377 lines
14 KiB
Python
377 lines
14 KiB
Python
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"""
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The httplib2 algorithms ported for use with requests.
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"""
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import logging
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import re
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import calendar
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import time
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from email.utils import parsedate_tz
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from requests.structures import CaseInsensitiveDict
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from .cache import DictCache
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from .serialize import Serializer
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logger = logging.getLogger(__name__)
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URI = re.compile(r"^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?")
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def parse_uri(uri):
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"""Parses a URI using the regex given in Appendix B of RFC 3986.
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(scheme, authority, path, query, fragment) = parse_uri(uri)
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"""
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groups = URI.match(uri).groups()
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return (groups[1], groups[3], groups[4], groups[6], groups[8])
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class CacheController(object):
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"""An interface to see if request should cached or not.
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"""
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def __init__(
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self, cache=None, cache_etags=True, serializer=None, status_codes=None
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):
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self.cache = DictCache() if cache is None else cache
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self.cache_etags = cache_etags
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self.serializer = serializer or Serializer()
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self.cacheable_status_codes = status_codes or (200, 203, 300, 301)
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@classmethod
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def _urlnorm(cls, uri):
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"""Normalize the URL to create a safe key for the cache"""
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(scheme, authority, path, query, fragment) = parse_uri(uri)
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if not scheme or not authority:
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raise Exception("Only absolute URIs are allowed. uri = %s" % uri)
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scheme = scheme.lower()
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authority = authority.lower()
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if not path:
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path = "/"
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# Could do syntax based normalization of the URI before
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# computing the digest. See Section 6.2.2 of Std 66.
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request_uri = query and "?".join([path, query]) or path
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defrag_uri = scheme + "://" + authority + request_uri
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return defrag_uri
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@classmethod
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def cache_url(cls, uri):
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return cls._urlnorm(uri)
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def parse_cache_control(self, headers):
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known_directives = {
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# https://tools.ietf.org/html/rfc7234#section-5.2
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"max-age": (int, True),
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"max-stale": (int, False),
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"min-fresh": (int, True),
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"no-cache": (None, False),
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"no-store": (None, False),
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"no-transform": (None, False),
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"only-if-cached": (None, False),
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"must-revalidate": (None, False),
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"public": (None, False),
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"private": (None, False),
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"proxy-revalidate": (None, False),
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"s-maxage": (int, True),
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}
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cc_headers = headers.get("cache-control", headers.get("Cache-Control", ""))
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retval = {}
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for cc_directive in cc_headers.split(","):
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if not cc_directive.strip():
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continue
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parts = cc_directive.split("=", 1)
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directive = parts[0].strip()
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try:
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typ, required = known_directives[directive]
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except KeyError:
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logger.debug("Ignoring unknown cache-control directive: %s", directive)
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continue
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if not typ or not required:
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retval[directive] = None
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if typ:
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try:
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retval[directive] = typ(parts[1].strip())
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except IndexError:
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if required:
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logger.debug(
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"Missing value for cache-control " "directive: %s",
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directive,
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)
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except ValueError:
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logger.debug(
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"Invalid value for cache-control directive " "%s, must be %s",
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directive,
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typ.__name__,
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)
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return retval
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def cached_request(self, request):
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"""
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Return a cached response if it exists in the cache, otherwise
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return False.
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"""
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cache_url = self.cache_url(request.url)
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logger.debug('Looking up "%s" in the cache', cache_url)
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cc = self.parse_cache_control(request.headers)
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# Bail out if the request insists on fresh data
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if "no-cache" in cc:
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logger.debug('Request header has "no-cache", cache bypassed')
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return False
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if "max-age" in cc and cc["max-age"] == 0:
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logger.debug('Request header has "max_age" as 0, cache bypassed')
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return False
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# Request allows serving from the cache, let's see if we find something
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cache_data = self.cache.get(cache_url)
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if cache_data is None:
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logger.debug("No cache entry available")
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return False
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# Check whether it can be deserialized
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resp = self.serializer.loads(request, cache_data)
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if not resp:
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logger.warning("Cache entry deserialization failed, entry ignored")
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return False
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# If we have a cached 301, return it immediately. We don't
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# need to test our response for other headers b/c it is
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# intrinsically "cacheable" as it is Permanent.
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# See:
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# https://tools.ietf.org/html/rfc7231#section-6.4.2
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#
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# Client can try to refresh the value by repeating the request
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# with cache busting headers as usual (ie no-cache).
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if resp.status == 301:
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msg = (
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'Returning cached "301 Moved Permanently" response '
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"(ignoring date and etag information)"
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)
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logger.debug(msg)
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return resp
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headers = CaseInsensitiveDict(resp.headers)
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if not headers or "date" not in headers:
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if "etag" not in headers:
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# Without date or etag, the cached response can never be used
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# and should be deleted.
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logger.debug("Purging cached response: no date or etag")
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self.cache.delete(cache_url)
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logger.debug("Ignoring cached response: no date")
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return False
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now = time.time()
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date = calendar.timegm(parsedate_tz(headers["date"]))
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current_age = max(0, now - date)
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logger.debug("Current age based on date: %i", current_age)
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# TODO: There is an assumption that the result will be a
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# urllib3 response object. This may not be best since we
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# could probably avoid instantiating or constructing the
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# response until we know we need it.
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resp_cc = self.parse_cache_control(headers)
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# determine freshness
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freshness_lifetime = 0
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# Check the max-age pragma in the cache control header
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if "max-age" in resp_cc:
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freshness_lifetime = resp_cc["max-age"]
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logger.debug("Freshness lifetime from max-age: %i", freshness_lifetime)
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# If there isn't a max-age, check for an expires header
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elif "expires" in headers:
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expires = parsedate_tz(headers["expires"])
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if expires is not None:
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expire_time = calendar.timegm(expires) - date
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freshness_lifetime = max(0, expire_time)
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logger.debug("Freshness lifetime from expires: %i", freshness_lifetime)
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# Determine if we are setting freshness limit in the
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# request. Note, this overrides what was in the response.
