兄弟连区块链入门教程eth源码分析p2p-udp.go源码分析(二)

兄弟连区块链培训 · · 192 次点击 · · 开始浏览    
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ping方法与pending的处理,之前谈到了pending是等待一个reply。 这里通过代码来分析是如何实现等待reply的。
pending方法把pending结构体发送给addpending. 然后等待消息的处理和接收。

// ping sends a ping message to the given node and waits for a reply.
func (t *udp) ping(toid NodeID, toaddr *net.UDPAddr) error {
    // TODO: maybe check for ReplyTo field in callback to measure RTT
    errc := t.pending(toid, pongPacket, func(interface{}) bool { return true })
    t.send(toaddr, pingPacket, &ping{
        Version: Version,
        From: t.ourEndpoint,
        To: makeEndpoint(toaddr, 0), // TODO: maybe use known TCP port from DB
        Expiration: uint64(time.Now().Add(expiration).Unix()),
    })
    return <-errc
}
// pending adds a reply callback to the pending reply queue.
// see the documentation of type pending for a detailed explanation.
func (t *udp) pending(id NodeID, ptype byte, callback func(interface{}) bool) <-chan error {
    ch := make(chan error, 1)
    p := &pending{from: id, ptype: ptype, callback: callback, errc: ch}
    select {
    case t.addpending <- p:
        // loop will handle it
    case <-t.closing:
        ch <- errClosed
    }
    return ch
}

addpending消息的处理。 之前创建udp的时候调用了newUDP方法。里面启动了两个goroutine。 其中的loop()就是用来处理pending消息的。

// loop runs in its own goroutine. it keeps track of
// the refresh timer and the pending reply queue.
func (t *udp) loop() {
    var (
        plist = list.New()
        timeout = time.NewTimer(0)
        nextTimeout *pending // head of plist when timeout was last reset
        contTimeouts = 0 // number of continuous timeouts to do NTP checks
        ntpWarnTime = time.Unix(0, 0)
    )
    <-timeout.C // ignore first timeout
    defer timeout.Stop()

    resetTimeout := func() {
        //这个方法的主要功能是查看队列里面是否有需要超时的pending消息。 如果有。那么
        //根据最先超时的时间设置超时醒来。
        if plist.Front() == nil || nextTimeout == plist.Front().Value {
            return
        }
        // Start the timer so it fires when the next pending reply has expired.
        now := time.Now()
        for el := plist.Front(); el != nil; el = el.Next() {
            nextTimeout = el.Value.(*pending)
            if dist := nextTimeout.deadline.Sub(now); dist < 2*respTimeout {
                timeout.Reset(dist)
                return
            }
            // Remove pending replies whose deadline is too far in the
            // future. These can occur if the system clock jumped
            // backwards after the deadline was assigned.
            //如果有消息的deadline在很远的未来,那么直接设置超时,然后移除。
            //这种情况在修改系统时间的时候有可能发生,如果不处理可能导致堵塞太长时间。
            nextTimeout.errc <- errClockWarp
            plist.Remove(el)
        }
        nextTimeout = nil
        timeout.Stop()
    }

    for {
        resetTimeout() //首先处理超时。

        select {
        case <-t.closing: //收到关闭信息。 超时所有的堵塞的队列
            for el := plist.Front(); el != nil; el = el.Next() {
                el.Value.(*pending).errc <- errClosed
            }
            return

        case p := <-t.addpending: //增加一个pending 设置deadline
            p.deadline = time.Now().Add(respTimeout)
            plist.PushBack(p)

        case r := <-t.gotreply: //收到一个reply 寻找匹配的pending
            var matched bool
            for el := plist.Front(); el != nil; el = el.Next() {
                p := el.Value.(*pending)
                if p.from == r.from && p.ptype == r.ptype { //如果来自同一个人。 而且类型相同
                    matched = true
                    // Remove the matcher if its callback indicates
                    // that all replies have been received. This is
                    // required for packet types that expect multiple
                    // reply packets.
                    if p.callback(r.data) { //如果callback返回值是true 。说明pending已经完成。 给p.errc写入nil。 pending完成。
                        p.errc <- nil
                        plist.Remove(el)
                    }
                    // Reset the continuous timeout counter (time drift detection)
                    contTimeouts = 0
                }
            }
            r.matched <- matched //写入reply的matched

        case now := <-timeout.C: //处理超时信息
            nextTimeout = nil

            // Notify and remove callbacks whose deadline is in the past.
            for el := plist.Front(); el != nil; el = el.Next() {
                p := el.Value.(*pending)
                if now.After(p.deadline) || now.Equal(p.deadline) { //如果超时写入超时信息并移除
                    p.errc <- errTimeout
                    plist.Remove(el)
                    contTimeouts++
                }
            }
            // If we've accumulated too many timeouts, do an NTP time sync check
            if contTimeouts > ntpFailureThreshold {
                //如果连续超时很多次。 那么查看是否是时间不同步。 和NTP服务器进行同步。
                if time.Since(ntpWarnTime) >= ntpWarningCooldown {
                    ntpWarnTime = time.Now()
                    go checkClockDrift()
                }
                contTimeouts = 0
            }
        }
    }
}

