if the DNS response Rcode contains an error the cache expires after just 10 seconds.

this should limit the cache in case of temporary upstream DNS errors.

02.cache.go

@@ -13,7 +13,7 @@ import (
 
 type cacheItem struct {
 	Query []byte
-	Date  time.Time
+	ExpireDate  time.Time
 }
 
 //DomainCache stores a domain name inside the cache
@@ -28,7 +28,17 @@ func DomainCache(s string, resp *dns.Msg) {
 	if err != nil {
 		fmt.Println("Problems packing the response: ", err.Error())
 	}
-	domain2cache.Date = time.Now()
+	if resp.Rcode == dns.RcodeSuccess{
+		// on success stores response normally
+		domain2cache.ExpireDate = time.Now().Add((time.Duration(ZabovCacheTTL) * time.Hour))
+	}else
+	{
+		// on failure stores response for a very short time
+		if ZabovDebug {
+			fmt.Println("DomainCache(): DNS error Rcode: ", resp.Rcode, s, "cache time reduced to 10 seconds...")
+		}
+		domain2cache.ExpireDate = time.Now().Add((time.Duration(10) * time.Second))
+	}
 
 	err = enc.Encode(domain2cache)
 
@@ -77,7 +87,10 @@ func GetDomainFromCache(s string) *dns.Msg {
 		return nil
 	}
 
-	if time.Since(record.Date) > (time.Duration(ZabovCacheTTL) * time.Hour) {
+	if time.Now().After(record.ExpireDate) {
+		if ZabovDebug {
+			fmt.Println("GetDomainFromCache(): entry expired:", s)
+		}
 		return nil
 	}