erigon-pulse/txpool/pool.go

/*
   Copyright 2021 Erigon contributors

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package txpool

import (
	"container/heap"
	"context"
	"fmt"
	"sync"
	"time"

	"github.com/google/btree"
	"github.com/holiman/uint256"
	"github.com/ledgerwatch/log/v3"
)

// Pool is interface for the transaction pool
// This interface exists for the convinience of testing, and not yet because
// there are multiple implementations
type Pool interface {
	// IdHashKnown check whether transaction with given Id hash is known to the pool
	IdHashKnown(hash []byte) bool

	NotifyNewPeer(peerID PeerID)
}

// SubPoolMarker ordered bitset responsible to sort transactions by sub-pools. Bits meaning:
// 1. Minimum fee requirement. Set to 1 if feeCap of the transaction is no less than in-protocol parameter of minimal base fee. Set to 0 if feeCap is less than minimum base fee, which means this transaction will never be included into this particular chain.
// 2. Absence of nonce gaps. Set to 1 for transactions whose nonce is N, state nonce for the sender is M, and there are transactions for all nonces between M and N from the same sender. Set to 0 is the transaction's nonce is divided from the state nonce by one or more nonce gaps.
// 3. Sufficient balance for gas. Set to 1 if the balance of sender's account in the state is B, nonce of the sender in the state is M, nonce of the transaction is N, and the sum of feeCap x gasLimit + transferred_value of all transactions from this sender with nonces N+1 ... M is no more than B. Set to 0 otherwise. In other words, this bit is set if there is currently a guarantee that the transaction and all its required prior transactions will be able to pay for gas.
// 4. Dynamic fee requirement. Set to 1 if feeCap of the transaction is no less than baseFee of the currently pending block. Set to 0 otherwise.
// 5. Local transaction. Set to 1 if transaction is local.
type SubPoolMarker uint8

func NewSubPoolMarker(enoughFeeCapProtocol, noNonceGaps, enoughBalance, enoughFeeCapBlock, isLocal bool) SubPoolMarker {
	var s SubPoolMarker
	if enoughFeeCapProtocol {
		s |= EnoughFeeCapProtocol
	}
	if noNonceGaps {
		s |= NoNonceGaps
	}
	if enoughBalance {
		s |= EnoughBalance
	}
	if enoughFeeCapBlock {
		s |= EnoughFeeCapBlock
	}
	if isLocal {
		s |= IsLocal
	}
	return s
}

const (
	EnoughFeeCapProtocol = 0b10000
	NoNonceGaps          = 0b01000
	EnoughBalance        = 0b00100
	EnoughFeeCapBlock    = 0b00010
	IsLocal              = 0b00001
)

// MetaTx holds transaction and some metadata
type MetaTx struct {
	SubPool                SubPoolMarker // Aggregated field
	SenderHasEnoughBalance bool          // Aggregated field; gasLimit x feeCap + transferred_value
	Tx                     *TxSlot
	bestIndex              int
	worstIndex             int
	currentSubPool         SubPoolType
}

type SubPoolType uint8

const PendingSubPool SubPoolType = 1
const BaseFeeSubPool SubPoolType = 2
const QueuedSubPool SubPoolType = 3

type BestQueue []*MetaTx

func (mt *MetaTx) Less(than *MetaTx) bool {
	if mt.SubPool != than.SubPool {
		return mt.SubPool < than.SubPool
	}
	// means that strict nonce ordering of transactions from the same sender must be observed.
	//if mt.Tx.sender != than.Tx.sender {
	//	return bytes.Compare(mt.Tx.sender[:], than.Tx.sender[:]) < 0
	//}
	//if mt.Tx.nonce != than.Tx.nonce {
	//	return mt.Tx.nonce < than.Tx.nonce
	//}
	return false
}

func (p BestQueue) Len() int           { return len(p) }
func (p BestQueue) Less(i, j int) bool { return !p[i].Less(p[j]) } // We want Pop to give us the highest, not lowest, priority so we use !less here.
func (p BestQueue) Swap(i, j int) {
	p[i], p[j] = p[j], p[i]
	p[i].bestIndex = i
	p[j].bestIndex = j
}
func (p *BestQueue) Push(x interface{}) {
	n := len(*p)
	item := x.(*MetaTx)
	item.bestIndex = n
	*p = append(*p, item)
}

