(This document is based on curl's CONTRIBUTE.md - thank you!)
This document is intended to offer guidelines on how to best contribute to the librdkafka project. This concerns new features as well as bug fixes and general improvements.
When contributing with code, you agree to put your changes and new code under the same license librdkafka is already using unless stated and agreed otherwise.
When changing existing source code, you do not alter the copyright of the original file(s). The copyright will still be owned by the original creator(s) or those who have been assigned copyright by the original author(s).
By submitting a patch to the librdkafka, 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 will 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!
Official librdkafka project maintainer(s) assume ownership of all accepted submissions.
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.
clang-format is used to check, and fix, the style for C/C++ files, while flake8 and autopep8 is used for the Python scripts.
You should check the style before committing by running make style-check
from the top-level directory, and if any style errors are reported you can
automatically fix them using make style-fix.
The Python code may need some manual fixing since autopep8 is unable to fix
all warnings reported by flake8, in particular it will not split long lines,
in which case a # noqa: E501 may be needed to turn off the warning.
See the end of this document for the C style guide to use in librdkafka.
It is annoying when you get a huge patch from someone that is said to fix 511 odd problems, but discussions and opinions don't agree with 510 of them - or 509 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 gives a lot of extra work.
Preferably, each fix that correct 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 when we track problems and regression in the future.
Please try to make your patches against latest master branch.
Bugfixes should also include a new test case in the regression test suite that verifies the bug is fixed. Create a new tests/00-<short_bug_description>.c file and try to reproduce the issue in its most simple form. Verify that the test case fails for earlier versions and passes with your bugfix in-place.
New features and APIs should also result in an added test case.
Submitted patches must pass all existing tests. For more information on the test suite see [tests/README.md]
File a pull request on github
Your change will be reviewed and discussed there and you will be expected to correct flaws pointed out and update accordingly, or the change risk stalling and eventually just get deleted without action. As a submitter of a change, you are the owner of that change until it has been merged.
Make sure to monitor your PR on github and answer questions and/or fix nits/flaws. This is very important. We will take lack of replies as a sign that you're not very anxious to get your patch accepted and we tend to simply drop such changes.
When you adjust your pull requests after review, please squash the commits so that we can review the full updated version more easily and keep history cleaner.
For example:
# Interactive rebase to let you squash/fixup commits
$ git rebase -i master
# Mark fixes-on-fixes commits as 'fixup' (or just 'f') in the
# first column. These will be silently integrated into the
# previous commit, so make sure to move the fixup-commit to
# the line beneath the parent commit.
# Since this probably rewrote the history of previously pushed
# commits you will need to make a force push, which is usually
# a bad idea but works good for pull requests.
$ git push --force origin your_feature_branch
A short guide to how to write good commit messages.
---- start ----
[area]: [short line describing the main effect] [(#issuenumber)]
-- empty line --
[full description, no wider than 72 columns that describe as much as
possible as to why this change is made, and possibly what things
it fixes and everything else that is related]
---- stop ----
Example:
cgrp: Restart query timer on all heartbeat failures (#10023)
If unhandled errors were received in HeartbeatResponse
the cgrp could get stuck in a state where it would not
refresh its coordinator.
Important: Rebase your PR branch on top of master (git rebase -i master)
and squash interim commits (to make a clean and readable git history)
before pushing. Use force push to keep your history clean even after
the initial PR push.
Note: Good PRs with bad commit messages or messy commit history such as "fixed review comment", will be squashed up in to a single commit with a proper commit message.
If the changes in the PR affects the end user in any way, such as for a user visible bug fix, new feature, API or doc change, etc, a release changelog item needs to be added to CHANGELOG.md for the next release.
Add a single line to the appropriate section (Enhancements, Fixes, ..) outlining the change, an issue number (if any), and your name or GitHub user id for attribution.
E.g.:
## Enhancements
* Improve commit() async parameter documentation (Paul Nit, #123)
Use self-explanatory hierarchical snake-case naming.
Pretty much all symbols should start with rd_kafka_, followed by
their subsystem (e.g., cgrp, broker, buf, etc..), followed by an
action (e.g, find, get, clear, ..).
For existing types use the type prefix as variable name. The type prefix is typically the first part of struct member fields. Example:
rd_kafka_broker_thas field names starting withrkb_.., thus broker variable names should be namedrkb
For other types use reasonably concise but descriptive names.
i and j are typical int iterators.
Variables must be declared at the head of a scope, no in-line variable declarations are allowed.
Use 8 spaces indent, same as the Linux kernel.
In emacs, use c-set-style "linux.
For C++, use Google's C++ style.
Fix formatting issues by running make style-fix prior to committing.
Use /* .. */ comments, not // ..
For functions, use doxygen syntax, e.g.:
/**
* @brief <short description>
* ..
* @returns <something..>
*/
Make sure to comment non-obvious code and situations where the full context of an operation is not easily graspable.
Also make sure to update existing comments when the code changes.
Try hard to keep line length below 80 characters, when this is not possible exceed it with reason.
Braces go on the same line as their enveloping statement:
int some_func (..) {
while (1) {
if (1) {
do something;
..
} else {
do something else;
..
}
}
/* Single line scopes should not have braces */
if (1)
hi();
else if (2)
/* Say hello */
hello();
else
bye();
All expression parentheses should be prefixed and suffixed with a single space:
int some_func (int a) {
if (1)
....;
for (i = 0 ; i < 19 ; i++) {
}
}
Use space around operators:
int a = 2;
if (b >= 3)
c += 2;
Except for these:
d++;
--e;
New blocks should be on a new line:
if (1)
new();
else
old();
Don't assume the reader knows C operator precedence by heart for complex statements, add parentheses to ease readability.
Avoid ifdef's as much as possible. Platform support checking should be performed in configure.librdkafka.
Follow Google's C++ style guide