package proxy

import (
	"encoding/binary"
	"net"
)

var v2sig = []byte("\r\n\r\n\x00\r\nQUIT\n")

// proxyV2Header builds a PROXY protocol v2 header carrying the client's real
// address so the backend can see it. Falls back to a LOCAL header if the
// addresses aren't TCP.
func proxyV2Header(src, dst net.Addr) []byte {
	s, sok := src.(*net.TCPAddr)
	d, dok := dst.(*net.TCPAddr)
	h := append([]byte{}, v2sig...)
	if !sok || !dok {
		return append(h, 0x20, 0x00, 0, 0)
	}
	if s4, d4 := s.IP.To4(), d.IP.To4(); s4 != nil && d4 != nil {
		h = append(h, 0x21, 0x11, 0, 12)
		h = append(h, s4...)
		h = append(h, d4...)
	} else {
		h = append(h, 0x21, 0x21, 0, 36)
		h = append(h, s.IP.To16()...)
		h = append(h, d.IP.To16()...)
	}
	h = binary.BigEndian.AppendUint16(h, uint16(s.Port))
	return binary.BigEndian.AppendUint16(h, uint16(d.Port))
}