zope.paste 0.3

Installing and configuring zope.paste

zope.paste can be installed as an egg anywhere onto your PYTHONPATH or simply dropped into your <INSTANCE_HOME>/lib/python directory. Then you need to enable zope.paste’s ZCML configuration by creating the file <INSTANCE_HOME>/etc/package-includes/zope.paste-configure.zcml with the following contents:

<include package="zope.paste" />

Configuring the server

We create a <server> directive in <INSTANCE_HOME>/etc/zope.conf to use zope.paste’s server definition, Paste.Main. That way the WSGI middlewares will be invoked when responses are served through this server:

<server>
  type Paste.Main
  address 8081
</server>

Configuring the WSGI stack

Now we configure a WSGI application using PasteDeploy syntax in <INSTANCE_HOME>/etc/paste.ini. Here’s an example of how to configure the Paste.Main application to use the Zope 3 publisher as a WSGI application, therefore doing the exact same thing that the regular HTTP server definition would do:

[app:Paste.Main]
paste.app_factory = zope.paste.application:zope_publisher_app_factory

That’s not really interesting, though. PasteDeploy allows you to chain various WSGI entities together, which is where it gets interesting. There seems to be a distinction between ‘apps’ and ‘filters’ (also referred to as ‘middleware’). An example that might be of interest is applying a XSLT transformation to the output of the Zope 3 WSGI application.

Happily enough, someone seems to have already created a WSGI filter for applying a XSLT stylesheet. You can find it at http://www.decafbad.com/2005/07/xmlwiki/lib/xmlwiki/xslfilter.py

If you wanted to apply this WSGI filter to Zope 3, you would need three things:

1. Put the xslfilter.py file somewhere in PYTHONPATH. <INSTANCE>/lib/python is a good place.

2. Add this snippet to the bottom of xslfilter.py:

   def filter_factory(global_conf, **local_conf):
       def filter(app):
           return XSLFilter(app)
       return filter

3. Change paste.ini file as follows:

   [pipeline:Paste.Main]
   pipeline = xslt main
   
   [app:main]
   paste.app_factory = zope.paste.application:zope_publisher_app_factory
   
   [filter:xslt]
   paste.filter_factory = xslfilter:filter_factory

   What this does is to define a pipeline. Learn more about this on the PasteDeploy website. Refer to the source of xslfilter.py for information about how to pass a stylesheet to the filter.

Configuring the application

zope.paste provides a PasteDeploy-compatible factory for Zope 3’s WSGI publisher application and registers it in an entry point. We can therefore create a very simple Zope 3 application in a PasteDeploy configuration file (e.g. paste.ini):

[app:main]
use = egg:zope.paste
site_definition = /path/to/site.zcml
file_storage = /path/to/Data.fs
devmode = on

In this case, /path/to/site.zcml refers to a site.zcml as known from a Zope 3 instance. You can, for example, put paste.ini into an existing Zope 3 instance, next to site.zcml.

Configuring the ZODB database

Instead of referring to a ZODB FileStorage using the file_storage setting, you can also configure multiple or other ZODB database backends in a ZConfig-style configuration file (much like zope.conf), e.g. the following configures a ZEO client:

<zodb>
  <zeoclient>
    server localhost:8100
    storage 1
    cache-size 20MB
  </zeoclient>
</zodb>

Refer to this file from paste.ini this way (and delete the file_storage setting):

db_definition = db.conf

Configuring the server

In order to be able to use our Zope application, we only need to add a server definition. We can use the one that comes with Paste or PasteScript, rather:

[server:main]
use = egg:PasteScript#wsgiutils
host = 127.0.0.1
port = 8080

Now we can start the application using the paster command that comes with PasteScript:

$ paster serve paste.ini

WSGI middlewares can be configured like described above or on the PasteDeploy website.