Codebase Documentation

This chapter covers the libraries that GNU MediaGoblin uses as well as various recipes for getting things done.

Note

This chapter is in flux. Clearly there are things here that aren’t documented. If there’s something you have questions about, please ask!

See the join page on the website for where we hang out.

For more information on how to get started hacking on GNU MediaGoblin, see the wiki, and specifically, go through the Hacking HOWTO which explains generally how to get going with running an instance for development.

What’s where

After you’ve run checked out MediaGoblin and followed the virtualenv instantiation instructions, you’re faced with the following directory tree:

mediagoblin/
|- mediagoblin/              # source code
|  |- db/                    # database setup
|  |- tools/                 # various utilities
|  |- init/                  # "initialization" tools (arguably should be in tools/)
|  |- tests/                 # unit tests
|  |- templates/             # templates for this application
|  |- media_types/           # code for processing, displaying different media
|  |- storage/               # different storage backends
|  |- gmg_commands/          # command line tools (./bin/gmg)
|  |- themes/                # pre-bundled themes
|  |
|  |  # ... some submodules here as well for different sections
|  |  # of the application... here's just a few
|  |- auth/                  # authentication (login/registration) code
|  |- user_dev/              # user pages (under /u/), including media pages
|  \- submit/                # submitting media for processing
|
|- docs/                     # documentation
|- devtools/                 # some scripts for developer convenience
|
|- user_dev/                 # local instance sessions, media, etc
|
|  # the below directories are installed into your virtualenv checkout
|
|- bin/                      # scripts
|- develop-eggs/
|- lib/                      # python libraries installed into your virtualenv
|- include/
|- mediagoblin.egg-info/
\- parts/

As you can see, all the code for GNU MediaGoblin is in the mediagoblin directory.

Here are some interesting files and what they do:

routing.py:maps URL paths to views
views.py:views handle HTTP requests
forms.py:wtforms stuff for this submodule

You’ll notice that there are several sub-directories: tests, templates, auth, submit, ...

tests holds the unit test code.

templates holds all the templates for the output.

auth and submit are modules that encapsulate authentication and media item submission. If you look in these directories, you’ll see they have their own routing.py, view.py, and forms.py in addition to some other code.

You’ll also notice that mediagoblin/db/ contains quite a few things, including the following:

models.py:This is where the database is set up
mixin.py:Certain functions appended to models from here
migrations.py:When creating a new migration (a change to the database structure), we put it here

Software Stack

  • Project infrastructure
    • Python: the language we’re using to write this
    • Py.Test: for unit tests
    • virtualenv: for setting up an isolated environment to keep MediaGoblin and related packages (potentially not required if MediaGoblin is packaged for your distro)
  • Data storage
    • SQLAlchemy: SQL ORM and database interaction library for Python. Currently we support SQLite and PostgreSQL as backends.
  • Web application
    • Paste Deploy and Paste Script: we’ll use this for configuring and launching the application
    • werkzeug: nice abstraction layer from HTTP requests, responses and WSGI bits
    • itsdangerous: for handling sessions
    • Jinja2: the templating engine
    • WTForms: for handling, validation, and abstraction from HTML forms
    • Celery: for task queuing (resizing images, encoding video, ...)
    • Babel: Used to extract and compile translations.
    • Markdown (for python): implementation of Markdown text-to-html tool to make it easy for people to write rich text comments, descriptions, and etc.
    • lxml: nice XML and HTML processing for python.
  • Media processing libraries
    • Python Imaging Library: used to resize and otherwise convert images for display.
    • GStreamer: (Optional, for video hosting sites only) Used to transcode video, and in the future, probably audio too.
    • chardet: (Optional, for ASCII art hosting sites only) Used to make ASCII art thumbnails.
  • Front end
    • jQuery: for groovy JavaScript things