text: # -*- coding: utf-8 -*-
  """
      werkzeug.http
      ~~~~~~~~~~~~~
  
      Werkzeug comes with a bunch of utilities that help Werkzeug to deal with
      HTTP data.  Most of the classes and functions provided by this module are
      used by the wrappers, but they are useful on their own, too, especially if
      the response and request objects are not used.
  
      This covers some of the more HTTP centric features of WSGI, some other
      utilities such as cookie handling are documented in the `werkzeug.utils`
      module.
  
  
      :copyright: (c) 2014 by the Werkzeug Team, see AUTHORS for more details.
      :license: BSD, see LICENSE for more details.
  """
  import re
  import warnings
  from time import time, gmtime
  try:
      from email.utils import parsedate_tz
  except ImportError:  # pragma: no cover
      from email.Utils import parsedate_tz
  try:
      from urllib.request import parse_http_list as _parse_list_header
      from urllib.parse import unquote_to_bytes as _unquote
  except ImportError:  # pragma: no cover
      from urllib2 import parse_http_list as _parse_list_header, \
          unquote as _unquote
  from datetime import datetime, timedelta
  from hashlib import md5
  import base64
  
  from werkzeug._internal import _cookie_quote, _make_cookie_domain, \
      _cookie_parse_impl
  from werkzeug._compat import to_unicode, iteritems, text_type, \
      string_types, try_coerce_native, to_bytes, PY2, \
      integer_types
  
  
  _cookie_charset = 'latin1'
  # for explanation of "media-range", etc. see Sections 5.3.{1,2} of RFC 7231
  _accept_re = re.compile(
      r'''(                       # media-range capturing-parenthesis
                [^\s;,]+              # type/subtype
                (?:[ \t]*;[ \t]*      # ";"
                  (?:                 # parameter non-capturing-parenthesis
                    [^\s;,q][^\s;,]*  # token that doesn't start with "q"
                  |                   # or
                    q[^\s;,=][^\s;,]* # token that is more than just "q"
                  )
                )*                    # zero or more parameters
              )                       # end of media-range
              (?:[ \t]*;[ \t]*q=      # weight is a "q" parameter
                (\d*(?:\.\d+)?)       # qvalue capturing-parentheses
                [^,]*                 # "extension" accept params: who cares?
              )?                      # accept params are optional
          ''', re.VERBOSE)
  _token_chars = frozenset("!#$%&'*+-.0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                           '^_`abcdefghijklmnopqrstuvwxyz|~')
  _etag_re = re.compile(r'([Ww]/)?(?:"(.*?)"|(.*?))(?:\s*,\s*|$)')
  _unsafe_header_chars = set('()<>@,;:\"/[]?={} \t')
  _option_header_piece_re = re.compile(r'''
      ;\s*
      (?P<key>
          "[^"\\]*(?:\\.[^"\\]*)*"  # quoted string
      |
          [^\s;,=*]+  # token
      )
      \s*
      (?:  # optionally followed by =value
          (?:  # equals sign, possibly with encoding
              \*\s*=\s*  # * indicates extended notation
              (?P<encoding>[^\s]+?)
              '(?P<language>[^\s]*?)'
          |
              =\s*  # basic notation
          )
          (?P<value>
              "[^"\\]*(?:\\.[^"\\]*)*"  # quoted string
          |
              [^;,]+  # token
          )?
      )?
      \s*
  ''', flags=re.VERBOSE)
  _option_header_start_mime_type = re.compile(r',\s*([^;,\s]+)([;,]\s*.+)?')
  
  _entity_headers = frozenset([
      'allow', 'content-encoding', 'content-language', 'content-length',
      'content-location', 'content-md5', 'content-range', 'content-type',
      'expires', 'last-modified'
  ])
  _hop_by_hop_headers = frozenset([
      'connection', 'keep-alive', 'proxy-authenticate',
      'proxy-authorization', 'te', 'trailer', 'transfer-encoding',
      'upgrade'
  ])
  
