CONTRIBUTING.md

Contributing to Tower HTTP

🎈 Thanks for your help improving the project! We are so happy to have you!

There are opportunities to contribute to tower-http at any level. It doesn't matter if you are just getting started with Rust or are the most weathered expert, we can use your help.

No contribution is too small and all contributions are valued.

This guide will help you get started. Do not let this guide intimidate you. It should be considered a map to help you navigate the process.

Don't know where to start? Check issues labeled with "E-help-wanted" or "E-easy".

You may also get help with contributing in the tower Discord channel, please join us!

Conduct

The tower-http project adheres to the Rust Code of Conduct. This describes the minimum behavior expected from all contributors.

Contributing in Issues

For any issue, there are fundamentally three ways an individual can contribute:

1. By opening the issue for discussion: For instance, if you believe that you have uncovered a bug in a tower-http crate, creating a new issue in the tower-rs/tower-http issue tracker is the way to report it.

2. By helping to triage the issue: This can be done by providing supporting details (a test case that demonstrates a bug), providing suggestions on how to address the issue, or ensuring that the issue is tagged correctly.

3. By helping to resolve the issue: Typically this is done either in the form of demonstrating that the issue reported is not a problem after all, or more often, by opening a Pull Request that changes some bit of something in tower-http in a concrete and reviewable manner.

Anybody can participate in any stage of contribution. We urge you to participate in the discussion around bugs and participate in reviewing PRs.

Asking for General Help

If you have reviewed existing documentation and still have questions or are having problems, you can open an issue asking for help.

In exchange for receiving help, we ask that you contribute back a documentation PR that helps others avoid the problems that you encountered.

Submitting a Bug Report

When opening a new issue in the tower-http issue tracker, users will be presented with a basic template that should be filled in. If you believe that you have uncovered a bug, please fill out this form, following the template to the best of your ability. Do not worry if you cannot answer every detail, just fill in what you can.

The two most important pieces of information we need in order to properly evaluate the report is a description of the behavior you are seeing and a simple test case we can use to recreate the problem on our own. If we cannot recreate the issue, it becomes harder for us to fix.

See How to create a Minimal, Complete, and Verifiable example.

Triaging a Bug Report

Once an issue has been opened, it is not uncommon for there to be discussion around it. Some contributors may have differing opinions about the issue, including whether the behavior being seen is a bug or a feature. This discussion is part of the process and should be kept focused, helpful, and professional.

Short, clipped responses—that provide neither additional context nor supporting detail—are not helpful or professional. To many, such responses are simply annoying and unfriendly.

Contributors are encouraged to help one another make forward progress as much as possible, empowering one another to solve issues collaboratively. If you choose to comment on an issue that you feel either is not a problem that needs to be fixed, or if you encounter information in an issue that you feel is incorrect, explain why you feel that way with additional supporting context, and be willing to be convinced that you may be wrong. By doing so, we can often reach the correct outcome much faster.

Resolving a Bug Report

In the majority of cases, issues are resolved by opening a Pull Request. The process for opening and reviewing a Pull Request is similar to that of opening and triaging issues, but carries with it a necessary review and approval workflow that ensures that the proposed changes meet the minimal quality.

Pull Requests

Pull Requests are the way concrete changes are made to the code, documentation, and dependencies in the tower-http repository.

Even tiny pull requests (e.g., one character pull request fixing a typo in API documentation) are greatly appreciated. Before making a large change, it is usually a good idea to first open an issue describing the change to solicit feedback and guidance. This will increase the likelihood of the PR getting merged.

Tests

If the change being proposed alters code (as opposed to only documentation for example), it is either adding new functionality to a crate or it is fixing existing, broken functionality. In both of these cases, the pull request should include one or more tests to ensure that the crate does not regress in the future.

Documentation tests

Ideally, every API has at least one documentation test that demonstrates how to use the API. Documentation tests are run with cargo test --doc. This ensures that the example is correct and provides additional test coverage.

The trick to documentation tests is striking a balance between being succinct for a reader to understand and actually testing the API.

All middleware should have at least one example that demonstrates how to use them. The example should highlight the most common use case that we expect most users to have. If the middleware can be configured there should be at least two examples: One that uses the default configuration (as that is probably the most common use case) and another that shows how to customize things.

The examples should be provided in the module that contains the middleware. So for tower_http::trace::Trace the examples should be in tower_http::trace. The docs for the Service and Layer types should have a line that tells users where to find the example:

/// See the [module docs](crate::trace) for more details.

In Rust documentation, lines that start with /// # are removed when the documentation is generated. They are only there to get the test to run.