上面看到了pending的处理。 不过loop()方法种还有一个gotreply的处理。 这个实在readLoop()这个goroutine中产生的。

// readLoop runs in its own goroutine. it handles incoming UDP packets.
func (t *udp) readLoop() {
    defer t.conn.Close()
    // Discovery packets are defined to be no larger than 1280 bytes.
    // Packets larger than this size will be cut at the end and treated
    // as invalid because their hash won't match.
    buf := make([]byte, 1280)
    for {
        nbytes, from, err := t.conn.ReadFromUDP(buf)
        if netutil.IsTemporaryError(err) {
            // Ignore temporary read errors.
            log.Debug("Temporary UDP read error", "err", err)
            continue
        } else if err != nil {
            // Shut down the loop for permament errors.
            log.Debug("UDP read error", "err", err)
            return
        }
        t.handlePacket(from, buf[:nbytes])
    }
}

func (t *udp) handlePacket(from *net.UDPAddr, buf []byte) error {
    packet, fromID, hash, err := decodePacket(buf)
    if err != nil {
        log.Debug("Bad discv4 packet", "addr", from, "err", err)
        return err
    }
    err = packet.handle(t, from, fromID, hash)
    log.Trace("<< "+packet.name(), "addr", from, "err", err)
    return err
}

func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
    if expired(req.Expiration) {
        return errExpired
    }
    t.send(from, pongPacket, &pong{
        To: makeEndpoint(from, req.From.TCP),
        ReplyTok: mac,
        Expiration: uint64(time.Now().Add(expiration).Unix()),
    })
    if !t.handleReply(fromID, pingPacket, req) {
        // Note: we're ignoring the provided IP address right now
        go t.bond(true, fromID, from, req.From.TCP)
    }
    return nil
}

func (t *udp) handleReply(from NodeID, ptype byte, req packet) bool {
    matched := make(chan bool, 1)
    select {
    case t.gotreply <- reply{from, ptype, req, matched}:
        // loop will handle it
        return <-matched
    case <-t.closing:
        return false
    }
}

上面介绍了udp的大致处理的流程。 下面介绍下udp的主要处理的业务。 udp主要发送两种请求,对应的也会接收别人发送的这两种请求, 对应这两种请求又会产生两种回应。

ping请求,可以看到ping请求希望得到一个pong回答。 然后返回。

// ping sends a ping message to the given node and waits for a reply.
func (t *udp) ping(toid NodeID, toaddr *net.UDPAddr) error {
    // TODO: maybe check for ReplyTo field in callback to measure RTT
    errc := t.pending(toid, pongPacket, func(interface{}) bool { return true })
    t.send(toaddr, pingPacket, &ping{
        Version: Version,
        From: t.ourEndpoint,
        To: makeEndpoint(toaddr, 0), // TODO: maybe use known TCP port from DB
        Expiration: uint64(time.Now().Add(expiration).Unix()),
    })
    return <-errc
}

pong回答,如果pong回答没有匹配到一个对应的ping请求。那么返回errUnsolicitedReply异常。

func (req *pong) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
    if expired(req.Expiration) {
        return errExpired
    }
    if !t.handleReply(fromID, pongPacket, req) {
        return errUnsolicitedReply
    }
    return nil
}

findnode请求, 发送findnode请求,然后等待node回应 k个邻居。

// findnode sends a findnode request to the given node and waits until
// the node has sent up to k neighbors.
func (t *udp) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node, error) {
    nodes := make([]*Node, 0, bucketSize)
    nreceived := 0
    errc := t.pending(toid, neighborsPacket, func(r interface{}) bool {
        reply := r.(*neighbors)
        for _, rn := range reply.Nodes {
            nreceived++
            n, err := t.nodeFromRPC(toaddr, rn)
            if err != nil {
                log.Trace("Invalid neighbor node received", "ip", rn.IP, "addr", toaddr, "err", err)
                continue
            }
            nodes = append(nodes, n)
        }
        return nreceived >= bucketSize
    })
    t.send(toaddr, findnodePacket, &findnode{
        Target: target,
        Expiration: uint64(time.Now().Add(expiration).Unix()),
    })
    err := <-errc
    return nodes, err
}

neighbors回应, 很简单。 把回应发送给gotreply队列。 如果没有找到匹配的findnode请求。返回errUnsolicitedReply错误

func (req *neighbors) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
    if expired(req.Expiration) {
        return errExpired
    }
    if !t.handleReply(fromID, neighborsPacket, req) {
        return errUnsolicitedReply
    }
    return nil
}