  
  HTTP_STATUS_CODES = {
      100:    'Continue',
      101:    'Switching Protocols',
      102:    'Processing',
      200:    'OK',
      201:    'Created',
      202:    'Accepted',
      203:    'Non Authoritative Information',
      204:    'No Content',
      205:    'Reset Content',
      206:    'Partial Content',
      207:    'Multi Status',
      226:    'IM Used',              # see RFC 3229
      300:    'Multiple Choices',
      301:    'Moved Permanently',
      302:    'Found',
      303:    'See Other',
      304:    'Not Modified',
      305:    'Use Proxy',
      307:    'Temporary Redirect',
      400:    'Bad Request',
      401:    'Unauthorized',
      402:    'Payment Required',     # unused
      403:    'Forbidden',
      404:    'Not Found',
      405:    'Method Not Allowed',
      406:    'Not Acceptable',
      407:    'Proxy Authentication Required',
      408:    'Request Timeout',
      409:    'Conflict',
      410:    'Gone',
      411:    'Length Required',
      412:    'Precondition Failed',
      413:    'Request Entity Too Large',
      414:    'Request URI Too Long',
      415:    'Unsupported Media Type',
      416:    'Requested Range Not Satisfiable',
      417:    'Expectation Failed',
      418:    'I\'m a teapot',  # see RFC 2324
      421:    'Misdirected Request',  # see RFC 7540
      422:    'Unprocessable Entity',
      423:    'Locked',
      424:    'Failed Dependency',
      426:    'Upgrade Required',
      428:    'Precondition Required',  # see RFC 6585
      429:    'Too Many Requests',
      431:    'Request Header Fields Too Large',
      449:    'Retry With',  # proprietary MS extension
      451:    'Unavailable For Legal Reasons',
      500:    'Internal Server Error',
      501:    'Not Implemented',
      502:    'Bad Gateway',
      503:    'Service Unavailable',
      504:    'Gateway Timeout',
      505:    'HTTP Version Not Supported',
      507:    'Insufficient Storage',
      510:    'Not Extended'
  }
  
  
  def wsgi_to_bytes(data):
      """coerce wsgi unicode represented bytes to real ones
  
      """
      if isinstance(data, bytes):
          return data
      return data.encode('latin1')  # XXX: utf8 fallback?
  
  
  def bytes_to_wsgi(data):
      assert isinstance(data, bytes), 'data must be bytes'
      if isinstance(data, str):
          return data
      else:
          return data.decode('latin1')
  
  
  def quote_header_value(value, extra_chars='', allow_token=True):
      """Quote a header value if necessary.
  
      .. versionadded:: 0.5
  
      :param value: the value to quote.
      :param extra_chars: a list of extra characters to skip quoting.
      :param allow_token: if this is enabled token values are returned
                          unchanged.
      """
      if isinstance(value, bytes):
          value = bytes_to_wsgi(value)
      value = str(value)
      if allow_token:
          token_chars = _token_chars | set(extra_chars)
          if set(value).issubset(token_chars):
              return value
      return '"%s"' % value.replace('\\', '\\\\').replace('"', '\\"')
  
  
  def unquote_header_value(value, is_filename=False):
      r"""Unquotes a header value.  (Reversal of :func:`quote_header_value`).
      This does not use the real unquoting but what browsers are actually
      using for quoting.
  
      .. versionadded:: 0.5
  
      :param value: the header value to unquote.
      """
      if value and value[0] == value[-1] == '"':
          # this is not the real unquoting, but fixing this so that the
          # RFC is met will result in bugs with internet explorer and
          # probably some other browsers as well.  IE for example is
          # uploading files with "C:\foo\bar.txt" as filename
          value = value[1:-1]
  
          # if this is a filename and the starting characters look like
          # a UNC path, then just return the value without quotes.  Using the
          # replace sequence below on a UNC path has the effect of turning
          # the leading double slash into a single slash and then
          # _fix_ie_filename() doesn't work correctly.  See #458.
          if not is_filename or value[:2] != '\\\\':
              return value.replace('\\\\', '\\').replace('\\"', '"')
      return value
  
  
  def dump_options_header(header, options):
      """The reverse function to :func:`parse_options_header`.
  
      :param header: the header to dump
      :param options: a dict of options to append.
      """
      segments = []
      if header is not None:
          segments.append(header)
      for key, value in iteritems(options):
          if value is None:
              segments.append(key)
          else:
              segments.append('%s=%s' % (key, quote_header_value(value)))
      return '; '.join(segments)
  
  
  def dump_header(iterable, allow_token=True):
      """Dump an HTTP header again.  This is the reversal of
      :func:`parse_list_header`, :func:`parse_set_header` and
      :func:`parse_dict_header`.  This also quotes strings that include an
      equals sign unless you pass it as dict of key, value pairs.
  
      >>> dump_header({'foo': 'bar baz'})
      'foo="bar baz"'
      >>> dump_header(('foo', 'bar baz'))
      'foo, "bar baz"'
  
      :param iterable: the iterable or dict of values to quote.
      :param allow_token: if set to `False` tokens as values are disallowed.
                          See :func:`quote_header_value` for more details.
      """
      if isinstance(iterable, dict):
          items = []
          for key, value in iteritems(iterable):
              if value is None:
                  items.append(key)
              else:
                  items.append('%s=%s' % (
                      key,
                      quote_header_value(value, allow_token=allow_token)
                  ))
      else:
          items = [quote_header_value(x, allow_token=allow_token)
                   for x in iterable]
      return ', '.join(items)
  
  
  def parse_list_header(value):
      """Parse lists as described by RFC 2068 Section 2.
  
