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Current Path : /proc/thread-self/root/lib/python3.6/site-packages/pip/_vendor/cachecontrol/ |
Current File : //proc/thread-self/root/lib/python3.6/site-packages/pip/_vendor/cachecontrol/heuristics.py |
import calendar import time from email.utils import formatdate, parsedate, parsedate_tz from datetime import datetime, timedelta TIME_FMT = "%a, %d %b %Y %H:%M:%S GMT" def expire_after(delta, date=None): date = date or datetime.now() return date + delta def datetime_to_header(dt): return formatdate(calendar.timegm(dt.timetuple())) class BaseHeuristic(object): def warning(self, response): """ Return a valid 1xx warning header value describing the cache adjustments. The response is provided too allow warnings like 113 http://tools.ietf.org/html/rfc7234#section-5.5.4 where we need to explicitly say response is over 24 hours old. """ return '110 - "Response is Stale"' def update_headers(self, response): """Update the response headers with any new headers. NOTE: This SHOULD always include some Warning header to signify that the response was cached by the client, not by way of the provided headers. """ return {} def apply(self, response): updated_headers = self.update_headers(response) if updated_headers: response.headers.update(updated_headers) warning_header_value = self.warning(response) if warning_header_value is not None: response.headers.update({'Warning': warning_header_value}) return response class OneDayCache(BaseHeuristic): """ Cache the response by providing an expires 1 day in the future. """ def update_headers(self, response): headers = {} if 'expires' not in response.headers: date = parsedate(response.headers['date']) expires = expire_after(timedelta(days=1), date=datetime(*date[:6])) headers['expires'] = datetime_to_header(expires) headers['cache-control'] = 'public' return headers class ExpiresAfter(BaseHeuristic): """ Cache **all** requests for a defined time period. """ def __init__(self, **kw): self.delta = timedelta(**kw) def update_headers(self, response): expires = expire_after(self.delta) return { 'expires': datetime_to_header(expires), 'cache-control': 'public', } def warning(self, response): tmpl = '110 - Automatically cached for %s. Response might be stale' return tmpl % self.delta class LastModified(BaseHeuristic): """ If there is no Expires header already, fall back on Last-Modified using the heuristic from http://tools.ietf.org/html/rfc7234#section-4.2.2 to calculate a reasonable value. Firefox also does something like this per https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching_FAQ http://lxr.mozilla.org/mozilla-release/source/netwerk/protocol/http/nsHttpResponseHead.cpp#397 Unlike mozilla we limit this to 24-hr. """ cacheable_by_default_statuses = set([ 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, 501 ]) def update_headers(self, resp): headers = resp.headers if 'expires' in headers: return {} if 'cache-control' in headers and headers['cache-control'] != 'public': return {} if resp.status not in self.cacheable_by_default_statuses: return {} if 'date' not in headers or 'last-modified' not in headers: return {} date = calendar.timegm(parsedate_tz(headers['date'])) last_modified = parsedate(headers['last-modified']) if date is None or last_modified is None: return {} now = time.time() current_age = max(0, now - date) delta = date - calendar.timegm(last_modified) freshness_lifetime = max(0, min(delta / 10, 24 * 3600)) if freshness_lifetime <= current_age: return {} expires = date + freshness_lifetime return {'expires': time.strftime(TIME_FMT, time.gmtime(expires))} def warning(self, resp): return None