Derek解读Bytom源码-P2P网络 地址簿

作者：Derek

简介

Github地址：https://github.com/Bytom/bytom

Gitee地址：https://gitee.com/BytomBlockchain/bytom

本章介绍bytom代码P2P网络中addrbook地址簿

作者使用MacOS操作系统，其他平台也大同小异

Golang Version: 1.8

addrbook介绍

addrbook用于存储P2P网络中保留最近的对端节点地址
在MacOS下，默认的地址簿路径存储在~/Library/Bytom/addrbook.json

地址簿格式

** ~/Library/Bytom/addrbook.json **

{
    "Key": "359be6d08bc0c6e21c84bbb2",
    "Addrs": [
        {
            "Addr": {
                "IP": "122.224.11.144",
                "Port": 46657
            },
            "Src": {
                "IP": "198.74.61.131",
                "Port": 46657
            },
            "Attempts": 0,
            "LastAttempt": "2018-05-04T12:58:23.894057702+08:00",
            "LastSuccess": "0001-01-01T00:00:00Z",
            "BucketType": 1,
            "Buckets": [
                181,
                10
            ]
        }
    ]
}

地址类型

在addrbook中存储的地址有两种：
** p2p/addrbook.go **

const (
	bucketTypeNew = 0x01  // 标识新地址，不可靠地址（未成功连接过）。只存储在一个bucket中
	bucketTypeOld = 0x02  // 标识旧地址，可靠地址（已成功连接过）。可以存储在多个bucket中，最多为maxNewBucketsPerAddress个
)

注意: 一个地址的类型变更不在此文章中做介绍，后期的文章会讨论该问题

地址簿相关结构体

地址簿

type AddrBook struct {
	cmn.BaseService

	mtx               sync.Mutex
	filePath          string  // 地址簿路径
	routabilityStrict bool  // 是否可路由，默认为true
	rand              *rand.Rand 
	key               string  // 地址簿标识，用于计算addrNew和addrOld的索引
	ourAddrs          map[string]*NetAddress  // 存储本地网络地址，用于添加p2p地址时做排除使用
	addrLookup        map[string]*knownAddress // 存储新、旧地址集，用于查询
	addrNew           []map[string]*knownAddress // 存储新地址
	addrOld           []map[string]*knownAddress // 存储旧地址
	wg                sync.WaitGroup
	nOld              int // 旧地址数量
	nNew              int // 新地址数量
}

已知地址

type knownAddress struct {
	Addr        *NetAddress // 已知peer的addr
	Src         *NetAddress // 已知peer的addr的来源addr
	Attempts    int32 // 连接peer的重试次数
	LastAttempt time.Time // 最近一次尝试连接的时间
	LastSuccess time.Time // 最近一次尝试成功连接的时间
	BucketType  byte // 地址的类型（表示可靠地址或不可靠地址）
	Buckets     []int // 当前addr所属的buckets
}

routabilityStrict参数表示地址簿是否存储的ip是否可路由。可路由是根据RFC划分，具体参考资料：RFC标准

初始化地址簿

// NewAddrBook creates a new address book.
// Use Start to begin processing asynchronous address updates.
func NewAddrBook(filePath string, routabilityStrict bool) *AddrBook {
	am := &AddrBook{
		rand:              rand.New(rand.NewSource(time.Now().UnixNano())),
		ourAddrs:          make(map[string]*NetAddress),
		addrLookup:        make(map[string]*knownAddress),
		filePath:          filePath,
		routabilityStrict: routabilityStrict,
	}
	am.init()
	am.BaseService = *cmn.NewBaseService(nil, "AddrBook", am)
	return am
}

// When modifying this, don't forget to update loadFromFile()
func (a *AddrBook) init() {
  // 地址簿唯一标识
	a.key = crypto.CRandHex(24) // 24/2 * 8 = 96 bits
	// New addr buckets， 默认为256个大小
	a.addrNew = make([]map[string]*knownAddress, newBucketCount)
	for i := range a.addrNew {
		a.addrNew[i] = make(map[string]*knownAddress)
	}
	// Old addr buckets，默认为64个大小
	a.addrOld = make([]map[string]*knownAddress, oldBucketCount)
	for i := range a.addrOld {
		a.addrOld[i] = make(map[string]*knownAddress)
	}
}

bytomd启动时加载本地地址簿

loadFromFile在bytomd启动时，首先会加载本地的地址簿

// OnStart implements Service.
func (a *AddrBook) OnStart() error {
	a.BaseService.OnStart()
	a.loadFromFile(a.filePath)
	a.wg.Add(1)
	go a.saveRoutine()
	return nil
}

