Merge: + dnsfilter: cache IP addresses of safebrowsing and parental control servers

Close #745

* commit 'd918e5b418de232d95ba1e3d642dca00664f0304':
  use maxDialCacheSize constant
  rename functions and container
  + dnsfilter: cache IP addresses of safebrowsing and parental control servers

dnsfilter/dnsfilter.go

@@ -33,6 +33,7 @@ const defaultSafebrowsingServer = "sb.adtidy.org"
 const defaultSafebrowsingURL = "http://%s/safebrowsing-lookup-hash.html?prefixes=%s"
 const defaultParentalServer = "pctrl.adguard.com"
 const defaultParentalURL = "http://%s/check-parental-control-hash?prefixes=%s&sensitivity=%d"
+const maxDialCacheSize = 2 // the number of host names for safebrowsing and parental control
 
 // ErrInvalidSyntax is returned by AddRule when the rule is invalid
 var ErrInvalidSyntax = errors.New("dnsfilter: invalid rule syntax")
@@ -157,6 +158,7 @@ const (
 // these variables need to survive coredns reload
 var (
 	stats             Stats
+	dialCache         gcache.Cache // "host" -> "IP" cache for safebrowsing and parental control servers
 	safebrowsingCache gcache.Cache
 	parentalCache     gcache.Cache
 	safeSearchCache   gcache.Cache
@@ -972,10 +974,34 @@ func (d *Dnsfilter) matchHost(host string) (Result, error) {
 // lifecycle helper functions
 //
 
+// Return TRUE if this host's IP should be cached
+func (d *Dnsfilter) shouldBeInDialCache(host string) bool {
+	return host == d.safeBrowsingServer ||
+		host == d.parentalServer
+}
+
+// Search for an IP address by host name
+func searchInDialCache(host string) string {
+	rawValue, err := dialCache.Get(host)
+	if err != nil {
+		return ""
+	}
+
+	ip, _ := rawValue.(string)
+	log.Debug("Found in cache: %s -> %s", host, ip)
+	return ip
+}
+
+// Add "hostname" -> "IP address" entry to cache
+func addToDialCache(host, ip string) {
+	dialCache.Set(host, ip)
+	log.Debug("Added to cache: %s -> %s", host, ip)
+}
+
 type dialFunctionType func(ctx context.Context, network, addr string) (net.Conn, error)
 
 // Connect to a remote server resolving hostname using our own DNS server
-func createCustomDialContext(resolverAddr string) dialFunctionType {
+func (d *Dnsfilter) createCustomDialContext(resolverAddr string) dialFunctionType {
 	return func(ctx context.Context, network, addr string) (net.Conn, error) {
 		log.Tracef("network:%v  addr:%v", network, addr)
 
@@ -993,6 +1019,15 @@ func createCustomDialContext(resolverAddr string) dialFunctionType {
 			return con, err
 		}
 
+		cache := d.shouldBeInDialCache(host)
+		if cache {
+			ip := searchInDialCache(host)
+			if len(ip) != 0 {
+				addr = fmt.Sprintf("%s:%s", ip, port)
+				return dialer.DialContext(ctx, network, addr)
+			}
+		}
+
 		r := upstream.NewResolver(resolverAddr, 30*time.Second)
 		addrs, e := r.LookupIPAddr(ctx, host)
 		log.Tracef("LookupIPAddr: %s: %v", host, addrs)
@@ -1011,6 +1046,11 @@ func createCustomDialContext(resolverAddr string) dialFunctionType {
 				}
 				continue
 			}
+
+			if cache {
+				addToDialCache(host, a.String())
+			}
+
 			return con, err
 		}
 		return nil, firstErr
@@ -1037,7 +1077,8 @@ func New(c *Config) *Dnsfilter {
 		ExpectContinueTimeout: 1 * time.Second,
 	}
 	if c != nil && len(c.ResolverAddress) != 0 {
-		d.transport.DialContext = createCustomDialContext(c.ResolverAddress)
+		dialCache = gcache.New(maxDialCacheSize).LRU().Expiration(defaultCacheTime).Build()
+		d.transport.DialContext = d.createCustomDialContext(c.ResolverAddress)
 	}
 	d.client = http.Client{
 		Transport: d.transport,