Sockopt: Add addressPortStrategy (query SRV or TXT) (#4416)

Co-authored-by: 风扇滑翔翼 <Fangliding.fshxy@outlook.com>

transport/internet/dialer.go

@@ -2,6 +2,9 @@ package internet
 
 import (
 	"context"
+	"fmt"
+	gonet "net"
+	"strings"
 
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/dice"
@@ -140,6 +143,93 @@ func redirect(ctx context.Context, dst net.Destination, obt string) net.Conn {
 	return nil
 }
 
+func checkAddressPortStrategy(ctx context.Context, dest net.Destination, sockopt *SocketConfig) (*net.Destination, error) {
+	if sockopt.AddressPortStrategy == AddressPortStrategy_None {
+		return nil, nil
+	}
+	newDest := dest
+	var OverridePort, OverrideAddress bool
+	var OverrideBy string
+	switch sockopt.AddressPortStrategy {
+	case AddressPortStrategy_SrvPortOnly:
+		OverridePort = true
+		OverrideAddress = false
+		OverrideBy = "srv"
+	case AddressPortStrategy_SrvAddressOnly:
+		OverridePort = false
+		OverrideAddress = true
+		OverrideBy = "srv"
+	case AddressPortStrategy_SrvPortAndAddress:
+		OverridePort = true
+		OverrideAddress = true
+		OverrideBy = "srv"
+	case AddressPortStrategy_TxtPortOnly:
+		OverridePort = true
+		OverrideAddress = false
+		OverrideBy = "txt"
+	case AddressPortStrategy_TxtAddressOnly:
+		OverridePort = false
+		OverrideAddress = true
+		OverrideBy = "txt"
+	case AddressPortStrategy_TxtPortAndAddress:
+		OverridePort = true
+		OverrideAddress = true
+		OverrideBy = "txt"
+	default:
+		return nil, errors.New("unknown AddressPortStrategy")
+	}
+
+	if !dest.Address.Family().IsDomain() {
+		return nil, nil
+	}
+
+	if OverrideBy == "srv" {
+		errors.LogDebug(ctx, "query SRV record for "+dest.Address.String())
+		parts := strings.SplitN(dest.Address.String(), ".", 3)
+		if len(parts) != 3 {
+			return nil, errors.New("invalid address format", dest.Address.String())
+		}
+		_, srvRecords, err := gonet.DefaultResolver.LookupSRV(context.Background(), parts[0][1:], parts[1][1:], parts[2])
+		if err != nil {
+			return nil, errors.New("failed to lookup SRV record").Base(err)
+		}
+		errors.LogDebug(ctx, "SRV record: "+fmt.Sprintf("addr=%s, port=%d, priority=%d, weight=%d", srvRecords[0].Target, srvRecords[0].Port, srvRecords[0].Priority, srvRecords[0].Weight))
+		if OverridePort {
+			newDest.Port = net.Port(srvRecords[0].Port)
+		}
+		if OverrideAddress {
+			newDest.Address = net.ParseAddress(srvRecords[0].Target)
+		}
+		return &newDest, nil
+	}
+	if OverrideBy == "txt" {
+		errors.LogDebug(ctx, "query TXT record for "+dest.Address.String())
+		txtRecords, err := gonet.DefaultResolver.LookupTXT(ctx, dest.Address.String())
+		if err != nil {
+			errors.LogError(ctx, "failed to lookup SRV record: "+err.Error())
+			return nil, errors.New("failed to lookup SRV record").Base(err)
+		}
+		for _, txtRecord := range txtRecords {
+			errors.LogDebug(ctx, "TXT record: "+txtRecord)
+			addr_s, port_s, _ := net.SplitHostPort(string(txtRecord))
+			addr := net.ParseAddress(addr_s)
+			port, err := net.PortFromString(port_s)
+			if err != nil {
+				continue
+			}
+
+			if OverridePort {
+				newDest.Port = port
+			}
+			if OverrideAddress {
+				newDest.Address = addr
+			}
+			return &newDest, nil
+		}
+	}
+	return nil, nil
+}
+
 // DialSystem calls system dialer to create a network connection.
 func DialSystem(ctx context.Context, dest net.Destination, sockopt *SocketConfig) (net.Conn, error) {
 	var src net.Address
@@ -152,6 +242,11 @@ func DialSystem(ctx context.Context, dest net.Destination, sockopt *SocketConfig
 		return effectiveSystemDialer.Dial(ctx, src, dest, sockopt)
 	}
 
+	if newDest, err := checkAddressPortStrategy(ctx, dest, sockopt); err == nil && newDest != nil {
+		errors.LogInfo(ctx, "replace destination with "+newDest.String())
+		dest = *newDest
+	}
+
 	if canLookupIP(ctx, dest, sockopt) {
 		ips, err := lookupIP(dest.Address.String(), sockopt.DomainStrategy, src)
 		if err == nil && len(ips) > 0 {