摘要：作者簡介地址地址本章介紹代碼網絡中地址簿作者使用操作系統，其他平臺也大同小異介紹用于存儲網絡中保留最近的對端節點地址在下，默認的地址簿路徑存儲在地址簿格式地址類型在中存儲的地址有兩種標識新地址，不可靠地址未成功連接過。

作者：Derek

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

Gitee地址：https://gitee.com/BytomBlockc...

本章介紹bytom代碼P2P網絡中addrbook地址簿

作者使用MacOS操作系統，其他平臺也大同小異
Golang Version: 1.8

addrbook用于存儲P2P網絡中保留最近的對端節點地址
在MacOS下，默認的地址簿路徑存儲在~/Library/Bytom/addrbook.json

~/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
            ]
        }
    ]
}

在addrbook中存儲的地址有兩種：
p2p/addrbook.go

const (
    bucketTypeNew = 0x01  // 標識新地址，不可靠地址（未成功連接過）。只存儲在一個bucket中
    bucketTypeOld = 0x02  // 標識舊地址，可靠地址（已成功連接過）?？梢源鎯υ诙鄠€bucket中，最多為maxNewBucketsPerAddress個
)

注意: 一個地址的類型變更不在此文章中做介紹，后期的文章會討論該問題

地址簿

type AddrBook struct {
    cmn.BaseService

    mtx               sync.Mutex
    filePath          string  // 地址簿路徑
    routabilityStrict bool  // 是否可路由，默認為true
    rand              *rand.Rand 
    key               string  // 地址簿標識，用于計算addrNew和addrOld的索引
    ourAddrs          map[string]*NetAddress  // 存儲本地網絡地址，用于添加p2p地址時做排除使用
    addrLookup        map[string]*knownAddress // 存儲新、舊地址集，用于查詢
    addrNew           []map[string]*knownAddress // 存儲新地址
    addrOld           []map[string]*knownAddress // 存儲舊地址
    wg                sync.WaitGroup
    nOld              int // 舊地址數量
    nNew              int // 新地址數量
}

已知地址

type knownAddress struct {
    Addr        *NetAddress // 已知peer的addr
    Src         *NetAddress // 已知peer的addr的來源addr
    Attempts    int32 // 連接peer的重試次數
    LastAttempt time.Time // 最近一次嘗試連接的時間
    LastSuccess time.Time // 最近一次嘗試成功連接的時間
    BucketType  byte // 地址的類型（表示可靠地址或不可靠地址）
    Buckets     []int // 當前addr所屬的buckets
}

routabilityStrict參數表示地址簿是否存儲的ip是否可路由。可路由是根據RFC劃分，具體參考資料：RFC標準

// 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() {
  // 地址簿唯一標識
    a.key = crypto.CRandHex(24) // 24/2 * 8 = 96 bits
    // New addr buckets， 默認為256個大小
    a.addrNew = make([]map[string]*knownAddress, newBucketCount)
    for i := range a.addrNew {
        a.addrNew[i] = make(map[string]*knownAddress)
    }
    // Old addr buckets，默認為64個大小
    a.addrOld = make([]map[string]*knownAddress, oldBucketCount)
    for i := range a.addrOld {
        a.addrOld[i] = make(map[string]*knownAddress)
    }
}

loadFromFile在bytomd啟動時，首先會加載本地的地址簿

// 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則直接返回
    _, err := os.Stat(filePath)
    if os.IsNotExist(err) {
        return false
    }

  // 加載地址簿json內容
    // 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
}

bytomd會定時更新本地地址簿，默認2分鐘一次

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")
    }
}

當peer之間交換addr時，節點會收到對端節點已知的地址信息，這些信息會被當前節點添加到地址簿中

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) {
    // 驗證地址是否為可路由地址
    if a.routabilityStrict && !addr.Routable() {
        log.Error(cmn.Fmt("Cannot add non-routable address %v", addr))
        return
    }
    // 驗證地址是否為本地節點地址
    if _, ok := a.ourAddrs[addr.String()]; ok {
        // Ignore our own listener address.
        return
    }

    // 驗證地址是否存在地址集中
    // 如果存在：則判斷該地址是否為old可靠地址、是否超過了最大buckets中。否則根據該地址已經被ka.Buckets引用的個數來隨機決定是否添加到地址集中
    // 如果不存在：則添加到地址集中。并標識為bucketTypeNew地址類型
    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)
    }

    // 找到該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())
}

地址簿中存儲眾多地址，在p2p網絡中需選擇最優的地址去連接
PickAddress(newBias int)函數中newBias是由pex_reactor產生的地址評分。如何計算地址分數在其他章節中再講
根據地址評分隨機選擇地址可增加區塊鏈安全性

// 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地址分數限制在0-100分數之間
    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)

  // 根據地址分數計算是否從addrOld或addrNew中隨機選擇一個地址
    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
}

當一個地址被標記為Bad時則從地址集中移除。目前bytomd的代碼版本并未調用過

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())
}