From e2a625a92e782fd0dd351afc9ce05a32451f832e Mon Sep 17 00:00:00 2001
From: bloved <bloved@fedibox.com>
Date: Thu, 16 Sep 2021 09:40:03 +0200
Subject: [PATCH] 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 | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/02.cache.go b/02.cache.go
index 7c4e1b5..ae40d26 100644
--- a/02.cache.go
+++ b/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)
 
@@ -65,7 +75,7 @@ func GetDomainFromCache(s string) *dns.Msg {
 
 	conf, errDB = MyZabovCDB.Get([]byte(s), nil)
 	if errDB != nil {
-		fmt.Println("Cant READ DB :" , errDB.Error() )
+		fmt.Println("Cant READ DB:" , errDB.Error() )
 		return nil
 	}
 
@@ -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
 	}