filecoin技术架构分析六:filecoin源码协议层分析之hello握手协议

我是先河系统CTO杨尉，欢迎大加关注的的Github: waynewyang，本文是filecoin技术架构分析系列文章第六章filecoin源码协议层分析之hello握手协议.

目的

• 处理节点上线后的区块同步握手。

源码信息

• version
  • master分支 619b0eb1（2019年３月２日）
• package
  • hello
• location
  • protocol/hello
  • node/node.go

源码分析

数据结构

• 定义协议名称

// Protocol is the libp2p protocol identifier for the hello protocol.
const protocol = "/fil/hello/1.0.0"

• 定义hello协议消息体结构
  • TipSet切片
  • TipSet高度
  • 创世区块cid

// Message is the data structure of a single message in the hello protocol.
type Message struct {
    HeaviestTipSetCids   []cid.Cid
    HeaviestTipSetHeight uint64
    GenesisHash          cid.Cid
}

• 同步回调函数类型定义

type syncCallback func(from peer.ID, cids []cid.Cid, height uint64)

• 获取Tipset函数类型定义

type getTipSetFunc func() types.TipSet

• Handler结构体,当连接到其他节点的时候，其一,会发送包含本节点信息的hello 消息给对端节点; 其二, 对端也会回复一个包含对端节点信息的消息体过来。
  • host 对应libp2p上的主机
  • 创世区块cid
  • 区块同步回调函数
  • 获取TipSet的函数

// Handler implements the 'Hello' protocol handler. Upon connecting to a new
// node, we send them a message containing some information about the state of
// our chain, and receive the same information from them. This is used to
// initiate a chainsync and detect connections to forks.
type Handler struct {
    host host.Host

    genesis cid.Cid

    // chainSyncCB is called when new peers tell us about their chain
    chainSyncCB syncCallback

    // getHeaviestTipSet is used to retrieve the current heaviest tipset
    // for filling out our hello messages.
    getHeaviestTipSet getTipSetFunc
}

• 错误的创世区块

// ErrBadGenesis is the error returned when a missmatch in genesis blocks happens.
var ErrBadGenesis = fmt.Errorf("bad genesis block")

• 以上基本是作为hello客户端的一些定义，以下作为hello服务端的一些定义

// New peer connection notifications
type helloNotify Handler

//　连接超时时间
const helloTimeout = time.Second * 10

方法

Handler 方法

• 流函数处理，接收远端节点的hello消息

func (h *Handler) handleNewStream(s net.Stream) {
    defer s.Close() // nolint: errcheck

    //获取远端节点实例
    from := s.Conn().RemotePeer()

    var hello Message
    // 读取流信息到hello结构体中
    if err := cbu.NewMsgReader(s).ReadMsg(&hello); err != nil {
        log.Warningf("bad hello message from peer %s: %s", from, err)
        return
    }

    // 调用processHelloMessage方法对接收到的消息进行处理
    switch err := h.processHelloMessage(from, &hello); err {
    // 如果创世区块不一样，关闭流连接退出，不予处理
    case ErrBadGenesis:
        log.Warningf("genesis cid: %s does not match: %s, disconnecting from peer: %s", &hello.GenesisHash, h.genesis, from)
        s.Conn().Close() // nolint: errcheck
        return
    case nil: // ok, noop
    default:
        log.Error(err)
    }
}

• 处理hello消息

func (h *Handler) processHelloMessage(from peer.ID, msg *Message) error {
    // 如果创世区块不一样，报错
    if !msg.GenesisHash.Equals(h.genesis) {
        return ErrBadGenesis
    }

    // 调用区块同步方法
    // 此回调函数实在node包实例化hello协议的时候中定义的
    h.chainSyncCB(from, msg.HeaviestTipSetCids, msg.HeaviestTipSetHeight)
    return nil
}

