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Contributing to rust-bitcoin

👍🎉 First off, thanks for taking the time to contribute! 🎉👍

The following is a set of guidelines for contributing to Rust Bitcoin implementation and other Rust Bitcoin-related projects, which are hosted in the Rust Bitcoin Community on GitHub. These are mostly guidelines, not rules. Use your best judgment, and feel free to propose changes to this document in a pull request.

Table Of Contents

General

The Rust Bitcoin project operates an open contributor model where anyone is welcome to contribute towards development in the form of peer review, documentation, testing and patches.

Anyone is invited to contribute without regard to technical experience, "expertise", OSS experience, age, or other concern. However, the development of standards & reference implementations demands a high-level of rigor, adversarial thinking, thorough testing and risk-minimization. Any bug may cost users real money. That being said, we deeply welcome people contributing for the first time to an open source project or pick up Rust while contributing. Don't be shy, you'll learn.

Communication channels

Communication about Rust Bitcoin happens primarily in #bitcoin-rust IRC chat on Libera with the logs available at http://gnusha.org/rust-bitcoin/.

Discussion about code base improvements happens in GitHub issues and on pull requests.

Major projects are tracked here. Major milestones are tracked here.

Asking questions

Note: Please don't file an issue to ask a question. You'll get faster results by using the resources below.

We have a dedicated developer channel on IRC, #rust-bitcoin@freenode.net where you may get helpful advice if you have questions.

Contribution workflow

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

To contribute a patch, the workflow is a as follows:

  1. Fork Repository
  2. Create topic branch
  3. Commit patches

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. Further, each commit, individually, should compile and pass tests, in order to ensure git bisect and other automated tools function properly.

When adding a new feature thought must be given to the long term technical debt. Every new features should be covered by unit tests.

When refactoring, structure your PR to make it easy to review and don't hesitate to split it into multiple small, focused PRs.

Commits should cover both the issue fixed and the solution's rationale. These guidelines should be kept in mind.

To facilitate communication with other contributors, the project is making use of GitHub's "assignee" field. First check that no one is assigned and then comment suggesting that you're working on it. If someone is already assigned, don't hesitate to ask if the assigned party or previous commenters are still working on it if it has been awhile.

Preparing PRs

The main library development happens in the master branch. This branch must always compile without errors (using GitHub CI). All external contributions are made within PRs into this branch.

Prerequisites that a PR must satisfy in order to be considered for merging into the master branch:

  • each commit within a PR must compile and pass unit tests with no errors, with every feature combination (excepting fuzztarget, but including compiling the fuzztests) on some reasonably recent compiler (this is partially automated with CI, so the rule is that if GitHub CI is not passing, the commit can't be accepted);
  • the tip of any PR branch must also compile and pass tests with no errors on MSRV (check [README.md] on current MSRV requirements) and pass fuzz tests on nightly rust;
  • contain all necessary tests for the introduced functional (either as a part of commits, or, more preferably, as separate commits, so that it's easy to reorder them during review and check that the new tests fail without the new code);
  • contain all inline docs for newly introduced API and pass doc tests;
  • be based on the recent master tip from the original repository at https://github.com/rust-bitcoin/rust-bitcoin.

NB: reviewers may run more complex test/CI scripts, thus, satisfying all the requirements above is just a preliminary, but not necessary sufficient step for getting the PR accepted as a valid candidate PR for the master branch.

PR authors may also find useful to run the following script locally in order to check that each of the commits within the PR satisfy the requirements above, before submitting the PR to review:

BITCOIN_MSRV=1.29.0 ./contrib/ci.sh

Where value in BITCOIN_MSRV=1.29.0 should be replaced with the current MSRV from [README.md].

NB: Please keep in mind that the script above replaces Cargo.lock file, which is necessary to support current MSRV, incompatible with stable and newer cargo versions.

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. PR should be reviewed first on the conceptual level before focusing on code style or grammar fixes.

Repository maintainers

For the pull request to be merged we require (a) that all CI test should pass and (2) at least two "accepts"/ACKs from the repository maintainers – and no main reasonable "rejects"/NACKs from anybody who reviewed the code.

Current list of the project maintainers:

Coding conventions

Overall, this library must reflect Bitcoin Core approach whenever possible. However, since many of the things in Bitcoin Core are maintained due to historical reasons and may represent poor design, Rust-idiomatic style is preferred to "how it looks in Core" if everyone agrees.

