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Contributing to Reactor

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

This document gives you guidelines and pointers at how you should approach contributing. Links to eg. create issues point to reactor/reactor-core repository. Amend this depending on the actual project you're targetting (eg. reactor-addons, BlockHound, reactor-netty...).

Start here:

The Reactor team appreciates your contributing effort! ❤️ ❤️ ❤️

Do you have a question?

Search Stack Overflow first; discuss if necessary

If you're unsure why something isn't working or wondering if there is a better way of doing it please check on Stack Overflow first and if necessary start a discussion. Use relevant tags among the ones we monitor for that purpose:

If you prefer real-time discussion, we also have a few Gitter channels:

  • reactor is the historic most active one, where most of the community can help
  • reactor-core is intended for more advanced pinpointed discussions around the inner workings of the library
  • reactor-netty is intended for netty-specific questions

Refer to each project's README for potential other sources of information.

🐞 Did you find a bug?

  • Do not open a GitHub issue if the bug is a security vulnerability in Reactor (see
  • Ensure the bug was not already reported: Do a bit of searching the relevant project's Issues (eg. reactor-core Issues) to see if you can find something similar
  • If you don't find something similar, open a new issue (eg. reactor-core new issue). Be sure to follow the template and to include a title and clear description. Add as much relevant information as possible, and a code sample or an executable test case demonstrating the expected behavior that is not occurring

🔧 Did you write a patch that fixes a bug?

  • Unless the fix is trivial (typo, cosmetic changes that don't modify the behavior, ...), there should be an issue associated with it.See Did you find a bug?.
  • Wait for issue triage before you start coding. This will determine from which branch to start. See Starting from the right branch section for more details
  • Be sure to sign the Contributor Licence Agreement(CLA). A bot will remind you about that anyway. The CLA form integrates with GitHub, just follow the steps
  • Try to create a branch with a meaningful name (see hints here)
  • Work on your change. Be sure to include JUnit test cases, this will greatly help maintainers while reviewing your change
  • Run all tests locally prior to submission: ./gradlew check
  • Finally, you're ready to submit your Pull-Request 👍

🔍 Do you intend to add a new feature or change an existing one?

  • Again, search for similar suggestions in existing issues (including closed ones)
  • If nothing like that has been suggested before, discuss it in a new issue first
  • If you gather positive feedback, work on the change following the guideline above

🎨 Code style

The Reactor code style can be imported into your IDE.

Please carefully follow the whitespace and formatting conventions already present in the codebase. Here is a short summary of the style:

  1. Tabs, not spaces
  2. Unix (LF), not DOS (CRLF) line endings
  3. Eliminate all trailing whitespace
  4. Wrap Javadoc at 120 characters
  5. Aim to wrap code at 120 characters, but favor readability over wrapping
  6. Preserve existing formatting; i.e. do not reformat code for its own sake
  7. Search the codebase using git grep and other tools to discover common naming conventions, etc.
  8. Latin-1 (ISO-8859-1) encoding for Java sources; use native2ascii to convert if necessary
  9. Open brackets on same line, close brackets isolated on a dedicated new line

PR and commit style

  • Commit early and commit often. Try to still have descriptive commit messages though. This helps during the review process, to see through which steps and train of thought you went
  • Once submitted, the review and discussion starts. If necessary, make adjustments in further commits
  • Use your real name in commits (see configuration hints)
  • Once the PR is approved , clean up and prepare for merge (see From PR to master)

From PR to master

For each PR, there will generally be a single commit that goes into master. We will try to use the squash-and-merge strategy on GitHub to that effect, but if you do that yourself once the PR is approved, it's even better ❤️

Another case where your help is needed in preparing for merge is if your PR has a few logical changes, and you'd like to have as many commits. (Note that if you have more than, say, 3 of these, it's probably that you actually need to do several PRs). If you want us to rebase-and-merge, you'll need to let us know and to perform a manual git rebase -i BASE_BRANCH in order to prepare the commits. You'll probably need to at least squash intermediate commits from the "commit early and often" side of things, and to ensure that the final commits all follow the message convention.

✒️ Commit Message Convention

We use the following convention for commit message title and body:


Longer description of the content of the commit and/or context of the
changed, hard-wrapped at 72 characters
  • PREFIX is either a [TAG] or a more conventional fix #ISSUE:
    • [TAG] is for smaller commits that don't have an issue. We notably use [test] for test amendments, [doc] for small docs changes like typos, [build] for fixes to the CI configuration.
    • most of the time, there should be an issue referenced instead. We prefix with the keyword fix so that GitHub will close the issue once the PR is merged. If the PR is a preparation or a follow-up, use see #ISSUE instead (eg. fix #1226 vs see #1226).
  • DESCRIPTION should be a short but meaningful description of the fix, preferably under 50 chars (the whole title line should NOT go over 72 chars)

💬 More details

Starting from the right branch

Issues are useful before opening a pull-request because they allow the Reactor team to do some triage, answer questions and help with designing a fix.

