feat(cache): shuffle record

cache/dns.go

@@ -3,6 +3,7 @@ package cache
 import (
 	"fmt"
 	"github.com/miekg/dns"
+	"math/rand"
 	"strconv"
 	"time"
 )
@@ -58,7 +59,12 @@ func (cache *DNSCache) Get(request *dns.Msg) *dns.Msg {
 		cacheKey += "." + subnet
 	}
 	if cacheHit, ok := cache.ttlMap.Get(cacheKey); ok {
-		return cacheHit.(*cacheEntry).Get()
+		r := cacheHit.(*cacheEntry).Get()
+		rand.Seed(time.Now().UnixNano()) // random record order
+		rand.Shuffle(len(r.Answer), func(i, j int) {
+			r.Answer[i], r.Answer[j] = r.Answer[j], r.Answer[i]
+		})
+		return r
 	}
 	return nil
 }

cache/dns_test.go

@@ -47,10 +47,13 @@ func TestGetDNSCache(t *testing.T) {
 }
 
 func TestTTLRewrite(t *testing.T) {
-	rr, _ := dns.NewRR("ip.cn. 0 IN A 1.1.1.1")
-	req, resp := &dns.Msg{}, &dns.Msg{Answer: []dns.RR{rr}}
+	rr1, _ := dns.NewRR("ip.cn. 0 IN A 1.1.1.1")
+	rr2, _ := dns.NewRR("ip.cn. 0 IN A 1.1.1.2")
+	req, resp := &dns.Msg{}, &dns.Msg{Answer: []dns.RR{rr1, rr2}}
 	req.SetQuestion("ip.cn.", dns.TypeA)
 	cache := NewDNSCache(1, time.Minute, time.Hour*24)
 	cache.Set(req, resp)
 	assert.NotEqual(t, resp.Answer[0].Header().Ttl, uint32(0))
+	// 顺便测试random record order
+	cache.Get(req)
 }