func (p *BestQueue) Pop() interface{} {
	old := *p
	n := len(old)
	item := old[n-1]
	old[n-1] = nil          // avoid memory leak
	item.bestIndex = -1     // for safety
	item.currentSubPool = 0 // for safety
	*p = old[0 : n-1]
	return item
}

type WorstQueue []*MetaTx

func (p WorstQueue) Len() int           { return len(p) }
func (p WorstQueue) Less(i, j int) bool { return p[i].Less(p[j]) }
func (p WorstQueue) Swap(i, j int) {
	p[i], p[j] = p[j], p[i]
	p[i].worstIndex = i
	p[j].worstIndex = j
}
func (p *WorstQueue) Push(x interface{}) {
	n := len(*p)
	item := x.(*MetaTx)
	item.worstIndex = n
	*p = append(*p, x.(*MetaTx))
}
func (p *WorstQueue) Pop() interface{} {
	old := *p
	n := len(old)
	item := old[n-1]
	old[n-1] = nil          // avoid memory leak
	item.worstIndex = -1    // for safety
	item.currentSubPool = 0 // for safety
	*p = old[0 : n-1]
	return item
}

type SubPool struct {
	best  *BestQueue
	worst *WorstQueue
}

func NewSubPool() *SubPool {
	return &SubPool{best: &BestQueue{}, worst: &WorstQueue{}}
}

func (p *SubPool) EnforceInvariants() {
	heap.Init(p.worst)
	heap.Init(p.best)
}
func (p *SubPool) Best() *MetaTx {
	if len(*p.best) == 0 {
		return nil
	}
	return (*p.best)[0]
}
func (p *SubPool) Worst() *MetaTx {
	if len(*p.worst) == 0 {
		return nil
	}
	return (*p.worst)[0]
}
func (p *SubPool) PopBest() *MetaTx {
	i := heap.Pop(p.best).(*MetaTx)
	heap.Remove(p.worst, i.worstIndex)
	return i
}
func (p *SubPool) PopWorst() *MetaTx {
	i := heap.Pop(p.worst).(*MetaTx)
	heap.Remove(p.best, i.bestIndex)
	return i
}
func (p *SubPool) Len() int { return p.best.Len() }
func (p *SubPool) Add(i *MetaTx, subPoolType SubPoolType) {
	i.currentSubPool = subPoolType
	heap.Push(p.best, i)
	heap.Push(p.worst, i)
}

// UnsafeRemove - does break Heap invariants, but it has O(1) instead of O(log(n)) complexity.
// Must manually call heap.Init after such changes.
// Make sense to batch unsafe changes
func (p *SubPool) UnsafeRemove(i *MetaTx) *MetaTx {
	// manually call funcs instead of heap.Pop
	p.worst.Swap(i.worstIndex, p.worst.Len()-1)
	p.worst.Pop()
	p.best.Swap(i.bestIndex, p.best.Len()-1)
	p.best.Pop()
	return i
}
func (p *SubPool) UnsafeAdd(i *MetaTx, subPoolType SubPoolType) {
	i.currentSubPool = subPoolType
	p.worst.Push(i)
	p.best.Push(i)
}
func (p *SubPool) DebugPrint() {
	for i, it := range *p.best {
		fmt.Printf("best: %d, %d, %d\n", i, it.SubPool, it.bestIndex)
	}
	for i, it := range *p.worst {
		fmt.Printf("worst: %d, %d, %d\n", i, it.SubPool, it.worstIndex)
	}
}

const PendingSubPoolLimit = 1024
const BaseFeeSubPoolLimit = 1024
const QueuedSubPoolLimit = 1024

type Nonce2Tx struct {
	*btree.BTree
}

type SenderInfo struct {
	balance    uint256.Int
	nonce      uint64
	txNonce2Tx *Nonce2Tx // sorted map of nonce => *MetaTx
}

type nonce2TxItem struct {
	*MetaTx
}

func (i *nonce2TxItem) Less(than btree.Item) bool {
	return i.MetaTx.Tx.nonce < than.(*nonce2TxItem).MetaTx.Tx.nonce
}

