本文主要是介绍etcd网络通讯层(一)——rafthttp中重要的接口，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
前面我们提到etcd-raft模块，etcd-raft模块并未提供网络层的相关实现，而是将待发送的消息封装进Ready实例返回给上层模块，然后由上层模块决定如何将这些消息发送到集群中的其他节点。etcd将网络层的相关实现单独封装成一个模块，也就是etcd-rafthttp模块。从而降低了etcd-raft和etcd-rafthttp之间的耦合，提高程序的可扩展性。
etcd-rafthttp的模块主要在https://github.com/etcd-io/etcd/tree/master/etcdserver/api/rafthttp 目录下。
在etcd集群中，每个节点启动时都会与集群中的其他节点建立连接(每个节点即是服务端,也是客户端)，这里以三个节点为例，最终形成如图的网络结构。
在etcd-rafthttp模块中，主要使用两个消息传输通道，Stream和Pipeline消息通道。
Stream消息通道维护的HTTP长连接，主要负责传输数据量较小、发送比较频繁的消息，例如，MsgApp消息、MsgHeartbeat消息、MsgVote消息等。
而Pipeline消息通道在传输数据完成后立即关闭连接，主要负责传输数据量较大、发送频率较低的消息，例如，MsgSnap消息等。
一、rafthttp.Transporter接口
Transporter接口是rafthttp包的核心接口，它定义了etcd网络层的核心功能，其具体定义如下：
type Transporter interface {// Start starts the given Transporter.// Start MUST be called before calling other functions in the interface.Start() error //初始化操作// Handler returns the HTTP handler of the transporter.// A transporter HTTP handler handles the HTTP requests// from remote peers.// The handler MUST be used to handle RaftPrefix(/raft)// endpoint.Handler() http.Handler //创建Handler实例，并关联到指定URL上// Send sends out the given messages to the remote peers.// Each message has a To field, which is an id that maps// to an existing peer in the transport.// If the id cannot be found in the transport, the message// will be ignored.Send(m []raftpb.Message) //发送消息// SendSnapshot sends out the given snapshot message to a remote peer.// The behavior of SendSnapshot is similar to Send.SendSnapshot(m snap.Message) //发送快照数据// AddRemote adds a remote with given peer urls into the transport.// A remote helps newly joined member to catch up the progress of cluster,// and will not be used after that.// It is the caller's responsibility to ensure the urls are all valid,// or it panics.AddRemote(id types.ID, urls []string) //在集群中添加一个节点时，其他节点会通过该方法添加该新加入节点的信息// AddPeer adds a peer with given peer urls into the transport.// It is the caller's responsibility to ensure the urls are all valid,// or it panics.// Peer urls are used to connect to the remote peer.//Peer接口是当前节点对集群中其他节点的抽象表示，而结构体Peer则是Peer接口的一个具体实现//下面几个方法是对Peer的操作AddPeer(id types.ID, urls []string)// RemovePeer removes the peer with given id.RemovePeer(id types.ID)// RemoveAllPeers removes all the existing peers in the transport.RemoveAllPeers()// UpdatePeer updates the peer urls of the peer with the given id.// It is the caller's responsibility to ensure the urls are all valid,// or it panics.UpdatePeer(id types.ID, urls []string)// ActiveSince returns the time that the connection with the peer// of the given id becomes active.// If the connection is active since peer was added, it returns the adding time.// If the connection is currently inactive, it returns zero time.ActiveSince(id types.ID) time.Time// ActivePeers returns the number of active peers.ActivePeers() int// Stop closes the connections and stops the transporter.Stop() //关闭操作
}
Start()方法完成初始化操作
Handler() 创建Handler实例，并关联到指定的URL上，创建HTTP服务时使用
Send()方法用于给对端发送消息
SendSnapshot()用于向对端发送快照数据
Peer接口是当前节点对集群中其他节点(对端)的抽象表示,AddPeer、RemovePeer、RemoveAllPeer、UpdatePeer分别用于添加节点、删除节点、删除所有节点和更新节点的操作。
二、Raft接口
Raft接口也是rafthttp包中非常重要的接口，用于集群中当前节点的网络层(etcd-rafthttp)向etcd-raft层发送消息。
type Raft interface {Process(ctx context.Context, m raftpb.Message) error //将指定消息传递到etcd-raft模块进行处理IsIDRemoved(id uint64) bool //检测当前节点是否从当前集群中被移除ReportUnreachable(id uint64) //通知底层的etcd-raft模块，当前节点与指定的节点无法连通ReportSnapshot(id uint64, status raft.SnapshotStatus) //通知底层的etcd-raft模块，快照数据是否发送成功
}
Raft接口提供了当前节点的网络层向底层的etcd-raft模块发送消息的功能
三、Peer接口
type Peer interface {// send sends the message to the remote peer. The function is non-blocking// and has no promise that the message will be received by the remote.// When it fails to send message out, it will report the status to underlying// raft.//发送单个消息给对端，该方法时非阻塞的，如果出现发送失败，则会将失败信息报告给底层的Raft接口send(m raftpb.Message)// sendSnap sends the merged snapshot message to the remote peer. Its behavior// is similar to send.//发送snap.Message，其他行为与上面的send()方法类似sendSnap(m snap.Message)// update updates the urls of remote peer.//更新对应节点暴露的URL地址update(urls types.URLs)// attachOutgoingConn attaches the outgoing connection to the peer for// stream usage. After the call, the ownership of the outgoing// connection hands over to the peer. The peer will close the connection// when it is no longer used./*将指定连接与当前的Peer绑定，Peer会将该连接作为Stream消息通道使用当Peer不再使用该连接时，会将该连接关闭*/attachOutgoingConn(conn *outgoingConn)// activeSince returns the time that the connection with the// peer becomes active./*activeSince返回与其他端(peer)的连接变为active状态的时间。*/activeSince() time.Time// stop performs any necessary finalization and terminates the peer// elegantly./*关闭当前Peer实例，会关闭底层的网络连接*/stop()
}
Peer接口是当前节点对集群中其他节点(对端)的抽象表示，该接口主要作用是向对端(集群中的其他节点)发送消息的功能。
后面会对这些接口的实现进行详细分析。
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