Formatting

We plan to utilize rustfmt for keeping the code formatting consistent. However, this will be a gradual process since a thorough peer review is required to make sure that no unintended changes are introduced with the change of formatting. Thus, all PRs introducing large blocks of re-formatted code will not be reviewed.

The current plan is to phase it in over multiple commits or even multiple PRs, which will introduce no other changes that re-formatting, such that each change may be independently re-reproduced by each reviewer. The first commit should add attributes to disable fmt for some parts of the code and a second one does the formatting – so only the first one needs review, the rest will be reproducible.

You may check the discussion on the formatting and how it is planned to coordinate it with crate refactoring

Derivation

Derivations applied to a data structures should be standardized:

  1. All non-error types should opportunistically derive, where it is possible, the following traits:

    • Copy
    • Clone
    • PartialEq and Eq
    • PartialOrd and Ord
    • Hash
    • Debug

    By "where possible" we mean that by default a code line

    #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]

    must be placed before each struct, and then those of these traits, which can't be auto-derived because of the member field restrictions should be removed.

  2. Eq, PartialEq, Ord, PartialOrd derivation must be skipped/removed from pt. 1 in the following situations:

    • for types that don't have reflexive equality/ordering
    • types which has lexicographic ordering defined as a part of a standard must provide manual implementation
    • types which may be more efficiently compared with bitcoin-specific rules should provide manual implementation

  3. Debug must not be derived on structs and enums which may contain secret data, and a manual Debug implementation should be provided instead.

  4. Default derivation should be performed whenever there is a rationale to have default constructor initializing "empty" data structure, i.e. this empty structure has a real use in the business logic outside of the scope of testing or creating dumb data. For instance, if the structure consists only of collection types which may be empty it should derive Default trait.

  5. Error types (both structs and enums) must implement Display and Error traits manually, and should provide Error::source function if some of the error cases contain other error type.

  6. Display should be implemented for all data types which may be presented to the end user (not developers!), for instance in command line or as a part of GUI. Here are some guidelines:

    • Normally, Display implementation should not just repeat Debug and structure the data in some visually-acceptable way.
    • One should pay attention to the ability of providing alternative ways of data formatting with {:#} formatting string option, detectable by std::fmt::Formatter::alternate() function. Other important options to look at are align, fill, pad, precision and width.
    • When displaying the member fields it is important to consider the ability to pass them display formatting options; thus, Display::fmt(&self.field, f)?; is preferable over write!(f, "{}", self.field)?;

  7. Serde serializers should be implemented for all data types which may persist or may be presented in the UI or API as JSON/YAML and other kinds of data representations (in fact, these are all data types).

The discussion about trait derivation can be read at the tracking issue.

MSRV

The Minimal Supported Rust Version (MSRV) is 1.29; it is enforced by our CI. Later we plan to increase MSRV to support Rust 2018 and you are welcome to check the tracking issue.

Naming conventions

Naming of data structures/enums and their fields/variants must follow names used in Bitcoin Core, with except to:

  • case, which should follow Rust standards (i.e. PascalCase for types and snake_case for fields and variants)
  • C-prefix, which should be omitted

Unsafe code

Use of unsafe code is prohibited unless there is a unanonymous decision among library maintainers on the exclusion from this rule. In such cases there is a requirement to test unsafe code with sanitizers including Miri.

Security

Security is the primary focus for this library; disclosure of security vulnerabilities helps prevent user loss of funds. If you believe a vulnerability may affect other implementations, please disclose this information according to the security guidelines, work on which is currently in progress. Before it is completed, feel free to send disclosure to Andrew Poelstra, apoelstra@wpsoftware.net, and encrypted with his public key, which may be found at https://www.wpsoftware.net/andrew/andrew.gpg.

Testing

Related to the security aspect, rust bitcoin developers must be taking testing very seriously. Due to the modular nature of the project, writing new test cases is easy and good test coverage of the codebase is an important goal. Refactoring the project to enable fine-grained unit testing is also an ongoing effort.

Fuzzing is heavily encouraged: feel free to add related material under fuzz/

Mutation testing is planned; any contribution there would be warmly welcomed.

Going further

You may be interested by Jon Atack guide on How to review Bitcoin Core PRs and How to make Bitcoin Core PRs. While there are differences between the projects in terms of context and maturity, many of the suggestions offered apply to this project.

Overall, have fun :)