Contributing guidelines

  • PEP 8, when sensible.
  • Test-driven: test ruthlessly and write docs for new features.
  • Human-driven: make sure any new logic is easy for others to understand.
  • If you add an extension to, add it to
  • Please update AUTHORS.rst when you contribute.

Setting up for development

Clone the repo:

$ git clone
$ cd modular-file-renderer

Configure development environment and install the development dependencies.


Python 3.6 or greater, R, and pspp are required. It’s recommended that a python version manager such as pyenv is used and that you use a virtual environment such as pyenv-virtualenv during development.

For Mac OS, here is an example of the commands that might be run to set up MFR. Linux users will probably do the same thing but with a different package manager. If someone wants to update this guide, please do.

$ brew install r pspp
$ pyenv virtualenv 3.6.4 mfr && echo mfr > .python-version
$ pip install setuptools==30.4.0
$ pip install invoke==0.13.0

Lastly, install MFR requirements with the development option.

$ inv install -d
$ inv server

Running tests

To run all tests (requires pytest)

$ inv test

You can also use pytest directly.

$ py.test --cov-report term-missing --cov mfr tests

Writing tests

Unit tests should be written for all rendering code.

Tests should be encapsulated within a class and written as functions. There are a few pytest fixtures to help you mock files. You can use them by simply including them as parameters to your test functions.

# in

from mfr.extensions.my_extension.render import MyExtensionRenderer

def metadata():
    return ProviderMetadata(

def test_render_html(extension, metadata, file_path, assets_url, export_url):
    assert MyExtensionRenderer(
    ).render() == '<p>Rendered file for my_extension</p>'

Check out pytest documentation to learn more about fixtures

Manual Local Testing

To make sure a new renderer is functioning properly, it’s recommended that you try to render a file of that type locally. The easiest way to do this would be to use the docker-compose files available inside the osf repository to get the MFR running, and then it should be straightforward to interact with the service using a tool such as postman. Alternatively, if you are familiar with OSF and its services, you can run full OSF and render files directly with it.

Writing an extension

An extension provides a ‘renderer’ and/or an ‘exporter’, and is registered in to allow the plugin to load when it is needed. Renderers and exporters subclasses mfr.core.extension.BaseRenderer or mfr.core.extension.BaseExporter respectively. A renderer takes a file path and some file metadata and returns a string of HTML that provides a representation of the file. The logic for the rendering happens in a renderer’s render() function. This is an abstract base class method, and thus is required for the implementation of a renderer. Similarly, BaseExporter has an export() method. This method should take a file and convert it to the desired output, and create the newly converted file at the ouput_file_path.

Renderers have an abstract property file_required. This is used to determine if the renderer needs the actual content of the file in order to render it. Renderers also have a property cache_result; this is used to determine whether the ouput of the renderer may be cached to improve future requests for the rendered version of the file.

Rendering Code

Renderers subclass mfr.core.extension.BaseRenderer, and implement a render function, a file_required property, and a cache_result property.

import os

from mako.lookup import TemplateLookup

from mfr.core import extension

class ImageRenderer(extension.BaseRenderer):

    TEMPLATE = TemplateLookup(
            os.path.join(os.path.dirname(__file__), 'templates')

    def render(self):
        return self.TEMPLATE.render(base=self.assets_url, url=self.url.geturl())

    def file_required(self):
        return False

    def cache_result(self):
        return False


Each plugin has its own directory. At a minimum, a plugin should include:

  • This should export the mfr.core.extensions.BaseExporter and mfr.core.extensions.BaseRenderer subclasses provided by the plugin

A typical extension plugin directory structure might look like this:

├── mfr
│       ├──
│       └── extensions
│               ├──
│               └── custom-plugin
│                       ├──
│                       ├──
│                       ├──
│                       ├──
│                       ├── static
│                       │       ├── css
│                       │       └── js
│                       ├── templates
│                       │       └── viewer.mako
│                       └── libs
│                               ├──
│                               └──
├── tests
│       ├──
│       └── extensions
│               ├──
│               └── custom-plugin
│                       ├──
│                       └──
└── requirements.txt


Contributions to the documentation are welcome. Documentation is written in reStructured Text (rST). A quick rST reference can be found here. Builds are powered by Sphinx.

To build docs:

$ pip install -r doc-requirements.txt
$ cd docs
$ make html
$ open _build/html/index.html

The -b (for “browse”) automatically opens up the docs in your browser after building.