code: def headers_received(self, first_line, headers):
      if self.request.expect_100_continue and first_line.code == 100:
          self._write_body(False)
          return
      self.code = first_line.code
      self.reason = first_line.reason
      self.headers = headers
  
      if self._should_follow_redirect():
          return
  
      if self.request.header_callback is not None:
          # Reassemble the start line.
          self.request.header_callback("%s %s %s\r\n" % first_line)
          for k, v in self.headers.get_all():
              self.request.header_callback("%s: %s\r\n" % (k, v))
          self.request.header_callback("\r\n")
  
imports: from __future__ import absolute_import, division, print_function
  from tornado.escape import utf8, _unicode
  from tornado import gen
  from tornado.httpclient import HTTPResponse, HTTPError, AsyncHTTPClient, main, _RequestProxy
  from tornado import httputil
  from tornado.http1connection import HTTP1Connection, HTTP1ConnectionParameters
  from tornado.iostream import StreamClosedError
  from tornado.netutil import Resolver, OverrideResolver, _client_ssl_defaults
  from tornado.log import gen_log
  from tornado import stack_context
  from tornado.tcpclient import TCPClient
  from tornado.util import PY3
  import base64
  import collections
  import copy
  import functools
  import re
  import socket
  import sys
  from io import BytesIO
label_desc: Use image node_id 13 for calling the _HTTPConnection obj's underlying member method code with example usage: obj.headers_received(first_line, headers) without return types