udp.go

package socks5

import (
	"bytes"
	"log"
	"net"
)

// UDP remote conn which u want to connect with your dialer.
// Error or OK both replied.
// Addr can be used to associate TCP connection with the coming UDP connection.
func (r *Request) UDP(c *net.TCPConn, serverAddr *net.UDPAddr) (*net.UDPAddr, error) {
	var clientAddr *net.UDPAddr
	var err error
	if bytes.Compare(r.DstPort, []byte{0x00, 0x00}) == 0 {
		// If the requested Host/Port is all zeros, the relay should simply use the Host/Port that sent the request.
		// https://stackoverflow.com/questions/62283351/how-to-use-socks-5-proxy-with-tidudpclient-properly
		clientAddr, err = net.ResolveUDPAddr("udp", c.RemoteAddr().String())
	} else {
		clientAddr, err = net.ResolveUDPAddr("udp", r.Address())
	}
	if err != nil {
		var p *Reply
		if r.Atyp == ATYPIPv4 || r.Atyp == ATYPDomain {
			p = NewReply(RepHostUnreachable, ATYPIPv4, []byte{0x00, 0x00, 0x00, 0x00}, []byte{0x00, 0x00})
		} else {
			p = NewReply(RepHostUnreachable, ATYPIPv6, []byte(net.IPv6zero), []byte{0x00, 0x00})
		}
		if _, err := p.WriteTo(c); err != nil {
			return nil, err
		}
		return nil, err
	}
	if Debug {
		log.Println("Client wants to start UDP talk use", clientAddr.String())
	}
	a, addr, port, err := ParseAddress(serverAddr.String())
	if err != nil {
		var p *Reply
		if r.Atyp == ATYPIPv4 || r.Atyp == ATYPDomain {
			p = NewReply(RepHostUnreachable, ATYPIPv4, []byte{0x00, 0x00, 0x00, 0x00}, []byte{0x00, 0x00})
		} else {
			p = NewReply(RepHostUnreachable, ATYPIPv6, []byte(net.IPv6zero), []byte{0x00, 0x00})
		}
		if _, err := p.WriteTo(c); err != nil {
			return nil, err
		}
		return nil, err
	}
	p := NewReply(RepSuccess, a, addr, port)
	if _, err := p.WriteTo(c); err != nil {
		return nil, err
	}

	return clientAddr, nil
}