# Contributing Guide - Synapse

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# Contributing

This document aims to get you started with contributing to Synapse!

# 1. Who can contribute to Synapse?

Everyone is welcome to contribute code to Synapse, provided that they are willing to license their contributions to Element under a Contributor License Agreement (CLA). This ensures that their contribution will be made available under an OSI-approved open-source license, currently Affero General Public License v3 (AGPLv3).

Please see the Element blog post for the full rationale.

# 2. What do I need?

If you are running Windows, the Windows Subsystem for Linux (WSL) is strongly recommended for development. More information about WSL can be found at https://docs.microsoft.com/en-us/windows/wsl/install. Running Synapse natively on Windows is not officially supported.

The code of Synapse is written in Python 3. To do pretty much anything, you’ll need a recent version of Python 3. Your Python also needs support for virtual environments. This is usually built-in, but some Linux distributions like Debian and Ubuntu split it out into its own package. Running `sudo apt install python3-venv` should be enough.

A recent version of the Rust compiler is needed to build the native modules. The easiest way of installing the latest version is to use rustup.

Synapse can connect to PostgreSQL via the psycopg2 Python library. Building this library from source requires access to PostgreSQL’s C header files. On Debian or Ubuntu Linux, these can be installed with `sudo apt install libpq-dev`.

The source code of Synapse is hosted on GitHub. You will also need a recent version of git.

For some tests, you will need a recent version of Docker.

# 3. Get the source.

The preferred and easiest way to contribute changes is to fork the relevant project on GitHub, and then create a pull request to ask us to pull your changes into our repo.

Please base your changes on the `develop` branch.

    git clone git@github.com:YOUR_GITHUB_USER_NAME/synapse.git
    git checkout develop

If you need help getting started with git, this is beyond the scope of the document, but you can find many good git tutorials on the web.

# 4. Install the dependencies

Before installing the Python dependencies, make sure you have installed a recent version of Rust (see the “What do I need?” section above). The easiest way of installing the latest version is to use rustup.

Synapse uses the poetry project to manage its dependencies and development environment. Once you have installed Python 3 and added the source, you should install `poetry`. Of their installation methods, we recommend installing `poetry` using `pipx`,

    pip install --user pipx
    pipx install poetry

but see poetry’s installation instructions for other installation methods.

Developing Synapse requires Poetry version 1.3.2 or later.

Next, open a terminal and install dependencies as follows:

    cd path/where/you/have/cloned/the/repository
    poetry install --extras all

This will install the runtime and developer dependencies for the project. Be sure to check that the `poetry install` step completed cleanly.

For OSX users, be sure to set `PKG_CONFIG_PATH` to support `icu4c`. Run `brew info icu4c` for more details.

## Running Synapse via poetry

To start a local instance of Synapse in the locked poetry environment, create a config file:

    cp docs/sample_config.yaml homeserver.yaml
    cp docs/sample_log_config.yaml log_config.yaml

Now edit `homeserver.yaml`, things you might want to change include:

- Set a `server_name`
- Adjusting paths to be correct for your system like the `log_config` to point to the log config you just copied
- Using a PostgreSQL database instead of SQLite
- Adding a `registration_shared_secret` so you can use `register_new_matrix_user` command.

And then run Synapse with the following command:

    poetry run python -m synapse.app.homeserver -c homeserver.yaml

If you get an error like the following:

    importlib.metadata.PackageNotFoundError: matrix-synapse

this probably indicates that the `poetry install` step did not complete cleanly - go back and resolve any issues and re-run until successful.

# 5. Get in touch.

Join our developer community on Matrix: #synapse-dev:matrix.org!

# 6. Pick an issue.

Fix your favorite problem or perhaps find a Good First Issue to work on.

# 7. Turn coffee into code and documentation!

There is a growing amount of documentation located in the `docs` directory, with a rendered version available online. This documentation is intended primarily for sysadmins running their own Synapse instance, as well as developers interacting externally with Synapse. `docs/development` exists primarily to house documentation for Synapse developers. `docs/admin_api` houses documentation regarding Synapse’s Admin API, which is used mostly by sysadmins and external service developers.

Synapse’s code style is documented here. Please follow it, including the conventions for configuration options and documentation.

We welcome improvements and additions to our documentation itself! When writing new pages, please build `docs` to a book to check that your contributions render correctly. The docs are written in GitHub-Flavoured Markdown.

When changes are made to any Rust code then you must call either `poetry install` or `maturin develop` (if installed) to rebuild the Rust code. Using `maturin` is quicker than `poetry install`, so is recommended when making frequent changes to the Rust code.

# 8. Test, test, test!

While you’re developing and before submitting a patch, you’ll want to test your code.

## Run the linters.

The linters look at your code and do two things:

- ensure that your code follows the coding style adopted by the project;
- catch a number of errors in your code.

The linter takes no time at all to run as soon as you’ve downloaded the dependencies.

    poetry run ./scripts-dev/lint.sh

Note that this script will modify your files to fix styling errors. Make sure that you have saved all your files.

