[web] set Vary response header to "Accept-Language" when using content negotiation
This is slightly annoying because the response actually only varies
based on the language we decide to send, which has much fewer possible
values than Accept-Language, but that's not in the request, so we can't
easily use it. Deployments using varnish or similar and controlling the
set of available languages will likely want to override this to allow
reasonable amounts of caching.
Closes #2105812
# -*- coding: utf-8 -*-
# copyright 2014 Logilab, PARIS
"""A set of utility functions to handle CORS requests
Unless specified, all references in this file are related to:
http://www.w3.org/TR/cors
The provided implementation roughly follows:
http://www.html5rocks.com/static/images/cors_server_flowchart.png
See also:
https://developer.mozilla.org/en-US/docs/HTTP/Access_control_CORS
"""
import urlparse
from cubicweb.web import LOGGER
info = LOGGER.info
class CORSFailed(Exception):
"""Raised when cross origin resource sharing checks failed"""
class CORSPreflight(Exception):
"""Raised when cross origin resource sharing checks detects the
request as a valid preflight request"""
def process_request(req, config):
"""
Process a request to apply CORS specification algorithms
Check whether the CORS specification is respected and set corresponding
headers to ensure response complies with the specification.
In case of non-compliance, no CORS-related header is set.
"""
base_url = urlparse.urlsplit(req.base_url())
expected_host = '://'.join((base_url.scheme, base_url.netloc))
if not req.get_header('Origin') or req.get_header('Origin') == expected_host:
# not a CORS request, nothing to do
return
try:
# handle cross origin resource sharing (CORS)
if req.http_method() == 'OPTIONS':
if req.get_header('Access-Control-Request-Method'):
# preflight CORS request
process_preflight(req, config)
else: # Simple CORS or actual request
process_simple(req, config)
except CORSFailed, exc:
info('Cross origin resource sharing failed: %s' % exc)
except CORSPreflight:
info('Cross origin resource sharing: valid Preflight request %s')
raise
def process_preflight(req, config):
"""cross origin resource sharing (preflight)
Cf http://www.w3.org/TR/cors/#resource-preflight-requests
"""
origin = check_origin(req, config)
allowed_methods = set(config['access-control-allow-methods'])
allowed_headers = set(config['access-control-allow-headers'])
try:
method = req.get_header('Access-Control-Request-Method')
except ValueError:
raise CORSFailed('Access-Control-Request-Method is incorrect')
if method not in allowed_methods:
raise CORSFailed('Method is not allowed')
try:
req.get_header('Access-Control-Request-Headers', ())
except ValueError:
raise CORSFailed('Access-Control-Request-Headers is incorrect')
req.set_header('Access-Control-Allow-Methods', allowed_methods, raw=False)
req.set_header('Access-Control-Allow-Headers', allowed_headers, raw=False)
process_common(req, config, origin)
raise CORSPreflight()
def process_simple(req, config):
"""Handle the Simple Cross-Origin Request case
"""
origin = check_origin(req, config)
exposed_headers = config['access-control-expose-headers']
if exposed_headers:
req.set_header('Access-Control-Expose-Headers', exposed_headers, raw=False)
process_common(req, config, origin)
def process_common(req, config, origin):
req.set_header('Access-Control-Allow-Origin', origin)
# in CW, we always support credential/authentication
req.set_header('Access-Control-Allow-Credentials', 'true')
def check_origin(req, config):
origin = req.get_header('Origin').lower()
allowed_origins = config.get('access-control-allow-origin')
if not allowed_origins:
raise CORSFailed('access-control-allow-origin is not configured')
if '*' not in allowed_origins and origin not in allowed_origins:
raise CORSFailed('Origin is not allowed')
# bit of sanity check; see "6.3 Security"
myhost = urlparse.urlsplit(req.base_url()).netloc
host = req.get_header('Host')
if host != myhost:
info('cross origin resource sharing detected possible '
'DNS rebinding attack Host header != host of base_url: '
'%s != %s' % (host, myhost))
raise CORSFailed('Host header and hostname do not match')
# include "Vary: Origin" header (see 6.4)
req.headers_out.addHeader('Vary', 'Origin')
return origin