mirror of
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299 lines
9.9 KiB
Python
299 lines
9.9 KiB
Python
"""
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The httplib2 algorithms ported for use with requests.
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"""
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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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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__(self, cache=None, cache_etags=True, serializer=None):
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self.cache = cache or DictCache()
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self.cache_etags = cache_etags
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self.serializer = serializer or Serializer()
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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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"""
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Parse the cache control headers returning a dictionary with values
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for the different directives.
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"""
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retval = {}
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cc_header = 'cache-control'
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if 'Cache-Control' in headers:
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cc_header = 'Cache-Control'
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if cc_header in headers:
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parts = headers[cc_header].split(',')
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parts_with_args = [
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tuple([x.strip().lower() for x in part.split("=", 1)])
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for part in parts if -1 != part.find("=")
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]
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parts_wo_args = [
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(name.strip().lower(), 1)
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for name in parts if -1 == name.find("=")
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]
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retval = dict(parts_with_args + parts_wo_args)
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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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cc = self.parse_cache_control(request.headers)
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# non-caching states
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no_cache = True if 'no-cache' in cc else False
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if 'max-age' in cc and cc['max-age'] == 0:
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no_cache = True
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# Bail out if no-cache was set
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if no_cache:
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return False
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# It is in the cache, so lets see if it is going to be
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# fresh enough
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resp = self.serializer.loads(request, self.cache.get(cache_url))
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# Check to see if we have a cached object
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if not resp:
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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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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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# With date or etag, the cached response can never be used
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# and should be deleted.
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if 'etag' not in headers:
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self.cache.delete(cache_url)
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return False
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now = time.time()
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date = calendar.timegm(
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parsedate_tz(headers['date'])
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)
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current_age = max(0, now - date)
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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 and resp_cc['max-age'].isdigit():
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freshness_lifetime = int(resp_cc['max-age'])
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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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# determine if we are setting freshness limit in the req
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if 'max-age' in cc:
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try:
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freshness_lifetime = int(cc['max-age'])
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except ValueError:
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freshness_lifetime = 0
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if 'min-fresh' in cc:
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try:
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min_fresh = int(cc['min-fresh'])
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except ValueError:
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min_fresh = 0
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# adjust our current age by our min fresh
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current_age += min_fresh
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# see how fresh we actually are
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fresh = (freshness_lifetime > current_age)
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if fresh:
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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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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):
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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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if response.status not in [200, 203, 300, 301]:
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return
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response_headers = CaseInsensitiveDict(response.headers)
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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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# Delete it from the cache if we happen to have it stored there
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no_store = cc.get('no-store') or cc_req.get('no-store')
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if no_store and self.cache.get(cache_url):
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self.cache.delete(cache_url)
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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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self.cache.set(
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cache_url,
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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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self.cache.set(
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cache_url,
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self.serializer.dumps(request, response)
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)
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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 cc and cc.get('max-age'):
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if int(cc['max-age']) > 0:
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self.cache.set(
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cache_url,
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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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self.cache.set(
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cache_url,
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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(
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request,
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self.cache.get(cache_url)
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)
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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 = [
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"content-length",
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]
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cached_response.headers.update(
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dict((k, v) 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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# 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(
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cache_url,
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self.serializer.dumps(request, cached_response),
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)
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return cached_response
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