filecoin源码协议层分析之hello握手协议

• master分支 619b0eb1（2019年３月２日）

• hello

• protocol/hello
• node/node.go

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

• 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
  }
  

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

type getTipSetFunc func() types.TipSet

• 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
  }
  

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

// New peer connection notifications
type helloNotify Handler
//　连接超时时间
const helloTimeout = time.Second * 10

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)
	}
}

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
}

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)
}

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

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)  {}

// 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
}

type Node struct {
    ......
	HelloSvc     *hello.Handler
    ......
}

// 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)
    ......
}