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Contributing to the curl project

This document is intended to offer guidelines on how to best contribute to the curl project. This concerns new features as well as corrections to existing flaws or bugs.

Join the Community

Skip over to https://curl.se/mail/ and join the appropriate mailing list(s). Read up on details before you post questions. Read this file before you start sending patches. We prefer questions sent to and discussions being held on the mailing list(s), not sent to individuals.

Before posting to one of the curl mailing lists, please read up on the mailing list etiquette.

We also hang out on IRC in #curl on libera.chat

If you are at all interested in the code side of things, consider clicking 'watch' on the curl repository on GitHub to be notified of pull requests and new issues posted there.

When contributing with code, you agree to put your changes and new code under the same license curl and libcurl is already using unless stated and agreed otherwise.

If you add a larger piece of code, you can opt to make that file or set of files to use a different license as long as they do not enforce any changes to the rest of the package and they make sense. Such "separate parts" can not be GPL licensed (as we do not want copyleft to affect users of libcurl) but they must use "GPL compatible" licenses (as we want to allow users to use libcurl properly in GPL licensed environments).

When changing existing source code, you do not alter the copyright of the original file(s). The copyright is still owned by the original creator(s) or those who have been assigned copyright by the original author(s).

By submitting a patch to the curl project, you are assumed to have the right to the code and to be allowed by your employer or whatever to hand over that patch/code to us. We credit you for your changes as far as possible, to give credit but also to keep a trace back to who made what changes. Please always provide us with your full real name when contributing,

What To Read

Source code, the man pages, the INTERNALS document, TODO, KNOWN_BUGS and the most recent changes in git. Just lurking on the curl-library mailing list gives you a lot of insights on what's going on right now. Asking there is a good idea too.

Write a good patch

Follow code style

When writing C code, follow the CODE_STYLE already established in the project. Consistent style makes code easier to read and mistakes less likely to happen. Run make checksrc before you submit anything, to make sure you follow the basic style. That script does not verify everything, but if it complains you know you have work to do.

Non-clobbering All Over

When you write new functionality or fix bugs, it is important that you do not fiddle all over the source files and functions. Remember that it is likely that other people have done changes in the same source files as you have and possibly even in the same functions. If you bring completely new functionality, try writing it in a new source file. If you fix bugs, try to fix one bug at a time and send them as separate patches.

Write Separate Changes

It is annoying when you get a huge patch from someone that is said to fix 11 odd problems, but discussions and opinions do not agree with 10 of them - or 9 of them were already fixed in a different way. Then the person merging this change needs to extract the single interesting patch from somewhere within the huge pile of source, and that creates a lot of extra work.

Preferably, each fix that corrects a problem should be in its own patch/commit with its own description/commit message stating exactly what they correct so that all changes can be selectively applied by the maintainer or other interested parties.

Also, separate changes enable bisecting much better for tracking problems and regression in the future.

Patch Against Recent Sources

Please try to get the latest available sources to make your patches against. It makes the lives of the developers so much easier. The best is if you get the most up-to-date sources from the git repository, but the latest release archive is quite OK as well.

Documentation

Writing docs is dead boring and one of the big problems with many open source projects but someone's gotta do it. It makes things a lot easier if you submit a small description of your fix or your new features with every contribution so that it can be swiftly added to the package documentation.

Documentation is mostly provided as manpages or plain ASCII files. The manpages are rendered from their source files that are usually written using markdown. Most HTML files on the website and in the release archives are generated from corresponding markdown and ASCII files.

Test Cases

Since the introduction of the test suite, we can quickly verify that the main features are working as they are supposed to. To maintain this situation and improve it, all new features and functions that are added need to be tested in the test suite. Every feature that is added should get at least one valid test case that verifies that it works as documented. If every submitter also posts a few test cases, it does not end up a heavy burden on a single person.

If you do not have test cases or perhaps you have done something that is hard to write tests for, do explain exactly how you have otherwise tested and verified your changes.

