add etcd provider

provider/etcd/provider_example_test.go

@@ -0,0 +1,121 @@
+package etcd_test
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"sync"
+	"time"
+
+	"gitoa.ru/go-4devs/config"
+	"gitoa.ru/go-4devs/config/provider/etcd"
+)
+
+func ExampleClient_Value() {
+	const (
+		namespace = "fdevs"
+		appName   = "config"
+	)
+
+	ctx := context.Background()
+
+	// configure etcd client
+	etcdClient, err := NewEtcd(ctx)
+	if err != nil {
+		log.Print(err)
+
+		return
+	}
+
+	config, err := config.New(
+		etcd.New(namespace, appName, etcdClient),
+	)
+	if err != nil {
+		log.Print(err)
+
+		return
+	}
+
+	enabled, err := config.Value(ctx, "maintain")
+	if err != nil {
+		log.Print("maintain ", err)
+
+		return
+	}
+
+	fmt.Printf("maintain from etcd: %v\n", enabled.Bool())
+	// Output:
+	// maintain from etcd: true
+}
+
+func ExampleClient_Watch() {
+	const (
+		namespace = "fdevs"
+		appName   = "config"
+	)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// configure etcd client
+	etcdClient, err := NewEtcd(ctx)
+	if err != nil {
+		log.Print(err)
+
+		return
+	}
+
+	_, err = etcdClient.KV.Put(ctx, "fdevs/config/example_db_dsn", "pgsql://user@pass:127.0.0.1:5432")
+	if err != nil {
+		log.Print(err)
+
+		return
+	}
+
+	defer func() {
+		cancel()
+
+		if _, err = etcdClient.KV.Delete(context.Background(), "fdevs/config/example_db_dsn"); err != nil {
+			log.Print(err)
+
+			return
+		}
+	}()
+
+	watcher, err := config.New(
+		etcd.New(namespace, appName, etcdClient),
+	)
+	if err != nil {
+		log.Print(err)
+
+		return
+	}
+
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+
+	err = watcher.Watch(ctx, func(_ context.Context, oldVar, newVar config.Value) error {
+		fmt.Println("update example_db_dsn old: ", oldVar.String(), " new:", newVar.String())
+		wg.Done()
+
+		return nil
+	}, "example_db_dsn")
+	if err != nil {
+		log.Print(err)
+
+		return
+	}
+
+	time.AfterFunc(time.Second, func() {
+		if _, err := etcdClient.KV.Put(ctx, "fdevs/config/example_db_dsn", "mysql://localhost:5432"); err != nil {
+			log.Print(err)
+
+			return
+		}
+	})
+
+	wg.Wait()
+
+	// Output:
+	// update example_db_dsn old:  pgsql://user@pass:127.0.0.1:5432  new: mysql://localhost:5432
+}