web/httpcache.py
author sylvain.thenault@logilab.fr
Wed, 18 Feb 2009 10:21:15 +0100
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update some imports
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"""HTTP cache managers
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:organization: Logilab
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:copyright: 2001-2009 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
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:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
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"""
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__docformat__ = "restructuredtext en"
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from mx.DateTime import DateTimeFromTicks, now, gmtime
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# time delta usable to convert localized time to GMT time
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GMTOFFSET = - (now() - gmtime())
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class NoHTTPCacheManager(object):
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    """default cache manager: set no-cache cache control policy"""
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    def __init__(self, view):
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        self.view = view
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        self.req = view.req
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        self.rset = view.rset
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    def set_headers(self):
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        self.req.set_header('Cache-control', 'no-cache')
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class MaxAgeHTTPCacheManager(NoHTTPCacheManager):
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    """max-age cache manager: set max-age cache control policy, with max-age
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    specified with the `cache_max_age` attribute of the view
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    """
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    def set_headers(self):
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        self.req.set_header('Cache-control',
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                            'max-age=%s' % self.view.cache_max_age)
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class EtagHTTPCacheManager(NoHTTPCacheManager):
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    """etag based cache manager for startup views
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    * etag is generated using the view name and the user's groups
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    * set policy to 'must-revalidate' and expires to the current time to force
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      revalidation on each request
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    """
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    # GMT time required
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    date_format = "%a, %d %b %Y %H:%M:%S GMT"
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    def etag(self):
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        return self.view.id + '/' + ','.join(sorted(self.req.user.groups))
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    def max_age(self):
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        # 0 to actually force revalidation
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        return 0
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    def last_modified(self):
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        return self.view.last_modified()
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    def set_headers(self):
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        req = self.req
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        try:
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            req.set_header('Etag', '"%s"' % self.etag())
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        except NoEtag:
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            self.req.set_header('Cache-control', 'no-cache')
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            return
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        req.set_header('Cache-control',
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                       'must-revalidate;max-age=%s' % self.max_age())
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        mdate = self.last_modified()
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        req.set_header('Last-modified', mdate.strftime(self.date_format))
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class EntityHTTPCacheManager(EtagHTTPCacheManager):
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    """etag based cache manager for view displaying a single entity
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    * etag is generated using entity's eid, the view name and the user's groups
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    * get last modified time from the entity definition (this may not be the
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      entity's modification time since a view may include some related entities
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      with a modification time to consider) using the `last_modified` method
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    """
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    def etag(self):
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        if self.rset is None or len(self.rset) == 0: # entity startup view for instance
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            return super(EntityHTTPCacheManager, self).etag()
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        if len(self.rset) > 1:
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            raise NoEtag()
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        etag = super(EntityHTTPCacheManager, self).etag()
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        eid = self.rset[0][0]
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        if self.req.user.owns(eid):
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            etag += ',owners'
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        return str(eid) + '/' + etag
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class NoEtag(Exception):
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    """an etag can't be generated"""
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__all__ = ('GMTOFFSET',
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           'NoHTTPCacheManager', 'MaxAgeHTTPCacheManager',
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           'EtagHTTPCacheManager', 'EntityHTTPCacheManager')
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# monkey patching, so view doesn't depends on this module and we have all
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# http cache related logic here
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from cubicweb import view
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def set_http_cache_headers(self):
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    self.http_cache_manager(self).set_headers()
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view.View.set_http_cache_headers = set_http_cache_headers
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def last_modified(self):
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    """return the date/time where this view should be considered as
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    modified. Take care of possible related objects modifications.
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    /!\ must return GMT time /!\
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    """
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    # XXX check view module's file modification time in dev mod ?
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    ctime = gmtime()
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    if self.cache_max_age:
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        mtime = self.req.header_if_modified_since()
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        if mtime:
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            if (ctime - mtime).seconds > self.cache_max_age:
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                mtime = ctime
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        else:
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            mtime = ctime
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    else:
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        mtime = ctime
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    # mtime = ctime will force page rerendering
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    return mtime
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view.View.last_modified = last_modified
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# configure default caching
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view.View.http_cache_manager = NoHTTPCacheManager
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# max-age=0 to actually force revalidation when needed
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view.View.cache_max_age = 0
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view.EntityView.http_cache_manager = EntityHTTPCacheManager
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view.StartupView.http_cache_manager = MaxAgeHTTPCacheManager
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view.StartupView.cache_max_age = 60*60*2 # stay in http cache for 2 hours by default