Feature: support domain in fallback filter (#964)

config/config.go

@@ -69,6 +69,7 @@ type DNS struct {
 type FallbackFilter struct {
 	GeoIP  bool         `yaml:"geoip"`
 	IPCIDR []*net.IPNet `yaml:"ipcidr"`
+	Domain []string     `yaml:"domain"`
 }
 
 // Experimental config
@@ -103,6 +104,7 @@ type RawDNS struct {
 type RawFallbackFilter struct {
 	GeoIP  bool     `yaml:"geoip"`
 	IPCIDR []string `yaml:"ipcidr"`
+	Domain []string `yaml:"domain"`
 }
 
 type RawConfig struct {
@@ -561,6 +563,7 @@ func parseDNS(cfg RawDNS, hosts *trie.DomainTrie) (*DNS, error) {
 	if fallbackip, err := parseFallbackIPCIDR(cfg.FallbackFilter.IPCIDR); err == nil {
 		dnsCfg.FallbackFilter.IPCIDR = fallbackip
 	}
+	dnsCfg.FallbackFilter.Domain = cfg.FallbackFilter.Domain
 
 	if cfg.UseHosts {
 		dnsCfg.Hosts = hosts

dns/filters.go

@@ -4,9 +4,10 @@ import (
 	"net"
 
 	"github.com/Dreamacro/clash/component/mmdb"
+	"github.com/Dreamacro/clash/component/trie"
 )
 
-type fallbackFilter interface {
+type fallbackIPFilter interface {
 	Match(net.IP) bool
 }
 
@@ -24,3 +25,22 @@ type ipnetFilter struct {
 func (inf *ipnetFilter) Match(ip net.IP) bool {
 	return inf.ipnet.Contains(ip)
 }
+
+type fallbackDomainFilter interface {
+	Match(domain string) bool
+}
+type domainFilter struct {
+	tree *trie.DomainTrie
+}
+
+func NewDomainFilter(domains []string) *domainFilter {
+	df := domainFilter{tree: trie.New()}
+	for _, domain := range domains {
+		df.tree.Insert(domain, "")
+	}
+	return &df
+}
+
+func (df *domainFilter) Match(domain string) bool {
+	return df.tree.Search(domain) != nil
+}

dns/resolver.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"math/rand"
 	"net"
+	"strings"
 	"time"
 
 	"github.com/Dreamacro/clash/common/cache"
@@ -38,7 +39,8 @@ type Resolver struct {
 	hosts                 *trie.DomainTrie
 	main                  []dnsClient
 	fallback              []dnsClient
-	fallbackFilters []fallbackFilter
+	fallbackDomainFilters []fallbackDomainFilter
+	fallbackIPFilters     []fallbackIPFilter
 	group                 singleflight.Group
 	lruCache              *cache.LruCache
 }
@@ -78,8 +80,8 @@ func (r *Resolver) ResolveIPv6(host string) (ip net.IP, err error) {
 	return r.resolveIP(host, D.TypeAAAA)
 }
 
-func (r *Resolver) shouldFallback(ip net.IP) bool {
-	for _, filter := range r.fallbackFilters {
+func (r *Resolver) shouldIPFallback(ip net.IP) bool {
+	for _, filter := range r.fallbackIPFilters {
 		if filter.Match(ip) {
 			return true
 		}
@@ -126,7 +128,7 @@ func (r *Resolver) exchangeWithoutCache(m *D.Msg) (msg *D.Msg, err error) {
 
 		isIPReq := isIPRequest(q)
 		if isIPReq {
-			return r.fallbackExchange(m)
+			return r.ipExchange(m)
 		}
 
 		return r.batchExchange(r.main, m)
@@ -170,19 +172,49 @@ func (r *Resolver) batchExchange(clients []dnsClient, m *D.Msg) (msg *D.Msg, err
 	return
 }
 
-func (r *Resolver) fallbackExchange(m *D.Msg) (msg *D.Msg, err error) {
+func (r *Resolver) shouldOnlyQueryFallback(m *D.Msg) bool {
+	if r.fallback == nil || len(r.fallbackDomainFilters) == 0 {
+		return false
+	}
+
+	domain := r.msgToDomain(m)
+
+	if domain == "" {
+		return false
+	}
+
+	for _, df := range r.fallbackDomainFilters {
+		if df.Match(domain) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (r *Resolver) ipExchange(m *D.Msg) (msg *D.Msg, err error) {
+
+	onlyFallback := r.shouldOnlyQueryFallback(m)
+
+	if onlyFallback {
+		res := <-r.asyncExchange(r.fallback, m)
+		return res.Msg, res.Error
+	}
+
 	msgCh := r.asyncExchange(r.main, m)
-	if r.fallback == nil {
+
+	if r.fallback == nil { // directly return if no fallback servers are available
 		res := <-msgCh
 		msg, err = res.Msg, res.Error
 		return
 	}
+
 	fallbackMsg := r.asyncExchange(r.fallback, m)
 	res := <-msgCh
 	if res.Error == nil {
 		if ips := r.msgToIP(res.Msg); len(ips) != 0 {
-			if !r.shouldFallback(ips[0]) {
-				msg = res.Msg
+			if !r.shouldIPFallback(ips[0]) {
+				msg = res.Msg // no need to wait for fallback result
 				err = res.Error
 				return msg, err
 			}
@@ -240,6 +272,14 @@ func (r *Resolver) msgToIP(msg *D.Msg) []net.IP {
 	return ips
 }
 
+func (r *Resolver) msgToDomain(msg *D.Msg) string {
+	if len(msg.Question) > 0 {
+		return strings.TrimRight(msg.Question[0].Name, ".")
+	}
+
+	return ""
+}
+
 func (r *Resolver) asyncExchange(client []dnsClient, msg *D.Msg) <-chan *result {
 	ch := make(chan *result, 1)
 	go func() {
@@ -257,6 +297,7 @@ type NameServer struct {
 type FallbackFilter struct {
 	GeoIP  bool
 	IPCIDR []*net.IPNet
+	Domain []string
 }
 
 type Config struct {
@@ -286,14 +327,19 @@ func NewResolver(config Config) *Resolver {
 		r.fallback = transform(config.Fallback, defaultResolver)
 	}
 
-	fallbackFilters := []fallbackFilter{}
+	fallbackIPFilters := []fallbackIPFilter{}
 	if config.FallbackFilter.GeoIP {
-		fallbackFilters = append(fallbackFilters, &geoipFilter{})
+		fallbackIPFilters = append(fallbackIPFilters, &geoipFilter{})
 	}
 	for _, ipnet := range config.FallbackFilter.IPCIDR {
-		fallbackFilters = append(fallbackFilters, &ipnetFilter{ipnet: ipnet})
+		fallbackIPFilters = append(fallbackIPFilters, &ipnetFilter{ipnet: ipnet})
+	}
+	r.fallbackIPFilters = fallbackIPFilters
+
+	if len(config.FallbackFilter.Domain) != 0 {
+		fallbackDomainFilters := []fallbackDomainFilter{NewDomainFilter(config.FallbackFilter.Domain)}
+		r.fallbackDomainFilters = fallbackDomainFilters
 	}
-	r.fallbackFilters = fallbackFilters
 
 	return r
 }

hub/executor/executor.go

@@ -118,6 +118,7 @@ func updateDNS(c *config.DNS) {
 		FallbackFilter: dns.FallbackFilter{
 			GeoIP:  c.FallbackFilter.GeoIP,
 			IPCIDR: c.FallbackFilter.IPCIDR,
+			Domain: c.FallbackFilter.Domain,
 		},
 		Default: c.DefaultNameserver,
 	}