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# Copyright (c) 2010-2012 OpenStack Foundation
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
CNAME Lookup Middleware
Middleware that translates an unknown domain in the host header to
something that ends with the configured storage_domain by looking up
the given domain's CNAME record in DNS.
This middleware will continue to follow a CNAME chain in DNS until it finds
a record ending in the configured storage domain or it reaches the configured
maximum lookup depth. If a match is found, the environment's Host header is
rewritten and the request is passed further down the WSGI chain.
"""
import six
from swift import gettext_ as _
try:
import dns.resolver
import dns.exception
except ImportError:
# catch this to allow docs to be built without the dependency
MODULE_DEPENDENCY_MET = False
else: # executed if the try block finishes with no errors
MODULE_DEPENDENCY_MET = True
from swift.common.middleware import RewriteContext
from swift.common.swob import Request, HTTPBadRequest, \
str_to_wsgi, wsgi_to_str
from swift.common.utils import cache_from_env, get_logger, is_valid_ip, \
list_from_csv, parse_socket_string
from swift.common.registry import register_swift_info
def lookup_cname(domain, resolver): # pragma: no cover
"""
Given a domain, returns its DNS CNAME mapping and DNS ttl.
:param domain: domain to query on
:param resolver: dns.resolver.Resolver() instance used for executing DNS
queries
:returns: (ttl, result)
"""
try:
answer = resolver.query(domain, 'CNAME').rrset
ttl = answer.ttl
result = list(answer.items)[0].to_text()
result = result.rstrip('.')
return ttl, result
except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
# As the memcache lib returns None when nothing is found in cache,
# returning false helps to distinguish between "nothing in cache"
# (None) and "nothing to cache" (False).
return 60, False
except (dns.exception.DNSException):
return 0, None
class _CnameLookupContext(RewriteContext):
base_re = r'^(https?://)%s(/.*)?$'
class CNAMELookupMiddleware(object):
"""
CNAME Lookup Middleware
See above for a full description.
:param app: The next WSGI filter or app in the paste.deploy
chain.
:param conf: The configuration dict for the middleware.
"""
def __init__(self, app, conf):
if not MODULE_DEPENDENCY_MET:
# reraise the exception if the dependency wasn't met
raise ImportError('dnspython is required for this module')
self.app = app
storage_domain = conf.get('storage_domain', 'example.com')
self.storage_domain = ['.' + s for s in
list_from_csv(storage_domain)
if not s.startswith('.')]
self.storage_domain += [s for s in list_from_csv(storage_domain)
if s.startswith('.')]
self.lookup_depth = int(conf.get('lookup_depth', '1'))
nameservers = list_from_csv(conf.get('nameservers'))
try:
for i, server in enumerate(nameservers):
ip_or_host, maybe_port = nameservers[i] = \
parse_socket_string(server, None)
if not is_valid_ip(ip_or_host):
raise ValueError
if maybe_port is not None:
int(maybe_port)
except ValueError:
raise ValueError('Invalid cname_lookup/nameservers configuration '
'found. All nameservers must be valid IPv4 or '
'IPv6, followed by an optional :<integer> port.')
self.resolver = dns.resolver.Resolver()
if nameservers:
self.resolver.nameservers = [ip for (ip, port) in nameservers]
self.resolver.nameserver_ports = {
ip: int(port) for (ip, port) in nameservers
if port is not None}
self.memcache = None
self.logger = get_logger(conf, log_route='cname-lookup')
def _domain_endswith_in_storage_domain(self, a_domain):
a_domain = '.' + a_domain
for domain in self.storage_domain:
if a_domain.endswith(domain):
return True
return False
def __call__(self, env, start_response):
if not self.storage_domain:
return self.app(env, start_response)
if 'HTTP_HOST' in env:
requested_host = env['HTTP_HOST']
else:
requested_host = env['SERVER_NAME']
given_domain = wsgi_to_str(requested_host)
port = ''
if ':' in given_domain:
given_domain, port = given_domain.rsplit(':', 1)
if is_valid_ip(given_domain):
return self.app(env, start_response)
a_domain = given_domain
if not self._domain_endswith_in_storage_domain(a_domain):
if self.memcache is None:
self.memcache = cache_from_env(env)
error = True
for tries in range(self.lookup_depth):
found_domain = None
if self.memcache:
memcache_key = ''.join(['cname-', a_domain])
found_domain = self.memcache.get(memcache_key)
if six.PY2 and found_domain:
found_domain = found_domain.encode('utf-8')
if found_domain is None:
ttl, found_domain = lookup_cname(a_domain, self.resolver)
if self.memcache and ttl > 0:
memcache_key = ''.join(['cname-', given_domain])
self.memcache.set(memcache_key, found_domain,
time=ttl)
if not found_domain or found_domain == a_domain:
# no CNAME records or we're at the last lookup
error = True
found_domain = None
break
elif self._domain_endswith_in_storage_domain(found_domain):
# Found it!
self.logger.info(
_('Mapped %(given_domain)s to %(found_domain)s') %
{'given_domain': given_domain,
'found_domain': found_domain})
if port:
env['HTTP_HOST'] = ':'.join([
str_to_wsgi(found_domain), port])
else:
env['HTTP_HOST'] = str_to_wsgi(found_domain)
error = False
break
else:
# try one more deep in the chain
self.logger.debug(
_('Following CNAME chain for '
'%(given_domain)s to %(found_domain)s') %
{'given_domain': given_domain,
'found_domain': found_domain})
a_domain = found_domain
if error:
if found_domain:
msg = 'CNAME lookup failed after %d tries' % \
self.lookup_depth
else:
msg = 'CNAME lookup failed to resolve to a valid domain'
resp = HTTPBadRequest(request=Request(env), body=msg,
content_type='text/plain')
return resp(env, start_response)
else:
context = _CnameLookupContext(self.app, requested_host,
env['HTTP_HOST'])
return context.handle_request(env, start_response)
return self.app(env, start_response)
def filter_factory(global_conf, **local_conf): # pragma: no cover
conf = global_conf.copy()
conf.update(local_conf)
register_swift_info('cname_lookup',
lookup_depth=int(conf.get('lookup_depth', '1')))
def cname_filter(app):
return CNAMELookupMiddleware(app, conf)
return cname_filter
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