DNS: Add allowUnexpectedIPs for DnsServerObject (#4497)

Closes #4424

Author: patterniha

app/dns/config.pb.go

@@ -28,6 +28,7 @@ message NameServer {
   repeated xray.app.router.GeoIP geoip = 3;
   repeated OriginalRule original_rules = 4;
   QueryStrategy query_strategy = 7;
+  bool allowUnexpectedIPs = 8;
 }
 
 enum DomainMatchingType {

app/dns/config.proto

@@ -25,11 +25,12 @@ type Server interface {
 
 // Client is the interface for DNS client.
 type Client struct {
-	server       Server
-	clientIP     net.IP
-	skipFallback bool
-	domains      []string
-	expectIPs    []*router.GeoIPMatcher
+	server             Server
+	clientIP           net.IP
+	skipFallback       bool
+	domains            []string
+	expectIPs          []*router.GeoIPMatcher
+	allowUnexpectedIPs bool
 }
 
 var errExpectedIPNonMatch = errors.New("expectIPs not match")
@@ -166,6 +167,7 @@ func NewClient(
 		client.skipFallback = ns.SkipFallback
 		client.domains = rules
 		client.expectIPs = matchers
+		client.allowUnexpectedIPs = ns.AllowUnexpectedIPs
 		return nil
 	})
 	return client, err
@@ -203,6 +205,9 @@ func (c *Client) MatchExpectedIPs(domain string, ips []net.IP) ([]net.IP, error)
 		}
 	}
 	if len(newIps) == 0 {
+		if c.allowUnexpectedIPs {
+			return ips, nil
+		}
 		return nil, errExpectedIPNonMatch
 	}
 	errors.LogDebug(context.Background(), "domain ", domain, " expectIPs ", newIps, " matched at server ", c.Name())

app/dns/nameserver.go

@@ -12,13 +12,14 @@ import (
 )
 
 type NameServerConfig struct {
-	Address       *Address   `json:"address"`
-	ClientIP      *Address   `json:"clientIp"`
-	Port          uint16     `json:"port"`
-	SkipFallback  bool       `json:"skipFallback"`
-	Domains       []string   `json:"domains"`
-	ExpectIPs     StringList `json:"expectIps"`
-	QueryStrategy string     `json:"queryStrategy"`
+	Address            *Address   `json:"address"`
+	ClientIP           *Address   `json:"clientIp"`
+	Port               uint16     `json:"port"`
+	SkipFallback       bool       `json:"skipFallback"`
+	Domains            []string   `json:"domains"`
+	ExpectIPs          StringList `json:"expectIps"`
+	QueryStrategy      string     `json:"queryStrategy"`
+	AllowUnexpectedIPs bool       `json:"allowUnexpectedIps"`
 }
 
 func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
@@ -29,13 +30,14 @@ func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
 	}
 
 	var advanced struct {
-		Address       *Address   `json:"address"`
-		ClientIP      *Address   `json:"clientIp"`
-		Port          uint16     `json:"port"`
-		SkipFallback  bool       `json:"skipFallback"`
-		Domains       []string   `json:"domains"`
-		ExpectIPs     StringList `json:"expectIps"`
-		QueryStrategy string     `json:"queryStrategy"`
+		Address            *Address   `json:"address"`
+		ClientIP           *Address   `json:"clientIp"`
+		Port               uint16     `json:"port"`
+		SkipFallback       bool       `json:"skipFallback"`
+		Domains            []string   `json:"domains"`
+		ExpectIPs          StringList `json:"expectIps"`
+		QueryStrategy      string     `json:"queryStrategy"`
+		AllowUnexpectedIPs bool       `json:"allowUnexpectedIps"`
 	}
 	if err := json.Unmarshal(data, &advanced); err == nil {
 		c.Address = advanced.Address
@@ -45,6 +47,7 @@ func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
 		c.Domains = advanced.Domains
 		c.ExpectIPs = advanced.ExpectIPs
 		c.QueryStrategy = advanced.QueryStrategy
+		c.AllowUnexpectedIPs = advanced.AllowUnexpectedIPs
 		return nil
 	}
 
@@ -111,12 +114,13 @@ func (c *NameServerConfig) Build() (*dns.NameServer, error) {
 			Address: c.Address.Build(),
 			Port:    uint32(c.Port),
 		},
-		ClientIp:          myClientIP,
-		SkipFallback:      c.SkipFallback,
-		PrioritizedDomain: domains,
-		Geoip:             geoipList,
-		OriginalRules:     originalRules,
-		QueryStrategy:     resolveQueryStrategy(c.QueryStrategy),
+		ClientIp:           myClientIP,
+		SkipFallback:       c.SkipFallback,
+		PrioritizedDomain:  domains,
+		Geoip:              geoipList,
+		OriginalRules:      originalRules,
+		QueryStrategy:      resolveQueryStrategy(c.QueryStrategy),
+		AllowUnexpectedIPs: c.AllowUnexpectedIPs,
 	}, nil
 }