# Developer Guide

Table of Contents

- Hacking
  - Running a local copy of the client
  - Find issues to work on
  - Testing
    - Integration testing with the boulder CA
- Code components and layout
  - Plugin-architecture
  - Authenticators
  - Installer
  - Installer Development
    - Display
- Writing your own plugin
- Coding style
- Submitting a pull request
- Updating the documentation
- Other methods for running the client
  - Vagrant
  - Docker
- Notes on OS dependencies
  - Debian
  - FreeBSD

## 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:

    git clone https://github.com/letsencrypt/letsencrypt
    cd letsencrypt
    ./letsencrypt-auto-source/letsencrypt-auto --os-packages-only
    ./tools/venv.sh

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

    source ./venv/bin/activate

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

    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.

### 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 coding style.

### Testing

The following tools are there to help you:

- `tox` starts a full set of tests. Please note that it includes apacheconftest, which uses the system’s Apache install to test config file parsing, so it should only be run on systems that have an experimental, non-production Apache2 install on them. `tox -e apacheconftest` can be used to run those specific Apache conf tests.
- `tox -e py27`, `tox -e py26` etc, run unit tests for specific Python versions.
- `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 testing with the boulder CA

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

However, if you prefer to run tests, you can use Vagrant, using the Vagrantfile in Let’s Encrypt’s repository. To execute the tests on a Vagrant box, the only command you are required to run is:

    ./tests/boulder-integration.sh

Otherwise, please follow the following instructions.

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.

If you can’t get packages of Go 1.5 for your Linux system, you can execute the following commands to install it:

    wget https://storage.googleapis.com/golang/go1.5.3.linux-amd64.tar.gz -P /tmp/
    sudo tar -C /usr/local -xzf /tmp/go1.5.3.linux-amd64.tar.gz
    if ! grep -Fxq "export GOROOT=/usr/local/go" ~/.profile ; then echo "export GOROOT=/usr/local/go" >> ~/.profile; fi
    if ! grep -Fxq "export PATH=\\$GOROOT/bin:\\$PATH" ~/.profile ; then echo "export PATH=\\$GOROOT/bin:\\$PATH" >> ~/.profile; fi

These commands download Go 1.5.3 to `/tmp/`, extracts to `/usr/local`, and then adds the export lines required to execute `boulder-start.sh` to `~/.profile` if they were not previously added

Make sure you execute the following command after Go finishes installing:

    if ! grep -Fxq "export GOPATH=\\$HOME/go" ~/.profile ; then echo "export GOPATH=\\$HOME/go" >> ~/.profile; fi

Afterwards, you’d be able to start Boulder using the following command:

    ./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 `/etc/hosts` entries pointing `le.wtf`, `le1.wtf`, `le2.wtf`, `le3.wtf` and `nginx.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.

## 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 and plugins/common.py.

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

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

### 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. `TLSSNI01`, `HTTP01`, `DNS`) and continuity specific challenges (subclasses of `ContinuityChallenge`, i.e. `RecoveryToken`, `RecoveryContact`, `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 `TLSSNI01` challenge currently. (You can set which challenges your authenticator can handle through the `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 `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 `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 `IDisplay` interface.

## 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 `IAuthenticator` or the `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.

## 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`.

## 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 `./tools/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.

## Updating the documentation

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

    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:

    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).

### 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:

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

## Notes on OS dependencies

OS-level dependencies can be installed like so:

    letsencrypt-auto-source/letsencrypt-auto --os-packages-only

In general...

- `sudo` is required as a suggested way of running privileged process
- Python 2.6/2.7 is required
- Augeas is required for the Python bindings
- `virtualenv` and `pip` are used for managing other python library dependencies

### Debian

For squeeze you will need to:

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

### FreeBSD

Package installation for FreeBSD uses `pkg`, not 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`.