mirror of https://github.com/evilhero/mylar
466 lines
17 KiB
Python
Executable File
466 lines
17 KiB
Python
Executable File
"""
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CherryPy implements a simple caching system as a pluggable Tool. This tool tries
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to be an (in-process) HTTP/1.1-compliant cache. It's not quite there yet, but
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it's probably good enough for most sites.
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In general, GET responses are cached (along with selecting headers) and, if
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another request arrives for the same resource, the caching Tool will return 304
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Not Modified if possible, or serve the cached response otherwise. It also sets
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request.cached to True if serving a cached representation, and sets
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request.cacheable to False (so it doesn't get cached again).
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If POST, PUT, or DELETE requests are made for a cached resource, they invalidate
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(delete) any cached response.
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Usage
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=====
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Configuration file example::
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[/]
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tools.caching.on = True
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tools.caching.delay = 3600
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You may use a class other than the default
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:class:`MemoryCache<cherrypy.lib.caching.MemoryCache>` by supplying the config
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entry ``cache_class``; supply the full dotted name of the replacement class
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as the config value. It must implement the basic methods ``get``, ``put``,
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``delete``, and ``clear``.
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You may set any attribute, including overriding methods, on the cache
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instance by providing them in config. The above sets the
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:attr:`delay<cherrypy.lib.caching.MemoryCache.delay>` attribute, for example.
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"""
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import datetime
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import sys
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import threading
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import time
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import cherrypy
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from cherrypy.lib import cptools, httputil
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from cherrypy._cpcompat import copyitems, ntob, set_daemon, sorted
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class Cache(object):
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"""Base class for Cache implementations."""
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def get(self):
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"""Return the current variant if in the cache, else None."""
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raise NotImplemented
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def put(self, obj, size):
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"""Store the current variant in the cache."""
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raise NotImplemented
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def delete(self):
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"""Remove ALL cached variants of the current resource."""
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raise NotImplemented
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def clear(self):
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"""Reset the cache to its initial, empty state."""
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raise NotImplemented
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# ------------------------------- Memory Cache ------------------------------- #
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class AntiStampedeCache(dict):
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"""A storage system for cached items which reduces stampede collisions."""
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def wait(self, key, timeout=5, debug=False):
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"""Return the cached value for the given key, or None.
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If timeout is not None, and the value is already
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being calculated by another thread, wait until the given timeout has
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elapsed. If the value is available before the timeout expires, it is
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returned. If not, None is returned, and a sentinel placed in the cache
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to signal other threads to wait.
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If timeout is None, no waiting is performed nor sentinels used.
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"""
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value = self.get(key)
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if isinstance(value, threading._Event):
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if timeout is None:
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# Ignore the other thread and recalc it ourselves.
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if debug:
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cherrypy.log('No timeout', 'TOOLS.CACHING')
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return None
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# Wait until it's done or times out.
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if debug:
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cherrypy.log('Waiting up to %s seconds' % timeout, 'TOOLS.CACHING')
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value.wait(timeout)
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if value.result is not None:
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# The other thread finished its calculation. Use it.
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if debug:
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cherrypy.log('Result!', 'TOOLS.CACHING')
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return value.result
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# Timed out. Stick an Event in the slot so other threads wait
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# on this one to finish calculating the value.
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if debug:
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cherrypy.log('Timed out', 'TOOLS.CACHING')
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e = threading.Event()
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e.result = None
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dict.__setitem__(self, key, e)
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return None
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elif value is None:
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# Stick an Event in the slot so other threads wait
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# on this one to finish calculating the value.
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if debug:
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cherrypy.log('Timed out', 'TOOLS.CACHING')
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e = threading.Event()
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e.result = None
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dict.__setitem__(self, key, e)
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return value
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def __setitem__(self, key, value):
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"""Set the cached value for the given key."""
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existing = self.get(key)
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dict.__setitem__(self, key, value)
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if isinstance(existing, threading._Event):
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# Set Event.result so other threads waiting on it have
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# immediate access without needing to poll the cache again.
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existing.result = value
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existing.set()
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class MemoryCache(Cache):
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"""An in-memory cache for varying response content.
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Each key in self.store is a URI, and each value is an AntiStampedeCache.
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The response for any given URI may vary based on the values of
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"selecting request headers"; that is, those named in the Vary
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response header. We assume the list of header names to be constant
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for each URI throughout the lifetime of the application, and store
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that list in ``self.store[uri].selecting_headers``.
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The items contained in ``self.store[uri]`` have keys which are tuples of
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request header values (in the same order as the names in its
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selecting_headers), and values which are the actual responses.
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"""
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maxobjects = 1000
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"""The maximum number of cached objects; defaults to 1000."""
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maxobj_size = 100000
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"""The maximum size of each cached object in bytes; defaults to 100 KB."""
