bootc/CONTRIBUTING.md

# Contributing to bootc

Thanks for your interest in contributing!  At the current time,
bootc is implemented in Rust, and calls out to important components
which are written in Go (e.g. https://github.com/containers/image)
as well as C (e.g. https://github.com/ostreedev/ostree/).  Depending
on what area you want to work on, you'll need to be familiar with
the relevant language.

## Note: Before writing a big patch

If you plan to contribute a large change, please get in touch *before*
submitting a pull request by e.g. filing an issue describing your proposed
change. This will help ensure alignment.

## Development environment

There isn't a single approach to working on bootc; however
the primary developers tend to use Linux host systems,
and test in Linux VMs.  One specifically recommended
approach is to use [toolbox](https://github.com/containers/toolbox/)
to create a containerized development environment
(it's possible, though not necessary to create the toolbox
 dev environment using a bootc image as well).

At the current time most upstream developers use a Fedora derivative
as a base, and the [hack/Containerfile](hack/Containerfile) defaults
to Fedora.  However, bootc itself is not intended to strongly tie to a particular
OS or distribution, and patches to handle others are gratefully
accepted!

## Key recommended ingredients:

- A development environment (toolbox or a host) with a Rust and C compiler, etc.
  While this isn't specific to bootc, you will find the experience of working on Rust
  is greatly aided with use of e.g. [rust-analyzer](https://github.com/rust-lang/rust-analyzer/).
- An installation of [podman-bootc](https://github.com/containers/podman-bootc-cli)
  which note on Linux requires that you set up "podman machine". This document
  assumes you have the environment variable `CONTAINER_CONNECTION` set to your
  podman machine's name.

## Ensure you're familiar with a bootc system

Worth stating: before you start diving into the code you should understand using
the system as a user and how it works.  See the user documentation for that.

## Creating your edit-compile-debug cycle

Edit the source code; a simple thing to do is add e.g.
`eprintln!("hello world);` into `run_from_opt` in [lib/src/cli.rs](lib/src/cli.rs).
You can run `make` or `cargo build` to build that locally.  However, a key
next step is to get that binary into a bootc container image.

Use e.g. `podman build -t localhost/bootc -f hack/Containerfile .`.

From there, you can create and spawn a VM from that container image
with your modified bootc code in exactly the same way as a systems operator
would test their own bootc images:

```
$ podman-bootc run localhost/bootc
```

### Faster iteration cycles

You don't need to create a whole new VM for each change, of course.
<https://github.com/containers/podman-bootc/pull/36> is an outstanding
PR to add virtiofsd support, which would allow easily accessing the locally-built
binaries.  Another avenue we'll likely investigate is supporting podman-bootc
accessing the container images which currently live in the podman-machine VM,
or having a local registry which frontends the built container images.

A simple hack though (assuming your development environment is compatible
with the target container host) is to just run a webserver on the host, e.g.
`python3 -m http.server` or whatever, and then from the podman-bootc guest
run `bootc usroverlay` once, and 
`curl -L -o /usr/bin/bootc http://10.0.1.2:8080/target/release/bootc && restorecon /usr/bin/bootc`.

### Debugging via lldb

The `hack/lldb` directory contains an example of how to use lldb to debug bootc code.
`hack/lldb/deploy.sh` can be used to build and deploy a bootc VM in libvirt with an lldb-server
running as a systemd service. Depending on your editor, you can then connect to the lldb server
to use an interactive debugger, and set up the editor to build and push the new binary to the VM.
`hack/lldb/dap-example-vim.lua` is an example for neovim.

The VM can be connected to via `ssh test@bootc-lldb` if you have [nss](https://libvirt.org/nss.html)
enabled.

For some bootc install commands, it's simpler to run the lldb-server in a container, e.g.

```bash
sudo podman run --pid=host --network=host --privileged --security-opt label=type:unconfined_t -v /var/lib/containers:/var/lib/containers -v /dev:/dev -v .:/output localhost/bootc-lldb lldb-server platform --listen "*:1234" --server
```

## Code linting

The `make validate` target runs checks locally that we gate on
in CI, currently around `cargo fmt` and `cargo clippy`.

## Running the tests

First, you can run many unit tests with `cargo test`.

### container tests

There's a small set of tests which are designed to run inside a bootc container
and are built into the default container image:

```
$ podman run --rm -ti localhost/bootc bootc-integration-tests container
```

## Submitting a patch

The podman project has some [generic useful guidance](https://github.com/containers/podman/blob/main/CONTRIBUTING.md#submitting-pull-requests);
like that project, a "Developer Certificate of Origin" is required.

### Sign your PRs

The sign-off is a line at the end of the explanation for the patch. Your
signature certifies that you wrote the patch or otherwise have the right to pass
it on as an open-source patch. The rules are simple: if you can certify
the below (from [developercertificate.org](https://developercertificate.org/)):

```
Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
660 York Street, Suite 102,
San Francisco, CA 94110 USA

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.
```

Then you just add a line to every git commit message:

    Signed-off-by: Joe Smith <joe.smith@email.com>

Use your real name (sorry, no pseudonyms or anonymous contributions.)

If you set your `user.name` and `user.email` git configs, you can sign your
commit automatically with `git commit -s`.

### Git commit style

Please look at `git log` and match the commit log style, which is very
similar to the
[Linux kernel](https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git).

You may use `Signed-off-by`, but we're not requiring it.

**General Commit Message Guidelines**:

1. Title
    - Specify the context or category of the changes e.g. `lib` for library changes, `docs` for document changes, `bin/<command-name>` for command changes, etc.
    - Begin the title with the first letter of the first word capitalized.
    - Aim for less than 50 characters, otherwise 72 characters max.
    - Do not end the title with a period.
    - Use an [imperative tone](https://en.wikipedia.org/wiki/Imperative_mood).
2. Body
    - Separate the body with a blank line after the title.
    - Begin a paragraph with the first letter of the first word capitalized.
    - Each paragraph should be formatted within 72 characters.
    - Content should be about what was changed and why this change was made.
    - If your commit fixes an issue, the commit message should end with `Closes: #<number>`.

Commit Message example:

```bash
<context>: Less than 50 characters for subject title

A paragraph of the body should be within 72 characters.

This paragraph is also less than 72 characters.
```

For more information see [How to Write a Git Commit Message](https://chris.beams.io/posts/git-commit/)