How to contribute

Identifying an area to contribute

There are several ways to identify an area where you can contribute to Corda:

  • Browse issues labelled as good first issue in the Corda GitHub Issues

    • Any issue with a good first issue label is considered ideal for open-source contributions
    • If there is a feature you would like to add and there isn’t a corresponding issue labelled as good first issue, that doesn’t mean your contribution isn’t welcome. Please reach out on the #design channel to clarify (see below)
  • Ask in the #design channel of the Corda Slack

Making the required changes

  • Create a fork of the master branch of the Corda repo
  • Clone the fork to your local machine
  • Build Corda by following the instructions here
  • Make the changes, in accordance with the code style guide

Things to check

Is your error handling up to scratch?

Errors should not leak to the UI. When writing tools intended for end users, like the node or command line tools, remember to add try/catch blocks. Throw meaningful errors. For example, instead of throwing an OutOfMemoryError, use the error message to indicate that a file is missing, a network socket was unreachable, etc. Tools should not dump stack traces to the end user.

Look for API breaks

We have an automated checker tool that runs as part of our continuous integration pipeline and helps a lot, but it can’t catch semantic changes where the behavior of an API changes in ways that might violate app developer expectations.

Suppress inevitable compiler warnings

Compiler warnings should have a @Suppress annotation on them if they’re expected and can’t be avoided.

Remove deprecated functionality

When deprecating functionality, make sure you remove the deprecated uses in the codebase.

Avoid making formatting changes as you work

In Kotlin 1.2.20, new style guide rules were implemented. The new Kotlin style guide is significantly more detailed than before and IntelliJ knows how to implement those rules. Re-formatting the codebase creates a lot of diffs that make merging more complicated.

Things to consider when writing CLI apps

  • Set exit codes using exitProcess. Zero means success. Other numbers mean errors. Setting a unique error code (starting from 1) for each thing that can conceivably break makes your tool shell-scripting friendly
  • Do a bit of work to figure out reasonable defaults. Nobody likes having to set a dozen flags before the tool will cooperate
  • Your --help text or other docs should ideally include examples. Writing examples is also a good way to find out that your program requires a dozen flags to do anything
  • Flags should have sensible defaults
  • Don’t print logging output to the console unless the user requested it via a –verbose flag (conventionally shortened to -v) or a –log-to-console flag. Logs should be either suppressed or saved to a text file during normal usage, except for errors, which are always OK to print

Testing the changes

Adding tests

Unit tests and integration tests for external API changes must cover Java and Kotlin. For internal API changes these tests can be scaled back to kotlin only.

Running the tests

Your changes must pass the tests described here.

Manual testing

Before sending that code for review, spend time poking and prodding the tool and thinking, “Would the experience of using this feature make my mum proud of me?”. Automated tests are not a substitute for dogfooding.

Building against the master branch

You can test your changes against CorDapps defined in other repos by following the instructions here.

Running the API scanner

Your changes must also not break compatibility with existing public API. We have an API scanning tool which runs as part of the build process which can be used to flag up any accidental changes, which is detailed here.

Updating the docs

Any changes to Corda’s public API must be documented as follows:

  • Add comments and javadocs/kdocs. API functions must have javadoc/kdoc comments and sentences must be terminated with a full stop. We also start comments with capital letters, even for inline comments. Where Java APIs have synonyms (e.g. %d and %date), we prefer the longer form for legibility reasons. You can configure your IDE to highlight these in bright yellow
  • Update the relevant .rst file(s)
  • Include the change in the changelog if the change is external and therefore visible to CorDapp developers and/or node operators
  • Build the docs locally
  • Check the built .html files (under docs/build/html) for the modified pages to ensure they render correctly
  • If relevant, add a sample. Samples are one of the key ways in which users learn about what the platform can do. If you add a new API or feature and don’t update the samples, your work will be much less impactful

Merging the changes back into Corda

  • Create a pull request from your fork to the master branch of the Corda repo

  • In the PR comments box:

  • Complete the pull-request checklist:

    • Have you run the unit, integration and smoke tests as described here?
    • If you added/changed public APIs, did you write/update the JavaDocs?
    • If the changes are of interest to application developers, have you added them to the changelog, and potentially release notes?
    • If you are contributing for the first time, please read the agreement in now and add to this Pull Request that you agree to it.
  • Add a clear description of the purpose of the PR

  • Add the following statement to confirm that your contribution is your own original work: “I hereby certify that my contribution is in accordance with the Developer Certificate of Origin (”

  • Request a review from a member of the Corda platform team via the #design channel

  • The reviewer will either:

  • Accept and merge your PR

  • Request that you make further changes. Do this by committing and pushing the changes onto the branch you are PRing into Corda. The PR will be updated automatically