dns: add edns0 subnet option support

cmd/gost/route.go

@@ -557,6 +557,8 @@ func (r *route) GenRouters() ([]router, error) {
 				gost.ChainResolverOption(chain),
 				gost.TimeoutResolverOption(timeout),
 				gost.TTLResolverOption(ttl),
+				gost.PreferResolverOption(node.Get("prefer")),
+				gost.SrcIPResolverOption(net.ParseIP(node.Get("ip"))),
 			)
 		}
 

resolver.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"context"
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -122,6 +123,8 @@ type resolverOptions struct {
 	chain   *Chain
 	timeout time.Duration
 	ttl     time.Duration
+	prefer  string
+	srcIP   net.IP
 }
 
 // ResolverOption allows a common way to set Resolver options.
@@ -148,6 +151,20 @@ func TTLResolverOption(ttl time.Duration) ResolverOption {
 	}
 }
 
+// PreferResolverOption sets the prefer for Resolver.
+func PreferResolverOption(prefer string) ResolverOption {
+	return func(opts *resolverOptions) {
+		opts.prefer = prefer
+	}
+}
+
+// SrcIPResolverOption sets the source IP for Resolver.
+func SrcIPResolverOption(ip net.IP) ResolverOption {
+	return func(opts *resolverOptions) {
+		opts.srcIP = ip
+	}
+}
+
 // Resolver is a name resolver for domain name.
 // It contains a list of name servers.
 type Resolver interface {
@@ -177,6 +194,7 @@ type resolver struct {
 	stopped chan struct{}
 	mux     sync.RWMutex
 	prefer  string // ipv4 or ipv6
+	srcIP   net.IP // for edns0 subnet option
 	options resolverOptions
 }
 
@@ -217,6 +235,12 @@ func (r *resolver) Init(opts ...ResolverOption) error {
 	if r.options.ttl != 0 {
 		r.ttl = r.options.ttl
 	}
+	if r.options.prefer != "" {
+		r.prefer = r.options.prefer
+	}
+	if r.options.srcIP != nil {
+		r.srcIP = r.options.srcIP
+	}
 
 	var nss []NameServer
 	for _, ns := range r.servers {
@@ -259,8 +283,9 @@ func (r *resolver) Resolve(host string) (ips []net.IP, err error) {
 		host = host + "." + domain
 	}
 
+	ctx := context.Background()
 	for _, ns := range r.copyServers() {
-		ips, err = r.resolve(ns.exchanger, host)
+		ips, err = r.resolve(ctx, ns.exchanger, host)
 		if err != nil {
 			log.Logf("[resolver] %s via %s : %s", host, ns.String(), err)
 			continue
@@ -277,7 +302,7 @@ func (r *resolver) Resolve(host string) (ips []net.IP, err error) {
 	return
 }
 
-func (r *resolver) resolve(ex Exchanger, host string) (ips []net.IP, err error) {
+func (r *resolver) resolve(ctx context.Context, ex Exchanger, host string) (ips []net.IP, err error) {
 	if ex == nil {
 		return
 	}
@@ -286,7 +311,6 @@ func (r *resolver) resolve(ex Exchanger, host string) (ips []net.IP, err error)
 	prefer := r.prefer
 	r.mux.RUnlock()
 
-	ctx := context.Background()
 	if prefer == "ipv6" { // prefer ipv6
 		mq := &dns.Msg{}
 		mq.SetQuestion(dns.Fqdn(host), dns.TypeAAAA)
@@ -302,9 +326,15 @@ func (r *resolver) resolve(ex Exchanger, host string) (ips []net.IP, err error)
 }
 
 func (r *resolver) resolveIPs(ctx context.Context, ex Exchanger, mq *dns.Msg) (ips []net.IP, err error) {
-	mr, _, err := r.exchangeMsg(ctx, ex, mq)
-	if err != nil {
-		return
+	key := newResolverCacheKey(&mq.Question[0])
+	mr := r.cache.loadCache(key)
+	if mr == nil {
+		r.addSubnetOpt(mq)
+		mr, err = r.exchangeMsg(ctx, ex, mq)
+		if err != nil {
+			return
+		}
+		r.cache.storeCache(key, mr, r.TTL())
 	}
 
 	for _, ans := range mr.Answer {
@@ -319,49 +349,73 @@ func (r *resolver) resolveIPs(ctx context.Context, ex Exchanger, mq *dns.Msg) (i
 	return
 }
 
