以太坊原始碼分析(45）p2p-dial.go原始碼分析

尹成發表於2018-05-14
原始碼Go
dial.go在p2p裡面主要負責建立連結的部分工作。 比如發現建立連結的節點。 與節點建立連結。 通過discover來查詢指定節點的地址。等功能。


dial.go裡面利用一個dailstate的資料結構來儲存中間狀態,是dial功能裡面的核心資料結構。

    // dialstate schedules dials and discovery lookups.
    // it get's a chance to compute new tasks on every iteration
    // of the main loop in Server.run.
    type dialstate struct {
        maxDynDials int                     //最大的動態節點連結數量
        ntab discoverTable           //discoverTable 用來做節點查詢的
        netrestrict *netutil.Netlist
    
        lookupRunning bool
        dialing map[discover.NodeID]connFlag      //正在連結的節點
        lookupBuf []*discover.Node // current discovery lookup results //當前的discovery查詢結果
        randomNodes []*discover.Node // filled from Table //從discoverTable隨機查詢的節點
        static map[discover.NodeID]*dialTask //靜態的節點。
        hist *dialHistory
    
        start time.Time // time when the dialer was first used
        bootnodes []*discover.Node // default dials when there are no peers //這個是內建的節點。 如果沒有找到其他節點。那麼使用連結這些節點。
    }

dailstate的建立過程。

    func newDialState(static []*discover.Node, bootnodes []*discover.Node, ntab discoverTable, maxdyn int, netrestrict *netutil.Netlist) *dialstate {
        s := &dialstate{
            maxDynDials: maxdyn,
            ntab: ntab,
            netrestrict: netrestrict,
            static: make(map[discover.NodeID]*dialTask),
            dialing: make(map[discover.NodeID]connFlag),
            bootnodes: make([]*discover.Node, len(bootnodes)),
            randomNodes: make([]*discover.Node, maxdyn/2),
            hist: new(dialHistory),
        }
        copy(s.bootnodes, bootnodes)
        for _, n := range static {
            s.addStatic(n)
        }
        return s
    }

dail最重要的方法是newTasks方法。這個方法用來生成task。 task是一個介面。有一個Do的方法。
    
    type task interface {
        Do(*Server)
    }

    func (s *dialstate) newTasks(nRunning int, peers map[discover.NodeID]*Peer, now time.Time) []task {
        if s.start == (time.Time{}) {
            s.start = now
        }
    
        var newtasks []task
        //addDial是一個內部方法， 首先通過checkDial檢查節點。然後設定狀態，最後把節點增加到newtasks佇列裡面。
        addDial := func(flag connFlag, n *discover.Node) bool {
            if err := s.checkDial(n, peers); err != nil {
                log.Trace("Skipping dial candidate", "id", n.ID, "addr", &net.TCPAddr{IP: n.IP, Port: int(n.TCP)}, "err", err)
                return false
            }
            s.dialing[n.ID] = flag
            newtasks = append(newtasks, &dialTask{flags: flag, dest: n})
            return true
        }
    
        // Compute number of dynamic dials necessary at this point.
        needDynDials := s.maxDynDials
        //首先判斷已經建立的連線的型別。如果是動態型別。那麼需要建立動態連結數量減少。
        for _, p := range peers {
            if p.rw.is(dynDialedConn) {
                needDynDials--
            }
        }
        //然後再判斷正在建立的連結。如果是動態型別。那麼需要建立動態連結數量減少。
        for _, flag := range s.dialing {
            if flag&dynDialedConn != 0 {
                needDynDials--
            }
        }
    
        // Expire the dial history on every invocation.
        s.hist.expire(now)
    