// Returns false if file does not exist.
// cmn.Panics if file is corrupt.
func (a *AddrBook) loadFromFile(filePath string) bool {
	// If doesn't exist, do nothing.
	// 如果本地地址簿不存在则直接返回
	_, err := os.Stat(filePath)
	if os.IsNotExist(err) {
		return false
	}

  // 加载地址簿json内容
	// Load addrBookJSON{}
	r, err := os.Open(filePath)
	if err != nil {
		cmn.PanicCrisis(cmn.Fmt("Error opening file %s: %v", filePath, err))
	}
	defer r.Close()
	aJSON := &addrBookJSON{}
	dec := json.NewDecoder(r)
	err = dec.Decode(aJSON)
	if err != nil {
		cmn.PanicCrisis(cmn.Fmt("Error reading file %s: %v", filePath, err))
	}

  // 填充addrNew、addrOld等
	// Restore all the fields...
	// Restore the key
	a.key = aJSON.Key
	// Restore .addrNew & .addrOld
	for _, ka := range aJSON.Addrs {
		for _, bucketIndex := range ka.Buckets {
			bucket := a.getBucket(ka.BucketType, bucketIndex)
			bucket[ka.Addr.String()] = ka
		}
		a.addrLookup[ka.Addr.String()] = ka
		if ka.BucketType == bucketTypeNew {
			a.nNew++
		} else {
			a.nOld++
		}
	}
	return true
}

定时更新地址簿

bytomd会定时更新本地地址簿，默认2分钟一次

func (a *AddrBook) saveRoutine() {
	dumpAddressTicker := time.NewTicker(dumpAddressInterval)
out:
	for {
		select {
		case <-dumpAddressTicker.C:
			a.saveToFile(a.filePath)
		case <-a.Quit:
			break out
		}
	}
	dumpAddressTicker.Stop()
	a.saveToFile(a.filePath)
	a.wg.Done()
	log.Info("Address handler done")
}

func (a *AddrBook) saveToFile(filePath string) {
	log.WithField("size", a.Size()).Info("Saving AddrBook to file")

	a.mtx.Lock()
	defer a.mtx.Unlock()
	// Compile Addrs
	addrs := []*knownAddress{}
	for _, ka := range a.addrLookup {
		addrs = append(addrs, ka)
	}

	aJSON := &addrBookJSON{
		Key:   a.key,
		Addrs: addrs,
	}

	jsonBytes, err := json.MarshalIndent(aJSON, "", "	")
	if err != nil {
		log.WithField("err", err).Error("Failed to save AddrBook to file")
		return
	}
	err = cmn.WriteFileAtomic(filePath, jsonBytes, 0644)
	if err != nil {
		log.WithFields(log.Fields{
			"file": filePath,
			"err":  err,
		}).Error("Failed to save AddrBook to file")
	}
}

添加新地址

当peer之间交换addr时，节点会收到对端节点已知的地址信息，这些信息会被当前节点添加到地址簿中

func (a *AddrBook) AddAddress(addr *NetAddress, src *NetAddress) {
	a.mtx.Lock()
	defer a.mtx.Unlock()
	log.WithFields(log.Fields{
		"addr": addr,
		"src":  src,
	}).Debug("Add address to book")
	a.addAddress(addr, src)
}


func (a *AddrBook) addAddress(addr, src *NetAddress) {
	// 验证地址是否为可路由地址
	if a.routabilityStrict && !addr.Routable() {
		log.Error(cmn.Fmt("Cannot add non-routable address %v", addr))
		return
	}
	// 验证地址是否为本地节点地址
	if _, ok := a.ourAddrs[addr.String()]; ok {
		// Ignore our own listener address.
		return
	}

