resolve to ip on demand

app/router/condition.go

@@ -258,8 +258,9 @@ func NewCIDRMatcher(ip []byte, mask uint32, onSource bool) (*CIDRMatcher, error)
 
 func (v *CIDRMatcher) Apply(ctx context.Context) bool {
 	ips := make([]net.IP, 0, 4)
-	if resolveIPs, ok := proxy.ResolvedIPsFromContext(ctx); ok {
-		for _, rip := range resolveIPs {
+	if resolver, ok := proxy.ResolvedIPsFromContext(ctx); ok {
+		resolvedIPs := resolver.Resolve()
+		for _, rip := range resolvedIPs {
 			if !rip.Family().IsIPv6() {
 				continue
 			}
@@ -301,8 +302,9 @@ func NewIPv4Matcher(ipnet *net.IPNetTable, onSource bool) *IPv4Matcher {
 
 func (v *IPv4Matcher) Apply(ctx context.Context) bool {
 	ips := make([]net.IP, 0, 4)
-	if resolveIPs, ok := proxy.ResolvedIPsFromContext(ctx); ok {
-		for _, rip := range resolveIPs {
+	if resolver, ok := proxy.ResolvedIPsFromContext(ctx); ok {
+		resolvedIPs := resolver.Resolve()
+		for _, rip := range resolvedIPs {
 			if !rip.Family().IsIPv4() {
 				continue
 			}

app/router/config.pb.go

@@ -54,17 +54,21 @@ const (
 	Config_UseIp Config_DomainStrategy = 1
 	// Resolve to IP if the domain doesn't match any rules.
 	Config_IpIfNonMatch Config_DomainStrategy = 2
+	// Resolve to IP if any rule requires IP matching.
+	Config_IpOnDemand Config_DomainStrategy = 3
 )
 
 var Config_DomainStrategy_name = map[int32]string{
 	0: "AsIs",
 	1: "UseIp",
 	2: "IpIfNonMatch",
+	3: "IpOnDemand",
 }
 var Config_DomainStrategy_value = map[string]int32{
 	"AsIs":         0,
 	"UseIp":        1,
 	"IpIfNonMatch": 2,
+	"IpOnDemand":   3,
 }
 
 func (x Config_DomainStrategy) String() string {
@@ -318,45 +322,45 @@ func init() {
 func init() { proto.RegisterFile("v2ray.com/core/app/router/config.proto", fileDescriptor0) }
 
 var fileDescriptor0 = []byte{
-	// 626 bytes of a gzipped FileDescriptorProto
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-	0x00, 0x00,
+	// 640 bytes of a gzipped FileDescriptorProto
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 }

app/router/config.proto

@@ -76,6 +76,9 @@ message Config {
 
     // Resolve to IP if the domain doesn't match any rules.
     IpIfNonMatch = 2;
+
+    // Resolve to IP if any rule requires IP matching.
+    IpOnDemand = 3;
   }
   DomainStrategy domain_strategy = 1;
   repeated RoutingRule rule = 2;

app/router/router.go

@@ -64,7 +64,42 @@ func (r *Router) resolveIP(dest net.Destination) []net.Address {
 	return dests
 }
 
+type ipResolver struct {
+	ip        []net.Address
+	domain    string
+	resolved  bool
+	dnsServer dns.Server
+}
+
+func (r *ipResolver) Resolve() []net.Address {
+	if r.resolved {
+		return r.ip
+	}
+
+	log.Trace(newError("looking for IP for domain: ", r.domain))
+	r.resolved = true
+	ips := r.dnsServer.Get(r.domain)
+	if len(ips) == 0 {
+		return nil
+	}
+	r.ip = make([]net.Address, len(ips))
+	for i, ip := range ips {
+		r.ip[i] = net.IPAddress(ip)
+	}
+	return r.ip
+}
+
 func (r *Router) TakeDetour(ctx context.Context) (string, error) {
+	resolver := &ipResolver{
+		dnsServer: r.dnsServer,
+	}
+	if r.domainStrategy == Config_IpOnDemand {
+		if dest, ok := proxy.TargetFromContext(ctx); ok && dest.Address.Family().IsDomain() {
+			resolver.domain = dest.Address.Domain()
+			ctx = proxy.ContextWithResolveIPs(ctx, resolver)
+		}
+	}
+
 	for _, rule := range r.rules {
 		if rule.Apply(ctx) {
 			return rule.Tag, nil
@@ -77,10 +112,10 @@ func (r *Router) TakeDetour(ctx context.Context) (string, error) {
 	}
 
 	if r.domainStrategy == Config_IpIfNonMatch && dest.Address.Family().IsDomain() {
-		log.Trace(newError("looking up IP for ", dest))
-		ipDests := r.resolveIP(dest)
-		if ipDests != nil {
-			ctx = proxy.ContextWithResolveIPs(ctx, ipDests)
+		resolver.domain = dest.Address.Domain()
+		ips := resolver.Resolve()
+		if len(ips) > 0 {
+			ctx = proxy.ContextWithResolveIPs(ctx, resolver)
 			for _, rule := range r.rules {
 				if rule.Apply(ctx) {
 					return rule.Tag, nil

proxy/context.go

@@ -64,11 +64,15 @@ func InboundTagFromContext(ctx context.Context) (string, bool) {
 	return v, ok
 }
 
-func ContextWithResolveIPs(ctx context.Context, ips []net.Address) context.Context {
-	return context.WithValue(ctx, resolvedIPsKey, ips)
+type IPResolver interface {
+	Resolve() []net.Address
 }
 
-func ResolvedIPsFromContext(ctx context.Context) ([]net.Address, bool) {
-	ips, ok := ctx.Value(resolvedIPsKey).([]net.Address)
+func ContextWithResolveIPs(ctx context.Context, f IPResolver) context.Context {
+	return context.WithValue(ctx, resolvedIPsKey, f)
+}
+
+func ResolvedIPsFromContext(ctx context.Context) (IPResolver, bool) {
+	ips, ok := ctx.Value(resolvedIPsKey).(IPResolver)
 	return ips, ok
 }