""" The httplib2 algorithms ported for use with requests. """ import re import calendar import time import os from cachecontrol.cache import DictCache from cachecontrol.compat import parsedate_tz 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, cache_force=False): self.cache = cache or DictCache() self.cache_etags = cache_etags self.cache_force = cache_force def _urlnorm(self, 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) authority = authority.lower() scheme = scheme.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 scheme = scheme.lower() defrag_uri = scheme + "://" + authority + request_uri return defrag_uri def cache_url(self, uri): return self._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, url, headers): cache_url = self.cache_url(url) cc = self.parse_cache_control(headers) # non-caching states no_cache = True if 'no-cache' in cc else False if 'max-age' in cc and cc['max-age'] == 0: no_cache = True # see if it is in the cache anyways in_cache = self.cache.get(cache_url) if no_cache or not in_cache: return False # It is in the cache, so lets see if it is going to be # fresh enough resp = self.cache.get(cache_url) # Check our Vary header to make sure our request headers match # up. We don't delete it from the though, we just don't return # our cached value. # # NOTE: Because httplib2 stores raw content, it denotes # headers that were sent in the original response by # adding -varied-$name. We don't have to do that b/c we # are storing the object which has a reference to the # original request. If that changes, then I'd propose # using the varied headers in the cache key to avoid the # situation all together. if 'vary' in resp.headers: varied_headers = resp.headers['vary'].replace(' ', '').split(',') original_headers = resp.request.headers for header in varied_headers: # If our headers don't match for the headers listed in # the vary header, then don't use the cached response if headers.get(header, None) != original_headers.get(header): return False now = time.time() date = calendar.timegm( parsedate_tz(resp.headers['date']) ) current_age = max(0, now - date) # TODO: There is an assumption that the result will be a # requests 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(resp.headers) # determine freshness freshness_lifetime = 0 if 'max-age' in resp_cc and resp_cc['max-age'].isdigit(): freshness_lifetime = int(resp_cc['max-age']) elif 'expires' in resp.headers: expires = parsedate_tz(resp.headers['expires']) if expires is not None: expire_time = calendar.timegm(expires) - date freshness_lifetime = max(0, expire_time) # determine if we are setting freshness limit in the req if 'max-age' in cc: try: freshness_lifetime = int(cc['max-age']) 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 # see how fresh we actually are fresh = (freshness_lifetime > current_age) if fresh: # make sure we set the from_cache to true resp.from_cache = True return resp # we're not fresh. If we don't have an Etag, clear it out if 'etag' not in resp.headers: self.cache.delete(cache_url) if 'etag' in resp.headers: headers['If-None-Match'] = resp.headers['ETag'] if 'last-modified' in resp.headers: headers['If-Modified-Since'] = resp.headers['Last-Modified'] # return the original handler return False def add_headers(self, url, resp=None): resp = self.cache.get(url) if resp and 'etag' in resp.headers: return {'If-None-Match': resp.headers['etag']} return {} def cache_response(self, request, resp): """ 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 if resp.status_code not in [200, 203]: return cc_req = self.parse_cache_control(request.headers) cc = self.parse_cache_control(resp.headers) cache_url = self.cache_url(request.url) # Delete it from the cache if we happen to have it stored there no_store = cc.get('no-store') or cc_req.get('no-store') if no_store and self.cache.get(cache_url): self.cache.delete(cache_url) # If we've been given an etag, then keep the response if self.cache_etags and 'etag' in resp.headers: self.cache.set(cache_url, resp) # 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 resp.headers: # cache when there is a max-age > 0 if cc and cc.get('max-age'): if int(cc['max-age']) > 0: self.cache.set(cache_url, resp) # If the request can expire, it means we should cache it # in the meantime. elif 'expires' in resp.headers: if resp.headers['expires']: self.cache.set(cache_url, resp) # If the request is for our local cache, it means we should cache it elif self.cache_force: resp.headers.update({'cache-control': 'max-age=21600, private'}) self.cache.set(cache_url, resp) 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) resp = self.cache.get(cache_url) if not resp: # we didn't have a cached response return response # did so lets update our headers resp.headers.update(resp.headers) # we want a 200 b/c we have content via the cache request.status_code = 200 # update the request as it has the if-none-match header + any # other headers that the server might have updated (ie Date, # Cache-Control, Expires, etc.) resp.request = request # update our cache self.cache.set(cache_url, resp) # Let everyone know this was from the cache. resp.from_cache = True return resp