feat: support cache no answer

README.md

@@ -70,6 +70,7 @@ TXT = [ 'text' ]
 | listen | `string[]` | ✔️ | | host and port to listen |
 | timeout | `uint` | | `5` | timeout in seconds for each DNS request, 0 to disable |
 | round_robin | `string` | | `'clock'` | upstream select round robin, can only be `'clock'`, `'random'`, `'wrandom'` or `'swrr'` |
+| cache_no_answer | `uint` | | `0` | Cache response for specified seconds even if query returns with no specified answer or domain was not exists |
 | no_cache | `boolean` | | `false` | disable global DNS result cache |
 | custom_ecs | `string[]` | | | custom EDNS Subnet to override |
 | fallback_no_ecs | `boolean` | | `false` | fallback to no_ecs=`true` when DNS request got no answer |

client/client.go

@@ -23,7 +23,8 @@ type Client struct {
 
 	servers []*dns.Server
 
-	cacher *cache.Cache
+	cacher        *cache.Cache
+	cacheNoAnswer uint32
 }
 
 func startDNSServer(server *dns.Server, logger *zap.SugaredLogger, results chan error) {

client/handler.go

@@ -104,24 +104,28 @@ func (client *Client) handlerFunc(w dns.ResponseWriter, r *dns.Msg, useTCP bool)
 	}
 	w.WriteMsg(response)
 
-	if client.cacher != nil && err == nil && response.Rcode == dns.RcodeSuccess && (len(response.Answer)+len(response.Ns)+len(response.Extra)) > 0 {
+	if client.cacher != nil && err == nil {
 		var minttl uint32
-		for _, answer := range response.Answer {
-			ttl := answer.Header().Ttl
-			if ttl > 0 && (minttl == 0 || ttl < minttl) {
-				minttl = ttl
+		if response.Rcode == dns.RcodeNameError || len(response.Answer)+len(response.Ns)+len(response.Extra) == 0 {
+			minttl = client.cacheNoAnswer
+		} else if response.Rcode == dns.RcodeSuccess {
+			for _, answer := range response.Answer {
+				ttl := answer.Header().Ttl
+				if ttl > 0 && (minttl == 0 || ttl < minttl) {
+					minttl = ttl
+				}
 			}
-		}
-		for _, ns := range response.Ns {
-			ttl := ns.Header().Ttl
-			if ttl > 0 && (minttl == 0 || ttl < minttl) {
-				minttl = ttl
+			for _, ns := range response.Ns {
+				ttl := ns.Header().Ttl
+				if ttl > 0 && (minttl == 0 || ttl < minttl) {
+					minttl = ttl
+				}
 			}
-		}
-		for _, extra := range response.Extra {
-			ttl := extra.Header().Ttl
-			if ttl > 0 && (minttl == 0 || ttl < minttl) {
-				minttl = ttl
+			for _, extra := range response.Extra {
+				ttl := extra.Header().Ttl
+				if ttl > 0 && (minttl == 0 || ttl < minttl) {
+					minttl = ttl
+				}
 			}
 		}
 		if minttl > 0 {

client/newClient.go

@@ -18,7 +18,7 @@ import (
 // NewClient returns a client with dnsClients
 func NewClient(logger *zap.SugaredLogger, conf *config.Config) (client *Client, err error) {
 	timeout := time.Duration(*conf.Config.Timeout) * time.Second
-	client = &Client{logger: logger, timeout: timeout}
+	client = &Client{logger: logger, timeout: timeout, cacheNoAnswer: conf.Config.CacheNoAnswer}
 
 	switch conf.Config.RoundRobin {
 	case config.SelectorClock:

config/config.go

@@ -23,10 +23,11 @@ type typeCustomSpecified struct {
 }
 
 type typeGeneralConfig struct {
-	Listen     []string  `toml:"listen"`
-	Timeout    *uint     `toml:"timeout"`     // seconds
-	RoundRobin Selectors `toml:"round_robin"` // default: clock
-	NoCache    bool      `toml:"no_cache"`
+	Listen        []string  `toml:"listen"`
+	Timeout       *uint     `toml:"timeout"`     // seconds
+	RoundRobin    Selectors `toml:"round_robin"` // default: clock
+	CacheNoAnswer uint32    `toml:"cache_no_answer"`
+	NoCache       bool      `toml:"no_cache"`
 	DNSSettings
 }