+func (r *resolver) addSubnetOpt(m *dns.Msg) {
+	if m == nil || r.srcIP == nil {
+		return
+	}
+	opt := new(dns.OPT)
+	opt.Hdr.Name = "."
+	opt.Hdr.Rrtype = dns.TypeOPT
+	e := new(dns.EDNS0_SUBNET)
+	e.Code = dns.EDNS0SUBNET
+	if ip := r.srcIP.To4(); ip != nil {
+		e.Family = 1
+		e.SourceNetmask = 32
+		e.Address = ip.To4()
+	} else {
+		e.Family = 2
+		e.SourceNetmask = 128
+		e.Address = r.srcIP
+	}
+	opt.Option = append(opt.Option, e)
+	m.Extra = append(m.Extra, opt)
+}
+
 func (r *resolver) Exchange(ctx context.Context, query []byte) (reply []byte, err error) {
 	mq := &dns.Msg{}
 	if err = mq.Unpack(query); err != nil {
 		return
 	}
 
-	var qs string
-	if len(mq.Question) > 0 {
-		qs = mq.Question[0].String()
+	if len(mq.Question) == 0 {
+		return nil, errors.New("empty question")
 	}
 
 	var mr *dns.Msg
-	for _, ns := range r.copyServers() {
-		var cache bool
-		mr, cache, err = r.exchangeMsg(ctx, ns.exchanger, mq)
-		log.Logf("[dns] exchange message %d via %s (cache hit: %v): %s", mq.Id, ns.String(), cache, qs)
-		if err == nil {
-			break
-		}
-		log.Logf("[dns] exchange message %d via %s: %s", mq.Id, ns.String(), err)
-	}
-	if err != nil {
-		return
-	}
-	return mr.Pack()
-}
-
-func (r *resolver) exchangeMsg(ctx context.Context, ex Exchanger, mq *dns.Msg) (mr *dns.Msg, cache bool, err error) {
 	// Only cache for single question.
 	if len(mq.Question) == 1 {
 		key := newResolverCacheKey(&mq.Question[0])
 		mr = r.cache.loadCache(key)
 		if mr != nil {
-			cache = true
+			log.Logf("[dns] exchange message %d (cached): %s", mq.Id, mq.Question[0].String())
 			mr.Id = mq.Id
-			return
+			return mr.Pack()
 		}
 
 		defer func() {
-			r.cache.storeCache(key, mr, r.TTL())
+			if mr != nil {
+				r.cache.storeCache(key, mr, r.TTL())
+			}
 		}()
 	}
 
+	r.addSubnetOpt(mq)
+
+	for _, ns := range r.copyServers() {
+		log.Logf("[dns] exchange message %d via %s: %s", mq.Id, ns.String(), mq.Question[0].String())
+		mr, err = r.exchangeMsg(ctx, ns.exchanger, mq)
+		if err == nil {
+			break
+		}
+		log.Logf("[dns] exchange message %d via %s: %s", mq.Id, ns.String(), err)
+	}
+	if err != nil {
+		return
+	}
+	return mr.Pack()
+}
+
+func (r *resolver) exchangeMsg(ctx context.Context, ex Exchanger, mq *dns.Msg) (mr *dns.Msg, err error) {
 	query, err := mq.Pack()
 	if err != nil {
 		return
@@ -386,6 +440,7 @@ func (r *resolver) TTL() time.Duration {
 func (r *resolver) Reload(rd io.Reader) error {
 	var ttl, timeout, period time.Duration
 	var domain, prefer string
+	var srcIP net.IP
 	var nss []NameServer
 
 	if rd == nil || r.Stopped() {
@@ -422,6 +477,10 @@ func (r *resolver) Reload(rd io.Reader) error {
 			if len(ss) > 1 {
 				prefer = strings.ToLower(ss[1])
 			}
+		case "ip":
+			if len(ss) > 1 {
+				srcIP = net.ParseIP(ss[1])
+			}
 		case "nameserver": // nameserver option, compatible with /etc/resolv.conf
 			if len(ss) <= 1 {
 				break
@@ -461,6 +520,7 @@ func (r *resolver) Reload(rd io.Reader) error {
 	r.domain = domain
 	r.period = period
 	r.prefer = prefer
+	r.srcIP = srcIP
 	r.servers = nss
 	r.mux.Unlock()