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if "max-age" in cc:
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freshness_lifetime = cc["max-age"]
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logger.debug(
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"Freshness lifetime from request max-age: %i", freshness_lifetime
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)
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if "min-fresh" in cc:
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min_fresh = cc["min-fresh"]
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# adjust our current age by our min fresh
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current_age += min_fresh
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logger.debug("Adjusted current age from min-fresh: %i", current_age)
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# Return entry if it is fresh enough
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if freshness_lifetime > current_age:
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logger.debug('The response is "fresh", returning cached response')
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logger.debug("%i > %i", freshness_lifetime, current_age)
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return resp
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# we're not fresh. If we don't have an Etag, clear it out
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if "etag" not in headers:
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logger.debug('The cached response is "stale" with no etag, purging')
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self.cache.delete(cache_url)
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# return the original handler
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return False
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def conditional_headers(self, request):
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cache_url = self.cache_url(request.url)
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resp = self.serializer.loads(request, self.cache.get(cache_url))
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new_headers = {}
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if resp:
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headers = CaseInsensitiveDict(resp.headers)
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if "etag" in headers:
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new_headers["If-None-Match"] = headers["ETag"]
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if "last-modified" in headers:
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new_headers["If-Modified-Since"] = headers["Last-Modified"]
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return new_headers
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def cache_response(self, request, response, body=None, status_codes=None):
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"""
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Algorithm for caching requests.
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This assumes a requests Response object.
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"""
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# From httplib2: Don't cache 206's since we aren't going to
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# handle byte range requests
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cacheable_status_codes = status_codes or self.cacheable_status_codes
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if response.status not in cacheable_status_codes:
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logger.debug(
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"Status code %s not in %s", response.status, cacheable_status_codes
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)
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return
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response_headers = CaseInsensitiveDict(response.headers)
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# If we've been given a body, our response has a Content-Length, that
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# Content-Length is valid then we can check to see if the body we've
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# been given matches the expected size, and if it doesn't we'll just
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# skip trying to cache it.
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if (
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body is not None
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and "content-length" in response_headers
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and response_headers["content-length"].isdigit()
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and int(response_headers["content-length"]) != len(body)
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):
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return
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cc_req = self.parse_cache_control(request.headers)
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cc = self.parse_cache_control(response_headers)
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cache_url = self.cache_url(request.url)
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logger.debug('Updating cache with response from "%s"', cache_url)
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# Delete it from the cache if we happen to have it stored there
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no_store = False
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if "no-store" in cc:
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no_store = True
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logger.debug('Response header has "no-store"')
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if "no-store" in cc_req:
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no_store = True
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logger.debug('Request header has "no-store"')
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if no_store and self.cache.get(cache_url):
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logger.debug('Purging existing cache entry to honor "no-store"')
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self.cache.delete(cache_url)
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if no_store:
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return
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# https://tools.ietf.org/html/rfc7234#section-4.1:
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# A Vary header field-value of "*" always fails to match.
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# Storing such a response leads to a deserialization warning
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# during cache lookup and is not allowed to ever be served,
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# so storing it can be avoided.
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if "*" in response_headers.get("vary", ""):
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logger.debug('Response header has "Vary: *"')
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return
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# If we've been given an etag, then keep the response
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if self.cache_etags and "etag" in response_headers:
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logger.debug("Caching due to etag")
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self.cache.set(
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cache_url, self.serializer.dumps(request, response, body=body)
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)
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# Add to the cache any 301s. We do this before looking that
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# the Date headers.
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elif response.status == 301:
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logger.debug("Caching permanant redirect")
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self.cache.set(cache_url, self.serializer.dumps(request, response))
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# Add to the cache if the response headers demand it. If there
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# is no date header then we can't do anything about expiring
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# the cache.
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elif "date" in response_headers:
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# cache when there is a max-age > 0
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if "max-age" in cc and cc["max-age"] > 0:
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logger.debug("Caching b/c date exists and max-age > 0")
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self.cache.set(
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cache_url, self.serializer.dumps(request, response, body=body)
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)
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# If the request can expire, it means we should cache it
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# in the meantime.
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elif "expires" in response_headers:
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if response_headers["expires"]:
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logger.debug("Caching b/c of expires header")
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self.cache.set(
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cache_url, self.serializer.dumps(request, response, body=body)
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)
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def update_cached_response(self, request, response):
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"""On a 304 we will get a new set of headers that we want to
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update our cached value with, assuming we have one.
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This should only ever be called when we've sent an ETag and
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gotten a 304 as the response.
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"""
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cache_url = self.cache_url(request.url)
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cached_response = self.serializer.loads(request, self.cache.get(cache_url))
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if not cached_response:
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# we didn't have a cached response
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return response
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# Lets update our headers with the headers from the new request:
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# http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-26#section-4.1
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#
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# The server isn't supposed to send headers that would make
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# the cached body invalid. But... just in case, we'll be sure
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# to strip out ones we know that might be problmatic due to
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# typical assumptions.
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excluded_headers = ["content-length"]
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cached_response.headers.update(
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dict(
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(k, v)
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for k, v in response.headers.items()
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if k.lower() not in excluded_headers
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)
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)
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# we want a 200 b/c we have content via the cache
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cached_response.status = 200
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# update our cache
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self.cache.set(cache_url, self.serializer.dumps(request, cached_response))
|
||
|
|
|
||
|
|
return cached_response
|