一个简单的etcdV3样例

func main() {
    cliConfig := clientv3.Config{
        Endpoints:   []string{"127.0.0.1:2379"},
        DialTimeout: 100,
    }
    cli, err := clientv3.New(cliConfig)
    if err != nil {
        println(err)
    }
    defer cli.Close()
    //Put
    if _, err = cli.Put(context.TODO(), "/test/k1", "v1"); err != nil {
        println(err)
    }
    //Get
    if resp, err := cli.Get(context.TODO(), "/etst/k1"); err != nil {
        fmt.Println(err.Error())
    } else {
        fmt.Println("resp:", resp)
    }
    //Del
    if _, err = cli.Delete(context.TODO(), "/test/k1"); err != nil {
        println(err)
    }

    //TXN
    ctx, cancel := context.WithTimeout(context.Background(), 1000)
    _, err = cli.Txn(ctx).If(clientv3.Compare(clientv3.Value("/test/k1"), ">", "v1")).Then(clientv3.OpPut("k1", "abc")).Else(clientv3.OpPut("k1", "ABC")).Commit()
    cancel()
    if err != nil {
        println(err)
    }

    //Watch
    rangeWatch := cli.Watch(context.Background(),"",clientv3.WithPrefix())
    for watchResp := range rangeWatch {
        for _,ev := range watchResp.Events{
            fmt.Printf("%s %q :%q\n",ev.Type,ev.Kv.Key,ev.Kv.Value)
        }
    }
}

即使是本机启动，连接超时时间也不能少于1秒。

v3版 get的数据结构发生了变化，获取的是KV集合，字节数组需要转换，按如下方式获取KV值。

resp,err := cli.Get(context.TODO(),"/test/key1")
    if err != nil {
        println(err)
    }
    fmt.Println(string(resp.Kvs[0].Key))
    fmt.Println(string(resp.Kvs[0].Value))

Get节点及子节点的值：

//添加WithPrefix()属性
resp,err = cli.Get(context.TODO(),"/test",clientv3.WithPrefix())
    if err != nil {
        println(err)
    }
    fmt.Println(string(resp.Kvs[0].Key),string(resp.Kvs[0].Value))

Txn事务完成了一次CAS原子操作。需要在context中配置超时时间。ctx用完有调用cancel()取消（不等待）。

调用了clientV3的Value方法取值，Compare方法比较，OpPut方法赋值，最后提交完成CAS操作。此处路径全部加/，使用的是绝对路径。

Watch方法由WatchChan返回若干个WatchResponse，

type WatchResponse struct {
    Header pb.ResponseHeader
    Events []*Event

    // CompactRevision is the minimum revision the watcher may receive.
    CompactRevision int64

    // Canceled is used to indicate watch failure.
    // If the watch failed and the stream was about to close, before the channel is closed,
    // the channel sends a final response that has Canceled set to true with a non-nil Err().
    Canceled bool

    // Created is used to indicate the creation of the watcher.
    Created bool

    closeErr error

    // cancelReason is a reason of canceling watch
    cancelReason string
}

Get方法和Watch方法的返回结果，都附带了响应头：

type ResponseHeader struct {
    // cluster_id is the ID of the cluster which sent the response.
    ClusterId uint64 `protobuf:"varint,1,opt,name=cluster_id,json=clusterId,proto3" json:"cluster_id,omitempty"`
    // member_id is the ID of the member which sent the response.
    MemberId uint64 `protobuf:"varint,2,opt,name=member_id,json=memberId,proto3" json:"member_id,omitempty"`
    // revision is the key-value store revision when the request was applied.
    // For watch progress responses, the header.revision indicates progress. All future events
    // recieved in this stream are guaranteed to have a higher revision number than the
    // header.revision number.
    Revision int64 `protobuf:"varint,3,opt,name=revision,proto3" json:"revision,omitempty"`
    // raft_term is the raft term when the request was applied.
    RaftTerm uint64 `protobuf:"varint,4,opt,name=raft_term,json=raftTerm,proto3" json:"raft_term,omitempty"`
}

%q为单引号围绕的字符字面值。watchEvent.Kv.Key是字节数组，用fmt.Printf()加点位符%q打印的方式更好。

rangeWatch := cli.Watch(context.Background(),"",clientv3.WithPrefix())
    for watchResp := range rangeWatch{
        for _,watchEvent := range watchResp.Events{
            fmt.Println(watchEvent.Type,string(watchEvent.Kv.Key))
        }
    }

rangeWatch := cli.Watch(context.Background(),"",clientv3.WithPrefix())
    for watchResp := range rangeWatch{
        for _,watchEvent := range watchResp.Events{
            fmt.Printf("%s,%q,%q",watchEvent.Type,watchEvent.Kv.Key,watchEvent.Kv.Value)
        }
    }

事务Txn为context包装了一个超时时间。

context.TODO()和contest.Background()都返回一个空的context。contest.Background()没有截止日期，也没有cancel方法取消，一般用作main方法的cli操作上下文。

context.TODO()只对一个操作，单独配置一个上下文，如Txn事务，用完后调用cancel句柄取消。