DNS: Add tag for DnsServerObject (#4515)

Author: Fangliding

app/dns/config.pb.go

@@ -29,6 +29,7 @@ message NameServer {
   repeated OriginalRule original_rules = 4;
   QueryStrategy query_strategy = 7;
   bool allowUnexpectedIPs = 8;
+  string tag = 9;
 }
 
 enum DomainMatchingType {

app/dns/config.proto

@@ -9,6 +9,7 @@ import (
 	"github.com/xtls/xray-core/app/router"
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/common/net"
+	"github.com/xtls/xray-core/common/session"
 	"github.com/xtls/xray-core/common/strmatcher"
 	"github.com/xtls/xray-core/core"
 	"github.com/xtls/xray-core/features/dns"
@@ -31,6 +32,7 @@ type Client struct {
 	domains            []string
 	expectIPs          []*router.GeoIPMatcher
 	allowUnexpectedIPs bool
+	tag        string
 }
 
 var errExpectedIPNonMatch = errors.New("expectIPs not match")
@@ -168,6 +170,7 @@ func NewClient(
 		client.domains = rules
 		client.expectIPs = matchers
 		client.allowUnexpectedIPs = ns.AllowUnexpectedIPs
+		client.tag = ns.Tag
 		return nil
 	})
 	return client, err
@@ -181,6 +184,13 @@ func (c *Client) Name() string {
 // QueryIP sends DNS query to the name server with the client's IP.
 func (c *Client) QueryIP(ctx context.Context, domain string, option dns.IPOption, disableCache bool) ([]net.IP, error) {
 	ctx, cancel := context.WithTimeout(ctx, 4*time.Second)
+	if len(c.tag) != 0 {
+		content := session.InboundFromContext(ctx)
+		errors.LogDebug(ctx, "DNS: client override tag from ", content.Tag, " to ", c.tag)
+		// create a new context to override the tag
+		// do not direct set *content.Tag, it might be used by other clients
+		ctx = session.ContextWithInbound(ctx, &session.Inbound{Tag: c.tag})
+	}
 	ips, err := c.server.QueryIP(ctx, domain, c.clientIP, option, disableCache)
 	cancel()
 

app/dns/nameserver.go

@@ -20,6 +20,7 @@ type NameServerConfig struct {
 	ExpectIPs          StringList `json:"expectIps"`
 	QueryStrategy      string     `json:"queryStrategy"`
 	AllowUnexpectedIPs bool       `json:"allowUnexpectedIps"`
+	Tag                string     `json:"tag"`
 }
 
 func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
@@ -38,6 +39,7 @@ func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
 		ExpectIPs          StringList `json:"expectIps"`
 		QueryStrategy      string     `json:"queryStrategy"`
 		AllowUnexpectedIPs bool       `json:"allowUnexpectedIps"`
+		Tag                string     `json:"tag"`
 	}
 	if err := json.Unmarshal(data, &advanced); err == nil {
 		c.Address = advanced.Address
@@ -48,6 +50,7 @@ func (c *NameServerConfig) UnmarshalJSON(data []byte) error {
 		c.ExpectIPs = advanced.ExpectIPs
 		c.QueryStrategy = advanced.QueryStrategy
 		c.AllowUnexpectedIPs = advanced.AllowUnexpectedIPs
+		c.Tag = advanced.Tag
 		return nil
 	}
 
@@ -121,6 +124,7 @@ func (c *NameServerConfig) Build() (*dns.NameServer, error) {
 		OriginalRules:      originalRules,
 		QueryStrategy:      resolveQueryStrategy(c.QueryStrategy),
 		AllowUnexpectedIPs: c.AllowUnexpectedIPs,
+		Tag:                c.Tag,
 	}, nil
 }