# How to Contribute to the Apple/container Project: A Complete Guide

> Contribute to the apple/container project by forking the repo, setting up Swift, creating a feature branch, and submitting a pull request. Learn how to make your first contribution today.

- Repository: [Apple/container](https://github.com/apple/container)
- Tags: how-to-guide
- Published: 2026-06-27

---

**You can contribute to the apple/container project by forking the repository on GitHub, setting up the Swift toolchain for macOS 26 or newer, creating a feature branch, and submitting a pull request after verifying your changes with the local test suite.**

The **apple/container** repository provides a Swift-based command-line tool that runs OCI-compatible containers as lightweight virtual machines on Apple Silicon Macs. This guide walks you through the architecture, setup, and submission process to help you contribute effectively to this open-source project.

## Understanding the Project Architecture

Before contributing, familiarize yourself with the three-layer architecture that separates concerns between user interaction, runtime management, and extensibility.

### CLI and Command Handling Layer

The **CLI layer** parses user commands and drives the system service through sub-processes. Key documentation resides in [`README.md`](https://github.com/apple/container/blob/main/README.md) and [`docs/command-reference.md`](https://github.com/apple/container/blob/main/docs/command-reference.md), while the main entry points orchestrate container lifecycle operations.

### Container Runtime Layer

The **runtime layer** handles low-level VM management, networking, and filesystem operations. This layer heavily utilizes the **containerization** Swift package and relies on [`Sources/ContainerXPC/XPCClient.swift`](https://github.com/apple/container/blob/main/Sources/ContainerXPC/XPCClient.swift) for inter-process communication. The `XPCClient` class implements async request/response handling, timeout logic, and graceful disconnect handling that the CLI uses to communicate with the background daemon.

### Plugins and Extension Points

The **plugin system** enables third-party services to extend core functionality via XPC. The two critical files for this subsystem are [`Sources/ContainerPlugin/PluginLoader.swift`](https://github.com/apple/container/blob/main/Sources/ContainerPlugin/PluginLoader.swift), which dynamically loads plugins from bundle directories, and [`Sources/ContainerPlugin/PluginFactory.swift`](https://github.com/apple/container/blob/main/Sources/ContainerPlugin/PluginFactory.swift), which maintains the registry mapping identifiers to concrete plugin types.

## Setting Up Your Development Environment

Begin by forking the repository and cloning your local copy:

```bash
git clone https://github.com/<your-username>/container.git
cd container

```

Install the Swift toolchain for **macOS 26 or newer**, then build the project and run the test suite:

```bash
swift build   # builds the CLI and its runtime

swift test    # runs the unit-test suite

```

The test suite resides under `Tests/` (e.g., `Tests/ContainerPluginTests/`). Running the full suite verifies that any change does not break existing functionality.

## Step-by-Step Contribution Workflow

Follow this structured workflow to ensure your contribution meets the project's standards:

1. **Read the contribution guide** – Start with [`CONTRIBUTING.md`](https://github.com/apple/container/blob/main/CONTRIBUTING.md) in the repository root, which points to the detailed guide in the containerization repository.

2. **Create a feature branch** using descriptive naming:

   ```bash
   git checkout -b feature/my-new-feature
   ```

3. **Make your changes** focusing on these common areas:
   - `Sources/ContainerPlugin/` – Add new plugins or modify the plugin loader
   - `Sources/ContainerXPC/` – Change XPC communication or add message types
   - `docs/` – Improve documentation or add tutorials

4. **Maintain code quality** by keeping Swift code idiomatic and well-documented with `///` doc comments for public APIs.

5. **Run tests locally** with debug symbols for better stack traces:

   ```bash
   swift test -c debug
   ```

   If you add functionality, write at least one new test case in the appropriate folder (e.g., `Tests/ContainerPluginTests/`).

6. **Commit and push** your changes:

   ```bash
   git add .
   git commit -m "Brief description of change"
   git push origin feature/my-new-feature
   ```

7. **Open a Pull Request** targeting the `main` branch. The PR template at [`.github/pull_request_template.md`](https://github.com/apple/container/blob/main/.github/pull_request_template.md) guides you to include descriptions, issue links, and test coverage indicators.

8. **Address CI feedback** – GitHub Actions workflows run `swift test`, `swift build`, and `swift lint`. Fix any failures before merge approval.

