durations are now optionally spans for jitter

config/duration.go

@@ -2,17 +2,29 @@ package config
 
 import (
 	"encoding/json"
+	"errors"
+	"math/rand"
+	"strings"
 	"time"
 )
 
-type Duration time.Duration
+type Duration struct {
+	least time.Duration
+	most  time.Duration
+}
 
 func (d Duration) Get() time.Duration {
-	return time.Duration(d)
+	jitter := d.most - d.least
+	if jitter >= time.Second {
+		jitter = time.Second * time.Duration(rand.Int()%int(jitter.Seconds()))
+	} else {
+		jitter = 0
+	}
+	return time.Duration(d.least + jitter)
 }
 
 func (d Duration) MarshalJSON() ([]byte, error) {
-	return json.Marshal(d.Get().String())
+	return json.Marshal(d.least.String() + ".." + d.most.String())
 }
 
 func (d *Duration) UnmarshalJSON(b []byte) error {
@@ -20,10 +32,25 @@ func (d *Duration) UnmarshalJSON(b []byte) error {
 	if err := json.Unmarshal(b, &s); err != nil {
 		return err
 	}
-	d2, err := time.ParseDuration(s)
+	if !strings.Contains(s, "..") {
+		s = s + ".." + s
+	}
+	splits := strings.Split(s, "..")
+	if len(splits) != 2 {
+		return errors.New("unexpected ..")
+	}
+	least, err := time.ParseDuration(splits[0])
 	if err != nil {
 		return err
 	}
-	*d = Duration(d2)
+	most, err := time.ParseDuration(splits[1])
+	if err != nil {
+		return err
+	}
+	if least > most {
+		most, least = least, most
+	}
+	d.most = most
+	d.least = least
 	return nil
 }