feat: add multiple addresses support for DNS modifier

modifier/interface.go

@@ -4,7 +4,7 @@ type Modifier interface {
 	// Name returns the name of the modifier.
 	Name() string
 	// New returns a new modifier instance.
-	New(args map[string]interface{}) (Instance, error)
+	New(args map[string][]interface{}) (Instance, error)
 }
 
 type Instance interface{}

modifier/udp/dns.go

@@ -1,7 +1,10 @@
 package udp
 
 import (
+	"encoding/binary"
 	"errors"
+	"hash/fnv"
+	"math/rand/v2"
 	"net"
 
 	"github.com/apernet/OpenGFW/modifier"
@@ -24,23 +27,28 @@ func (m *DNSModifier) Name() string {
 	return "dns"
 }
 
-func (m *DNSModifier) New(args map[string]interface{}) (modifier.Instance, error) {
+func (m *DNSModifier) New(args map[string][]interface{}) (modifier.Instance, error) {
 	i := &dnsModifierInstance{}
-	aStr, ok := args["a"].(string)
+	i.seed = rand.Uint32()
+	for _, arg := range args["a"] {
+		aStr, ok := arg.(string)
 		if ok {
 			a := net.ParseIP(aStr).To4()
 			if a == nil {
 				return nil, &modifier.ErrInvalidArgs{Err: errInvalidIP}
 			}
-		i.A = a
+			i.A = append(i.A, a)
 		}
-	aaaaStr, ok := args["aaaa"].(string)
+	}
+	for _, arg := range args["aaaa"] {
+		aaaaStr, ok := arg.(string)
 		if ok {
 			aaaa := net.ParseIP(aaaaStr).To16()
 			if aaaa == nil {
 				return nil, &modifier.ErrInvalidArgs{Err: errInvalidIP}
 			}
-		i.AAAA = aaaa
+			i.AAAA = append(i.AAAA, aaaa)
+		}
 	}
 	return i, nil
 }
@@ -48,8 +56,9 @@ func (m *DNSModifier) New(args map[string]interface{}) (modifier.Instance, error
 var _ modifier.UDPModifierInstance = (*dnsModifierInstance)(nil)
 
 type dnsModifierInstance struct {
-	A    net.IP
-	AAAA net.IP
+	A    []net.IP
+	AAAA []net.IP
+	seed uint32
 }
 
 func (i *dnsModifierInstance) Process(data []byte) ([]byte, error) {
@@ -64,26 +73,41 @@ func (i *dnsModifierInstance) Process(data []byte) ([]byte, error) {
 	if len(dns.Questions) == 0 {
 		return nil, &modifier.ErrInvalidPacket{Err: errEmptyDNSQuestion}
 	}
+
+	// Hash the query name so that DNS response is fixed for a given query.
+	// Use a random seed to avoid determinism.
+	hashStringToIndex := func(b []byte, sliceLength int, seed uint32) int {
+        h := fnv.New32a()
+		seedBytes := make([]byte, 4)
+        binary.LittleEndian.PutUint32(seedBytes, seed)
+		h.Write(seedBytes)
+        h.Write(b)
+        hashValue := h.Sum32()
+        return int(hashValue % uint32(sliceLength))
+    }
+
 	// In practice, most if not all DNS clients only send one question
 	// per packet, so we don't care about the rest for now.
 	q := dns.Questions[0]
 	switch q.Type {
 	case layers.DNSTypeA:
 		if i.A != nil {
+			idx := hashStringToIndex(q.Name, len(i.A), i.seed)
 			dns.Answers = []layers.DNSResourceRecord{{
 				Name:  q.Name,
 				Type:  layers.DNSTypeA,
 				Class: layers.DNSClassIN,
-				IP:    i.A,
+				IP:    i.A[idx],
 			}}
 		}
 	case layers.DNSTypeAAAA:
 		if i.AAAA != nil {
+			idx := hashStringToIndex(q.Name, len(i.AAAA), i.seed)
 			dns.Answers = []layers.DNSResourceRecord{{
 				Name:  q.Name,
 				Type:  layers.DNSTypeAAAA,
 				Class: layers.DNSClassIN,
-				IP:    i.AAAA,
+				IP:    i.AAAA[idx],
 			}}
 		}
 	}

ruleset/expr.go

@@ -33,7 +33,7 @@ type ExprRule struct {
 
 type ModifierEntry struct {
 	Name string                   `yaml:"name"`
-	Args map[string]interface{} `yaml:"args"`
+	Args map[string][]interface{} `yaml:"args"`
 }
 
 func ExprRulesFromYAML(file string) ([]ExprRule, error) {