Controlling Cache headers with zope.testbrowser

On a Plone website, setting the cache headers with CacheFu or other tools is quite easy, but when you need to check on a given page which headers are inserted, it's not always easy to know what will be called in the stack of rules you have set.

You can look at each page properties in you web browser to check this, but it is a pain and you won't be able to make sure nothing is broken when you change, for example, your CacheFu settings.

So, having a dedicated functional test to control your website cache settings is a good way to avoid regressions. zope.testbrowser allows you to write this on a doctest, so it's easy to gather all your cache headers control in one text file. To install it, you can use Easy Install:

$ easy_install zope.testbrowser

Here's an example of such doctest (cache.txt):

=============

Testing cache

=============



    >>> from zope.testbrowser.browser import Browser



This method is used to print a page headers::



    >>> def headers(url, login=None, password=None):

    ...     b = Browser()

    ...     if login is not None and password is not None:

    ...         b.addHeader('Authorization',

    ...                     'Basic %s:%s' % (login, password))

    ...     b.open(url)

    ...     print b.headers



Let's try on the python front page::



    >>> headers('http://python.org')

    Date: ...

    Server: Apache/2.2.3 (Debian) DAV/2 SVN/1.4.2 mod_ssl/2.2.3 OpenSSL/0.9.8c

    Last-Modified: ...

    ETag: "60193-3fd1-b811ca00"

    Accept-Ranges: bytes

    Content-Length: 16337

    Connection: close

    content-type: text/html; charset=utf-8



The page returns an ETag header, which tells the browser if the page has changed.



Let's try Plone's one::



    >>> headers('http://plone.org')

    Server: nginx/0.5.26

    Date: ...

    Connection: close

    Content-Language: en

    X-Cache-Headers-Set-By: CachingPolicyManager: /plone.org/caching_policy_manager

    Expires: ...

    Vary: Accept-Encoding

    Last-Modified: Sun, 04 Dec 2005 12:13:31 GMT

    X-Cache-Rules-Applied: yes

    X-Caching-Rule-Id: frontpage

    Cache-Control: max-age=0, s-maxage=3600, must-revalidate

    X-Header-Set-Id: cache-in-proxy-1-hour

    Content-Length: 44947

    X-Varnish: 783893351 783878475

    Age: 3364

    Via: 1.1 varnish

    Content-Type: text/html;charset=utf-8

    imagetoolbar: no



It has more complex cache information (CacheFu) used by Varnish cache software.

Notice the use of Ellipsis (...) that replaces changing data like Dates. It can be called using a python module that can look like this:

import os

import unittest

import doctest



OPTIONFLAGS = (doctest.REPORT_ONLY_FIRST_FAILURE |

                        doctest.ELLIPSIS |

                        doctest.NORMALIZE_WHITESPACE)



def test_suite():

    return doctest.DocFileSuite(os.path.basename('cache.txt'),

                                         optionflags=OPTIONFLAGS)



if __name__ == '__main__':

    test_suite()

This is not specific to Plone, and can be used on any website. Added to the stack of tests, this helps a lot on making sure the cache settings are doing what they are supposed to.

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