// OnNewBlocks
// 1. New best block arrives, which potentially changes the balance and the nonce of some senders.
// We use senderIds data structure to find relevant senderId values, and then use senders data structure to
// modify state_balance and state_nonce, potentially remove some elements (if transaction with some nonce is
// included into a block), and finally, walk over the transaction records and update SubPool fields depending on
// the actual presence of nonce gaps and what the balance is.
func OnNewBlocks(senderInfo map[uint64]SenderInfo, minedTxs []*TxSlot, protocolBaseFee, blockBaseFee uint64, pending, baseFee, queued *SubPool) {
	// TODO: change sender.nonce

	for _, tx := range minedTxs {
		sender, ok := senderInfo[tx.senderID]
		if !ok {
			panic("not implemented yet")
		}
		// delete mined transactions from everywhere
		sender.txNonce2Tx.Ascend(func(i btree.Item) bool {
			it := i.(*nonce2TxItem)
			if it.MetaTx.Tx.nonce > sender.nonce {
				return false
			}
			// TODO: save local transactions to cache with TTL, in case of re-org - to restore isLocal flag of re-injected transactions

			// del from nonce2tx mapping
			sender.txNonce2Tx.Delete(i)
			// del from sub-pool
			switch it.MetaTx.currentSubPool {
			case PendingSubPool:
				pending.UnsafeRemove(it.MetaTx)
			case BaseFeeSubPool:
				baseFee.UnsafeRemove(it.MetaTx)
			case QueuedSubPool:
				queued.UnsafeRemove(it.MetaTx)
			default:
				//already removed
			}
			return true
		})

		// TODO: aggregate changed senders before call this func
		onSenderChange(sender, protocolBaseFee, blockBaseFee)
	}

	pending.EnforceInvariants()
	baseFee.EnforceInvariants()
	queued.EnforceInvariants()

	PromoteStep(pending, baseFee, queued)
}

// Unwind
// This can be thought of a reverse operation from the one described before.
// When a block that was deemed "the best" of its height, is no longer deemed "the best", the
// transactions contained in it, are now viable for inclusion in other blocks, and therefore should
// be returned into the transaction pool.
// An interesting note here is that if the block contained any transactions local to the node,
// by being first removed from the pool (from the "local" part of it), and then re-injected,
// they effective lose their priority over the "remote" transactions. In order to prevent that,
// somehow the fact that certain transactions were local, needs to be remembered for some
// time (up to some "immutability threshold").
func Unwind(senderInfo map[uint64]SenderInfo, unwindedTxs []*TxSlot, pending *SubPool) {
	// TODO: change sender.nonce

	for _, tx := range unwindedTxs {
		sender, ok := senderInfo[tx.senderID]
		if !ok {
			panic("not implemented yet")
		}
		//TODO: restore isLocal flag
		mt := &MetaTx{Tx: tx}
		// TODO: Если у сендера много транзакций с одинаковым nonce, то из них выбирается одна
		// с наибольшим effectiveTip. Кстати, интересно, как это правильно вычислять
		// наверное нужно просто брать с наибольшим tip
		// implement it for all inserts
		sender.txNonce2Tx.Has(&nonce2TxItem{mt})
		sender.txNonce2Tx.ReplaceOrInsert(&nonce2TxItem{mt})
		pending.UnsafeAdd(mt, PendingSubPool)
	}
	pending.EnforceInvariants()
}

func onSenderChange(sender SenderInfo, protocolBaseFee, blockBaseFee uint64) {
	prevNonce := -1
	accumulatedSenderSpent := uint256.NewInt(0)
	sender.txNonce2Tx.Ascend(func(i btree.Item) bool {
		it := i.(*nonce2TxItem)

		// Sender has enough balance for: gasLimit x feeCap + transferred_value
		balanceNeed := uint256.NewInt(0)
		balanceNeed.Mul(uint256.NewInt(it.MetaTx.Tx.gas), uint256.NewInt(it.MetaTx.Tx.feeCap))
		balanceNeed.Add(balanceNeed, &it.MetaTx.Tx.value)
		it.MetaTx.SenderHasEnoughBalance = sender.balance.Gt(balanceNeed) || sender.balance.Eq(balanceNeed)

		// 1. Minimum fee requirement. Set to 1 if feeCap of the transaction is no less than in-protocol
		// parameter of minimal base fee. Set to 0 if feeCap is less than minimum base fee, which means
		// this transaction will never be included into this particular chain.
		it.MetaTx.SubPool &^= EnoughFeeCapProtocol
		if it.MetaTx.Tx.feeCap >= protocolBaseFee {
			it.MetaTx.SubPool &= EnoughFeeCapProtocol
		}

