package redir import ( "errors" "net" "syscall" "unsafe" "github.com/Dreamacro/go-shadowsocks2/socks" ) const ( SO_ORIGINAL_DST = 80 // from linux/include/uapi/linux/netfilter_ipv4.h IP6T_SO_ORIGINAL_DST = 80 // from linux/include/uapi/linux/netfilter_ipv6/ip6_tables.h ) func parserPacket(conn net.Conn) (socks.Addr, error) { c, ok := conn.(*net.TCPConn) if !ok { return nil, errors.New("only work with TCP connection") } rc, err := c.SyscallConn() if err != nil { return nil, err } var addr socks.Addr rc.Control(func(fd uintptr) { addr, err = getorigdst(fd) }) return addr, err } // Call getorigdst() from linux/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c func getorigdst(fd uintptr) (socks.Addr, error) { raw := syscall.RawSockaddrInet4{} siz := unsafe.Sizeof(raw) if err := socketcall(GETSOCKOPT, fd, syscall.IPPROTO_IP, SO_ORIGINAL_DST, uintptr(unsafe.Pointer(&raw)), uintptr(unsafe.Pointer(&siz)), 0); err != nil { return nil, err } addr := make([]byte, 1+net.IPv4len+2) addr[0] = socks.AtypIPv4 copy(addr[1:1+net.IPv4len], raw.Addr[:]) port := (*[2]byte)(unsafe.Pointer(&raw.Port)) // big-endian addr[1+net.IPv4len], addr[1+net.IPv4len+1] = port[0], port[1] return addr, nil }