Feature: can set custom interface for dns nameserver (#2126)

config/config.go

@@ -477,6 +477,10 @@ func parseNameServer(servers []string) ([]dns.NameServer, error) {
 			return nil, fmt.Errorf("DNS NameServer[%d] format error: %s", idx, err.Error())
 		}
 
+		// parse with specific interface
+		// .e.g 10.0.0.1#en0
+		interfaceName := u.Fragment
+
 		var addr, dnsNetType string
 		switch u.Scheme {
 		case "udp":
@@ -508,6 +512,7 @@ func parseNameServer(servers []string) ([]dns.NameServer, error) {
 			dns.NameServer{
 				Net:       dnsNetType,
 				Addr:      addr,
+				Interface: interfaceName,
 			},
 		)
 	}

dns/doh.go

@@ -79,7 +79,7 @@ func (dc *dohClient) doRequest(req *http.Request) (msg *D.Msg, err error) {
 	return msg, err
 }
 
-func newDoHClient(url string, r *Resolver) *dohClient {
+func newDoHClient(url, iface string, r *Resolver) *dohClient {
 	return &dohClient{
 		url: url,
 		transport: &http.Transport{
@@ -95,7 +95,12 @@ func newDoHClient(url string, r *Resolver) *dohClient {
 					return nil, err
 				}
 
-				return dialer.DialContext(ctx, "tcp", net.JoinHostPort(ip.String(), port))
+				options := []dialer.Option{}
+				if iface != "" {
+					options = append(options, dialer.WithInterface(iface))
+				}
+
+				return dialer.DialContext(ctx, "tcp", net.JoinHostPort(ip.String(), port), options...)
 			},
 		},
 	}

dns/util.go

@@ -51,7 +51,7 @@ func transform(servers []NameServer, resolver *Resolver) []dnsClient {
 	for _, s := range servers {
 		switch s.Net {
 		case "https":
-			ret = append(ret, newDoHClient(s.Addr, resolver))
+			ret = append(ret, newDoHClient(s.Addr, s.Interface, resolver))
 			continue
 		case "dhcp":
 			ret = append(ret, newDHCPClient(s.Addr))