      In particular, parse comma-separated lists where the elements of
      the list may include quoted-strings.  A quoted-string could
      contain a comma.  A non-quoted string could have quotes in the
      middle.  Quotes are removed automatically after parsing.
  
      It basically works like :func:`parse_set_header` just that items
      may appear multiple times and case sensitivity is preserved.
  
      The return value is a standard :class:`list`:
  
      >>> parse_list_header('token, "quoted value"')
      ['token', 'quoted value']
  
      To create a header from the :class:`list` again, use the
      :func:`dump_header` function.
  
      :param value: a string with a list header.
      :return: :class:`list`
      """
      result = []
      for item in _parse_list_header(value):
          if item[:1] == item[-1:] == '"':
              item = unquote_header_value(item[1:-1])
          result.append(item)
      return result
  
  
  def parse_dict_header(value, cls=dict):
      """Parse lists of key, value pairs as described by RFC 2068 Section 2 and
      convert them into a python dict (or any other mapping object created from
      the type with a dict like interface provided by the `cls` argument):
  
      >>> d = parse_dict_header('foo="is a fish", bar="as well"')
      >>> type(d) is dict
      True
      >>> sorted(d.items())
      [('bar', 'as well'), ('foo', 'is a fish')]
  
      If there is no value for a key it will be `None`:
  
      >>> parse_dict_header('key_without_value')
      {'key_without_value': None}
  
      To create a header from the :class:`dict` again, use the
      :func:`dump_header` function.
  
      .. versionchanged:: 0.9
         Added support for `cls` argument.
  
      :param value: a string with a dict header.
      :param cls: callable to use for storage of parsed results.
      :return: an instance of `cls`
      """
      result = cls()
      if not isinstance(value, text_type):
          # XXX: validate
          value = bytes_to_wsgi(value)
      for item in _parse_list_header(value):
          if '=' not in item:
              result[item] = None
              continue
          name, value = item.split('=', 1)
          if value[:1] == value[-1:] == '"':
              value = unquote_header_value(value[1:-1])
          result[name] = value
      return result
  
  
  def parse_options_header(value, multiple=False):
      """Parse a ``Content-Type`` like header into a tuple with the content
      type and the options:
  
      >>> parse_options_header('text/html; charset=utf8')
      ('text/html', {'charset': 'utf8'})
  
      This should not be used to parse ``Cache-Control`` like headers that use
      a slightly different format.  For these headers use the
      :func:`parse_dict_header` function.
  
      .. versionadded:: 0.5
  
      :param value: the header to parse.
      :param multiple: Whether try to parse and return multiple MIME types
      :return: (mimetype, options) or (mimetype, options, mimetype, options, …)
               if multiple=True
      """
      if not value:
          return '', {}
  
      result = []
  
      value = "," + value.replace("\n", ",")
      while value:
          match = _option_header_start_mime_type.match(value)
          if not match:
              break
          result.append(match.group(1))  # mimetype
          options = {}
          # Parse options
          rest = match.group(2)
          while rest:
              optmatch = _option_header_piece_re.match(rest)
              if not optmatch:
                  break
              option, encoding, _, option_value = optmatch.groups()
              option = unquote_header_value(option)
              if option_value is not None:
                  option_value = unquote_header_value(
                      option_value,
                      option == 'filename')
                  if encoding is not None:
                      option_value = _unquote(option_value).decode(encoding)
              options[option] = option_value
              rest = rest[optmatch.end():]
          result.append(options)
          if multiple is False:
              return tuple(result)
          value = rest
  
      return tuple(result) if result else ('', {})
  
  
  def parse_accept_header(value, cls=None):
      """Parses an HTTP Accept-* header.  This does not implement a complete
      valid algorithm but one that supports at least value and quality
      extraction.
  
      Returns a new :class:`Accept` object (basically a list of ``(value, quality)``
      tuples sorted by the quality with some additional accessor methods).
  
      The second parameter can be a subclass of :class:`Accept` that is created
      with the parsed values and returned.
  
      :param value: the accept header string to be parsed.
      :param cls: the wrapper class for the return value (can be
                           :class:`Accept` or a subclass thereof)
      :return: an instance of `cls`.
      """
      if cls is None:
          cls = Accept
  
      if not value:
          return cls(None)
  
      result = []
      for match in _accept_re.finditer(value):
          quality = match.group(2)
          if not quality:
              quality = 1
          else:
              quality = max(min(float(quality), 1), 0)
          result.append((match.group(1), quality))
      return cls(result)
  
  
  def parse_cache_control_header(value, on_update=None, cls=None):
      """Parse a cache control header.  The RFC differs between response and
      request cache control, this method does not.  It's your responsibility
      to not use the wrong control statements.
  
