fix: ACL IP rules not working for domain requests if resolver not set

app/cmd/server.go

@@ -368,6 +368,7 @@ func (c *serverConfig) fillOutboundConfig(hyConfig *server.Config) error {
 	var uOb outbounds.PluggableOutbound // "unified" outbound
 
 	// ACL
+	hasACL := false
 	if c.ACL.File != "" && len(c.ACL.Inline) > 0 {
 		return configError{Field: "acl", Err: errors.New("cannot set both acl.file and acl.inline")}
 	}
@@ -377,12 +378,14 @@ func (c *serverConfig) fillOutboundConfig(hyConfig *server.Config) error {
 		DownloadErrFunc: geoipDownloadErrFunc,
 	}
 	if c.ACL.File != "" {
+		hasACL = true
 		acl, err := outbounds.NewACLEngineFromFile(c.ACL.File, obs, gLoader.Load)
 		if err != nil {
 			return configError{Field: "acl.file", Err: err}
 		}
 		uOb = acl
 	} else if len(c.ACL.Inline) > 0 {
+		hasACL = true
 		acl, err := outbounds.NewACLEngineFromString(strings.Join(c.ACL.Inline, "\n"), obs, gLoader.Load)
 		if err != nil {
 			return configError{Field: "acl.inline", Err: err}
@@ -396,7 +399,12 @@ func (c *serverConfig) fillOutboundConfig(hyConfig *server.Config) error {
 	// Resolver
 	switch strings.ToLower(c.Resolver.Type) {
 	case "", "system":
-		// Do nothing. DirectOutbound will use system resolver by default.
+		if hasACL {
+			// If the user uses ACL, we must put a resolver in front of it,
+			// for IP rules to work on domain requests.
+			uOb = outbounds.NewSystemResolver(uOb)
+		}
+		// Otherwise we can just rely on outbound handling on its own.
 	case "tcp":
 		if c.Resolver.TCP.Addr == "" {
 			return configError{Field: "resolver.tcp.addr", Err: errors.New("empty resolver address")}

extras/outbounds/dns_system.go

@@ -0,0 +1,41 @@
+package outbounds
+
+import (
+	"net"
+)
+
+// systemResolver is a PluggableOutbound DNS resolver that resolves hostnames
+// using the default system DNS server.
+// Outbounds typically don't require a resolver, as they can do DNS resolution
+// themselves. However, when using ACL, it's necessary to place a resolver in
+// front of it in the pipeline (for IP rules to work on domain requests).
+type systemResolver struct {
+	Next PluggableOutbound
+}
+
+func NewSystemResolver(next PluggableOutbound) PluggableOutbound {
+	return &systemResolver{
+		Next: next,
+	}
+}
+
+func (r *systemResolver) resolve(reqAddr *AddrEx) {
+	ips, err := net.LookupIP(reqAddr.Host)
+	if err != nil {
+		reqAddr.ResolveInfo = &ResolveInfo{Err: err}
+		return
+	}
+	info := &ResolveInfo{}
+	info.IPv4, info.IPv6 = splitIPv4IPv6(ips)
+	reqAddr.ResolveInfo = info
+}
+
+func (r *systemResolver) TCP(reqAddr *AddrEx) (net.Conn, error) {
+	r.resolve(reqAddr)
+	return r.Next.TCP(reqAddr)
+}
+
+func (r *systemResolver) UDP(reqAddr *AddrEx) (UDPConn, error) {
+	r.resolve(reqAddr)
+	return r.Next.UDP(reqAddr)
+}