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maxsize = 10000000
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"""The maximum size of the entire cache in bytes; defaults to 10 MB."""
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delay = 600
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"""Seconds until the cached content expires; defaults to 600 (10 minutes)."""
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antistampede_timeout = 5
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"""Seconds to wait for other threads to release a cache lock."""
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expire_freq = 0.1
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"""Seconds to sleep between cache expiration sweeps."""
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debug = False
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def __init__(self):
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self.clear()
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# Run self.expire_cache in a separate daemon thread.
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t = threading.Thread(target=self.expire_cache, name='expire_cache')
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self.expiration_thread = t
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set_daemon(t, True)
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t.start()
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def clear(self):
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"""Reset the cache to its initial, empty state."""
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self.store = {}
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self.expirations = {}
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self.tot_puts = 0
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self.tot_gets = 0
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self.tot_hist = 0
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self.tot_expires = 0
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self.tot_non_modified = 0
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self.cursize = 0
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def expire_cache(self):
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"""Continuously examine cached objects, expiring stale ones.
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This function is designed to be run in its own daemon thread,
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referenced at ``self.expiration_thread``.
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"""
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# It's possible that "time" will be set to None
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# arbitrarily, so we check "while time" to avoid exceptions.
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# See tickets #99 and #180 for more information.
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while time:
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now = time.time()
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# Must make a copy of expirations so it doesn't change size
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# during iteration
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for expiration_time, objects in copyitems(self.expirations):
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if expiration_time <= now:
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for obj_size, uri, sel_header_values in objects:
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try:
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del self.store[uri][tuple(sel_header_values)]
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self.tot_expires += 1
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self.cursize -= obj_size
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except KeyError:
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# the key may have been deleted elsewhere
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pass
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del self.expirations[expiration_time]
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time.sleep(self.expire_freq)
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def get(self):
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"""Return the current variant if in the cache, else None."""
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request = cherrypy.serving.request
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self.tot_gets += 1
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uri = cherrypy.url(qs=request.query_string)
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uricache = self.store.get(uri)
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if uricache is None:
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return None
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header_values = [request.headers.get(h, '')
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for h in uricache.selecting_headers]
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variant = uricache.wait(key=tuple(sorted(header_values)),
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timeout=self.antistampede_timeout,
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debug=self.debug)
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if variant is not None:
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self.tot_hist += 1
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return variant
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def put(self, variant, size):
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"""Store the current variant in the cache."""
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request = cherrypy.serving.request
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response = cherrypy.serving.response
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uri = cherrypy.url(qs=request.query_string)
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uricache = self.store.get(uri)
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if uricache is None:
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uricache = AntiStampedeCache()
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uricache.selecting_headers = [
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e.value for e in response.headers.elements('Vary')]
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self.store[uri] = uricache
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if len(self.store) < self.maxobjects:
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total_size = self.cursize + size
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# checks if there's space for the object
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if (size < self.maxobj_size and total_size < self.maxsize):
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# add to the expirations list
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expiration_time = response.time + self.delay
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bucket = self.expirations.setdefault(expiration_time, [])
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bucket.append((size, uri, uricache.selecting_headers))
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# add to the cache
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header_values = [request.headers.get(h, '')
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for h in uricache.selecting_headers]
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uricache[tuple(sorted(header_values))] = variant
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self.tot_puts += 1
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self.cursize = total_size
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def delete(self):
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"""Remove ALL cached variants of the current resource."""
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uri = cherrypy.url(qs=cherrypy.serving.request.query_string)
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self.store.pop(uri, None)
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def get(invalid_methods=("POST", "PUT", "DELETE"), debug=False, **kwargs):
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"""Try to obtain cached output. If fresh enough, raise HTTPError(304).
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If POST, PUT, or DELETE:
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* invalidates (deletes) any cached response for this resource
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* sets request.cached = False
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* sets request.cacheable = False
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else if a cached copy exists:
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* sets request.cached = True
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* sets request.cacheable = False
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* sets response.headers to the cached values
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* checks the cached Last-Modified response header against the
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current If-(Un)Modified-Since request headers; raises 304
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if necessary.
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* sets response.status and response.body to the cached values
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* returns True
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otherwise:
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* sets request.cached = False
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* sets request.cacheable = True
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* returns False
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"""
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request = cherrypy.serving.request
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response = cherrypy.serving.response
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if not hasattr(cherrypy, "_cache"):
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# Make a process-wide Cache object.
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cherrypy._cache = kwargs.pop("cache_class", MemoryCache)()
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# Take all remaining kwargs and set them on the Cache object.
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for k, v in kwargs.items():
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setattr(cherrypy._cache, k, v)
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cherrypy._cache.debug = debug
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# POST, PUT, DELETE should invalidate (delete) the cached copy.
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# See http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.10.