      .. versionadded:: 0.5
         The `cls` was added.  If not specified an immutable
         :class:`~werkzeug.datastructures.RequestCacheControl` is returned.
  
      :param value: a cache control header to be parsed.
      :param on_update: an optional callable that is called every time a value
                        on the :class:`~werkzeug.datastructures.CacheControl`
                        object is changed.
      :param cls: the class for the returned object.  By default
                  :class:`~werkzeug.datastructures.RequestCacheControl` is used.
      :return: a `cls` object.
      """
      if cls is None:
          cls = RequestCacheControl
      if not value:
          return cls(None, on_update)
      return cls(parse_dict_header(value), on_update)
  
  
  def parse_set_header(value, on_update=None):
      """Parse a set-like header and return a
      :class:`~werkzeug.datastructures.HeaderSet` object:
  
      >>> hs = parse_set_header('token, "quoted value"')
  
      The return value is an object that treats the items case-insensitively
      and keeps the order of the items:
  
      >>> 'TOKEN' in hs
      True
      >>> hs.index('quoted value')
      1
      >>> hs
      HeaderSet(['token', 'quoted value'])
  
      To create a header from the :class:`HeaderSet` again, use the
      :func:`dump_header` function.
  
      :param value: a set header to be parsed.
      :param on_update: an optional callable that is called every time a
                        value on the :class:`~werkzeug.datastructures.HeaderSet`
                        object is changed.
      :return: a :class:`~werkzeug.datastructures.HeaderSet`
      """
      if not value:
          return HeaderSet(None, on_update)
      return HeaderSet(parse_list_header(value), on_update)
  
  
  def parse_authorization_header(value):
      """Parse an HTTP basic/digest authorization header transmitted by the web
      browser.  The return value is either `None` if the header was invalid or
      not given, otherwise an :class:`~werkzeug.datastructures.Authorization`
      object.
  
      :param value: the authorization header to parse.
      :return: a :class:`~werkzeug.datastructures.Authorization` object or `None`.
      """
      if not value:
          return
      value = wsgi_to_bytes(value)
      try:
          auth_type, auth_info = value.split(None, 1)
          auth_type = auth_type.lower()
      except ValueError:
          return
      if auth_type == b'basic':
          try:
              username, password = base64.b64decode(auth_info).split(b':', 1)
          except Exception:
              return
          return Authorization('basic', {'username':  bytes_to_wsgi(username),
                                         'password': bytes_to_wsgi(password)})
      elif auth_type == b'digest':
          auth_map = parse_dict_header(auth_info)
          for key in 'username', 'realm', 'nonce', 'uri', 'response':
              if key not in auth_map:
                  return
          if 'qop' in auth_map:
              if not auth_map.get('nc') or not auth_map.get('cnonce'):
                  return
          return Authorization('digest', auth_map)
  
  
  def parse_www_authenticate_header(value, on_update=None):
      """Parse an HTTP WWW-Authenticate header into a
      :class:`~werkzeug.datastructures.WWWAuthenticate` object.
  
      :param value: a WWW-Authenticate header to parse.
      :param on_update: an optional callable that is called every time a value
                        on the :class:`~werkzeug.datastructures.WWWAuthenticate`
                        object is changed.
      :return: a :class:`~werkzeug.datastructures.WWWAuthenticate` object.
      """
      if not value:
          return WWWAuthenticate(on_update=on_update)
      try:
          auth_type, auth_info = value.split(None, 1)
          auth_type = auth_type.lower()
      except (ValueError, AttributeError):
          return WWWAuthenticate(value.strip().lower(), on_update=on_update)
      return WWWAuthenticate(auth_type, parse_dict_header(auth_info),
                             on_update)
  
  
  def parse_if_range_header(value):
      """Parses an if-range header which can be an etag or a date.  Returns
      a :class:`~werkzeug.datastructures.IfRange` object.
  
      .. versionadded:: 0.7
      """
      if not value:
          return IfRange()
      date = parse_date(value)
      if date is not None:
          return IfRange(date=date)
      # drop weakness information
      return IfRange(unquote_etag(value)[0])
  
  
  def parse_range_header(value, make_inclusive=True):
      """Parses a range header into a :class:`~werkzeug.datastructures.Range`
      object.  If the header is missing or malformed `None` is returned.
      `ranges` is a list of ``(start, stop)`` tuples where the ranges are
      non-inclusive.
  