        // Create dials for static nodes if they are not connected.
        //檢視所有的靜態型別。如果可以那麼也建立連結。
        for id, t := range s.static {
            err := s.checkDial(t.dest, peers)
            switch err {
            case errNotWhitelisted, errSelf:
                log.Warn("Removing static dial candidate", "id", t.dest.ID, "addr", &net.TCPAddr{IP: t.dest.IP, Port: int(t.dest.TCP)}, "err", err)
                delete(s.static, t.dest.ID)
            case nil:
                s.dialing[id] = t.flags
                newtasks = append(newtasks, t)
            }
        }
        // If we don't have any peers whatsoever, try to dial a random bootnode. This
        // scenario is useful for the testnet (and private networks) where the discovery
        // table might be full of mostly bad peers, making it hard to find good ones.
        //如果當前還沒有任何連結。 而且20秒(fallbackInterval)內沒有建立任何連結。 那麼就使用bootnode建立連結。
        if len(peers) == 0 && len(s.bootnodes) > 0 && needDynDials > 0 && now.Sub(s.start) > fallbackInterval {
            bootnode := s.bootnodes[0]
            s.bootnodes = append(s.bootnodes[:0], s.bootnodes[1:]...)
            s.bootnodes = append(s.bootnodes, bootnode)
    
            if addDial(dynDialedConn, bootnode) {
                needDynDials--
            }
        }
        // Use random nodes from the table for half of the necessary
        // dynamic dials.
        //否則使用1/2的隨機節點建立連結。
        randomCandidates := needDynDials / 2
        if randomCandidates > 0 {
            n := s.ntab.ReadRandomNodes(s.randomNodes)
            for i := 0; i < randomCandidates && i < n; i++ {
                if addDial(dynDialedConn, s.randomNodes[i]) {
                    needDynDials--
                }
            }
        }
        // Create dynamic dials from random lookup results, removing tried
        // items from the result buffer.
        i := 0
        for ; i < len(s.lookupBuf) && needDynDials > 0; i++ {
            if addDial(dynDialedConn, s.lookupBuf[i]) {
                needDynDials--
            }
        }
        s.lookupBuf = s.lookupBuf[:copy(s.lookupBuf, s.lookupBuf[i:])]
        // Launch a discovery lookup if more candidates are needed.
        // 如果就算這樣也不能建立足夠動態連結。 那麼建立一個discoverTask用來再網路上查詢其他的節點。放入lookupBuf
        if len(s.lookupBuf) < needDynDials && !s.lookupRunning {
            s.lookupRunning = true
            newtasks = append(newtasks, &discoverTask{})
        }
    
        // Launch a timer to wait for the next node to expire if all
        // candidates have been tried and no task is currently active.
        // This should prevent cases where the dialer logic is not ticked
        // because there are no pending events.
        // 如果當前沒有任何任務需要做，那麼建立一個睡眠的任務返回。
        if nRunning == 0 && len(newtasks) == 0 && s.hist.Len() > 0 {
            t := &waitExpireTask{s.hist.min().exp.Sub(now)}
            newtasks = append(newtasks, t)
        }
        return newtasks
    }


checkDial方法， 用來檢查任務是否需要建立連結。

    func (s *dialstate) checkDial(n *discover.Node, peers map[discover.NodeID]*Peer) error {
        _, dialing := s.dialing[n.ID]
        switch {
        case dialing:                   //正在建立
            return errAlreadyDialing
        case peers[n.ID] != nil:        //已經連結了
            return errAlreadyConnected
        case s.ntab != nil && n.ID == s.ntab.Self().ID: //建立的物件不是自己
            return errSelf
        case s.netrestrict != nil && !s.netrestrict.Contains(n.IP): //網路限制。 對方的IP地址不在白名單裡面。
            return errNotWhitelisted
        case s.hist.contains(n.ID): // 這個ID曾經連結過。
            return errRecentlyDialed
        }
        return nil
    }

taskDone方法。 這個方法再task完成之後會被呼叫。 檢視task的型別。如果是連結任務，那麼增加到hist裡面。 並從正在連結的佇列刪除。 如果是查詢任務。 把查詢的記過放在lookupBuf裡面。

