Basic Egg cooking

Since Trac 0.11, Genshi is used as the new template engine. Some APIs have also been changed.

This tutorial shows how to make an egg, and load an egg in Trac. In the advanced parts you'll learn how to serve templates and static content from an egg.

You should be familiar with ​component architecture and ​plugin development. This plugin is based on the example in the plugin development article. Here we extend it a bit further.

Required items

• setuptools>=0.6b1. For instructions and files see ​EasyInstall page.
• Trac 0.11. Download it from the ​TracDownload page.
• Genshi>-0.4. Download it from the ​GenshiDownload page.

Directories

To develop a plugin you need to create a few directories to keep things together.

So let's create following directories:

./helloworld-plugin/
./helloworld-plugin/helloworld/

Main plugin

The first step is to generate the main module for this plugin. We will construct a simple plugin that will display "Hello world!" on the screen when accessed through the /helloworld URL. The plugin also provides a "Hello" button that is, by default, rendered on the far right in the main navigation bar.

So create helloworld.py in ./helloworld-plugin/helloworld/:

# Helloworld plugin

import re

from genshi.builder import tag

from trac.core import *
from trac.web import IRequestHandler
from trac.web.chrome import INavigationContributor

class HelloWorldPlugin(Component):
    implements(INavigationContributor, IRequestHandler)

    # INavigationContributor methods
    def get_active_navigation_item(self, req):
        return 'helloworld'
    
    def get_navigation_items(self, req):
        yield ('mainnav', 'helloworld',
               tag.a('Hello World', href=req.href.helloworld()))
    
    # IRequestHandler methods
    def match_request(self, req):
        return re.match(r'/helloworld(?:_trac)?(?:/.*)?$', req.path_info)
    
    def process_request(self, req):
        req.send_response(200)
        req.send_header('Content-Type', 'text/plain')
        req.end_headers()
        req.write('Hello world!')

To help understand how that works, read the ​INavigationContributor and ​IRequestHandler interface specifications.

Make it a module

To make the plugin a module, you simply create an __init__.py in ./helloworld-plugin/helloworld/:

# Helloworld module
from helloworld import *

Make it an egg

Now it's time to make it an egg. For that we need a chicken called setup.py in ./helloworld-plugin/:

from setuptools import find_packages, setup

# name can be any name.  This name will be used to create .egg file.
# name that is used in packages is the one that is used in the trac.ini file.
# use package name as entry_points
setup(
    name='Trachelloworld', version='1.1',
    packages=find_packages(exclude=['*.tests*']),
    entry_points = """
        [trac.plugins]
        helloworld = helloworld
    """,
)

You done need to add special ​egg metadata in Trac 0.11.

First deployment

Now try to build the plugin. Run the command python setup.py bdist_egg in the directory where you created it. If everything went OK you should have a .egg file in ./dist directory. Copy this .egg file to /[your trac env]/plugins directory.

During development you can run the command python setup.py develop in the directory where you created it. This way you don't need to do it every time you change the code. Check ​TracDev/PluginDevelopment for more deployment options.

Edit the conf/trac.ini file by adding helloworld.* = enabled in the [components] section.

Restart the trac server. If you're using mod_python you have to restart Apache.

Now you should see Hello World link at far right in main navigation bar when accessing your site. Click it.

Aftermath

Now you have successfully created your first egg. You can continue further to learn how to use templates in your plugins, and make its output look like other Trac pages.

Cook even better eggs

After you read Basic Egg Cooking and created your first egg, it's time to make it a bit better.

First we integrate our output to other Trac layout in form of Genshi template.

Adding template

To have a template we need a directory and of course the template itself. We will keep the same simple "Hello world!" text, but this time we will integrate our fine words into a Trac layout.

For that we need to create one additional directory:

./helloworld-plugin/helloworld/templates/

In that directory create a new file helloworld.html:

<!DOCTYPE html
    PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:py="http://genshi.edgewall.org/"
      xmlns:xi="http://www.w3.org/2001/XInclude">
  <xi:include href="layout.html" />
  <head>
    <title>Helloworld</title>
  </head>

  <body>
    <div id="ctxtnav" class="nav"></div>

    <div id="content" class="helloworld">
      <h1>Hello World!</h1>
    </div>
  </body>
</html>

Now you have created the template for the plugin.

Tell Trac where template is

Trac doesn't know where your template is so you have to tell it. This is done by implementing the ITemplateProvider interface in helloworld.py.

So you change few lines as following:

Line 7 is changed from

from trac.web.chrome import INavigationContributor

to

from trac.web.chrome import INavigationContributor, ITemplateProvider

Line 10 is changed from

    implements(INavigationContributor, IRequestHandler)

    implements(INavigationContributor, IRequestHandler, ITemplateProvider)

Starting from line 24 old process_request method is replaced by

    def process_request(self, req):
        data = {}        
        # This tuple is for Genshi (template_name, data, content_type)
        # Without data the trac layout will not appear.
        return 'helloworld.html', data, None

And to end of file you need to tell where your template is located

    # ITemplateProvider methods
    # Used to add the plugin's templates and htdocs 
    def get_templates_dirs(self):
        from pkg_resources import resource_filename
        return [resource_filename(__name__, 'templates')]

Complete version of helloworld.py:

# Helloworld plugin

import re

from genshi.builder import tag

from trac.core import *
from trac.web import IRequestHandler
from trac.web.chrome import INavigationContributor, ITemplateProvider

class HelloWorldPlugin(Component):
    implements(INavigationContributor, IRequestHandler, ITemplateProvider)

    # INavigationContributor methods
    def get_active_navigation_item(self, req):
        return 'helloworld'

    def get_navigation_items(self, req):
        yield ('mainnav', 'helloworld',
               tag.a('Hello World', href=req.href.helloworld()))

    # IRequestHandler methods
    def match_request(self, req):
        return re.match(r'/helloworld(?:_trac)?(?:/.*)?$', req.path_info)

    def process_request(self, req):
        data = {}        
        # This tuple is for Genshi (template_name, data, content_type)
        # Without data the trac layout will not appear.
        return 'helloworld.html', data, None

    # ITemplateProvider methods
    # Used to add the plugin's templates and htdocs 
    def get_templates_dirs(self):
        from pkg_resources import resource_filename
        return [resource_filename(__name__, 'templates')]

Copy template to egg

Finally you have to include the new template directory in an egg.

So change setup.py to be like:

from setuptools import find_packages, setup

# name can be any name.  This name will be used to create .egg file.
# name that is used in packages is the one that is used in the trac.ini file.
# use package name as entry_points
setup(
    name='Trachelloworld', version='1.1',
    packages=find_packages(exclude=['*.tests*']),
    entry_points = """
        [trac.plugins]
        helloworld = helloworld
    """,
    package_data={'helloworld': ['templates/*.html']},
)

Building and deploying

Building and deployment goes exactly the same as it did in the previous section First Deployment.

Now you should see a big "Hello world!" integrated into your Trac layout when you press that fancy button in the main navigation bar.

Aftermath

Now that you have added a basic template for your plugin let's add the final twist, putting some static content like a stylesheet and an image. Continue to EggCookingTutorialTrac0.11

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