      .. versionadded:: 0.7
      """
      if not value or '=' not in value:
          return None
  
      ranges = []
      last_end = 0
      units, rng = value.split('=', 1)
      units = units.strip().lower()
  
      for item in rng.split(','):
          item = item.strip()
          if '-' not in item:
              return None
          if item.startswith('-'):
              if last_end < 0:
                  return None
              try:
                  begin = int(item)
              except ValueError:
                  return None
              end = None
              last_end = -1
          elif '-' in item:
              begin, end = item.split('-', 1)
              begin = begin.strip()
              end = end.strip()
              if not begin.isdigit():
                  return None
              begin = int(begin)
              if begin < last_end or last_end < 0:
                  return None
              if end:
                  if not end.isdigit():
                      return None
                  end = int(end) + 1
                  if begin >= end:
                      return None
              else:
                  end = None
              last_end = end
          ranges.append((begin, end))
  
      return Range(units, ranges)
  
  
  def parse_content_range_header(value, on_update=None):
      """Parses a range header into a
      :class:`~werkzeug.datastructures.ContentRange` object or `None` if
      parsing is not possible.
  
      .. versionadded:: 0.7
  
      :param value: a content range header to be parsed.
      :param on_update: an optional callable that is called every time a value
                        on the :class:`~werkzeug.datastructures.ContentRange`
                        object is changed.
      """
      if value is None:
          return None
      try:
          units, rangedef = (value or '').strip().split(None, 1)
      except ValueError:
          return None
  
      if '/' not in rangedef:
          return None
      rng, length = rangedef.split('/', 1)
      if length == '*':
          length = None
      elif length.isdigit():
          length = int(length)
      else:
          return None
  
      if rng == '*':
          return ContentRange(units, None, None, length, on_update=on_update)
      elif '-' not in rng:
          return None
  
      start, stop = rng.split('-', 1)
      try:
          start = int(start)
          stop = int(stop) + 1
      except ValueError:
          return None
  
      if is_byte_range_valid(start, stop, length):
          return ContentRange(units, start, stop, length, on_update=on_update)
  
  
  def quote_etag(etag, weak=False):
      """Quote an etag.
  
      :param etag: the etag to quote.
      :param weak: set to `True` to tag it "weak".
      """
      if '"' in etag:
          raise ValueError('invalid etag')
      etag = '"%s"' % etag
      if weak:
          etag = 'W/' + etag
      return etag
  
  
  def unquote_etag(etag):
      """Unquote a single etag:
  
      >>> unquote_etag('W/"bar"')
      ('bar', True)
      >>> unquote_etag('"bar"')
      ('bar', False)
  
      :param etag: the etag identifier to unquote.
      :return: a ``(etag, weak)`` tuple.
      """
      if not etag:
          return None, None
      etag = etag.strip()
      weak = False
      if etag.startswith(('W/', 'w/')):
          weak = True
          etag = etag[2:]
      if etag[:1] == etag[-1:] == '"':
          etag = etag[1:-1]
      return etag, weak
  
  
  def parse_etags(value):
      """Parse an etag header.
  
      :param value: the tag header to parse
      :return: an :class:`~werkzeug.datastructures.ETags` object.
      """
      if not value:
          return ETags()
      strong = []
      weak = []
      end = len(value)
      pos = 0
      while pos < end:
          match = _etag_re.match(value, pos)
          if match is None:
              break
          is_weak, quoted, raw = match.groups()
          if raw == '*':
              return ETags(star_tag=True)
          elif quoted:
              raw = quoted
          if is_weak:
              weak.append(raw)
          else:
              strong.append(raw)
          pos = match.end()
      return ETags(strong, weak)
  
  
  def generate_etag(data):
      """Generate an etag for some data."""
      return md5(data).hexdigest()
  
  
  def parse_date(value):
      """Parse one of the following date formats into a datetime object:
  
      .. sourcecode:: text
  
          Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
          Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
          Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
  
      If parsing fails the return value is `None`.
  
      :param value: a string with a supported date format.
      :return: a :class:`datetime.datetime` object.
      """
      if value:
          t = parsedate_tz(value.strip())
          if t is not None:
              try:
                  year = t[0]
                  # unfortunately that function does not tell us if two digit
                  # years were part of the string, or if they were prefixed
                  # with two zeroes.  So what we do is to assume that 69-99
                  # refer to 1900, and everything below to 2000
                  if year >= 0 and year <= 68:
                      year += 2000
                  elif year >= 69 and year <= 99:
                      year += 1900
                  return datetime(*((year,) + t[1:7])) - \
                      timedelta(seconds=t[-1] or 0)
              except (ValueError, OverflowError):
                  return None
  
  
  def _dump_date(d, delim):
      """Used for `http_date` and `cookie_date`."""
      if d is None:
          d = gmtime()
      elif isinstance(d, datetime):
          d = d.utctimetuple()
      elif isinstance(d, (integer_types, float)):
          d = gmtime(d)
      return '%s, %02d%s%s%s%s %02d:%02d:%02d GMT' % (
          ('Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun')[d.tm_wday],
          d.tm_mday, delim,
          ('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep',
           'Oct', 'Nov', 'Dec')[d.tm_mon - 1],
          delim, str(d.tm_year), d.tm_hour, d.tm_min, d.tm_sec
      )
  
  
  def cookie_date(expires=None):
      """Formats the time to ensure compatibility with Netscape's cookie
      standard.
  
