feat: support eureka registry (#464)

Signed-off-by: charlie <qianglin98@qq.com>

registry/eureka/client/plan.go

@@ -0,0 +1,80 @@
+// Copyright (c) 2022 Alibaba Group Holding Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package client
+
+import (
+	"github.com/hudl/fargo"
+	"istio.io/pkg/log"
+)
+
+type Handler func(application *fargo.Application) error
+
+/*
+ * Plan can be used to get the latest information of a service
+ *
+ *                       (service B)  ┌──────┐
+ *                      ┌────────────►│Plan B│
+ *                      │   Timer     └──────┘
+ *                      │
+ * ┌───────────────┐    │
+ * │ eureka-server ├────┤
+ * └───────────────┘    │
+ *                      │
+ *                      │
+ *                      │(service A)  ┌──────┐
+ *                      └────────────►│Plan A│
+ *                          Timer     └──────┘
+ */
+
+type Plan struct {
+	client  EurekaHttpClient
+	stop    chan struct{}
+	handler Handler
+}
+
+func NewPlan(client EurekaHttpClient, serviceName string, handler Handler) *Plan {
+	p := &Plan{
+		client:  client,
+		stop:    make(chan struct{}),
+		handler: handler,
+	}
+
+	ch := client.ScheduleAppUpdates(serviceName, p.stop)
+	go p.watch(ch)
+	return p
+}
+
+func (p *Plan) Stop() {
+	defer close(p.stop)
+	p.stop <- struct{}{}
+}
+
+func (p *Plan) watch(ch <-chan fargo.AppUpdate) {
+	for {
+		select {
+		case <-p.stop:
+			log.Info("stop eureka plan")
+			return
+		case updateItem := <-ch:
+			if updateItem.Err != nil {
+				log.Error("get eureka application failed, error : %v", updateItem.Err)
+				continue
+			}
+			if err := p.handler(updateItem.App); err != nil {
+				log.Error("handle eureka application failed, error : %v", err)
+			}
+		}
+	}
+}