		// 2. Absence of nonce gaps. Set to 1 for transactions whose nonce is N, state nonce for
		// the sender is M, and there are transactions for all nonces between M and N from the same
		// sender. Set to 0 is the transaction's nonce is divided from the state nonce by one or more nonce gaps.
		it.MetaTx.SubPool &^= NoNonceGaps
		if prevNonce == -1 || uint64(prevNonce)+1 == it.MetaTx.Tx.nonce {
			it.MetaTx.SubPool &= NoNonceGaps
		}
		prevNonce = int(it.Tx.nonce)

		// 3. Sufficient balance for gas. Set to 1 if the balance of sender's account in the
		// state is B, nonce of the sender in the state is M, nonce of the transaction is N, and the
		// sum of feeCap x gasLimit + transferred_value of all transactions from this sender with
		// nonces N+1 ... M is no more than B. Set to 0 otherwise. In other words, this bit is
		// set if there is currently a guarantee that the transaction and all its required prior
		// transactions will be able to pay for gas.
		it.MetaTx.SubPool &^= EnoughBalance
		if sender.balance.Gt(accumulatedSenderSpent) || sender.balance.Eq(accumulatedSenderSpent) {
			it.MetaTx.SubPool &= EnoughBalance
		}
		accumulatedSenderSpent.Add(accumulatedSenderSpent, balanceNeed) // already deleted all transactions with nonce <= sender.nonce

		// 4. Dynamic fee requirement. Set to 1 if feeCap of the transaction is no less than
		// baseFee of the currently pending block. Set to 0 otherwise.
		it.MetaTx.SubPool &^= EnoughFeeCapBlock
		if it.MetaTx.Tx.feeCap >= blockBaseFee {
			it.MetaTx.SubPool &= EnoughFeeCapBlock
		}

		// 5. Local transaction. Set to 1 if transaction is local.
		// can't change

		return true
	})
}

func PromoteStep(pending, baseFee, queued *SubPool) {
	//1. If top element in the worst green queue has SubPool != 0b1111 (binary), it needs to be removed from the green pool.
	//   If SubPool < 0b1000 (not satisfying minimum fee), discard.
	//   If SubPool == 0b1110, demote to the yellow pool, otherwise demote to the red pool.
	for worst := pending.Worst(); pending.Len() > 0; worst = pending.Worst() {
		if worst.SubPool >= 0b11110 {
			break
		}
		if worst.SubPool >= 0b11100 {
			baseFee.Add(pending.PopWorst(), BaseFeeSubPool)
			continue
		}
		if worst.SubPool >= 0b10000 {
			queued.Add(pending.PopWorst(), QueuedSubPool)
			continue
		}
		pending.PopWorst()
	}

	//2. If top element in the worst green queue has SubPool == 0b1111, but there is not enough room in the pool, discard.
	for worst := pending.Worst(); pending.Len() > PendingSubPoolLimit; worst = pending.Worst() {
		if worst.SubPool >= 0b11111 { // TODO: here must 'SubPool == 0b1111' or 'SubPool <= 0b1111' ?
			break
		}
		pending.PopWorst()
	}

	//3. If the top element in the best yellow queue has SubPool == 0b1111, promote to the green pool.
	for best := baseFee.Best(); baseFee.Len() > 0; best = baseFee.Best() {
		if best.SubPool < 0b11110 {
			break
		}
		pending.Add(baseFee.PopBest(), PendingSubPool)
	}

	//4. If the top element in the worst yellow queue has SubPool != 0x1110, it needs to be removed from the yellow pool.
	//   If SubPool < 0b1000 (not satisfying minimum fee), discard. Otherwise, demote to the red pool.
	for worst := baseFee.Worst(); baseFee.Len() > 0; worst = baseFee.Worst() {
		if worst.SubPool >= 0b11100 {
			break
		}
		if worst.SubPool >= 0b10000 {
			queued.Add(baseFee.PopWorst(), QueuedSubPool)
			continue
		}
		baseFee.PopWorst()
	}

	//5. If the top element in the worst yellow queue has SubPool == 0x1110, but there is not enough room in the pool, discard.
	for worst := baseFee.Worst(); baseFee.Len() > BaseFeeSubPoolLimit; worst = baseFee.Worst() {
		if worst.SubPool >= 0b11110 {
			break
		}
		baseFee.PopWorst()
	}