      Accepts a floating point number expressed in seconds since the epoch in, a
      datetime object or a timetuple.  All times in UTC.  The :func:`parse_date`
      function can be used to parse such a date.
  
      Outputs a string in the format ``Wdy, DD-Mon-YYYY HH:MM:SS GMT``.
  
      :param expires: If provided that date is used, otherwise the current.
      """
      return _dump_date(expires, '-')
  
  
  def http_date(timestamp=None):
      """Formats the time to match the RFC1123 date format.
  
      Accepts a floating point number expressed in seconds since the epoch in, a
      datetime object or a timetuple.  All times in UTC.  The :func:`parse_date`
      function can be used to parse such a date.
  
      Outputs a string in the format ``Wdy, DD Mon YYYY HH:MM:SS GMT``.
  
      :param timestamp: If provided that date is used, otherwise the current.
      """
      return _dump_date(timestamp, ' ')
  
  
  def parse_age(value=None):
      """Parses a base-10 integer count of seconds into a timedelta.
  
      If parsing fails, the return value is `None`.
  
      :param value: a string consisting of an integer represented in base-10
      :return: a :class:`datetime.timedelta` object or `None`.
      """
      if not value:
          return None
      try:
          seconds = int(value)
      except ValueError:
          return None
      if seconds < 0:
          return None
      try:
          return timedelta(seconds=seconds)
      except OverflowError:
          return None
  
  
  def dump_age(age=None):
      """Formats the duration as a base-10 integer.
  
      :param age: should be an integer number of seconds,
                  a :class:`datetime.timedelta` object, or,
                  if the age is unknown, `None` (default).
      """
      if age is None:
          return
      if isinstance(age, timedelta):
          # do the equivalent of Python 2.7's timedelta.total_seconds(),
          # but disregarding fractional seconds
          age = age.seconds + (age.days * 24 * 3600)
  
      age = int(age)
      if age < 0:
          raise ValueError('age cannot be negative')
  
      return str(age)
  
  
  def is_resource_modified(environ, etag=None, data=None, last_modified=None,
                           ignore_if_range=True):
      """Convenience method for conditional requests.
  
      :param environ: the WSGI environment of the request to be checked.
      :param etag: the etag for the response for comparison.
      :param data: or alternatively the data of the response to automatically
                   generate an etag using :func:`generate_etag`.
      :param last_modified: an optional date of the last modification.
      :param ignore_if_range: If `False`, `If-Range` header will be taken into
                              account.
      :return: `True` if the resource was modified, otherwise `False`.
      """
      if etag is None and data is not None:
          etag = generate_etag(data)
      elif data is not None:
          raise TypeError('both data and etag given')
      if environ['REQUEST_METHOD'] not in ('GET', 'HEAD'):
          return False
  
      unmodified = False
      if isinstance(last_modified, string_types):
          last_modified = parse_date(last_modified)
  
      # ensure that microsecond is zero because the HTTP spec does not transmit
      # that either and we might have some false positives.  See issue #39
      if last_modified is not None:
          last_modified = last_modified.replace(microsecond=0)
  
      if_range = None
      if not ignore_if_range and 'HTTP_RANGE' in environ:
          # https://tools.ietf.org/html/rfc7233#section-3.2
          # A server MUST ignore an If-Range header field received in a request
          # that does not contain a Range header field.
          if_range = parse_if_range_header(environ.get('HTTP_IF_RANGE'))
  
      if if_range is not None and if_range.date is not None:
          modified_since = if_range.date
      else:
          modified_since = parse_date(environ.get('HTTP_IF_MODIFIED_SINCE'))
  
      if modified_since and last_modified and last_modified <= modified_since:
          unmodified = True
  
      if etag:
          etag, _ = unquote_etag(etag)
          if if_range is not None and if_range.etag is not None:
              unmodified = parse_etags(if_range.etag).contains(etag)
          else:
              if_none_match = parse_etags(environ.get('HTTP_IF_NONE_MATCH'))
              if if_none_match:
                  # https://tools.ietf.org/html/rfc7232#section-3.2
                  # "A recipient MUST use the weak comparison function when comparing
                  # entity-tags for If-None-Match"
                  unmodified = if_none_match.contains_weak(etag)
  
