How to contribute

Identifying an area to contribute

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

The easiest is just to message one of the Community Maintainers <community-maintainers> saying "I want to help!". They'll work with you to find an area for you to contribute
If you have a specific contribution in mind, confirm whether the contribution is appropriate first by reaching out in the #contributing channel of the Corda Slack or contacting one of the Community Maintainers <community-maintainers> directly
If you do not have a specific contribution in mind, you can also browse the issues labelled as help wanted on the Corda GitHub issues page
- Issues that additionally have the good first issue label are considered ideal for first-timers

Contribution guidelines

We believe one of the things that makes Corda special is its coherent design and we seek to retain this defining characteristic. From the outset we defined some guidelines to ensure new contributions only ever enhance the project:

Quality: Code in the Corda project should meet the Corda coding style guidelines <codestyle>, with sufficient test-cases, descriptive commit messages, evidence that the contribution does not break any compatibility commitments or cause adverse feature interactions, and evidence of high-quality peer-review
Size: The Corda project's culture is one of small pull-requests, regularly submitted. The larger a pull-request, the more likely it is that you will be asked to resubmit as a series of self-contained and individually reviewable smaller PRs
Scope: We try to ensure the Corda project remains coherent and focused so we ask that the feature's scope is within the definition specified in the Corda Technical Whitepaper
Maintainability: If the feature will require ongoing maintenance (eg support for a particular brand of database), we may ask you to accept responsibility for maintaining this feature
Non-duplicative: If the contribution duplicates features that already exist or are already in progress, you may be asked to work with the project maintainers to reconcile this. As the major contributor to Corda, many employees of R3 will be working on features at any given time. To avoid surprises and foster transparency, our Jira work tracking system is public. If in doubt, reach out to one of the Community Maintainers <community-maintainers>

Making the required changes

You should make your changes as follows:

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 </building-corda>
Make the changes, in accordance with the code style guide </codestyle>

Things to check

Make sure your error handling is 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: Make sure any changes to CLI applications conform to the cli-ux-guidelines

Extending the flow state machine

If you are interested in extending the flow state machine, you can find instructions on how to do this here </contributing-flow-state-machines>.

Testing the changes

You should test your changes as follows:

Add 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
Run the tests: Your changes must pass the tests described here <testing>
Perform 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
Build against the master branch: You can test your changes against CorDapps defined in other repos by following the instructions here <building-against-master>
Run 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 <api-scanner>

Updating the docs

You should document any changes to Corda's public API 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 </changelog> if the change is external and therefore visible to CorDapp developers and/or node operators
Build the docs locally </building-the-docs> and check that the resulting .html files (under docs/build/html) for the modified 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

You should merge the changes back into Corda as follows:

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? https://docs.corda.net/head/testing.html

[ ] 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 CONTRIBUTING.md 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 (https://developercertificate.org/)."

Request a review by reaching out in the #contributing channel of the Corda Slack or contacting one of the Community Maintainers <community-maintainers> directly
The reviewer will either:

Accept and merge your PR

Leave comments requesting changes via the GitHub PR interface

You should make the changes by pushing directly to your existing PR branch. The PR will be updated automatically

(Optional) Open an additional PR to add yourself to the contributors list
- The format is generally firstname surname (company), but the company can be omitted if desired

Developer Certificate of Origin

All contributions to this project are subject to the terms of the Developer Certificate of Origin, available here and reproduced below:

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
1 Letterman Drive
Suite D4700
San Francisco, CA, 94129

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.

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