• 响应远端节点的连接，回复hello消息体

func (h *Handler) getOurHelloMessage() *Message {
    heaviest := h.getHeaviestTipSet()
    height, err := heaviest.Height()
    if err != nil {
        panic("somehow heaviest tipset is empty")
    }

    return &Message{
        GenesisHash:          h.genesis,
        HeaviestTipSetCids:   heaviest.ToSortedCidSet().ToSlice(),
        HeaviestTipSetHeight: height,
    }
}

func (h *Handler) sayHello(ctx context.Context, p peer.ID) error {
    s, err := h.host.NewStream(ctx, p, protocol)
    if err != nil {
        return err
    }
    defer s.Close() // nolint: errcheck

    //获取本节点的hello消息体
    msg := h.getOurHelloMessage()

    //向远端节点发送消息体
    return cbu.NewMsgWriter(s).WriteMsg(&msg)
}

helloNotify方法

• hello方法，返回一个handler实例

func (hn *helloNotify) hello() *Handler {
    return (*Handler)(hn)
}

• helloNotify实现了libp2p-net/interface.go中的Notifiee接口

func (hn *helloNotify) Connected(n net.Network, c net.Conn) {
    go func() {
        ctx, cancel := context.WithTimeout(context.Background(), helloTimeout)
        defer cancel()
        p := c.RemotePeer()
        // 有其他节点连接的时候调用sayHello,发送hello消息体
        if err := hn.hello().sayHello(ctx, p); err != nil {
            log.Warningf("failed to send hello handshake to peer %s: %s", p, err)
        }
    }()
}

func (hn *helloNotify) Listen(n net.Network, a ma.Multiaddr)      {}
func (hn *helloNotify) ListenClose(n net.Network, a ma.Multiaddr) {}
func (hn *helloNotify) Disconnected(n net.Network, c net.Conn)    {}
func (hn *helloNotify) OpenedStream(n net.Network, s net.Stream)  {}
func (hn *helloNotify) ClosedStream(n net.Network, s net.Stream)  {}

函数

• 创建hello实例

// New creates a new instance of the hello protocol and registers it to
// the given host, with the provided callbacks.
func New(h host.Host, gen cid.Cid, syncCallback syncCallback, getHeaviestTipSet getTipSetFunc) *Handler {
    hello := &Handler{
        host:              h,
        genesis:           gen,
        chainSyncCB:       syncCallback,
        getHeaviestTipSet: getHeaviestTipSet,
    }

    //设置流处理回调函数
    h.SetStreamHandler(protocol, hello.handleNewStream)

    //注册网络状态改变通知回调函数
    // register for connection notifications
    h.Network().Notify((*helloNotify)(hello))

    return hello
}

//上文中的helloNotify 实现了libp2p-net/interface.go中的Notifiee接口
// Notifiee is an interface for an object wishing to receive
// notifications from a Network.
type Notifiee interface {
    Listen(Network, ma.Multiaddr)      // called when network starts listening on an addr
    ListenClose(Network, ma.Multiaddr) // called when network stops listening on an addr
    Connected(Network, Conn)           // called when a connection opened
    Disconnected(Network, Conn)        // called when a connection closed
    OpenedStream(Network, Stream)      // called when a stream opened
    ClosedStream(Network, Stream)      // called when a stream closed

    // TODO
    // PeerConnected(Network, peer.ID)    // called when a peer connected
    // PeerDisconnected(Network, peer.ID) // called when a peer disconnected
}

实例化及业务逻辑

• location: node/node.go

• Node节点中定义了hello服务

type Node struct {
    ......

    HelloSvc     *hello.Handler
    ......
}

• 启动hello服务

// Start boots up the node.
func (node *Node) Start(ctx context.Context) error {
    ......

    // Start up 'hello' handshake service
    // 定义区块同步的回调函数
    syncCallBack := func(pid libp2ppeer.ID, cids []cid.Cid, height uint64) {
        // TODO it is possible the syncer interface should be modified to
        // make use of the additional context not used here (from addr + height).
        // To keep things simple for now this info is not used.
        // 触发调用会启动同步区块的动作
        err := node.Syncer.HandleNewBlocks(context.Background(), cids)
        if err != nil {
            log.Infof("error handling blocks: %s", types.NewSortedCidSet(cids...).String())
        }
    }
    //实例化hello服务
    node.HelloSvc = hello.New(node.Host(), node.ChainReader.GenesisCid(), syncCallBack, node.ChainReader.Head)

    ......
}

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