package server

/**
 * WARNING WARNING WARNING
 * This file contains MANY DIRTY HACKS, and most of them made much assume to go internal code layout.
 * For every new go version, you MUST try to use every function, make sure they didn't panic for you.
 */

// WARZONE BEGINS HERE! MIND YOUR HEAD!

import (
	"reflect"
	"net"
	"golang.org/x/sys/unix"
)

const (
	SO_ORIGINAL_DST = 80
)

func GetFDFromTCPConn(conn *net.TCPConn) int {
	// Actual fd is stored at: (*(*TCPConn).conn.fd).sysfd
	v := reflect.ValueOf(*conn)
	c := v.FieldByName("conn")
	fdp := c.FieldByName("fd")
	fd := reflect.Indirect(fdp)
	sysfd := fd.FieldByName("sysfd")
	return int(sysfd.Int())
}

func GetAddr4FromFD(fd int) *net.TCPAddr {
	mtuinfo, err := unix.GetsockoptIPv6MTUInfo(fd, unix.IPPROTO_IP, SO_ORIGINAL_DST)
	if err != nil {
		panic(err)
	}
	addr := mtuinfo.Addr
	/*
		RawSockaddrInet6 layout:
			Family 2byte ignore or assert == AF_INET
			Port 2byte ipv4 port
			Flowinfo 4byte ipv4 address
			Addr 16byte ignore for ipv4
			Scope_id 4byte ignore for ipv4
	 */
	addr.Flowinfo = be32toh(addr.Flowinfo)
	a, b, c, d := byte(addr.Flowinfo >> 24), byte((addr.Flowinfo >> 16) & 255), byte((addr.Flowinfo >> 8) & 255), byte(addr.Flowinfo & 255)
	ip := net.IPv4(a, b, c, d)
	return &net.TCPAddr{IP: ip, Port: int(be16toh(addr.Port)), Zone: ""}
}

func GetAddr6FromFD(fd int) *net.TCPAddr {
	mtuinfo, err := unix.GetsockoptIPv6MTUInfo(fd, unix.IPPROTO_IPV6, SO_ORIGINAL_DST)
	if err != nil {
		panic(err)
	}
	addr := mtuinfo.Addr
	/*
		RawSockaddrInet6 layout:
			Family 2byte ignore or assert == AF_INET6
			Port 2byte ipv6 port
			Flowinfo 4byte ipv6 flowinfo ignore
			Addr 16byte ipv6 addr
			Scope_id 4byte ipv6 scope id ignore
	 */
	v6addr := make(net.IP, 16)
	// Make GC happy?
	copy(v6addr, addr.Addr[:])
	return &net.TCPAddr{IP: v6addr, Port: int(be16toh(addr.Port)), Zone: ""}
}