impl config State and config Interval

config/duration.go

@@ -0,0 +1,25 @@
+package config
+
+import (
+	"encoding/json"
+	"time"
+)
+
+type Duration time.Duration
+
+func (d Duration) Get() time.Duration {
+	return time.Duration(d)
+}
+
+func (d *Duration) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+	d2, err := time.ParseDuration(s)
+	if err != nil {
+		return err
+	}
+	*d = Duration(d2)
+	return nil
+}