code: def write_headers(
      self, start_line, headers, chunk=None, callback=None
  ):
      if self.method == "HEAD":
          self._expected_content_remaining = 0
      elif "Content-Length" in headers:
          self._expected_content_remaining = int(
              headers["Content-Length"]
          )
      else:
          self._expected_content_remaining = None
      self.start_response(
          "%s %s" % (start_line.code, start_line.reason),
          [
              (native_str(k), native_str(v))
              for (k, v) in headers.get_all()
          ],
      )
      if chunk is not None:
          self.write(chunk, callback)
      elif callback is not None:
          callback()
      return _dummy_future
  
imports: from __future__ import absolute_import, division, print_function
  import sys
  from io import BytesIO
  import tornado
  from tornado.concurrent import Future
  from tornado import escape
  from tornado import httputil
  from tornado.log import access_log
  from tornado import web
  from tornado.escape import native_str
  from tornado.util import unicode_type, PY3
label_desc: Use image node_id 3 for calling the _WSGIConnection obj's underlying member method code with example usage: obj.write_headers(start_line, headers, chunk, callback) and returns: _dummy_future