	// 验证地址是否存在地址集中
	// 如果存在：则判断该地址是否为old可靠地址、是否超过了最大buckets中。否则根据该地址已经被ka.Buckets引用的个数来随机决定是否添加到地址集中
	// 如果不存在：则添加到地址集中。并标识为bucketTypeNew地址类型
	ka := a.addrLookup[addr.String()]

	if ka != nil {
		// Already old.
		if ka.isOld() {
			return
		}
		// Already in max new buckets.
		if len(ka.Buckets) == maxNewBucketsPerAddress {
			return
		}
		// The more entries we have, the less likely we are to add more.
		factor := int32(2 * len(ka.Buckets))
		if a.rand.Int31n(factor) != 0 {
			return
		}
	} else {
		ka = newKnownAddress(addr, src)
	}

	// 找到该地址在地址集的索引位置并添加
	bucket := a.calcNewBucket(addr, src)
	a.addToNewBucket(ka, bucket)

	log.Info("Added new address ", "address:", addr, " total:", a.size())
}

选择最优节点

地址簿中存储众多地址，在p2p网络中需选择最优的地址去连接
PickAddress(newBias int)函数中newBias是由pex_reactor产生的地址评分。如何计算地址分数在其他章节中再讲
根据地址评分随机选择地址可增加区块链安全性

// Pick an address to connect to with new/old bias.
func (a *AddrBook) PickAddress(newBias int) *NetAddress {
	a.mtx.Lock()
	defer a.mtx.Unlock()

	if a.size() == 0 {
		return nil
	}
	// newBias地址分数限制在0-100分数之间
	if newBias > 100 {
		newBias = 100
	}
	if newBias < 0 {
		newBias = 0
	}

	// Bias between new and old addresses.
	oldCorrelation := math.Sqrt(float64(a.nOld)) * (100.0 - float64(newBias))
	newCorrelation := math.Sqrt(float64(a.nNew)) * float64(newBias)

  // 根据地址分数计算是否从addrOld或addrNew中随机选择一个地址
	if (newCorrelation+oldCorrelation)*a.rand.Float64() < oldCorrelation {
		// pick random Old bucket.
		var bucket map[string]*knownAddress = nil
		num := 0
		for len(bucket) == 0 && num < oldBucketCount {
			bucket = a.addrOld[a.rand.Intn(len(a.addrOld))]
			num++
		}
		if num == oldBucketCount {
			return nil
		}
		// pick a random ka from bucket.
		randIndex := a.rand.Intn(len(bucket))
		for _, ka := range bucket {
			if randIndex == 0 {
				return ka.Addr
			}
			randIndex--
		}
		cmn.PanicSanity("Should not happen")
	} else {
		// pick random New bucket.
		var bucket map[string]*knownAddress = nil
		num := 0
		for len(bucket) == 0 && num < newBucketCount {
			bucket = a.addrNew[a.rand.Intn(len(a.addrNew))]
			num++
		}
		if num == newBucketCount {
			return nil
		}
		// pick a random ka from bucket.
		randIndex := a.rand.Intn(len(bucket))
		for _, ka := range bucket {
			if randIndex == 0 {
				return ka.Addr
			}
			randIndex--
		}
		cmn.PanicSanity("Should not happen")
	}
	return nil
}

移除一个地址

当一个地址被标记为Bad时则从地址集中移除。目前bytomd的代码版本并未调用过

func (a *AddrBook) MarkBad(addr *NetAddress) {
	a.RemoveAddress(addr)
}

// RemoveAddress removes the address from the book.
func (a *AddrBook) RemoveAddress(addr *NetAddress) {
	a.mtx.Lock()
	defer a.mtx.Unlock()
	ka := a.addrLookup[addr.String()]
	if ka == nil {
		return
	}
	log.WithField("addr", addr).Info("Remove address from book")
	a.removeFromAllBuckets(ka)
}

func (a *AddrBook) removeFromAllBuckets(ka *knownAddress) {
	for _, bucketIdx := range ka.Buckets {
		bucket := a.getBucket(ka.BucketType, bucketIdx)
		delete(bucket, ka.Addr.String())
	}
	ka.Buckets = nil
	if ka.BucketType == bucketTypeNew {
		a.nNew--
	} else {
		a.nOld--
	}
	delete(a.addrLookup, ka.Addr.String())
}