certbot/docs/contributing.rst

===============
Developer Guide
===============

.. contents:: Table of Contents
   :local:


.. _hacking:

Hacking
=======

Running a local copy of the client
----------------------------------

Running the client in developer mode from your local tree is a little
different than running ``letsencrypt-auto``.  To get set up, do these things
once:

.. code-block:: shell

   git clone https://github.com/letsencrypt/letsencrypt
   cd letsencrypt
   ./bootstrap/install-deps.sh
   ./bootstrap/dev/venv.sh

Then in each shell where you're working on the client, do:

.. code-block:: shell

   source ./venv/bin/activate

After that, your shell will be using the virtual environment, and you run the
client by typing:

.. code-block:: shell

   letsencrypt

Activating a shell in this way makes it easier to run unit tests
with ``tox`` and integration tests, as described below. To reverse this, you
can type ``deactivate``.  More information can be found in the `virtualenv docs`_.

.. _`virtualenv docs`: https://virtualenv.pypa.io

Find issues to work on
----------------------

You can find the open issues in the `github issue tracker`_.  Comparatively
easy ones are marked `Good Volunteer Task`_.  If you're starting work on
something, post a comment to let others know and seek feedback on your plan
where appropriate.

Once you've got a working branch, you can open a pull request.  All changes in
your pull request must have thorough unit test coverage, pass our
`integration`_ tests, and be compliant with the :ref:`coding style
<coding-style>`.

.. _github issue tracker: https://github.com/letsencrypt/letsencrypt/issues
.. _Good Volunteer Task: https://github.com/letsencrypt/letsencrypt/issues?q=is%3Aopen+is%3Aissue+label%3A%22Good+Volunteer+Task%22

Testing
-------

The following tools are there to help you:

- ``tox`` starts a full set of tests. Please make sure you run it
  before submitting a new pull request.

- ``tox -e cover`` checks the test coverage only. Calling the
  ``./tox.cover.sh`` script directly (or even ``./tox.cover.sh $pkg1
  $pkg2 ...`` for any subpackages) might be a bit quicker, though.

- ``tox -e lint`` checks the style of the whole project, while
  ``pylint --rcfile=.pylintrc path`` will check a single file or
  specific directory only.

- For debugging, we recommend ``pip install ipdb`` and putting
  ``import ipdb; ipdb.set_trace()`` statement inside the source
  code. Alternatively, you can use Python's standard library `pdb`,
  but you won't get TAB completion...


.. _integration:

Integration testing with the boulder CA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Generally it is sufficient to open a pull request and let Github and Travis run
integration tests for you.

Mac OS X users: Run `./tests/mac-bootstrap.sh` instead of `boulder-start.sh` to
install dependencies, configure the environment, and start boulder.

Otherwise, install `Go`_ 1.5, libtool-ltdl, mariadb-server and
rabbitmq-server and then start Boulder_, an ACME CA server::

  ./tests/boulder-start.sh

The script will download, compile and run the executable; please be
patient - it will take some time... Once its ready, you will see
``Server running, listening on 127.0.0.1:4000...``. Add an
``/etc/hosts`` entry pointing ``le.wtf`` to 127.0.0.1.  You may now
run (in a separate terminal)::

  ./tests/boulder-integration.sh && echo OK || echo FAIL

If you would like to test `letsencrypt_nginx` plugin (highly
encouraged) make sure to install prerequisites as listed in
``letsencrypt-nginx/tests/boulder-integration.sh`` and rerun
the integration tests suite.

.. _Boulder: https://github.com/letsencrypt/boulder
.. _Go: https://golang.org


Code components and layout
==========================

acme
  contains all protocol specific code
letsencrypt
  all client code


Plugin-architecture
-------------------

Let's Encrypt has a plugin architecture to facilitate support for
different webservers, other TLS servers, and operating systems.
The interfaces available for plugins to implement are defined in
`interfaces.py`_.

The most common kind of plugin is a "Configurator", which is likely to
implement the `~letsencrypt.interfaces.IAuthenticator` and
`~letsencrypt.interfaces.IInstaller` interfaces (though some
Configurators may implement just one of those).

There are also `~letsencrypt.interfaces.IDisplay` plugins,
which implement bindings to alternative UI libraries.

