Feature: dns server could lookup hosts (#872)

dns/middleware.go

@@ -1,9 +1,11 @@
 package dns
 
 import (
+	"net"
 	"strings"
 
 	"github.com/Dreamacro/clash/component/fakeip"
+	"github.com/Dreamacro/clash/component/trie"
 	"github.com/Dreamacro/clash/log"
 
 	D "github.com/miekg/dns"
@@ -12,6 +14,52 @@ import (
 type handler func(w D.ResponseWriter, r *D.Msg)
 type middleware func(next handler) handler
 
+func withHosts(hosts *trie.DomainTrie) middleware {
+	return func(next handler) handler {
+		return func(w D.ResponseWriter, r *D.Msg) {
+			q := r.Question[0]
+
+			if !isIPRequest(q) {
+				next(w, r)
+				return
+			}
+
+			record := hosts.Search(strings.TrimRight(q.Name, "."))
+			if record == nil {
+				next(w, r)
+				return
+			}
+
+			ip := record.Data.(net.IP)
+			msg := r.Copy()
+
+			if v4 := ip.To4(); v4 != nil && q.Qtype == D.TypeA {
+				rr := &D.A{}
+				rr.Hdr = D.RR_Header{Name: q.Name, Rrtype: D.TypeA, Class: D.ClassINET, Ttl: dnsDefaultTTL}
+				rr.A = v4
+
+				msg.Answer = []D.RR{rr}
+			} else if v6 := ip.To16(); v6 != nil && q.Qtype == D.TypeAAAA {
+				rr := &D.AAAA{}
+				rr.Hdr = D.RR_Header{Name: q.Name, Rrtype: D.TypeAAAA, Class: D.ClassINET, Ttl: dnsDefaultTTL}
+				rr.AAAA = v6
+
+				msg.Answer = []D.RR{rr}
+			} else {
+				next(w, r)
+				return
+			}
+
+			msg.SetRcode(r, D.RcodeSuccess)
+			msg.Authoritative = true
+			msg.RecursionAvailable = true
+
+			w.WriteMsg(msg)
+			return
+		}
+	}
+}
+
 func withFakeIP(fakePool *fakeip.Pool) middleware {
 	return func(next handler) handler {
 		return func(w D.ResponseWriter, r *D.Msg) {
@@ -100,6 +148,10 @@ func compose(middlewares []middleware, endpoint handler) handler {
 func newHandler(resolver *Resolver) handler {
 	middlewares := []middleware{}
 
+	if resolver.hosts != nil {
+		middlewares = append(middlewares, withHosts(resolver.hosts))
+	}
+
 	if resolver.FakeIPEnabled() {
 		middlewares = append(middlewares, withFakeIP(resolver.pool))
 	}

dns/resolver.go

@@ -14,6 +14,7 @@ import (
 	"github.com/Dreamacro/clash/common/picker"
 	"github.com/Dreamacro/clash/component/fakeip"
 	"github.com/Dreamacro/clash/component/resolver"
+	"github.com/Dreamacro/clash/component/trie"
 
 	D "github.com/miekg/dns"
 	"golang.org/x/sync/singleflight"
@@ -37,6 +38,7 @@ type Resolver struct {
 	ipv6            bool
 	mapping         bool
 	fakeip          bool
+	hosts           *trie.DomainTrie
 	pool            *fakeip.Pool
 	main            []dnsClient
 	fallback        []dnsClient
@@ -308,6 +310,7 @@ type Config struct {
 	EnhancedMode   EnhancedMode
 	FallbackFilter FallbackFilter
 	Pool           *fakeip.Pool
+	Hosts          *trie.DomainTrie
 }
 
 func New(config Config) *Resolver {
@@ -323,6 +326,7 @@ func New(config Config) *Resolver {
 		mapping:  config.EnhancedMode == MAPPING,
 		fakeip:   config.EnhancedMode == FAKEIP,
 		pool:     config.Pool,
+		hosts:    config.Hosts,
 	}
 
 	if len(config.Fallback) != 0 {