Commits

It is a recommended best practice to keep your changes as logically grouped as possible within individual commits. There is no limit to the number of commits any single Pull Request may have, and many contributors find it easier to review changes that are split across multiple commits.

Note that multiple commits often get squashed when they are landed (see the notes about [commit squashing]).

Commit message guidelines

A good commit message should describe what changed and why.

1. The first line should:

• Contain a short description of the change (preferably 50 characters or less, and no more than 72 characters)

2. Keep the second line blank.

3. Wrap all other lines at 72 columns (except for long URLs).

4. If your patch fixes an open issue, you can add a reference to it at the end of the log. Use the Fixes: # prefix and the issue number. For other references use Refs: #. Refs may include multiple issues, separated by a comma.

   Examples:

   • Fixes: #1337
   • Refs: #1234, #42

Opening the Pull Request

From within GitHub, opening a new Pull Request will present you with a template that should be filled out. Please try to do your best at filling out the details, but feel free to skip parts if you're not sure what to put.

Discuss and update

You will probably get feedback or requests for changes to your Pull Request. This is a big part of the submission process so don't be discouraged! Some contributors may sign off on the Pull Request right away, others may have more detailed comments or feedback. This is a necessary part of the process in order to evaluate whether the changes are correct and necessary.

Any community member can review a PR and you might get conflicting feedback. Keep an eye out for comments from code owners to provide guidance on conflicting feedback.

Once the PR is open, do not rebase the commits. See [Commit Squashing] for more details.

Commit Squashing

In most cases, do not squash commits that you add to your Pull Request during the review process. When the commits in your Pull Request land, they may be squashed into one commit per logical change. Metadata will be added to the commit message (including links to the Pull Request, links to relevant issues, and the names of the reviewers). The commit history of your Pull Request, however, will stay intact on the Pull Request page.

Reviewing Pull Requests

Any Tokio, Hyperium, and Tower community member is welcome to review any pull request.

All contributors who choose to review and provide feedback on Pull Requests have a responsibility to both the project and the individual making the contribution. Reviews and feedback must be helpful, insightful, and geared towards improving the contribution as opposed to simply blocking it. If there are reasons why you feel the PR should not land, explain what those are. Do not expect to be able to block a Pull Request from advancing simply because you say "No" without giving an explanation. Be open to having your mind changed. Be open to working with the contributor to make the Pull Request better.

Reviews that are dismissive or disrespectful of the contributor or any other reviewers are strictly counter to the Code of Conduct.

When reviewing a Pull Request, the primary goals are for the codebase to improve and for the person submitting the request to succeed. Even if a Pull Request does not land, the submitters should come away from the experience feeling like their effort was not wasted or unappreciated. Every Pull Request from a new contributor is an opportunity to grow the community.

Review a bit at a time.

Do not overwhelm new contributors.

It is tempting to micro-optimize and make everything about relative performance, perfect grammar, or exact style matches. Do not succumb to that temptation.

Focus first on the most significant aspects of the change:

1. Does this change make sense for tower-http?
2. Does this change make tower-http better, even if only incrementally?
3. Are there clear bugs or larger scale issues that need attending to?
4. Is the commit message readable and correct? If it contains a breaking change is it clear enough?

Note that only incremental improvement is needed to land a PR. This means that the PR does not need to be perfect, only better than the status quo. Follow up PRs may be opened to continue iterating.

When changes are necessary, request them, do not demand them, and do not assume that the submitter already knows how to add a test or run a benchmark.

Specific performance optimization techniques, coding styles and conventions change over time. The first impression you give to a new contributor never does.

Nits (requests for small changes that are not essential) are fine, but try to avoid stalling the Pull Request. Most nits can typically be fixed by the Tower Collaborator landing the Pull Request but they can also be an opportunity for the contributor to learn a bit more about the project.

It is always good to clearly indicate nits when you comment: e.g. Nit: change foo() to bar(). But this is not blocking.

If your comments were addressed but were not folded automatically after new commits or if they proved to be mistaken, please, hide them with the appropriate reason to keep the conversation flow concise and relevant.

Be aware of the person behind the code

Be aware that how you communicate requests and reviews in your feedback can have a significant impact on the success of the Pull Request. Yes, we may land a particular change that makes tower-http better, but the individual might just not want to have anything to do with tower-http ever again. The goal is not just having good code.

Abandoned or Stalled Pull Requests

If a Pull Request appears to be abandoned or stalled, it is polite to first check with the contributor to see if they intend to continue the work before checking if they would mind if you took it over (especially if it just has nits left). When doing so, it is courteous to give the original contributor credit for the work they started (either by preserving their name and email address in the commit log, or by using an Author: meta-data tag in the commit.