              # https://tools.ietf.org/html/rfc7232#section-3.1
              # "Origin server MUST use the strong comparison function when
              # comparing entity-tags for If-Match"
              if_match = parse_etags(environ.get('HTTP_IF_MATCH'))
              if if_match:
                  unmodified = not if_match.is_strong(etag)
  
      return not unmodified
  
  
  def remove_entity_headers(headers, allowed=('expires', 'content-location')):
      """Remove all entity headers from a list or :class:`Headers` object.  This
      operation works in-place.  `Expires` and `Content-Location` headers are
      by default not removed.  The reason for this is :rfc:`2616` section
      10.3.5 which specifies some entity headers that should be sent.
  
      .. versionchanged:: 0.5
         added `allowed` parameter.
  
      :param headers: a list or :class:`Headers` object.
      :param allowed: a list of headers that should still be allowed even though
                      they are entity headers.
      """
      allowed = set(x.lower() for x in allowed)
      headers[:] = [(key, value) for key, value in headers if
                    not is_entity_header(key) or key.lower() in allowed]
  
  
  def remove_hop_by_hop_headers(headers):
      """Remove all HTTP/1.1 "Hop-by-Hop" headers from a list or
      :class:`Headers` object.  This operation works in-place.
  
      .. versionadded:: 0.5
  
      :param headers: a list or :class:`Headers` object.
      """
      headers[:] = [(key, value) for key, value in headers if
                    not is_hop_by_hop_header(key)]
  
  
  def is_entity_header(header):
      """Check if a header is an entity header.
  
      .. versionadded:: 0.5
  
      :param header: the header to test.
      :return: `True` if it's an entity header, `False` otherwise.
      """
      return header.lower() in _entity_headers
  
  
  def is_hop_by_hop_header(header):
      """Check if a header is an HTTP/1.1 "Hop-by-Hop" header.
  
      .. versionadded:: 0.5
  
      :param header: the header to test.
      :return: `True` if it's an HTTP/1.1 "Hop-by-Hop" header, `False` otherwise.
      """
      return header.lower() in _hop_by_hop_headers
  
  
  def parse_cookie(header, charset='utf-8', errors='replace', cls=None):
      """Parse a cookie.  Either from a string or WSGI environ.
  
      Per default encoding errors are ignored.  If you want a different behavior
      you can set `errors` to ``'replace'`` or ``'strict'``.  In strict mode a
      :exc:`HTTPUnicodeError` is raised.
  
      .. versionchanged:: 0.5
         This function now returns a :class:`TypeConversionDict` instead of a
         regular dict.  The `cls` parameter was added.
  
      :param header: the header to be used to parse the cookie.  Alternatively
                     this can be a WSGI environment.
      :param charset: the charset for the cookie values.
      :param errors: the error behavior for the charset decoding.
      :param cls: an optional dict class to use.  If this is not specified
                         or `None` the default :class:`TypeConversionDict` is
                         used.
      """
      if isinstance(header, dict):
          header = header.get('HTTP_COOKIE', '')
      elif header is None:
          header = ''
  
      # If the value is an unicode string it's mangled through latin1.  This
      # is done because on PEP 3333 on Python 3 all headers are assumed latin1
      # which however is incorrect for cookies, which are sent in page encoding.
      # As a result we
      if isinstance(header, text_type):
          header = header.encode('latin1', 'replace')
  
      if cls is None:
          cls = TypeConversionDict
  
      def _parse_pairs():
          for key, val in _cookie_parse_impl(header):
              key = to_unicode(key, charset, errors, allow_none_charset=True)
              if not key:
                  continue
              val = to_unicode(val, charset, errors, allow_none_charset=True)
              yield try_coerce_native(key), val
  
      return cls(_parse_pairs())
  
  
  def dump_cookie(key, value='', max_age=None, expires=None, path='/',
                  domain=None, secure=False, httponly=False,
                  charset='utf-8', sync_expires=True, max_size=4093,
                  samesite=None):
      """Creates a new Set-Cookie header without the ``Set-Cookie`` prefix
      The parameters are the same as in the cookie Morsel object in the
      Python standard library but it accepts unicode data, too.
  
      On Python 3 the return value of this function will be a unicode
      string, on Python 2 it will be a native string.  In both cases the
      return value is usually restricted to ascii as the vast majority of
      values are properly escaped, but that is no guarantee.  If a unicode
      string is returned it's tunneled through latin1 as required by
      PEP 3333.
  
      The return value is not ASCII safe if the key contains unicode
      characters.  This is technically against the specification but
      happens in the wild.  It's strongly recommended to not use
      non-ASCII values for the keys.
  
