Cache DNS lookups when resolving safebrowsing or parental servers, also cache replacement hostnames as well.

coredns_plugin/coredns_plugin.go

@@ -45,6 +45,16 @@ func init() {
 	})
 }
 
+type cacheEntry struct {
+	answer      []dns.RR
+	lastUpdated time.Time
+}
+
+var (
+	lookupCacheTime = time.Minute * 30
+	lookupCache     = map[string]cacheEntry{}
+)
+
 type plugSettings struct {
 	SafeBrowsingBlockHost string
 	ParentalBlockHost     string
@@ -324,6 +334,8 @@ func (p *plug) replaceHostWithValAndReply(ctx context.Context, w dns.ResponseWri
 		records = append(records, result)
 	} else {
 		// this is a domain name, need to look it up
+		cacheentry := lookupCache[val]
+		if time.Since(cacheentry.lastUpdated) > lookupCacheTime {
 			req := new(dns.Msg)
 			req.SetQuestion(dns.Fqdn(val), question.Qtype)
 			req.RecursionDesired = true
@@ -338,6 +350,13 @@ func (p *plug) replaceHostWithValAndReply(ctx context.Context, w dns.ResponseWri
 					answer.Header().Name = question.Name
 				}
 				records = result.Answer
+				cacheentry.answer = result.Answer
+				cacheentry.lastUpdated = time.Now()
+				lookupCache[val] = cacheentry
+			}
+		} else {
+			// get from cache
+			records = cacheentry.answer
 		}
 	}
 	m := new(dns.Msg)

dnsfilter/dnsfilter.go

@@ -16,6 +16,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	_ "github.com/benburkert/dns/init"
 	"github.com/bluele/gcache"
 	"golang.org/x/net/publicsuffix"
 )