	//6. If the top element in the best red queue has SubPool == 0x1110, promote to the yellow pool. If SubPool == 0x1111, promote to the green pool.
	for best := queued.Best(); queued.Len() > 0; best = queued.Best() {
		if best.SubPool < 0b11100 {
			break
		}
		if best.SubPool < 0b11110 {
			baseFee.Add(queued.PopBest(), BaseFeeSubPool)
			continue
		}

		pending.Add(queued.PopBest(), PendingSubPool)
	}

	//7. If the top element in the worst red queue has SubPool < 0b1000 (not satisfying minimum fee), discard.
	for worst := queued.Worst(); queued.Len() > 0; worst = queued.Worst() {
		if worst.SubPool >= 0b10000 {
			break
		}

		queued.PopWorst()
	}

	//8. If the top element in the worst red queue has SubPool >= 0b100, but there is not enough room in the pool, discard.
	for _ = queued.Worst(); queued.Len() > QueuedSubPoolLimit; _ = queued.Worst() {
		queued.PopWorst()
	}
}

func CheckInvariants(pending, baseFee, queued *SubPool) {
	//1. If top element in the worst green queue has SubPool != 0b1111 (binary), it needs to be removed from the green pool.
	//   If SubPool < 0b1000 (not satisfying minimum fee), discard.
	//   If SubPool == 0b1110, demote to the yellow pool, otherwise demote to the red pool.
	for worst := pending.Worst(); pending.Len() > 0; worst = pending.Worst() {
		if worst.SubPool >= 0b11110 {
			break
		}
		if worst.SubPool >= 0b11100 {
			baseFee.Add(pending.PopWorst(), BaseFeeSubPool)
			continue
		}
		if worst.SubPool >= 0b11000 {
			queued.Add(pending.PopWorst(), QueuedSubPool)
			continue
		}
		pending.PopWorst()
	}

	//2. If top element in the worst green queue has SubPool == 0b1111, but there is not enough room in the pool, discard.
	for worst := pending.Worst(); pending.Len() > PendingSubPoolLimit; worst = pending.Worst() {
		if worst.SubPool >= 0b11110 { // TODO: here must 'SubPool == 0b1111' or 'SubPool <= 0b1111' ?
			break
		}
		pending.PopWorst()
	}

	//3. If the top element in the best yellow queue has SubPool == 0b1111, promote to the green pool.
	for best := baseFee.Best(); baseFee.Len() > 0; best = baseFee.Best() {
		if best.SubPool < 0b11110 {
			break
		}
		pending.Add(baseFee.PopWorst(), PendingSubPool)
	}

	//4. If the top element in the worst yellow queue has SubPool != 0x1110, it needs to be removed from the yellow pool.
	//   If SubPool < 0b1000 (not satisfying minimum fee), discard. Otherwise, demote to the red pool.
	for worst := baseFee.Worst(); baseFee.Len() > 0; worst = baseFee.Worst() {
		if worst.SubPool >= 0b11100 {
			break
		}
		if worst.SubPool >= 0b11000 {
			queued.Add(baseFee.PopWorst(), QueuedSubPool)
			continue
		}
		baseFee.PopWorst()
	}

	//5. If the top element in the worst yellow queue has SubPool == 0x1110, but there is not enough room in the pool, discard.
	for worst := baseFee.Worst(); baseFee.Len() > BaseFeeSubPoolLimit; worst = baseFee.Worst() {
		if worst.SubPool >= 0b11110 {
			break
		}
		baseFee.PopWorst()
	}

	//6. If the top element in the best red queue has SubPool == 0x1110, promote to the yellow pool. If SubPool == 0x1111, promote to the green pool.
	for best := queued.Best(); queued.Len() > 0; best = queued.Best() {
		if best.SubPool < 0b11100 {
			break
		}
		if best.SubPool < 0b11110 {
			baseFee.Add(queued.PopWorst(), BaseFeeSubPool)
			continue
		}

		pending.Add(queued.PopWorst(), PendingSubPool)
	}

	//7. If the top element in the worst red queue has SubPool < 0b1000 (not satisfying minimum fee), discard.
	for worst := queued.Worst(); queued.Len() > 0; worst = queued.Worst() {
		if worst.SubPool >= 0b10000 {
			break
		}

