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How to Contribute to ZooKeeper

This page describes the mechanics of how to contribute software to ZooKeeper. For ideas about what you might contribute, please see the ProjectSuggestions page.

Getting the source code

First of all, you need the ZooKeeper source code.

Get the source code on your local drive using SVN. Most development is done on the "trunk":

You may also want to develop against a specific release. To do so, visit https://svn.apache.org/repos/asf/zookeeper/tags/ and find the release that you are interested in developing against. To checkout this release, run:

If you prefer to use Eclipse for development, there are instructions for setting up SVN access from within Eclipse at EclipseEnvironment.

Making Changes

Before you start, send a message to the ZooKeeper developer mailing list, or file a bug report in Jira. Describe your proposed changes and check that they fit in with what others are doing and have planned for the project. Be patient, it may take folks a while to understand your requirements.

Modify the source code and add some (very) nice features using your favorite IDE.

But take care about the following points

  • All public classes and methods should have informative Javadoc comments.
    • Do not use @author tags.
  • Code should be formatted according to Sun's conventions, with these exceptions:
    • Indent four spaces per level, not two or six or eight, etc... four.
    • No tabs for indentation, spaces only
  • Contributions should pass existing unit tests.
  • New unit tests should be provided to demonstrate bugs and fixes. JUnit is our test framework:
    • You must implement a class that extends junit.framework.TestCase and whose class name ends with Test.
    • Define methods within your class whose names begin with test, and call JUnit's many assert methods to verify conditions; these methods will be executed when you run ant test.
    • By default, do not let tests write any temporary files to /tmp. Instead, the tests should write to the location specified by the test.build.data system property.
    • Place your class in the src/java/test tree.
    • ClientTest.java is an example of a client-server test.
    • You can run all the unit test with the command ant test, or you can run a specific unit test with the command ant -Dtestcase=<class name without package prefix> test (for example ant -Dtestcase=ClientTest test)

Understanding Ant

ZooKeeper is built by Ant, a Java building tool. This section will eventually describe how Ant is used within ZooKeeper. To start, simply read a good Ant tutorial. The following is a good tutorial, though keep in mind that ZooKeeper isn't structured according to the ways outlined in the tutorial. Use the tutorial to get a basic understand of Ant but not to understand how Ant is used for Hadoop:

Unit Tests

Please make sure that all unit tests succeed before constructing your patch and that no new javac compiler warnings are introduced by your patch.

After a while, if you see

all is ok, but if you see

then please examine error messages in build/test and fix things before proceeding.

Javadoc

Please also check the javadoc.

Examine all public classes you've changed to see that documentation is complete, informative, and properly formatted. Your patch must not generate any javadoc warnings.

Creating a patch

Check to see what files you have modified with:

Add any new files with:

In order to create a patch, type:

If using git (via one of the available git-svn mirrors) create the patch as follows

This will report all modifications done on ZooKeeper sources on your local disk and save them into the ZOOKEEPER-1234.patch file. Read the patch file.
Make sure it includes ONLY the modifications required to fix a single issue.

Please do not:

  • reformat code unrelated to the bug being fixed: formatting changes should be separate patches/commits.
  • comment out code that is now obsolete: just remove it.
  • insert comments around each change, marking the change: folks can use subversion to figure out what's changed and by whom.
  • make things public which are not required by end users.

Please do:

  • try to adhere to the coding style of files you edit;
  • comment code whose function or rationale is not obvious;
  • update documentation (e.g., package.html files, this wiki, etc.)
  • name the patch file after the JIRA – ZOOKEEPER-<JIRA#>.patch

If you need to rename files in your patch:

  1. Write a shell script that uses 'svn mv' to rename the original files.
  2. Edit files as needed (e.g., to change package names).
  3. Create a patch file with 'svn diff --no-diff-deleted --notice-ancestry'.
  4. Submit both the shell script and the patch file.
    This way other developers can preview your change by running the script and then applying the patch.

