First commit to add etcd registry support

registry/etcd/watcher.go

@@ -0,0 +1,88 @@
+package etcd
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/coreos/etcd/clientv3"
+	"github.com/micro/go-micro/registry"
+)
+
+type etcdWatcher struct {
+	stop    chan bool
+	w       clientv3.WatchChan
+	client  *clientv3.Client
+	timeout time.Duration
+}
+
+func newEtcdWatcher(r *etcdRegistry, timeout time.Duration, opts ...registry.WatchOption) (registry.Watcher, error) {
+	var wo registry.WatchOptions
+	for _, o := range opts {
+		o(&wo)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	stop := make(chan bool, 1)
+
+	go func() {
+		<-stop
+		cancel()
+	}()
+
+	watchPath := prefix
+	if len(wo.Service) > 0 {
+		watchPath = servicePath(wo.Service) + "/"
+	}
+
+	return &etcdWatcher{
+		stop:    stop,
+		w:       r.client.Watch(ctx, watchPath, clientv3.WithPrefix(), clientv3.WithPrevKV()),
+		client:  r.client,
+		timeout: timeout,
+	}, nil
+}
+
+func (ew *etcdWatcher) Next() (*registry.Result, error) {
+	for wresp := range ew.w {
+		if wresp.Err() != nil {
+			return nil, wresp.Err()
+		}
+		for _, ev := range wresp.Events {
+			service := decode(ev.Kv.Value)
+			var action string
+
+			switch ev.Type {
+			case clientv3.EventTypePut:
+				if ev.IsCreate() {
+					action = "create"
+				} else if ev.IsModify() {
+					action = "update"
+				}
+			case clientv3.EventTypeDelete:
+				action = "delete"
+
+				// get service from prevKv
+				service = decode(ev.PrevKv.Value)
+			}
+
+			if service == nil {
+				continue
+			}
+			return &registry.Result{
+				Action:  action,
+				Service: service,
+			}, nil
+		}
+	}
+	return nil, errors.New("could not get next")
+}
+
+func (ew *etcdWatcher) Stop() {
+	select {
+	case <-ew.stop:
+		return
+	default:
+		close(ew.stop)
+	}
+}