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if request.method in invalid_methods:
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if debug:
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cherrypy.log('request.method %r in invalid_methods %r' %
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(request.method, invalid_methods), 'TOOLS.CACHING')
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cherrypy._cache.delete()
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request.cached = False
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request.cacheable = False
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return False
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if 'no-cache' in [e.value for e in request.headers.elements('Pragma')]:
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request.cached = False
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request.cacheable = True
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return False
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cache_data = cherrypy._cache.get()
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request.cached = bool(cache_data)
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request.cacheable = not request.cached
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if request.cached:
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# Serve the cached copy.
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max_age = cherrypy._cache.delay
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for v in [e.value for e in request.headers.elements('Cache-Control')]:
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atoms = v.split('=', 1)
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directive = atoms.pop(0)
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if directive == 'max-age':
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if len(atoms) != 1 or not atoms[0].isdigit():
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raise cherrypy.HTTPError(400, "Invalid Cache-Control header")
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max_age = int(atoms[0])
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break
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elif directive == 'no-cache':
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if debug:
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cherrypy.log('Ignoring cache due to Cache-Control: no-cache',
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'TOOLS.CACHING')
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request.cached = False
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request.cacheable = True
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return False
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if debug:
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cherrypy.log('Reading response from cache', 'TOOLS.CACHING')
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s, h, b, create_time = cache_data
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age = int(response.time - create_time)
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if (age > max_age):
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if debug:
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cherrypy.log('Ignoring cache due to age > %d' % max_age,
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'TOOLS.CACHING')
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request.cached = False
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request.cacheable = True
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return False
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# Copy the response headers. See http://www.cherrypy.org/ticket/721.
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response.headers = rh = httputil.HeaderMap()
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for k in h:
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dict.__setitem__(rh, k, dict.__getitem__(h, k))
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# Add the required Age header
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response.headers["Age"] = str(age)
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try:
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# Note that validate_since depends on a Last-Modified header;
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# this was put into the cached copy, and should have been
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# resurrected just above (response.headers = cache_data[1]).
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cptools.validate_since()
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except cherrypy.HTTPRedirect:
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x = sys.exc_info()[1]
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if x.status == 304:
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cherrypy._cache.tot_non_modified += 1
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raise
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# serve it & get out from the request
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response.status = s
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response.body = b
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else:
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if debug:
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cherrypy.log('request is not cached', 'TOOLS.CACHING')
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return request.cached
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def tee_output():
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"""Tee response output to cache storage. Internal."""
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# Used by CachingTool by attaching to request.hooks
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request = cherrypy.serving.request
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if 'no-store' in request.headers.values('Cache-Control'):
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return
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def tee(body):
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"""Tee response.body into a list."""
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if ('no-cache' in response.headers.values('Pragma') or
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'no-store' in response.headers.values('Cache-Control')):
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for chunk in body:
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yield chunk
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return
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output = []
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for chunk in body:
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output.append(chunk)
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yield chunk
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# save the cache data
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body = ntob('').join(output)
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cherrypy._cache.put((response.status, response.headers or {},
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body, response.time), len(body))
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response = cherrypy.serving.response
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response.body = tee(response.body)
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def expires(secs=0, force=False, debug=False):
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"""Tool for influencing cache mechanisms using the 'Expires' header.
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secs
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Must be either an int or a datetime.timedelta, and indicates the
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number of seconds between response.time and when the response should
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expire. The 'Expires' header will be set to response.time + secs.
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If secs is zero, the 'Expires' header is set one year in the past, and
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the following "cache prevention" headers are also set:
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* Pragma: no-cache
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* Cache-Control': no-cache, must-revalidate
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force
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If False, the following headers are checked:
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* Etag
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* Last-Modified
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* Age
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* Expires
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If any are already present, none of the above response headers are set.
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"""
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response = cherrypy.serving.response
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headers = response.headers
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cacheable = False
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if not force:
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# some header names that indicate that the response can be cached
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for indicator in ('Etag', 'Last-Modified', 'Age', 'Expires'):
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if indicator in headers:
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cacheable = True
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break
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if not cacheable and not force:
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if debug:
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cherrypy.log('request is not cacheable', 'TOOLS.EXPIRES')
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else:
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if debug:
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cherrypy.log('request is cacheable', 'TOOLS.EXPIRES')
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if isinstance(secs, datetime.timedelta):
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secs = (86400 * secs.days) + secs.seconds
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if secs == 0:
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if force or ("Pragma" not in headers):
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headers["Pragma"] = "no-cache"
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if cherrypy.serving.request.protocol >= (1, 1):
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if force or "Cache-Control" not in headers:
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headers["Cache-Control"] = "no-cache, must-revalidate"
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# Set an explicit Expires date in the past.
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expiry = httputil.HTTPDate(1169942400.0)
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else:
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expiry = httputil.HTTPDate(response.time + secs)
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if force or "Expires" not in headers:
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headers["Expires"] = expiry
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