    func (s *dialstate) taskDone(t task, now time.Time) {
        switch t := t.(type) {
        case *dialTask:
            s.hist.add(t.dest.ID, now.Add(dialHistoryExpiration))
            delete(s.dialing, t.dest.ID)
        case *discoverTask:
            s.lookupRunning = false
            s.lookupBuf = append(s.lookupBuf, t.results...)
        }
    }



dialTask.Do方法，不同的task有不同的Do方法。 dailTask主要負責建立連結。 如果t.dest是沒有ip地址的。 那麼嘗試通過resolve查詢ip地址。 然後呼叫dial方法建立連結。 對於靜態的節點。如果第一次失敗，那麼會嘗試再次resolve靜態節點。然後再嘗試dial（因為靜態節點的ip是配置的。 如果靜態節點的ip地址變動。那麼我們嘗試resolve靜態節點的新地址，然後呼叫連結。）

    func (t *dialTask) Do(srv *Server) {
        if t.dest.Incomplete() {
            if !t.resolve(srv) {
                return
            }
        }
        success := t.dial(srv, t.dest)
        // Try resolving the ID of static nodes if dialing failed.
        if !success && t.flags&staticDialedConn != 0 {
            if t.resolve(srv) {
                t.dial(srv, t.dest)
            }
        }
    }

resolve方法。這個方法主要呼叫了discover網路的Resolve方法。如果失敗，那麼超時再試

    // resolve attempts to find the current endpoint for the destination
    // using discovery.
    //
    // Resolve operations are throttled with backoff to avoid flooding the
    // discovery network with useless queries for nodes that don't exist.
    // The backoff delay resets when the node is found.
    func (t *dialTask) resolve(srv *Server) bool {
        if srv.ntab == nil {
            log.Debug("Can't resolve node", "id", t.dest.ID, "err", "discovery is disabled")
            return false
        }
        if t.resolveDelay == 0 {
            t.resolveDelay = initialResolveDelay
        }
        if time.Since(t.lastResolved) < t.resolveDelay {
            return false
        }
        resolved := srv.ntab.Resolve(t.dest.ID)
        t.lastResolved = time.Now()
        if resolved == nil {
            t.resolveDelay *= 2
            if t.resolveDelay > maxResolveDelay {
                t.resolveDelay = maxResolveDelay
            }
            log.Debug("Resolving node failed", "id", t.dest.ID, "newdelay", t.resolveDelay)
            return false
        }
        // The node was found.
        t.resolveDelay = initialResolveDelay
        t.dest = resolved
        log.Debug("Resolved node", "id", t.dest.ID, "addr", &net.TCPAddr{IP: t.dest.IP, Port: int(t.dest.TCP)})
        return true
    }
    

dial方法,這個方法進行了實際的網路連線操作。 主要通過srv.SetupConn方法來完成， 後續再分析Server.go的時候再分析這個方法。

    // dial performs the actual connection attempt.
    func (t *dialTask) dial(srv *Server, dest *discover.Node) bool {
        fd, err := srv.Dialer.Dial(dest)
        if err != nil {
            log.Trace("Dial error", "task", t, "err", err)
            return false
        }
        mfd := newMeteredConn(fd, false)
        srv.SetupConn(mfd, t.flags, dest)
        return true
    }

discoverTask和waitExpireTask的Do方法，

    func (t *discoverTask) Do(srv *Server) {
        // newTasks generates a lookup task whenever dynamic dials are
        // necessary. Lookups need to take some time, otherwise the
        // event loop spins too fast.
        next := srv.lastLookup.Add(lookupInterval)
        if now := time.Now(); now.Before(next) {
            time.Sleep(next.Sub(now))
        }
        srv.lastLookup = time.Now()
        var target discover.NodeID
        rand.Read(target[:])
        t.results = srv.ntab.Lookup(target)
    }

    
    func (t waitExpireTask) Do(*Server) {
        time.Sleep(t.Duration)

    }





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