Contributing to Exonum

The Exonum core project and other public Exonum repositories operate an open contributor model where anyone is welcome to contribute towards development in the form of peer review, testing and patches. This document explains the practical process and guidelines for contributing. It is partially derived from the Bitcoin contribution guide.

See a guide in the core Exonum repository for more technical details how to contribute.


Use pull requests, use git commit message conventions, test your contributions, listen to peer reviews, and you should be fine.

Contributor Hierarchy

In terms of structure, there is no particular concept of “Exonum core developers” in the sense of privileged people. Open source often naturally revolves around meritocracy where longer term contributors gain more trust from the developer community. However, some hierarchy is necessary for practical purposes. As such, each Exonum repository has maintainers who are responsible for merging pull requests, and a lead maintainer who is responsible for the release cycle, overall merging, moderation and appointment of maintainers.

Contributor Workflow

The codebase is maintained using the contributor workflow where everyone without exception contributes patch proposals using pull requests (PRs). This facilitates social contribution, easy testing and peer review.

To contribute a patch, the workflow is as follows:

  • Fork the relevant repository
  • Create a topic branch
  • Push commits to the branch
  • Create a pull request for merging the topic branch

Doing Research

Before starting to code, it makes sense to check if the analogous PR hasn’t been submitted (or even accepted) before. Accordingly, you may want to search pull requests and issues of the targeted repository by keywords, tags, etc.

If you want to start contributing and not sure where to start, a good frame of reference are open GitHub issues in repositories. Issues are commonly tagged by their relevance, topic and milestone, which should provide some insight into most topical issues relevant to your expertise.

Another option with low entry barrier is contributing to Exonum documentation, which is also open-sourced. You can jump to the source of a particular documentation page by clicking a pencil icon at the top of the page.


Besides GitHub, Exonum issues and solutions are discussed on gitter and Reddit.

Adding Commits

In general commits should be atomic and diffs should be easy to read. For this reason do not mix any formatting fixes or code moves with actual code changes. However, we merge pull requests using the “squash-and-merge” strategy, so commit messages are only important for the review stage.


Further explanation about commit message conventions is available here. In short, the title line of the commit should be capitalized, not end with a period, and describe the action performed by the commit in the imperative mood, so that it can complete the sentence “If applied, this commit will <commit title line>”. Note that commits automatically created by git (say, merge commits) satisfy these criteria.

If a particular commit references another issue or PR, please add the reference, for example refs #1234, or fixes #4321. Using the fixes or closes keywords will cause the corresponding issue to be closed when the pull request is merged.

Testing PRs Locally

Every Exonum repository features test suite(s) and continuous integration (CI) via Travis, so any proposed changes are tested automatically. A successful CI build is a necessary (but not sufficient) condition for a PR to be accepted.

It’s generally a good idea to test your PR locally; in particular, it helps get a successful CI build faster and with less hassle. Follow installation instructions from the repository and recreate test steps from .travis.yml; usually, they perform code linting (e.g., via clippy) and unit testing (e.g., cargo test), although some repositories may use more complicated tests.

Patches that introduce new functionality should cover it with tests to assure code quality and prevent regression in the future. Bug fixes should also include tests to prove that the bug had existed and was fixed. Generally, more tests are always welcome.


A separate nightly Rust toolchain is required if you want to run the clippy linter locally. Clippy is used in CI builds of Exonum and other repositories to detect common Rust anti-patterns. It can be installed with

rustup component add clippy

Consult the clippy installation guide for more details.

After installing nightly Rust, clippy checks can be run with

cargo clippy --all --tests --examples --benches


rustfmt is used to perform automatic code formatting and code style checks in CI builds. Note that Exonum repositories pin the version of rustfmt in order to get consistent formatting.

You can install the formatter locally with

rustup component add rustfmt

After installing the formatter, its checks can be run with

cargo fmt --all -- --check

Consult the rustfmt readme for more details.

Pull Request Naming and Descriptions

If a pull request is specifically not to be considered for merging (yet), please mark it with a “Work in Progress” label. You may use task lists in the body of the pull request to indicate pending tasks.

