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File Content: `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
Name	Size	Permission
__pycache__	---	0755
caches	---	0755
__init__.py	302 bytes	0644
_cmd.py	1320 bytes	0644
adapter.py	4608 bytes	0644
cache.py	790 bytes	0644
compat.py	380 bytes	0644
controller.py	13024 bytes	0644
filewrapper.py	2531 bytes	0644
heuristics.py	4141 bytes	0644
serialize.py	6536 bytes	0644
wrapper.py	498 bytes	0644
File Content: heuristics.py

File Content: `heuristics.py`
