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"""
The httplib2 algorithms ported for use with requests.
"""
import logging
import re
import calendar
import time
from email.utils import parsedate_tz
from pip._vendor.requests.structures import CaseInsensitiveDict
from .cache import DictCache
from .serialize import Serializer
logger = logging.getLogger(__name__)
URI = re.compile(r"^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?")
def parse_uri(uri):
"""Parses a URI using the regex given in Appendix B of RFC 3986.
(scheme, authority, path, query, fragment) = parse_uri(uri)
"""
groups = URI.match(uri).groups()
return (groups[1], groups[3], groups[4], groups[6], groups[8])
class CacheController(object):
"""An interface to see if request should cached or not.
"""
def __init__(self, cache=None, cache_etags=True, serializer=None):
self.cache = cache or DictCache()
self.cache_etags = cache_etags
self.serializer = serializer or Serializer()
@classmethod
def _urlnorm(cls, uri):
"""Normalize the URL to create a safe key for the cache"""
(scheme, authority, path, query, fragment) = parse_uri(uri)
if not scheme or not authority:
raise Exception("Only absolute URIs are allowed. uri = %s" % uri)
scheme = scheme.lower()
authority = authority.lower()
if not path:
path = "/"
# Could do syntax based normalization of the URI before
# computing the digest. See Section 6.2.2 of Std 66.
request_uri = query and "?".join([path, query]) or path
defrag_uri = scheme + "://" + authority + request_uri
return defrag_uri
@classmethod
def cache_url(cls, uri):
return cls._urlnorm(uri)
def parse_cache_control(self, headers):
"""
Parse the cache control headers returning a dictionary with values
for the different directives.
"""
retval = {}
cc_header = 'cache-control'
if 'Cache-Control' in headers:
cc_header = 'Cache-Control'
if cc_header in headers:
parts = headers[cc_header].split(',')
parts_with_args = [
tuple([x.strip().lower() for x in part.split("=", 1)])
for part in parts if -1 != part.find("=")
]
parts_wo_args = [
(name.strip().lower(), 1)
for name in parts if -1 == name.find("=")
]
retval = dict(parts_with_args + parts_wo_args)
return retval
def cached_request(self, request):
"""
Return a cached response if it exists in the cache, otherwise
return False.
"""
cache_url = self.cache_url(request.url)
logger.debug('Looking up "%s" in the cache', cache_url)
cc = self.parse_cache_control(request.headers)
# Bail out if the request insists on fresh data
if 'no-cache' in cc:
logger.debug('Request header has "no-cache", cache bypassed')
return False
if 'max-age' in cc and cc['max-age'] == 0:
logger.debug('Request header has "max_age" as 0, cache bypassed')
return False
# Request allows serving from the cache, let's see if we find something
cache_data = self.cache.get(cache_url)
if cache_data is None:
logger.debug('No cache entry available')
return False
# Check whether it can be deserialized
resp = self.serializer.loads(request, cache_data)
if not resp:
logger.warning('Cache entry deserialization failed, entry ignored')
return False
# If we have a cached 301, return it immediately. We don't
# need to test our response for other headers b/c it is
# intrinsically "cacheable" as it is Permanent.
# See:
# https://tools.ietf.org/html/rfc7231#section-6.4.2
#
# Client can try to refresh the value by repeating the request
# with cache busting headers as usual (ie no-cache).
if resp.status == 301:
msg = ('Returning cached "301 Moved Permanently" response '
'(ignoring date and etag information)')
logger.debug(msg)
return resp
headers = CaseInsensitiveDict(resp.headers)
if not headers or 'date' not in headers:
if 'etag' not in headers:
# Without date or etag, the cached response can never be used
# and should be deleted.
logger.debug('Purging cached response: no date or etag')
self.cache.delete(cache_url)
logger.debug('Ignoring cached response: no date')
return False
now = time.time()
date = calendar.timegm(
parsedate_tz(headers['date'])
)
current_age = max(0, now - date)
logger.debug('Current age based on date: %i', current_age)
# TODO: There is an assumption that the result will be a
# urllib3 response object. This may not be best since we
# could probably avoid instantiating or constructing the
# response until we know we need it.
resp_cc = self.parse_cache_control(headers)
# determine freshness
freshness_lifetime = 0
# Check the max-age pragma in the cache control header
if 'max-age' in resp_cc and resp_cc['max-age'].isdigit():
freshness_lifetime = int(resp_cc['max-age'])
logger.debug('Freshness lifetime from max-age: %i',
freshness_lifetime)
# If there isn't a max-age, check for an expires header
elif 'expires' in headers:
expires = parsedate_tz(headers['expires'])
if expires is not None:
expire_time = calendar.timegm(expires) - date
freshness_lifetime = max(0, expire_time)
logger.debug("Freshness lifetime from expires: %i",
freshness_lifetime)
