使用GO语言写一个基于etcd的服务发现

```go package main import ( "context" "fmt" etcd "github.com/coreos/etcd/clientv3" // etcd客户端库 ) // 服务发现结构体 type ServiceDiscovery struct { // 定义一个服务发现的struct，用于存储相关信息 prefix string // 服务前缀，用于标识服务名称 client *etcd.Client // etcd客户端，用于连接etcd服务器 serviceChan chan []string // 服务列表通道，存放所有发现的服务列表 stopChan chan bool // 停止信号通道，用于传达停止信号 exitChan chan bool // 退出信号通道，用于传达退出信号 } func NewServiceDiscovery(endpoints []string, prefix string) (*ServiceDiscovery, error) { // 构造函数，新建一个服务发现对象 client, err := etcd.New(etcd.Config{ // 连接到etcd集群 Endpoints: endpoints, }) if err != nil { return nil, err } return &ServiceDiscovery{ prefix: prefix, client: client, serviceChan: make(chan []string), stopChan: make(chan bool), exitChan: make(chan bool), }, nil } func (s *ServiceDiscovery) GetServices() ([]string, error) { services := make([]string, 0) resp, err := s.client.Get(context.Background(), s.prefix+"/", etcd.WithPrefix()) if err != nil { return services, fmt.Errorf("get services failed with error : %v",err ) } for _ ,kv := range resp.Kvs{ services = append(services , string(kv.Key)) } return services ,nil}func (s *ServiceDiscovery) Watch(){ for{ rch := s._watch() for wresp := range rch { var services []string for _ , ev := range wresp .Events{ switch ev .Type{ case mvccpb .PUT : key := string (ev .Kv .Key ) if ! strings .HasPrefix (key , s .prefix ) { continue } serviceName : = strings .TrimPrefix (key , s .prefix + "/") services = append (services , serviceName ) case mvccpb .DELETE : key : = string (ev .Kv .Key ) if !strings .HasPrefix (key ,s .) continue serviceName : = strings TrimPrefix (key ,s .) deleteServices () default : fmt Println ("other opration type " + ev Type String ()) } } select { case s Service Chan <- Services : case <- s Stop Chan : goto END_WATCH default : fmt Println ("default branch") } END_WATCH: close () return }}func main(){ endpoints := []string{"127.0 0 1 ：2379"} prefix := "/services/" sd ：= NewServiceDiscover y （endpoints ，prefix ）if sd == nil || sd Err !=nil{ panic("create service discovery failed")}go sd Watch ()for i ;i<5 ;i ++{ time Sleep （time Second*2 ） fmt Println ("get servies " + strconv Itoa i ) servies List ，err ListServies ()if err !=nil || len ServiesList ==0{ panic("list servies failed")}fmt Println ("servies list is "+ strconv Itoa len ServiesList + ":"+strings Join ServicesList ,",")}sd Stop Chan <- truesd Exit Chan <- truefmt Println ("exit watch goroutine")}```