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

This reverts commit a5d1053520.

This cache had unintended side effects.

coredns_plugin/coredns_plugin.go

@@ -41,16 +41,6 @@ func init() {
 	})
 }
 
-type cacheEntry struct {
-	answer      []dns.RR
-	lastUpdated time.Time
-}
-
-var (
-	lookupCacheTime = time.Minute * 30
-	lookupCache     = map[string]cacheEntry{}
-)
-
 type plugFilter struct {
 	ID   int64
 	Path string
@@ -345,29 +335,20 @@ 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
-			reqstate := request.Request{W: w, Req: req, Context: ctx}
-			result, err := p.upstream.Lookup(reqstate, dns.Fqdn(val), reqstate.QType())
-			if err != nil {
-				log.Printf("Got error %s\n", err)
-				return dns.RcodeServerFailure, fmt.Errorf("plugin/dnsfilter: %s", err)
+		req := new(dns.Msg)
+		req.SetQuestion(dns.Fqdn(val), question.Qtype)
+		req.RecursionDesired = true
+		reqstate := request.Request{W: w, Req: req, Context: ctx}
+		result, err := p.upstream.Lookup(reqstate, dns.Fqdn(val), reqstate.QType())
+		if err != nil {
+			log.Printf("Got error %s\n", err)
+			return dns.RcodeServerFailure, fmt.Errorf("plugin/dnsfilter: %s", err)
+		}
+		if result != nil {
+			for _, answer := range result.Answer {
+				answer.Header().Name = question.Name
 			}
-			if result != nil {
-				for _, answer := range result.Answer {
-					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
+			records = result.Answer
 		}
 	}
 	m := new(dns.Msg)

dnsfilter/dnsfilter.go

@@ -17,7 +17,6 @@ import (
 	"sync/atomic"
 	"time"
 
-	_ "github.com/benburkert/dns/init"
 	"github.com/bluele/gcache"
 	"golang.org/x/net/publicsuffix"
 )