text: from __future__ import absolute_import
  from base64 import b64encode
  
  from ..packages.six import b, integer_types
  from ..exceptions import UnrewindableBodyError
  
  ACCEPT_ENCODING = 'gzip,deflate'
  _FAILEDTELL = object()
  
  
  def make_headers(keep_alive=None, accept_encoding=None, user_agent=None,
                   basic_auth=None, proxy_basic_auth=None, disable_cache=None):
      """
      Shortcuts for generating request headers.
  
      :param keep_alive:
          If ``True``, adds 'connection: keep-alive' header.
  
      :param accept_encoding:
          Can be a boolean, list, or string.
          ``True`` translates to 'gzip,deflate'.
          List will get joined by comma.
          String will be used as provided.
  
      :param user_agent:
          String representing the user-agent you want, such as
          "python-urllib3/0.6"
  
      :param basic_auth:
          Colon-separated username:password string for 'authorization: basic ...'
          auth header.
  
      :param proxy_basic_auth:
          Colon-separated username:password string for 'proxy-authorization: basic ...'
          auth header.
  
      :param disable_cache:
          If ``True``, adds 'cache-control: no-cache' header.
  
      Example::
  
          >>> make_headers(keep_alive=True, user_agent="Batman/1.0")
          {'connection': 'keep-alive', 'user-agent': 'Batman/1.0'}
          >>> make_headers(accept_encoding=True)
          {'accept-encoding': 'gzip,deflate'}
      """
      headers = {}
      if accept_encoding:
          if isinstance(accept_encoding, str):
              pass
          elif isinstance(accept_encoding, list):
              accept_encoding = ','.join(accept_encoding)
          else:
              accept_encoding = ACCEPT_ENCODING
          headers['accept-encoding'] = accept_encoding
  
      if user_agent:
          headers['user-agent'] = user_agent
  
      if keep_alive:
          headers['connection'] = 'keep-alive'
  
      if basic_auth:
          headers['authorization'] = 'Basic ' + \
              b64encode(b(basic_auth)).decode('utf-8')
  
      if proxy_basic_auth:
          headers['proxy-authorization'] = 'Basic ' + \
              b64encode(b(proxy_basic_auth)).decode('utf-8')
  
      if disable_cache:
          headers['cache-control'] = 'no-cache'
  
      return headers
  
  
  def set_file_position(body, pos):
      """
      If a position is provided, move file to that point.
      Otherwise, we'll attempt to record a position for future use.
      """
      if pos is not None:
          rewind_body(body, pos)
      elif getattr(body, 'tell', None) is not None:
          try:
              pos = body.tell()
          except (IOError, OSError):
              # This differentiates from None, allowing us to catch
              # a failed `tell()` later when trying to rewind the body.
              pos = _FAILEDTELL
  
      return pos
  
  
  def rewind_body(body, body_pos):
      """
      Attempt to rewind body to a certain position.
      Primarily used for request redirects and retries.
  
      :param body:
          File-like object that supports seek.
  
      :param int pos:
          Position to seek to in file.
      """
      body_seek = getattr(body, 'seek', None)
      if body_seek is not None and isinstance(body_pos, integer_types):
          try:
              body_seek(body_pos)
          except (IOError, OSError):
              raise UnrewindableBodyError("An error occured when rewinding request "
                                          "body for redirect/retry.")
      elif body_pos is _FAILEDTELL:
          raise UnrewindableBodyError("Unable to record file position for rewinding "
                                      "request body during a redirect/retry.")
      else:
          raise ValueError("body_pos must be of type integer, "
                           "instead it was %s." % type(body_pos))
  