Additionally, during the triage process the team will evaluate the criticality of the reported issue and decide wether or not it should also be fixed in current maintenance branche(s).

If this is the case, the fix should be implemented against the earliest relevant maintenance branch, which will be indicated in the issue as the milestone.

For instance, if an issue should be fixed in both 3.1 and 3.2, the later being developed on master, the fix PR should be opened against 3.1.x (and the issue will be triaged into 3.1.x Maintenance Backlog).

If on the other hand the issue should only be fixed in the next feature release, it will be affected to the Backlog triage milestone and should be developed against master.

Creating a branch with representative name

Branches used when submitting pull requests should preferably be named according to the xxx-shortDescription convention:

  • xxx is the github issue number
  • use a - separator, at least after issue number
  • shortDescription should be a few representative words about the issue

For example: 1226-lastOnEmptyCallable.

More about commits

Message convention

Here is a more detailed example of the commit message convention:

    fix #ISSUE Prefer short (50 chars) summary of changes

    More detailed explanatory text, if necessary. Wrap it to about 72
    characters or so. In some contexts, the first line is treated as the
    subject of an email and the rest of the text as the body. The blank
    line separating the summary from the body is critical (unless you omit
    the body entirely); tools like rebase can get confused if you run the
    two together.

    Further paragraphs come after blank lines.

     - Bullet points are okay, too

     - Typically a hyphen or asterisk is used for the bullet, preceded by a
       single space, with blank lines in between, but conventions vary here

    Related Issues: #1234, gh-1235
  1. Use imperative statements in the subject line, e.g. "Fix broken Javadoc link".
  2. Begin the DESCRIPTION with a capitalized verb, e.g. "Add, Prune, Fix, Introduce, Avoid, etc."
  3. Prefix the subject line with "fix #XXX " if the commit is fixing issue XXX (or replace "fix" with "see" if it is only related to an issue without closing it)
  4. Do not end the subject line with a period.
  5. Restrict the subject line to 72 characters or less.
  6. Wrap lines in the body at 72 characters or less.
  7. In the body of the commit message, explain how things worked before this commit, what has changed, and how things work now.

Using real names

Please configure git to use your real first and last name for any commits you intend to submit as pull requests. For example, this is not acceptable:

Author: Nickname <>

Rather, please include your first and last name, properly capitalized, as submitted against the Spring Individual Contributor License Agreement (ICLA):

Author: First Last <>

This helps ensure traceability against the ICLA and also goes a long way to ensuring useful output from tools like git shortlog and others.

You can configure this via the account admin area in GitHub (useful for fork-and-edit cases); globally on your machine with

git config --global "First Last"
git config --global

or locally for the reactor-core repository only by omitting the '--global' flag:

cd reactor-core
git config "First Last"
git config

Importing and following the Reactor Code Style

Using your IDE code style support: some projects like reactor-core have an exported configuration included. The reactor-core one can be considered a default for all projects in the reactor organization.

Eclipse users can import the content of $PROJECT_DIR/codequality/eclipse

IntelliJ users can import the xml from $PROJECT_DIR/codequality/idea.

IntelliJ users: If your IDE doesn't support import of xml files (versions prior to 2016.1) you can copy manually into $HOME/.IntelliJIdea{version}/codestyles

Add Apache license header to all new classes

 * Copyright (c) 2011-Present Pivotal Software Inc, All Rights Reserved.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package ...;

Update Apache license header in modified files as necessary

Always check the date range in the license header. For example, if you've modified a file in 2019 whose header still reads:

 * Copyright (c) 2011-2015 Pivotal Software Inc, All Rights Reserved.

Then be sure to update it to:

 * Copyright (c) 2011-Present Pivotal Software Inc, All Rights Reserved.

🎓 Learning more about the tools we use


Not sure what a pull request is, or how to submit one? Take a look at GitHub's excellent help documentation first.

Follow the same conventions for pull request subject lines as mentioned above for commit message subject lines.

In the body:

  1. Explain your use case. What led you to submit this change? Why were existing mechanisms in the framework insufficient? Make a case that this is a general-purpose problem and that yours is a general-purpose solution, etc.
  2. Add any additional information and ask questions; start a conversation or continue one from the original GitHub issue.
  3. Mention the Github issue ID if there is one.

Note that for pull requests containing a single commit, GitHub will default the subject line and body of the pull request to match the subject line and body of the commit message. This is fine, but please also include the items above in the body of the request.

Squashing Commits

To learn more about these techniques, like git rebase --interactive --autosquash, git add --patch, and other tools to "squash" multiple commits into a single atomic commit, in addition to the man pages for git. The Rewriting History section of Pro Git provides a good overview about these tools.

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