If you wish to restrict the linters to only the files changed since the last commit (much faster!), you can instead run:

    poetry run ./scripts-dev/lint.sh -d

Or if you know exactly which files you wish to lint, you can instead run:

    poetry run ./scripts-dev/lint.sh path/to/file1.py path/to/file2.py path/to/folder

## Run the unit tests (Twisted trial).

The unit tests run parts of Synapse, including your changes, to see if anything was broken. They are slower than the linters but will typically catch more errors.

    poetry run trial tests

You can run unit tests in parallel by specifying `-jX` argument to `trial` where `X` is the number of parallel runners you want. To use 4 cpu cores, you would run them like:

    poetry run trial -j4 tests

If you wish to only run some unit tests, you may specify another module instead of `tests` - or a test class or a method:

    poetry run trial tests.rest.admin.test_room tests.handlers.test_admin.ExfiltrateData.test_invite

If your tests fail, you may wish to look at the logs (the default log level is `ERROR`):

    less _trial_temp/test.log

To increase the log level for the tests, set `SYNAPSE_TEST_LOG_LEVEL`:

    SYNAPSE_TEST_LOG_LEVEL=DEBUG poetry run trial tests

By default, tests will use an in-memory SQLite database for test data. For additional help with debugging, one can use an on-disk SQLite database file instead, in order to review database state during and after running tests. This can be done by setting the `SYNAPSE_TEST_PERSIST_SQLITE_DB` environment variable. Doing so will cause the database state to be stored in a file named `test.db` under the trial process’ working directory. Typically, this ends up being `_trial_temp/test.db`. For example:

    SYNAPSE_TEST_PERSIST_SQLITE_DB=1 poetry run trial tests

The database file can then be inspected with:

    sqlite3 _trial_temp/test.db

Note that the database file is cleared at the beginning of each test run. Thus it will always only contain the data generated by the last run test. Though generally when debugging, one is only running a single test anyway.

### Running tests under PostgreSQL

Invoking `trial` as above will use an in-memory SQLite database. This is great for quick development and testing. However, we recommend using a PostgreSQL database in production (and indeed, we have some code paths specific to each database). This means that we need to run our unit tests against PostgreSQL too. Our CI does this automatically for pull requests and release candidates, but it’s sometimes useful to reproduce this locally.

#### Using Docker

The easiest way to do so is to run Postgres via a docker container. In one terminal:

    docker run --rm -e POSTGRES_PASSWORD=mysecretpassword -e POSTGRES_USER=postgres -e POSTGRES_DB=postgres -p 5432:5432 postgres:14

If you see an error like

    docker: Error response from daemon: driver failed programming external connectivity on endpoint nice_ride (b57bbe2e251b70015518d00c9981e8cb8346b5c785250341a6c53e3c899875f1): Error starting userland proxy: listen tcp4 0.0.0.0:5432: bind: address already in use.

then something is already bound to port 5432. You’re probably already running postgres locally.

Once you have a postgres server running, invoke `trial` in a second terminal:

    SYNAPSE_POSTGRES=1 SYNAPSE_POSTGRES_HOST=127.0.0.1 SYNAPSE_POSTGRES_USER=postgres SYNAPSE_POSTGRES_PASSWORD=mysecretpassword poetry run trial tests

#### Using an existing Postgres installation

If you have postgres already installed on your system, you can run `trial` with the following environment variables matching your configuration:

- `SYNAPSE_POSTGRES` to anything nonempty
- `SYNAPSE_POSTGRES_HOST` (optional if it’s the default: UNIX socket)
- `SYNAPSE_POSTGRES_PORT` (optional if it’s the default: 5432)
- `SYNAPSE_POSTGRES_USER` (optional if using a UNIX socket)
- `SYNAPSE_POSTGRES_PASSWORD` (optional if using a UNIX socket)

For example:

    export SYNAPSE_POSTGRES=1
    export SYNAPSE_POSTGRES_HOST=localhost
    export SYNAPSE_POSTGRES_USER=postgres
    export SYNAPSE_POSTGRES_PASSWORD=mydevenvpassword
    trial

You don’t need to specify the host, user, port or password if your Postgres server is set to authenticate you over the UNIX socket (i.e. if the `psql` command works without further arguments).

Your Postgres account needs to be able to create databases; see the postgres docs for `ALTER ROLE`.

## Run the integration tests (Sytest).

The integration tests are a more comprehensive suite of tests. They run a full version of Synapse, including your changes, to check if anything was broken. They are slower than the unit tests but will typically catch more errors.

The following command will let you run the integration test with the most common configuration:

    $ docker run --rm -it -v /path/where/you/have/cloned/the/repository\:/src:ro -v /path/to/where/you/want/logs\:/logs matrixdotorg/sytest-synapse:bookworm

(Note that the paths must be full paths! You could also write `$(realpath relative/path)` if needed.)

This configuration should generally cover your needs.

- To run with Postgres, supply the `-e POSTGRES=1 -e MULTI_POSTGRES=1` environment flags.
- To run with Synapse in worker mode, supply the `-e WORKERS=1 -e REDIS=1` environment flags (in addition to the Postgres flags).

For more details about other configurations, see the Docker-specific documentation in the SyTest repo.

