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, "", "\t")
    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())
}