code: def nextheader(fobj):
      return struct.unpack(">4sI", fobj.read(HEADERSIZE))
  
imports: from __future__ import annotations
  import io
  import os
  import struct
  import sys
  from .None import Image, ImageFile, PngImagePlugin, features
label_desc: Use image node_id 1 for calling a global function with example usage: nextheader(fobj) and returns: struct