.. _interfaces.py: https://github.com/letsencrypt/letsencrypt/blob/master/letsencrypt/interfaces.py


Authenticators
--------------

Authenticators are plugins designed to prove that this client deserves a
certificate for some domain name by solving challenges received from
the ACME server. From the protocol, there are essentially two
different types of challenges. Challenges that must be solved by
individual plugins in order to satisfy domain validation (subclasses
of `~.DVChallenge`, i.e. `~.challenges.TLSSNI01`,
`~.challenges.HTTP01`, `~.challenges.DNS`) and continuity specific
challenges (subclasses of `~.ContinuityChallenge`,
i.e. `~.challenges.RecoveryToken`, `~.challenges.RecoveryContact`,
`~.challenges.ProofOfPossession`). Continuity challenges are
always handled by the `~.ContinuityAuthenticator`, while plugins are
expected to handle `~.DVChallenge` types.
Right now, we have two authenticator plugins, the `~.ApacheConfigurator`
and the `~.StandaloneAuthenticator`. The Standalone and Apache
authenticators only solve the `~.challenges.TLSSNI01` challenge currently.
(You can set which challenges your authenticator can handle through the
:meth:`~.IAuthenticator.get_chall_pref`.

(FYI: We also have a partial implementation for a `~.DNSAuthenticator`
in a separate branch).


Installer
---------

Installers plugins exist to actually setup the certificate in a server,
possibly tweak the security configuration to make it more correct and secure
(Fix some mixed content problems, turn on HSTS, redirect to HTTPS, etc).
Installer plugins tell the main client about their abilities to do the latter
via the :meth:`~.IInstaller.supported_enhancements` call. We currently
have two Installers in the tree, the `~.ApacheConfigurator`. and the
`~.NginxConfigurator`.  External projects have made some progress toward
support for IIS, Icecast and Plesk.

Installers and Authenticators will oftentimes be the same class/object
(because for instance both tasks can be performed by a webserver like nginx)
though this is not always the case (the standalone plugin is an authenticator
that listens on port 443, but it cannot install certs; a postfix plugin would
be an installer but not an authenticator).

Installers and Authenticators are kept separate because
it should be possible to use the `~.StandaloneAuthenticator` (it sets
up its own Python server to perform challenges) with a program that
cannot solve challenges itself (Such as MTA installers).


Installer Development
---------------------

There are a few existing classes that may be beneficial while
developing a new `~letsencrypt.interfaces.IInstaller`.
Installers aimed to reconfigure UNIX servers may use Augeas for
configuration parsing and can inherit from `~.AugeasConfigurator` class
to handle much of the interface. Installers that are unable to use
Augeas may still find the `~.Reverter` class helpful in handling
configuration checkpoints and rollback.