The body of the pull request should contain enough description about what the patch does together with any justification or reasoning. You should include references to any discussions.

Peer Reviews and PR Amendments

After submitting a PR to the relevant repository, one should expect comments and review from other contributors. You can add more commits to your pull request by committing them locally and pushing to your fork until you have satisfied all feedback.

The length of time required for peer review is unpredictable and will vary from pull request to pull request.


Please refrain from creating several pull requests for the same change. Use the pull request that is already open (or was created earlier) to amend changes. This preserves the discussion and review that happened earlier for the respective change set.

Merge Strategy

We use “squash and merge” strategy to merge PRs.

Pull Request Philosophy

Pull requests should always be focused. For example, a pull request could add a feature, fix a bug, or refactor code; but not a mixture. Please also avoid super pull requests which attempt to do too much, are overly large, or overly complex as this makes review difficult.


When adding a new feature, thought must be given to the long term technical debt and maintenance that feature may require after inclusion. Before proposing a new feature that will require maintenance, please consider if you are willing to maintain it (including bug fixing). If features get orphaned with no maintainer in the future, they may be removed by the repository maintainer.


Refactoring is a necessary part of any software project’s evolution. The following guidelines cover refactoring pull requests for the project.

There are three categories of refactoring:

  • Code only moves
  • Code style fixes
  • Code refactoring

In general, refactoring pull requests should not mix these three kinds of activity in order to make refactoring pull requests easy to review and uncontroversial. In all cases, refactoring PRs must not change the behavior of code within the pull request (bugs must be preserved as is).

Project maintainers aim for a quick turnaround on refactoring pull requests, so where possible keep them short, non-complex and easy to verify.

Decision Making Process

Whether a pull request is merged into the targeted Exonum repository rests with the project merge maintainers and ultimately the lead maintainer.

Maintainers will take into consideration if a patch is in line with the general principles of the project; meets the minimum standards for inclusion; and will judge the general consensus of contributors.

In general, all pull requests must:

  • Have a clear use case, fix a demonstrable bug or serve the greater good of the project (for example refactoring for modularization)
  • Be well peer reviewed
  • Have unit tests and sandbox tests where appropriate
  • Follow code style guidelines
  • Not break the existing test suite
  • Where bugs are fixed, where possible, there should be unit tests demonstrating the bug and also proving the fix. This helps prevent regression

Peer Review

Anyone may participate in peer review which is expressed by comments in the pull request. Typically reviewers will review the code for obvious errors, as well as test out the patch set and opine on the technical merits of the patch. Project maintainers take into account the peer review when determining if there is consensus to merge a pull request.


It’s possible to check out a pull request locally, for example, to test it manually or to suggest code improvements. This can be accomplished via

git fetch exonum pull/<pr-number>/head:<pr-local-branch>
git checkout <pr-local-branch>
# Emulate merging the PR
git merge master

Here, exonum is a git remote pointing to the original Exonum repository (not its fork used by the topic branch).

See this GitHub guide for more details.

The following language is used within pull-request comments:

  • LGTM means “Looks Good To Me”
  • Concept LGTM means “I agree in the general principle of this pull request”

Reviewers should include the commit hash which they reviewed in their comments.

Project maintainers reserve the right to weigh the opinions of peer reviewers using common sense judgment and also may weight based on meritocracy: Those that have demonstrated a deeper commitment and understanding towards the project (over time) or have clear domain expertise may naturally have more weight, as one would expect in all walks of life.

Where a patch set affects consensus critical code, the bar will be set much higher in terms of discussion and peer review requirements, keeping in mind that mistakes could be very costly to the wider community. This includes refactoring of consensus critical code.

Release Policy

The lead maintainer of the Exonum core repository is the release manager for each Exonum core release. Likewise, releases of other projects are managed by the respective lead maintainers. The core releases are synchronized with releases of other Exonum projects through informal communication among repository maintainers.

By contributing to a public Exonum repository, you agree to license your work under the license specified in the LICENSE file of the relevant repository unless specified otherwise at the top of the file itself. Any work contributed where you are not the original author must contain its license header with the original author(s) and source.