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