Display
~~~~~~~

We currently offer a pythondialog and "text" mode for displays. Display
plugins implement the `~letsencrypt.interfaces.IDisplay`
interface.

.. _dev-plugin:

Writing your own plugin
=======================

Let's Encrypt client supports dynamic discovery of plugins through the
`setuptools entry points`_. This way you can, for example, create a
custom implementation of `~letsencrypt.interfaces.IAuthenticator` or
the `~letsencrypt.interfaces.IInstaller` without having to merge it
with the core upstream source code. An example is provided in
``examples/plugins/`` directory.

.. warning:: Please be aware though that as this client is still in a
   developer-preview stage, the API may undergo a few changes. If you
   believe the plugin will be beneficial to the community, please
   consider submitting a pull request to the repo and we will update
   it with any necessary API changes.

.. _`setuptools entry points`:
  https://pythonhosted.org/setuptools/setuptools.html#dynamic-discovery-of-services-and-plugins


.. _coding-style:

Coding style
============

Please:

1. **Be consistent with the rest of the code**.

2. Read `PEP 8 - Style Guide for Python Code`_.

3. Follow the `Google Python Style Guide`_, with the exception that we
   use `Sphinx-style`_ documentation::

        def foo(arg):
            """Short description.

            :param int arg: Some number.

            :returns: Argument
            :rtype: int

            """
            return arg

4. Remember to use ``pylint``.

.. _Google Python Style Guide:
  https://google-styleguide.googlecode.com/svn/trunk/pyguide.html
.. _Sphinx-style: http://sphinx-doc.org/
.. _PEP 8 - Style Guide for Python Code:
  https://www.python.org/dev/peps/pep-0008

Submitting a pull request
=========================

Steps:

1. Write your code!
2. Make sure your environment is set up properly and that you're in your
   virtualenv. You can do this by running ``./bootstrap/dev/venv.sh``.
   (this is a **very important** step)
3. Run ``./pep8.travis.sh`` to do a cursory check of your code style.
   Fix any errors.
4. Run ``tox -e lint`` to check for pylint errors. Fix any errors.
5. Run ``tox`` to run the entire test suite including coverage. Fix any errors.
6. If your code touches communication with an ACME server/Boulder, you
   should run the integration tests, see `integration`_. See `Known Issues`_
   for some common failures that have nothing to do with your code.
7. Submit the PR.
8. Did your tests pass on Travis? If they didn't, it might not be your fault!
   See `Known Issues`_. If it's not a known issue, fix any errors.

.. _Known Issues:
  https://github.com/letsencrypt/letsencrypt/wiki/Known-issues

Updating the documentation
==========================

In order to generate the Sphinx documentation, run the following
commands:

.. code-block:: shell

   make -C docs clean html

This should generate documentation in the ``docs/_build/html``
directory.


Other methods for running the client
====================================

Vagrant
-------

If you are a Vagrant user, Let's Encrypt comes with a Vagrantfile that
automates setting up a development environment in an Ubuntu 14.04
LTS VM. To set it up, simply run ``vagrant up``. The repository is
synced to ``/vagrant``, so you can get started with:

.. code-block:: shell

  vagrant ssh
  cd /vagrant
  sudo ./venv/bin/letsencrypt

Support for other Linux distributions coming soon.

.. note::
   Unfortunately, Python distutils and, by extension, setup.py and
   tox, use hard linking quite extensively. Hard linking is not
   supported by the default sync filesystem in Vagrant. As a result,
   all actions with these commands are *significantly slower* in
   Vagrant. One potential fix is to `use NFS`_ (`related issue`_).

.. _use NFS: http://docs.vagrantup.com/v2/synced-folders/nfs.html
.. _related issue: https://github.com/ClusterHQ/flocker/issues/516


Docker
------

OSX users will probably find it easiest to set up a Docker container for
development. Let's Encrypt comes with a Dockerfile (``Dockerfile-dev``)
for doing so. To use Docker on OSX, install and setup docker-machine using the
instructions at https://docs.docker.com/installation/mac/.

To build the development Docker image::

  docker build -t letsencrypt -f Dockerfile-dev .

Now run tests inside the Docker image:

.. code-block:: shell

  docker run -it letsencrypt bash
  cd src
  tox -e py27


.. _prerequisites:

Notes on OS dependencies
========================

OS level dependencies are managed by scripts in ``bootstrap``.  Some notes
are provided here mainly for the :ref:`developers <hacking>` reference.

In general:

* ``sudo`` is required as a suggested way of running privileged process
* `Augeas`_ is required for the Python bindings
* ``virtualenv`` and ``pip`` are used for managing other python library
  dependencies

.. _Augeas: http://augeas.net/
.. _Virtualenv: https://virtualenv.pypa.io

Ubuntu
------

.. code-block:: shell

   sudo ./bootstrap/ubuntu.sh


Debian
------

.. code-block:: shell

   sudo ./bootstrap/debian.sh

For squeeze you will need to:

- Use ``virtualenv --no-site-packages -p python`` instead of ``-p python2``.


.. _`#280`: https://github.com/letsencrypt/letsencrypt/issues/280


Mac OSX
-------

.. code-block:: shell

   ./bootstrap/mac.sh


Fedora
------

.. code-block:: shell

   sudo ./bootstrap/fedora.sh


Centos 7
--------

.. code-block:: shell

   sudo ./bootstrap/centos.sh


FreeBSD
-------

.. code-block:: shell

   sudo ./bootstrap/freebsd.sh

Bootstrap script for FreeBSD uses ``pkg`` for package installation,
i.e. it does not use ports.

FreeBSD by default uses ``tcsh``. In order to activate virtualenv (see
below), you will need a compatible shell, e.g. ``pkg install bash &&
bash``.