Fix: unexpected proxy dial behavior on mapping mode

constant/dns.go

@@ -0,0 +1,70 @@
+package constant
+
+import (
+	"encoding/json"
+	"errors"
+)
+
+// DNSModeMapping is a mapping for EnhancedMode enum
+var DNSModeMapping = map[string]DNSMode{
+	DNSNormal.String():  DNSNormal,
+	DNSFakeIP.String():  DNSFakeIP,
+	DNSMapping.String(): DNSMapping,
+}
+
+const (
+	DNSNormal DNSMode = iota
+	DNSFakeIP
+	DNSMapping
+)
+
+type DNSMode int
+
+// UnmarshalYAML unserialize EnhancedMode with yaml
+func (e *DNSMode) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var tp string
+	if err := unmarshal(&tp); err != nil {
+		return err
+	}
+	mode, exist := DNSModeMapping[tp]
+	if !exist {
+		return errors.New("invalid mode")
+	}
+	*e = mode
+	return nil
+}
+
+// MarshalYAML serialize EnhancedMode with yaml
+func (e DNSMode) MarshalYAML() (interface{}, error) {
+	return e.String(), nil
+}
+
+// UnmarshalJSON unserialize EnhancedMode with json
+func (e *DNSMode) UnmarshalJSON(data []byte) error {
+	var tp string
+	json.Unmarshal(data, &tp)
+	mode, exist := DNSModeMapping[tp]
+	if !exist {
+		return errors.New("invalid mode")
+	}
+	*e = mode
+	return nil
+}
+
+// MarshalJSON serialize EnhancedMode with json
+func (e DNSMode) MarshalJSON() ([]byte, error) {
+	return json.Marshal(e.String())
+}
+
+func (e DNSMode) String() string {
+	switch e {
+	case DNSNormal:
+		return "normal"
+	case DNSFakeIP:
+		return "fake-ip"
+	case DNSMapping:
+		return "redir-host"
+	default:
+		return "unknown"
+	}
+}

constant/metadata.go

@@ -71,6 +71,7 @@ type Metadata struct {
 	DstPort  string  `json:"destinationPort"`
 	AddrType int     `json:"-"`
 	Host     string  `json:"host"`
+	DNSMode  DNSMode `json:"dnsMode"`
 }
 
 func (m *Metadata) RemoteAddress() string {
@@ -85,6 +86,23 @@ func (m *Metadata) Resolved() bool {
 	return m.DstIP != nil
 }
 
+// Pure is used to solve unexpected behavior
+// when dialing proxy connection in DNSMapping mode.
+func (m *Metadata) Pure() *Metadata {
+	if m.DNSMode == DNSMapping && m.DstIP != nil {
+		copy := *m
+		copy.Host = ""
+		if copy.DstIP.To4() != nil {
+			copy.AddrType = AtypIPv4
+		} else {
+			copy.AddrType = AtypIPv6
+		}
+		return &copy
+	}
+
+	return m
+}
+
 func (m *Metadata) UDPAddr() *net.UDPAddr {
 	if m.NetWork != UDP || m.DstIP == nil {
 		return nil