zulip/docs/production/modifying-zulip.md

Modifying or patching Zulip

Zulip is 100% free and open source software, and you're welcome to modify it! This page explains how to make and maintain modifications in a safe and convenient fashion.

If you do modify Zulip and then report an issue you see in your modified version of Zulip, please be responsible about communicating that fact:

• Ideally, you'd reproduce the issue in an unmodified version (e.g. on chat.zulip.org or zulipchat.com).
• Where that is difficult or you think it's very unlikely your changes are related to the issue, just mention your changes in the issue report.

Making changes

One way to modify Zulip is to just edit files under /home/zulip/deployments/current and then restart the server. This can work OK for testing small changes to Python code or shell scripts. But we don't recommend this approach for maintaining changes because:

• You cannot modify JavaScript, CSS, or other frontend files this way, because we don't include them in editable form in our production release tarballs (doing so would make our release tarballs much larger without any runtime benefit).
• You will need to redo your changes after you next upgrade your Zulip server (or they will be lost).
• You need to remember to restart the server or your changes won't have effect.
• Your changes aren't tracked, so mistakes can be hard to debug.

Instead, we recommend the following GitHub-based workflow (see our Git guide if you need a primer):

• Decide where you're going to edit Zulip's code. We recommend using the Zulip development environment on a desktop or laptop as it will make it extremely convenient for you to test your changes without deploying them in production. But if your changes are small or you're OK with risking downtime, you don't strictly need it; you just need an environment with Git installed.
• Important. Determine what Zulip version you're running on your server. You can check by inspecting ZULIP_VERSION in /home/zulip/deployments/current/version.py (we'll use 2.0.4 below). If you apply your changes to the wrong version of Zulip, it's likely to fail and potentially cause downtime.
• Fork and clone the zulip/zulip repository on GitHub.
• Create a branch (named acme-branch below) containing your changes:

cd zulip
git checkout -b acme-branch 2.0.4

• Use your favorite code editor to modify Zulip.
• Commit your changes and push them to GitHub:

git commit -a

# Use `git diff` to verify your changes are what you expect
git diff 2.0.4 acme-branch

# Push the changes to your GitHub fork
git push origin +acme-branch

• Login to your Zulip server and configure and use upgrade-zulip-from-git to install the changes; remember to configure git_repo_url to point to your fork on GitHub and run it as upgrade-zulip-from-git acme-branch.

This workflow solves all of the problems described above: your change will be compiled and installed correctly (restarting the server), and your changes will be tracked so that it's convenient to maintain them across future Zulip releases.

Upgrading to future releases

Eventually, you'll want to upgrade to a new Zulip release (e.g. 2.1.0 in this example). If your changes were integrated into that Zulip release or are otherwise no longer needed, you can just use upgrade-zulip as usual. Otherwise, you'll need to update your branch by rebasing your changes (starting from a clone of the zulip/zulip repository):

cd zulip
git fetch --tags upstream
git checkout acme-branch
git rebase 2.1.0
# Fix any errors or merge conflicts; see Zulip's Git Guide for advice

# Use `git diff` to verify your changes are what you expect
git diff 2.1.0 acme-branch

git push origin +acme-branch

And then use upgrade-zulip-from-git to install your updated branch, as before.

Making changes with docker-zulip

If you are using docker-zulip, there are two things that are different from the above:

• Because of how container images work, editing files directly is even more precarious, because Docker is designed for working with container images and may lose your changes.
• Instead of running upgrade-zulip-from-git, you will need to use the docker upgrade workflow to build a container image based on your modified version of Zulip.

Applying changes from master

If you are experiencing an issue that has already been fixed by the Zulip development community, and you'd like to get the fix now, you have a few options. There are two possible ways you might get those fixes on your local Zulip server without waiting for an official release.

Applying a small change

Many bugs have small/simple fixes. In this case, you can use the Git workflow described above, using:

git fetch upstream
git cherry-pick abcd1234

instead of "making changes locally" (where abcd1234 is the commit ID of the change you'd like).

In general, we can't provide community support for issues caused by cherry-picking changes in this way. There is a major exception to this rule.

Zulip can be deployed in a wide variety of configurations and environments, and so we often merge fixes to bugs that we can reproduce in an automated test but have not directly reproduced in a production system. In these cases, we'll ask the user(s) who reported the bug to apply the patch to their production system to verify the fix works for them.

Generally, we'll only request this if we expect the fix in question to apply cleanly to the latest release without introducing regressions, and you can expect the Zulip community to be responsive in debugging any problems any caused by the patch.

Upgrading to master

It's unsafe to backport arbitrary patches from master to an older version. Common issues include:

• Changes containing database migrations (new files under zerver/migrations/), which includes most new major features. We don't support applying database migrations out of order.
• Changes that are stacked on top of other changes to the same system.
• Essentially any patch with hundreds of lines of changes.

While it's possible to backport these sorts of changes, you're unlikely to succeed without help from the core team via a support contract.

If you need an unreleased feature, the right path is usually to Zulip master using upgrade-zulip-from-git. Before upgrading to master, make sure you understand:

• The master branch is under very active development; dozens of new changes are integrated into it on most days. Master can have thousands of changes not present in the latest release (all of which will be included in our next release). There are probably some bugs.
• That said we deploy master to chat.zulip.org and zulipchat.com on a regular basis (often daily), so it's very important to the project that it be stable. Most regressions will be minor UX issues or be fixed quickly.
• The development community is very interested in helping debug issues that arise when upgrading from the latest release to master, since they provide us an opportunity to fix that category of issue before our next major release. (Much more so than we are in helping folks debug other custom changes). That said, we cannot make any guarantees about how quickly we'll resolve an issue to folks without a formal support contract.
• We do not support downgrading from master to earlier versions, so if downtime for your Zulip server is unacceptable, make sure you have a current backup in case the upgrade fails.
• Our changelog contains draft release notes available listing major changes since the last release. The Upgrade notes section will always be current, even if some new features aren't documented.

Contributing patches

Zulip contains thousands of changes submitted by volunteer contributors like you. If your changes are likely to be of useful to other organizations, consider contributing them.