      :param max_age: should be a number of seconds, or `None` (default) if
                      the cookie should last only as long as the client's
                      browser session.  Additionally `timedelta` objects
                      are accepted, too.
      :param expires: should be a `datetime` object or unix timestamp.
      :param path: limits the cookie to a given path, per default it will
                   span the whole domain.
      :param domain: Use this if you want to set a cross-domain cookie. For
                     example, ``domain=".example.com"`` will set a cookie
                     that is readable by the domain ``www.example.com``,
                     ``foo.example.com`` etc. Otherwise, a cookie will only
                     be readable by the domain that set it.
      :param secure: The cookie will only be available via HTTPS
      :param httponly: disallow JavaScript to access the cookie.  This is an
                       extension to the cookie standard and probably not
                       supported by all browsers.
      :param charset: the encoding for unicode values.
      :param sync_expires: automatically set expires if max_age is defined
                           but expires not.
      :param max_size: Warn if the final header value exceeds this size. The
          default, 4093, should be safely `supported by most browsers
          <cookie_>`_. Set to 0 to disable this check.
      :param samesite: Limits the scope of the cookie such that it will only
                       be attached to requests if those requests are "same-site".
  
      .. _`cookie`: http://browsercookielimits.squawky.net/
      """
      key = to_bytes(key, charset)
      value = to_bytes(value, charset)
  
      if path is not None:
          path = iri_to_uri(path, charset)
      domain = _make_cookie_domain(domain)
      if isinstance(max_age, timedelta):
          max_age = (max_age.days * 60 * 60 * 24) + max_age.seconds
      if expires is not None:
          if not isinstance(expires, string_types):
              expires = cookie_date(expires)
      elif max_age is not None and sync_expires:
          expires = to_bytes(cookie_date(time() + max_age))
  
      samesite = samesite.title() if samesite else None
      if samesite not in ('Strict', 'Lax', None):
          raise ValueError("invalid SameSite value; must be 'Strict', 'Lax' or None")
  
      buf = [key + b'=' + _cookie_quote(value)]
  
      # XXX: In theory all of these parameters that are not marked with `None`
      # should be quoted.  Because stdlib did not quote it before I did not
      # want to introduce quoting there now.
      for k, v, q in ((b'Domain', domain, True),
                      (b'Expires', expires, False,),
                      (b'Max-Age', max_age, False),
                      (b'Secure', secure, None),
                      (b'HttpOnly', httponly, None),
                      (b'Path', path, False),
                      (b'SameSite', samesite, False)):
          if q is None:
              if v:
                  buf.append(k)
              continue
  
          if v is None:
              continue
  
          tmp = bytearray(k)
          if not isinstance(v, (bytes, bytearray)):
              v = to_bytes(text_type(v), charset)
          if q:
              v = _cookie_quote(v)
          tmp += b'=' + v
          buf.append(bytes(tmp))
  
      # The return value will be an incorrectly encoded latin1 header on
      # Python 3 for consistency with the headers object and a bytestring
      # on Python 2 because that's how the API makes more sense.
      rv = b'; '.join(buf)
      if not PY2:
          rv = rv.decode('latin1')
  
      # Warn if the final value of the cookie is less than the limit. If the
      # cookie is too large, then it may be silently ignored, which can be quite
      # hard to debug.
      cookie_size = len(rv)
  
      if max_size and cookie_size > max_size:
          value_size = len(value)
          warnings.warn(
              'The "{key}" cookie is too large: the value was {value_size} bytes'
              ' but the header required {extra_size} extra bytes. The final size'
              ' was {cookie_size} bytes but the limit is {max_size} bytes.'
              ' Browsers may silently ignore cookies larger than this.'.format(
                  key=key,
                  value_size=value_size,
                  extra_size=cookie_size - value_size,
                  cookie_size=cookie_size,
                  max_size=max_size
              ),
              stacklevel=2
          )
  
      return rv
  
  
  def is_byte_range_valid(start, stop, length):
      """Checks if a given byte content range is valid for the given length.
  
      .. versionadded:: 0.7
      """
      if (start is None) != (stop is None):
          return False
      elif start is None:
          return length is None or length >= 0
      elif length is None:
          return 0 <= start < stop
      elif start >= stop:
          return False
      return 0 <= start < length
  
  
  # circular dependency fun
  from werkzeug.datastructures import Accept, HeaderSet, ETags, Authorization, \
      WWWAuthenticate, TypeConversionDict, IfRange, Range, ContentRange, \
      RequestCacheControl
  
  
  # DEPRECATED
  # backwards compatible imports
  from werkzeug.datastructures import (  # noqa
      MIMEAccept, CharsetAccept, LanguageAccept, Headers
  )
  from werkzeug.urls import iri_to_uri
  