## Writing Your First Plugin

Below is a minimal example of a new plugin that prints a greeting when the container daemon starts. It demonstrates how to **register** the plugin via `PluginFactory` and **expose** functionality through XPC.

```swift
// File: Sources/ContainerPlugin/GreetingPlugin.swift
import ContainerXPC
import ContainerPlugin

public final class GreetingPlugin: Plugin {
    public static let identifier = "com.apple.container.greeting"

    public init() {}

    public func start() async throws {
        // Use XPC to send a log message to the daemon
        let client = XPCClient(service: "com.apple.container.daemon")
        let msg = XPCMessage()
        msg.setString("Greeting from plugin!", forKey: "message")
        try await client.send(msg)
    }
}

// Register the plugin (see PluginFactory.swift for the registration API)
PluginFactory.register(GreetingPlugin.self, for: GreetingPlugin.identifier)

```

This implementation works because the `Plugin` protocol (defined in [`Sources/ContainerPlugin/Plugin.swift`](https://github.com/apple/container/blob/main/Sources/ContainerPlugin/Plugin.swift)) requires a `start()` method that the daemon calls when loading the plugin. The `XPCClient` provides async message sending with automatic timeout handling, matching the daemon's expectations for inter-process communication.

## Key Source Files for Contributors

Understanding these specific files accelerates your contribution process:

- **[`CONTRIBUTING.md`](https://github.com/apple/container/blob/main/CONTRIBUTING.md)** – Entry point for contribution guidelines
- **[`Package.swift`](https://github.com/apple/container/blob/main/Package.swift)** – Declares Swift packages, dependencies, and tool targets
- **[`Sources/ContainerXPC/XPCClient.swift`](https://github.com/apple/container/blob/main/Sources/ContainerXPC/XPCClient.swift)** – Core XPC wrapper handling connection lifecycle and async send/receive
- **[`Sources/ContainerPlugin/PluginLoader.swift`](https://github.com/apple/container/blob/main/Sources/ContainerPlugin/PluginLoader.swift)** – Dynamic plugin loading from bundle directories
- **[`Sources/ContainerPlugin/PluginFactory.swift`](https://github.com/apple/container/blob/main/Sources/ContainerPlugin/PluginFactory.swift)** – Registry mapping identifiers to plugin types
- **[`Tests/ContainerPluginTests/PluginLoaderTest.swift`](https://github.com/apple/container/blob/main/Tests/ContainerPluginTests/PluginLoaderTest.swift)** – Example unit test ensuring plugins load correctly
- **[`scripts/update-container.sh`](https://github.com/apple/container/blob/main/scripts/update-container.sh)** – Helper script for binary upgrades that may need updates for new release assets

## Summary

- **Fork and clone** the repository, then install Swift toolchain for macOS 26+
- **Build with** `swift build` **and test with** `swift test` before submitting changes
- **Focus contributions** on `Sources/ContainerPlugin/`, `Sources/ContainerXPC/`, or `docs/` directories
- **Register new plugins** using `PluginFactory.register()` and implement the `Plugin` protocol's `start()` method
- **Submit PRs** targeting `main` branch and ensure CI passes all checks

## Frequently Asked Questions

### What is the minimum Swift version required to contribute to the apple/container project?

The project requires the Swift toolchain for **macOS 26 or newer**. This ensures compatibility with the async/await patterns used in [`XPCClient.swift`](https://github.com/apple/container/blob/main/XPCClient.swift) and the modern Swift Package Manager features defined in [`Package.swift`](https://github.com/apple/container/blob/main/Package.swift).

### How do I test my changes locally before submitting a pull request?

Run `swift test -c debug` from the repository root to execute the unit-test suite with debug symbols. This command runs tests in `Tests/ContainerPluginTests/` and other test directories to verify that your changes do not break existing functionality.

### Where should I add new test cases for plugin contributions?

Add test cases to the appropriate subdirectory under `Tests/`, such as `Tests/ContainerPluginTests/` for plugin functionality. Follow the existing patterns in [`PluginLoaderTest.swift`](https://github.com/apple/container/blob/main/PluginLoaderTest.swift) to ensure your tests integrate with the CI workflow.

### How does the XPC communication layer work in the container project?

The **XPCClient** class in [`Sources/ContainerXPC/XPCClient.swift`](https://github.com/apple/container/blob/main/Sources/ContainerXPC/XPCClient.swift) wraps macOS XPC services to provide async request/response handling between the CLI and the background daemon. It manages connection lifecycles, implements timeout logic, and handles graceful disconnects, allowing plugins to communicate securely with the container runtime.