be
// created
func (b *builder) notifyBlockReady() {
select {
case b.toEngine <- common.PendingTxs:
default:
b.txExecutorBackend.Ctx.Log.Debug("dropping message to consensus engine")
}
}
// [timestamp] is min(max(now, parent timestamp), next staker change time)
func buildBlock(
builder *builder,
parentID ids.ID,
height uint64,
timestamp time.Time,
forceAdvanceTime bool,
parentState state.Chain,
) (blocks.Block, error) {
// Try rewarding stakers whose staking period ends at the new chain time.
// This is done first to prioritize advancing the timestamp as quickly as
// possible.
stakerTxID, shouldReward, err := getNextStakerToReward(timestamp, parentState)
if err != nil {
return nil, fmt.Errorf("could not find next staker to reward: %w", err)
}
if shouldReward {
rewardValidatorTx, err := builder.txBuilder.NewRewardValidatorTx(stakerTxID)
if err != nil {
return nil, fmt.Errorf("could not build tx to reward staker: %w", err)
}
return blocks.NewBanffProposalBlock(
timestamp,
parentID,
height,
rewardValidatorTx,
)
}
// Clean out the mempool's transactions with invalid timestamps.
builder.dropExpiredStakerTxs(timestamp)
// If there is no reason to build a block, don't.
if !builder.Mempool.HasTxs() && !forceAdvanceTime {
builder.txExecutorBackend.Ctx.Log.Debug("no pending txs to issue into a block")
return nil, ErrNoPendingBlocks
}
// Issue a block with as many transactions as possible.
return blocks.NewBanffStandardBlock(
timestamp,
parentID,
height,
builder.Mempool.PeekTxs(targetBlockSize),
)
}
// getNextStakerToReward returns the next staker txID to remove from the staking
// set with a RewardValidatorTx rather than an AdvanceTimeTx. [chainTimestamp]
// is the timestamp of the chain at the time this validator would be getting
// removed and is used to calculate [shouldReward].
// Returns:
// - [txID] of the next staker to reward
// - [shouldReward] if the txID exists and is ready to be rewarded
// - [err] if something bad happened
func getNextStakerToReward(
chainTimestamp time.Time,
preferredState state.Chain,
) (ids.ID, bool, error) {
if !chainTimestamp.Before(mockable.MaxTime) {
return ids.Empty, false, ErrEndOfTime
}
currentStakerIterator, err := preferredState.GetCurrentStakerIterator()
if err != nil {
return ids.Empty, false, err
}
defer currentStakerIterator.Release()
for currentStakerIterator.Next() {
currentStaker := currentStakerIterator.Value()
priority := currentStaker.Priority
// If the staker is a permissionless staker (not a permissioned subnet
// validator), it's the next staker we will want to remove with a
// RewardValidatorTx rather than an AdvanceTimeTx.
if priority != txs.SubnetPermissionedValidatorCurrentPriority {
return currentStaker.TxID, chainTimestamp.Equal(currentStaker.EndTime), nil
}
}
return ids.Empty, false, nil
}