收到别的节点发送的ping请求,发送pong回答。 如果没有匹配上一个pending(说明不是自己方请求的结果)。 就调用bond方法把这个节点加入自己的bucket缓存。(这部分原理在table.go里面会详细介绍)

func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
    if expired(req.Expiration) {
        return errExpired
    }
    t.send(from, pongPacket, &pong{
        To: makeEndpoint(from, req.From.TCP),
        ReplyTok: mac,
        Expiration: uint64(time.Now().Add(expiration).Unix()),
    })
    if !t.handleReply(fromID, pingPacket, req) {
        // Note: we're ignoring the provided IP address right now
        go t.bond(true, fromID, from, req.From.TCP)
    }
    return nil
}

收到别人发送的findnode请求。这个请求希望把和target距离相近的k个节点发送回去。 算法的详细请参考references目录下面的pdf文档。


func (req *findnode) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
    if expired(req.Expiration) {
        return errExpired
    }
    if t.db.node(fromID) == nil {
        // No bond exists, we don't process the packet. This prevents
        // an attack vector where the discovery protocol could be used
        // to amplify traffic in a DDOS attack. A malicious actor
        // would send a findnode request with the IP address and UDP
        // port of the target as the source address. The recipient of
        // the findnode packet would then send a neighbors packet
        // (which is a much bigger packet than findnode) to the victim.
        return errUnknownNode
    }
    target := crypto.Keccak256Hash(req.Target[:])
    t.mutex.Lock()
    //获取bucketSize个和target距离相近的节点。 这个方法在table.go内部实现。后续会详细介绍
    closest := t.closest(target, bucketSize).entries
    t.mutex.Unlock()

    p := neighbors{Expiration: uint64(time.Now().Add(expiration).Unix())}
    // Send neighbors in chunks with at most maxNeighbors per packet
    // to stay below the 1280 byte limit.
    for i, n := range closest {
        if netutil.CheckRelayIP(from.IP, n.IP) != nil {
            continue
        }
        p.Nodes = append(p.Nodes, nodeToRPC(n))
        if len(p.Nodes) == maxNeighbors || i == len(closest)-1 {
            t.send(from, neighborsPacket, &p)
            p.Nodes = p.Nodes[:0]
        }
    }
    return nil
}

udp信息加密和安全问题

discover协议因为没有承载什么敏感数据,所以数据是以明文传输,但是为了确保数据的完整性和不被篡改,所以在数据包的包头加上了数字签名。


func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) ([]byte, error) {
    b := new(bytes.Buffer)
    b.Write(headSpace)
    b.WriteByte(ptype)
    if err := rlp.Encode(b, req); err != nil {
        log.Error("Can't encode discv4 packet", "err", err)
        return nil, err
    }
    packet := b.Bytes()
    sig, err := crypto.Sign(crypto.Keccak256(packet[headSize:]), priv)
    if err != nil {
        log.Error("Can't sign discv4 packet", "err", err)
        return nil, err
    }
    copy(packet[macSize:], sig)
    // add the hash to the front. Note: this doesn't protect the
    // packet in any way. Our public key will be part of this hash in
    // The future.
    copy(packet, crypto.Keccak256(packet[macSize:]))
    return packet, nil
}

func decodePacket(buf []byte) (packet, NodeID, []byte, error) {
    if len(buf) < headSize+1 {
        return nil, NodeID{}, nil, errPacketTooSmall
    }
    hash, sig, sigdata := buf[:macSize], buf[macSize:headSize], buf[headSize:]
    shouldhash := crypto.Keccak256(buf[macSize:])
    if !bytes.Equal(hash, shouldhash) {
        return nil, NodeID{}, nil, errBadHash
    }
    fromID, err := recoverNodeID(crypto.Keccak256(buf[headSize:]), sig)
    if err != nil {
        return nil, NodeID{}, hash, err
    }
    var req packet
    switch ptype := sigdata[0]; ptype {
    case pingPacket:
        req = new(ping)
    case pongPacket:
        req = new(pong)
    case findnodePacket:
        req = new(findnode)
    case neighborsPacket:
        req = new(neighbors)
    default:
        return nil, fromID, hash, fmt.Errorf("unknown type: %d", ptype)
    }
    s := rlp.NewStream(bytes.NewReader(sigdata[1:]), 0)
    err = s.Decode(req)
    return req, fromID, hash, err
}


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本文来自:Segmentfault

感谢作者:兄弟连区块链培训

查看原文:兄弟连区块链入门教程eth源码分析p2p-udp.go源码分析(二)

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