# Determine if we are setting freshness limit in the
# request. Note, this overrides what was in the response.
if 'max-age' in cc:
try:
freshness_lifetime = int(cc['max-age'])
logger.debug('Freshness lifetime from request max-age: %i',
freshness_lifetime)
except ValueError:
freshness_lifetime = 0
if 'min-fresh' in cc:
try:
min_fresh = int(cc['min-fresh'])
except ValueError:
min_fresh = 0
# adjust our current age by our min fresh
current_age += min_fresh
logger.debug('Adjusted current age from min-fresh: %i',
current_age)
# Return entry if it is fresh enough
if freshness_lifetime > current_age:
logger.debug('The response is "fresh", returning cached response')
logger.debug('%i > %i', freshness_lifetime, current_age)
return resp
# we're not fresh. If we don't have an Etag, clear it out
if 'etag' not in headers:
logger.debug(
'The cached response is "stale" with no etag, purging'
)
self.cache.delete(cache_url)
# return the original handler
return False
def conditional_headers(self, request):
cache_url = self.cache_url(request.url)
resp = self.serializer.loads(request, self.cache.get(cache_url))
new_headers = {}
if resp:
headers = CaseInsensitiveDict(resp.headers)
if 'etag' in headers:
new_headers['If-None-Match'] = headers['ETag']
if 'last-modified' in headers:
new_headers['If-Modified-Since'] = headers['Last-Modified']
return new_headers
def cache_response(self, request, response, body=None):
"""
Algorithm for caching requests.
This assumes a requests Response object.
"""
# From httplib2: Don't cache 206's since we aren't going to
# handle byte range requests
cacheable_status_codes = [200, 203, 300, 301]
if response.status not in cacheable_status_codes:
logger.debug(
'Status code %s not in %s',
response.status,
cacheable_status_codes
)
return
response_headers = CaseInsensitiveDict(response.headers)
# If we've been given a body, our response has a Content-Length, that
# Content-Length is valid then we can check to see if the body we've
# been given matches the expected size, and if it doesn't we'll just
# skip trying to cache it.
if (body is not None and
"content-length" in response_headers and
response_headers["content-length"].isdigit() and
int(response_headers["content-length"]) != len(body)):
return
cc_req = self.parse_cache_control(request.headers)
cc = self.parse_cache_control(response_headers)
cache_url = self.cache_url(request.url)
logger.debug('Updating cache with response from "%s"', cache_url)
# Delete it from the cache if we happen to have it stored there
no_store = False
if cc.get('no-store'):
no_store = True
logger.debug('Response header has "no-store"')
if cc_req.get('no-store'):
no_store = True
logger.debug('Request header has "no-store"')
if no_store and self.cache.get(cache_url):
logger.debug('Purging existing cache entry to honor "no-store"')
self.cache.delete(cache_url)
# If we've been given an etag, then keep the response
if self.cache_etags and 'etag' in response_headers:
logger.debug('Caching due to etag')
self.cache.set(
cache_url,
self.serializer.dumps(request, response, body=body),
)
# Add to the cache any 301s. We do this before looking that
# the Date headers.
elif response.status == 301:
logger.debug('Caching permanant redirect')
self.cache.set(
cache_url,
self.serializer.dumps(request, response)
)
# Add to the cache if the response headers demand it. If there
# is no date header then we can't do anything about expiring
# the cache.
elif 'date' in response_headers:
# cache when there is a max-age > 0
if cc and cc.get('max-age'):
if cc['max-age'].isdigit() and int(cc['max-age']) > 0:
logger.debug('Caching b/c date exists and max-age > 0')
self.cache.set(
cache_url,
self.serializer.dumps(request, response, body=body),
)
# If the request can expire, it means we should cache it
# in the meantime.
elif 'expires' in response_headers:
if response_headers['expires']:
logger.debug('Caching b/c of expires header')
self.cache.set(
cache_url,
self.serializer.dumps(request, response, body=body),
)
def update_cached_response(self, request, response):
"""On a 304 we will get a new set of headers that we want to
update our cached value with, assuming we have one.
This should only ever be called when we've sent an ETag and
gotten a 304 as the response.
"""
cache_url = self.cache_url(request.url)
cached_response = self.serializer.loads(
request,
self.cache.get(cache_url)
)
if not cached_response:
# we didn't have a cached response
return response
# Lets update our headers with the headers from the new request:
# http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-26#section-4.1
#
# The server isn't supposed to send headers that would make
# the cached body invalid. But... just in case, we'll be sure
# to strip out ones we know that might be problmatic due to
# typical assumptions.
excluded_headers = [
"content-length",
]
cached_response.headers.update(
dict((k, v) for k, v in response.headers.items()
if k.lower() not in excluded_headers)
)
# we want a 200 b/c we have content via the cache
cached_response.status = 200
# update our cache
self.cache.set(
cache_url,
self.serializer.dumps(request, cached_response),
)
return cached_response