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.. -*- mode: rst -*-
.. _server-plugins-connectors-templatehelper:
==============
TemplateHelper
==============
The TemplateHelper plugin is a connector plugin that adds Python
classes and methods to client metadata instances for use in
templates. This allows you to easily reuse code that is common
amongst multiple templates and add convenience methods.
Using TemplateHelper
====================
First, ``mkdir /var/lib/bcfg2/TemplateHelper`` and add
**TemplateHelper** to your ``plugins`` line in ``/etc/bcfg2.conf``.
Restart ``bcfg2-server``.
Now, any ``.py`` file placed in ``/var/lib/bcfg2/TemplateHelper/``
will be read and added to matching client metadata objects. See
:ref:`writing-templatehelpers` below for more information on how to
write TemplateHelper scripts.
TemplateHelper does not support group- or host-specific helpers. All
helpers will be available to all clients.
.. _writing-templatehelpers:
Writing Helpers
===============
A helper module is just a Python module with several special conditions:
* The filename must end with ``.py``
* The module must have an attribute, ``__export__``, that lists all of
the classes, functions, variables, or other symbols you wish to
export from the module.
* ``data``, ``name``, ``fam``, ``Index``, and ``HandleEvent`` are
reserved names. You should not include symbols with a reserved name
in ``__export__``. Additionally, including symbols that start with
an underscore or double underscore is bad form, and may also produce
errors.
Additionally, the module *may* have an attribute, ``__default__``,
that lists all of the symbols that you wish to include by default in
the template namespace. ``name``, ``metadata``, ``source_path``,
``repo``, and ``path`` are reserved names, and should not be included
in ``__default__``.
See ``examples/TemplateHelper`` for examples of helper modules.
Usage
=====
Specific helpers can be referred to in templates as
``metadata.TemplateHelper[<modulename>]``. That returns a HelperModule
object which will have, as attributes, all symbols listed in
``__export__``. For example, consider this helper module::
__export__ = ["hello"]
__default__ = ["pining"]
def hello(metadata):
return "Hello, %s!" % metadata.hostname
def pining(text):
return "It's pinin' for the %s!" % text
To use this in a Genshi template, we could do::
${metadata.TemplateHelper['hello'].hello(metadata)}
${pining("fjords")}
The template would produce::
Hello, foo.example.com!
It's pinin' for the fjords!
Note that the client metadata object is not passed to a helper module
in any magical way; if you want to access the client metadata object
in a helper function or class, you must pass the object to the
function manually.
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