## Run the integration tests (Complement).

See our Complement docs for how to use the `./scripts-dev/complement.sh` test runner script.

### Prettier formatting with `gotestfmt`

If you want to format the output of the tests the same way as it looks in CI, install gotestfmt.

You can then use this incantation to format the tests appropriately:

    COMPLEMENT_DIR=../complement ./scripts-dev/complement.sh -json | gotestfmt -hide successful-tests

(Remove `-hide successful-tests` if you don’t want to hide successful tests.)

# 9. Submit your patch.

Once you’re happy with your patch, it’s time to prepare a Pull Request.

To prepare a Pull Request, please:

1. verify that all the tests pass, including the coding style;
2. sign off your contribution;
3. `git push` your commit to your fork of Synapse;
4. on GitHub, create the Pull Request;
5. add a changelog entry and push it to your Pull Request;
6. that’s it for now, a non-draft pull request will automatically request review from the team;
7. if you need to update your PR, please avoid rebasing and just add new commits to your branch.

## Changelog

All changes, even minor ones, need a corresponding changelog / newsfragment entry. These are managed by Towncrier.

To create a changelog entry, make a new file in the `changelog.d` directory named in the format of `PRnumber.type`. The type can be one of the following:

- `feature`
- `bugfix`
- `docker` (for updates to the Docker image)
- `doc` (for updates to the documentation)
- `removal` (also used for deprecations)
- `misc` (for internal-only changes)

This file will become part of our changelog at the next release, so the content of the file should be a short description of your change in the same style as the rest of the changelog. The file can contain Markdown formatting, and must end with a full stop (.) or an exclamation mark (!) for consistency.

Adding credits to the changelog is encouraged, we value your contributions and would like to have you shouted out in the release notes!

For example, a fix in PR #1234 would have its changelog entry in `changelog.d/1234.bugfix`, and contain content like:

> The security levels of Florbs are now validated when received via the `/federation/florb` endpoint. Contributed by Jane Matrix.

If there are multiple pull requests involved in a single bugfix/feature/etc, then the content for each `changelog.d` file and file extension should be the same. Towncrier will merge the matching files together into a single changelog entry when we come to release.

### How do I know what to call the changelog file before I create the PR?

Obviously, you don’t know if you should call your newsfile `1234.bugfix` or `5678.bugfix` until you create the PR, which leads to a chicken-and-egg problem.

There are two options for solving this:

1. Open the PR without a changelog file, see what number you got, and then add the changelog file to your branch, or:

2. Look at the list of all issues/PRs, add one to the highest number you see, and quickly open the PR before somebody else claims your number.

   This script might be helpful if you find yourself doing this a lot.

Sorry, we know it’s a bit fiddly, but it’s really helpful for us when we come to put together a release!

### Debian changelog

Changes which affect the debian packaging files (in `debian`) are an exception to the rule that all changes require a `changelog.d` file.

In this case, you will need to add an entry to the debian changelog for the next release. For this, run the following command:

    dch

This will make up a new version number (if there isn’t already an unreleased version in flight), and open an editor where you can add a new changelog entry. (Our release process will ensure that the version number and maintainer name is corrected for the release.)

If your change affects both the debian packaging and files outside the debian directory, you will need both a regular newsfragment and an entry in the debian changelog. (Though typically such changes should be submitted as two separate pull requests.)

## Sign off

After you make a PR a comment from @CLAassistant will appear asking you to sign the CLA. This will link a page to allow you to confirm that you have read and agreed to the CLA by signing in with GitHub.

Alternatively, you can sign off before opening a PR by going to https://cla-assistant.io/element-hq/synapse.

We accept contributions under a legally identifiable name, such as your name on government documentation or common-law names (names claimed by legitimate usage or repute). Unfortunately, we cannot accept anonymous contributions at this time.

# 10. Turn feedback into better code.

Once the Pull Request is opened, you will see a few things:

1. our automated CI (Continuous Integration) pipeline will run (again) the linters, the unit tests, the integration tests and more;
2. one or more of the developers will take a look at your Pull Request and offer feedback.

From this point, you should:

1. Look at the results of the CI pipeline.
   - If there is any error, fix the error.
2. If a developer has requested changes, make these changes and let us know if it is ready for a developer to review again.
   - A pull request is a conversation, if you disagree with the suggestions, please respond and discuss it.
3. Create a new commit with the changes.
   - Please do NOT overwrite the history. New commits make the reviewer’s life easier.
   - Push this commits to your Pull Request.
4. Back to 1.
5. Once the pull request is ready for review again please re-request review from whichever developer did your initial review (or leave a comment in the pull request that you believe all required changes have been done).

Once both the CI and the developers are happy, the patch will be merged into Synapse and released shortly!

# 11. Find a new issue.

By now, you know the drill!

# Notes for maintainers on merging PRs etc

There are some notes for those with commit access to the project on how we manage git here.

# Conclusion

That’s it! Matrix is a very open and collaborative project as you might expect given our obsession with open communication. If we’re going to successfully matrix together all the fragmented communication technologies out there we are reliant on contributions and collaboration from the community to do so. So please get involved - and we hope you have as much fun hacking on Matrix as we do!