fixes and improvements (#55)

* util/router: sync from github
* config: add watcher interface

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

config/default_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"testing"
+	"time"
 
 	"github.com/unistack-org/micro/v3/config"
 )
@@ -17,6 +18,57 @@ type Cfg struct {
 	IntValue int `default:"99"`
 }
 
+func TestWatch(t *testing.T) {
+	ctx := context.Background()
+
+	conf := &Cfg{IntValue: 10}
+
+	cfg := config.NewConfig(config.Struct(conf))
+	if err := cfg.Init(); err != nil {
+		t.Fatal(err)
+	}
+	if err := cfg.Load(ctx); err != nil {
+		t.Fatal(err)
+	}
+
+	w, err := cfg.Watch(ctx, config.WatchInterval(500*time.Millisecond))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() {
+		_ = w.Stop()
+	}()
+
+	done := make(chan struct{})
+
+	go func() {
+		for {
+			mp, err := w.Next()
+			if err != nil && err != config.ErrWatcherStopped {
+				t.Fatal(err)
+			} else if err == config.ErrWatcherStopped {
+				return
+			}
+			if len(mp) != 1 {
+				t.Fatal(fmt.Errorf("default watcher err: %v", mp))
+			}
+
+			v, ok := mp["IntValue"]
+			if !ok {
+				t.Fatal(fmt.Errorf("default watcher err: %v", v))
+			}
+			if nv, ok := v.(int); !ok || nv != 99 {
+				t.Fatal(fmt.Errorf("default watcher err: %v", v))
+			}
+			close(done)
+			return
+		}
+	}()
+
+	<-done
+}
+
 func TestDefault(t *testing.T) {
 	ctx := context.Background()
 	conf := &Cfg{IntValue: 10}
@@ -47,6 +99,6 @@ func TestDefault(t *testing.T) {
 	if conf.StringValue != "after_load" {
 		t.Fatal("AfterLoad option not working")
 	}
-
-	t.Logf("%#+v\n", conf)
+	_ = conf
+	//t.Logf("%#+v\n", conf)
 }