Testing your patch

Before submitting your patch, you are encouraged to run the same tools that the automated Jenkins CI system will run on your patch. This enables you to fix problems with your patch before you submit it. The test Ant target will run your patch through the same checks that Jenkins currently does.

To use this target, you must run it from a clean workspace (ie svn stat shows no modifications or additions). From your clean workspace, run:

At the end, you should get a message on your console that indicates success.

Some things to note:

  • you may need to explicitly set ANT_HOME. Running ant -diagnostics will tell you the default value on your system.
  • you may need to explicitly set JAVA_HOME.

Applying a patch

To apply a patch either you generated or found from JIRA, you can issue

if you just want to check whether the patch applies you can run patch with --dry-run option

If you are an Eclipse user, you can apply a patch by : # Right click project name in Package Explorer , 2. Team -> Apply Patch

Contributing your work

Finally, patches should be attached to an issue report in Jira via the Attach File link on the issue's Jira. Please add a comment that asks for a code review following our code review checklist. Please note that the attachment should be granted license to ASF for inclusion in ASF works (as per the Apache License §5).

When you believe that your patch is ready to be committed, select the Submit Patch link on the issue's Jira.

Folks should run ant clean test javadoc before selecting Submit Patch. Tests should all pass. Javadoc should report no warnings or errors. Jenkin's tests are meant to double-check things, and not be used as a primary patch tester, which would create too much noise on the mailing list and in Jira. Submitting patches that fail Jenkins testing is frowned on, (unless the failure is not actually due to the patch).

If your patch involves performance optimizations, they should be validated by benchmarks that demonstrate an improvement.

If your patch creates an incompatibility with the latest major release, then you must set the Incompatible change flag on the issue's Jira 'and' fill in the Release Note field with an explanation of the impact of the incompatibility and the necessary steps users must take.

If your patch implements a major feature or improvement, then you must fill in the Release Note field on the issue's Jira with an explanation of the feature that will be comprehensible by the end user.

Once a "+1" comment is received from the automated patch testing system and a code reviewer has set the Reviewed flag on the issue's Jira, a committer should then evaluate it within a few days and either: commit it; or reject it with an explanation.

Please be patient. Committers are busy people too. If no one responds to your patch after a few days, please make friendly reminders. Please incorporate other's suggestions into your patch if you think they're reasonable. Finally, remember that even a patch that is not committed is useful to the community.

Should your patch receive a "-1" from the Jenkins testing, select the Resume Progress on the issue's Jira, upload a new patch with necessary fixes, and then select the Submit Patch link again.

In some cases a patch may need to be updated based on review comments. In this case the updated patch should be re-attached to the Jira with the same name. Jira will archive the older version of the patch and make the new patch the active patch. This will enable a history of patches on the Jira. As stated above patch naming is generally ZOOKEEPER-#.patch where ZOOKEEPER-# is the id of the Jira.

Committers: for non-trivial changes, it is best to get another committer to review your patches before commit. Use Submit Patch link like other contributors, and then wait for a "+1" from another committer before committing. Please also try to frequently review things in the patch queue.

Committing Guidelines for committers

Apply the patch uploaded by the user. Edit the CHANGES.txt file, adding a description of the change, including the bug number it fixes. Add it to the appropriate section - BUGFIXES, IMPROVEMENTS, NEW FEATURES. Please follow the format in CHANGES.txt file. While adding an entry please add it to the end of a section. Use the same entry for the svn commit message.

Jira Guidelines

Please comment on issues in Jira, making their concerns known. Please also vote for issues that are a high priority for you.

Please refrain from editing descriptions and comments if possible, as edits spam the mailing list and clutter Jira's "All" display, which is otherwise very useful. Instead, preview descriptions and comments using the preview button (on the right) before posting them. Keep descriptions brief and save more elaborate proposals for comments, since descriptions are included in Jira's automatically sent messages. If you change your mind, note this in a new comment, rather than editing an older comment. The issue should preserve this history of the discussion.

Stay involved

Contributors should join the ZooKeeper mailing lists. In particular, the commit list (to see changes as they are made), the dev list (to join discussions of changes) and the user list (to help others).

See Also

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