Submit Your Changes

Get your changes merged

Ideally you file a pull request on GitHub, but you can also send your plain patch to the curl-library mailing list.

If you opt to post a patch on the mailing list, chances are someone converts it into a pull request for you, to have the CI jobs verify it proper before it can be merged. Be prepared that some feedback on the proposed change might then come on GitHub.

Your changes be reviewed and discussed and you are expected to correct flaws pointed out and update accordingly, or the change risks stalling and eventually just getting deleted without action. As a submitter of a change, you are the owner of that change until it has been merged.

Respond on the list or on GitHub about the change and answer questions and/or fix nits/flaws. This is important. We take lack of replies as a sign that you are not anxious to get your patch accepted and we tend to simply drop such changes.

About pull requests

With GitHub it is easy to send a pull request to the curl project to have changes merged.

We strongly prefer pull requests to mailed patches, as it makes it a proper git commit that is easy to merge and they are easy to track and not that easy to lose in the flood of many emails, like they sometimes do on the mailing lists.

Every pull request submitted is automatically tested in several different ways. See the CI document for more information.

Sometimes the tests fail due to a dependency service temporarily being offline or otherwise unavailable, e.g. package downloads. In this case you can just try to update your pull requests to rerun the tests later as described below.

You can update your pull requests by pushing new commits or force-pushing changes to existing commits. Force-pushing an amended commit without any actual content changed also allows you to retrigger the tests for that commit.

When you adjust your pull requests after review, consider squashing the commits so that we can review the full updated version more easily.

A pull request sent to the project might get labeled needs-votes by a project maintainer. This label means that in addition to meeting all other checks and qualifications this pull request must also receive more "votes" of user support. More signs that people want this to happen. It could be in the form of messages saying so, or thumbs-up reactions on GitHub.

When the pull request is approved

If it does not seem to get approved when you think it is ready - feel free to ask for approval.

Once your pull request has been approved it can be merged by a maintainer.

For new features, or changes, we require that the feature window is open for the pull request to be merged. This is typically a three week period that starts ten days after a previous release. New features submitted as pull requests while the window is closed simply have to wait until it opens to get merged.

If time passes without your approved pull request gets merged: feel free to ask what more you can do to make it happen.

Making quality changes

Make the patch against as recent source versions as possible.

If you have followed the tips in this document and your patch still has not been incorporated or responded to after some weeks, consider resubmitting it to the list or better yet: change it to a pull request.

Commit messages

How to write git commit messages in the curl project.

---- start ----
[area]: [short line describing the main effect]
       -- empty line --
[full description, no wider than 72 columns that describes as much as
possible as to why this change is made, and possibly what things
it fixes and everything else that is related,
-- end --

The first line is a succinct description of the change and should ideally work as a single line in the RELEASE NOTES.

The [area] in the first line can be http2, cookies, openssl or similar. There is no fixed list to select from but using the same "area" as other related changes could make sense.

Commit message keywords

Use the following ways to improve the message and provide pointers to related work.

Do not forget to use commit with --author if you commit someone else's work, and make sure that you have your own user and email setup correctly in git before you commit.

Add whichever header lines as appropriate, with one line per person if more than one person was involved. There is no need to credit yourself unless you are using --author which hides your identity. Do not include people's email addresses in headers to avoid spam, unless they are already public from a previous commit; saying {userid} on github is OK.

Push Access

If you are a frequent contributor, you may be given push access to the git repository and then you are able to push your changes straight into the git repository instead of sending changes as pull requests or by mail as patches.

Just ask if this is what you would want. You are required to have posted several high quality patches first, before you can be granted push access.

Useful resources

Update copyright and license information

There is a CI job called REUSE compliance / check that runs on every pull request and commit to verify that the REUSE state of all files are still fine.

This means that all files need to have their license and copyright information clearly stated. Ideally by having the standard curl source code header, with the SPDX-License-Identifier included. If the header does not work, you can use a smaller header or add the information for a specific file to the REUSE.toml file.

You can manually verify the copyright and compliance status by running the REUSE helper tool: reuse lint