		queued.PopWorst()
	}

	//8. If the top element in the worst red queue has SubPool >= 0b100, but there is not enough room in the pool, discard.
	for worst := queued.Worst(); queued.Len() > QueuedSubPoolLimit; worst = queued.Worst() {
		if worst.SubPool >= 0b10000 {
			break
		}

		queued.PopWorst()
	}
}

// Below is a draft code, will convert it to Loop and LoopStep funcs later

type PoolImpl struct {
	recentlyConnectedPeers     *recentlyConnectedPeers
	lastTxPropagationTimestamp time.Time
	logger                     log.Logger
}

func NewPool() *PoolImpl {
	return &PoolImpl{
		recentlyConnectedPeers: &recentlyConnectedPeers{},
	}
}

// Loop - does:
// send pending txs to p2p:
//      - new txs
//      - all pooled txs to recently connected peers
//      - all local pooled txs to random peers periodically
// promote/demote transactions
// reorgs
func (p *PoolImpl) Loop(ctx context.Context, send *Send, timings Timings) {
	propagateAllNewTxsEvery := time.NewTicker(timings.propagateAllNewTxsEvery)
	defer propagateAllNewTxsEvery.Stop()

	syncToNewPeersEvery := time.NewTicker(timings.syncToNewPeersEvery)
	defer syncToNewPeersEvery.Stop()

	broadcastLocalTransactionsEvery := time.NewTicker(timings.broadcastLocalTransactionsEvery)
	defer broadcastLocalTransactionsEvery.Stop()

	localTxHashes := make([]byte, 0, 128)
	remoteTxHashes := make([]byte, 0, 128)

	for {
		select {
		case <-ctx.Done():
			return
		case <-propagateAllNewTxsEvery.C: // new txs
			last := p.lastTxPropagationTimestamp
			p.lastTxPropagationTimestamp = time.Now()

			// first broadcast all local txs to all peers, then non-local to random sqrt(peersAmount) peers
			localTxHashes = localTxHashes[:0]
			p.FillLocalHashesSince(last, localTxHashes)
			initialAmount := len(localTxHashes)
			sentToPeers := send.BroadcastLocalPooledTxs(localTxHashes)
			if initialAmount == 1 {
				p.logger.Info("local tx propagated", "to_peers_amount", sentToPeers, "tx_hash", localTxHashes)
			} else {
				p.logger.Info("local txs propagated", "to_peers_amount", sentToPeers, "txs_amount", initialAmount)
			}

			remoteTxHashes = remoteTxHashes[:0]
			p.FillRemoteHashesSince(last, remoteTxHashes)
			send.BroadcastRemotePooledTxs(remoteTxHashes)
		case <-syncToNewPeersEvery.C: // new peer
			newPeers := p.recentlyConnectedPeers.GetAndClean()
			if len(newPeers) == 0 {
				continue
			}
			p.FillRemoteHashes(remoteTxHashes[:0])
			send.PropagatePooledTxsToPeersList(newPeers, remoteTxHashes)
		case <-broadcastLocalTransactionsEvery.C: // periodically broadcast local txs to random peers
			p.FillLocalHashes(localTxHashes[:0])
			send.BroadcastLocalPooledTxs(localTxHashes)
		}
	}
}

func (p *PoolImpl) FillLocalHashesSince(since time.Time, to []byte)  {}
func (p *PoolImpl) FillRemoteHashesSince(since time.Time, to []byte) {}
func (p *PoolImpl) FillLocalHashes(to []byte)                        {}
func (p *PoolImpl) FillRemoteHashes(to []byte)                       {}

// recentlyConnectedPeers does buffer IDs of recently connected good peers
// then sync of pooled Transaction can happen to all of then at once
// DoS protection and performance saving
// it doesn't track if peer disconnected, it's fine
type recentlyConnectedPeers struct {
	lock  sync.RWMutex
	peers []PeerID
}

func (l *recentlyConnectedPeers) AddPeer(p PeerID) {
	l.lock.Lock()
	defer l.lock.Unlock()
	l.peers = append(l.peers, p)
}

func (l *recentlyConnectedPeers) GetAndClean() []PeerID {
	l.lock.Lock()
	defer l.lock.Unlock()
	peers := l.peers
	l.peers = nil
	return peers
}