balena-cli/CONTRIBUTING.md

# Contributing

The balena CLI is an open source project and your contribution is welcome!

* Install the dependencies listed in the [NPM Installation](./INSTALL.md#npm-installation)
  section of the `INSTALL.md` file. Check the section [Additional
  Dependencies](./INSTALL.md#additional-dependencies) too.
* Clone the `balena-cli` repository, `cd` to it and run `npm install`.
* Build the CLI with `npm run build` or `npm test`, and execute it with `./bin/balena`
  (on a Windows command prompt, you may need to run `node .\bin\balena`).

In order to ease development:

* `npm run build:fast` skips some of the build steps for interactive testing, or
* `./bin/balena-dev` uses `ts-node/register` and `coffeescript/register` to transpile on the fly.

Before opening a PR, test your changes with `npm test`. Keep compatibility in mind, as the CLI is
meant to run on Linux, macOS and Windows. balena CI will run test code on all three platforms, but
this will only help if you add some test cases for your new code!

## ./bin/balena-dev and oclif

When using `./bin/balena-dev` with oclif-converted commands, it is currently necessary to manually
edit the `oclif` section of `package.json` to replace `./build` with `./lib` as follows:

Change from:
```
  "oclif": {
    "commands": "./build/actions-oclif",
    "hooks": {
      "prerun": "./build/hooks/prerun/track"
```

To:
```
  "oclif": {
    "commands": "./lib/actions-oclif",
    "hooks": {
      "prerun": "./lib/hooks/prerun/track"
```

And then remember to change it back before pushing the pull request. This is obviously error prone
and inconvenient, and improvement suggestions are welcome: is there a better solution than
automatically editing `package.json`? It is doable, if it is what needs to be done.

## Semantic versioning and commit messages

The CLI version numbering adheres to [Semantic Versioning](http://semver.org/). The following
header/row is required in the body of a commit message, and will cause the CI build to fail if absent:

```
Change-type: patch|minor|major
```

Version numbers and commit messages are automatically added to the `CHANGELOG.md` file by the CI
build flow, after a pull request is merged. It should not be manually edited.

## Editing documentation files (CHANGELOG, README, website...)

The `doc/cli.markdown` file is automatically generated by running `npm run build:doc` (which also
runs as part of `npm run build`). That file is then pulled by scripts in the
[balena-io/docs](https://github.com/balena-io/docs/) GitHub repo for publishing at the [CLI
Documentation page](https://www.balena.io/docs/reference/cli/).

The content sources for the auto generation of `doc/cli.markdown` are:

* Selected sections of the README file.
* The CLI's command documentation in source code (both Capitano and oclif commands), for example:
  * `lib/actions/build.coffee`
  * `lib/actions-oclif/env/add.ts`

The README file is manually edited, but subsections are automatically extracted for inclusion in
`doc/cli.markdown` by the `getCapitanoDoc()` function in
[`automation/capitanodoc/capitanodoc.ts`](https://github.com/balena-io/balena-cli/blob/master/automation/capitanodoc/capitanodoc.ts).

The `INSTALL.md` and `TROUBLESHOOTING.md` files are also manually edited.

## Windows

Please note that `npm run build:installer` (which generates the `.exe` executable installer on
Windows) specifically requires [MSYS2](https://www.msys2.org/) to be installed. Other than that,
the standard Command Prompt or PowerShell can be used (though MSYS2 is still handy, as it provides
'git' and a number of common unix utilities). If you make changes to `package.json` scripts, check
they also run on a standard Windows Command Prompt.

## Updating the 'npm-shrinkwrap.json' file

The `npm-shrinkwrap.json` file is used to control package dependencies, as documented at
https://docs.npmjs.com/files/shrinkwrap.json.

While developing, the `package.json` file is often modified by, or before, running `npm install`
in order to add, remove or modify dependencies. When `npm install` is executed, it automatically
updates the `npm-shrinkwrap.json` file as well, **taking into account not only the `package.json`
file but also the current state of the `node_modules` folder in your computer.**

Meanwhile, as a text (JSON) file, `git` is capable of merging the `npm-shrinkwrap.json` file during
operations like `rebase`, `cherry-pick` and `pull`. But git's automated merge is not the
recommended way of updating the `npm-shrinkwrap.json` file, because it does not take into account
duplicates or conflicts in the dependency tree, or indeed the state of the `package.json` file
(which may have just been merged). In extreme cases, the automated merge may actually result in a
broken installation. For these reasons, automatic merging of the `npm-shrinkwrap.json` was disabled
through the `.gitattributes` file (the "binary merge driver" allows diff'ing but prevents automatic
merging). Operations like `git rebase` may then result in an error like:

```text
$ git rebase master
warning: Cannot merge binary files: npm-shrinkwrap.json (HEAD vs. c34942b9... test)
Auto-merging npm-shrinkwrap.json
CONFLICT (content): Merge conflict in npm-shrinkwrap.json
error: Failed to merge in the changes.
```

Whether or not there is a merge error, the following commands are the recommended way of updating
and committing the `npm-shrinkwrap.json` file:

```bash
$ rm -rf node_modules  # Linux / Mac
$ rmdir /s node_modules  # Windows Command Prompt
$ npm checkout master -- npm-shrinkwrap.json  # revert it to the master branch state
$ npm install  # "cleanly" update the npm-shrinkwrap.json file
$ git add npm-shrinkwrap.json  # add it for committing (solve merge errors)
```

## TypeScript vs CoffeeScript, and Capitano vs oclif

The CLI was originally written in [CoffeeScript](https://coffeescript.org), but we decided to
migrate to [TypeScript](https://www.typescriptlang.org/) in order to take advantage of static
typing and formal programming interfaces. The migration is taking place gradually, as part of
maintenance work or the implementation of new features. The recommended way of making the
conversion is to first generate plain Javascript, for example using the command:  

```
npx decaffeinate --use-js-modules file.coffee
```

Then manually convert plain Javascript to Typescript. There is also a ["Coffeescript Preview"
Visual Studio Code
extension](https://marketplace.visualstudio.com/items?itemName=drewbarrett.vscode-coffeescript-preview)
that you may find handy.

Similarly, [Capitano](https://github.com/balena-io/capitano) was originally adopted as the CLI's
framework, but later we decided to take advantage of [oclif](https://oclif.io/)'s features such
as native installers for Windows, macOS and Linux, and support for custom flag parsing (for
example, we're still battling with Capitano's behavior of dropping leading zeros of arguments that
look like integers, such as some abbreviated UUIDs). Again, the migration is taking place
gradually, with some CLI commands parsed by oclif and others by Capitano. A simple command line
pre-parsing takes place in `preparser.ts`, to decide whether to route full parsing to Capitano or
to oclif.

## Programming style

`npm run build` also runs [balena-lint](https://www.npmjs.com/package/@balena/lint), which automatically
reformats the code. Beyond that, we have a preference for Javascript promises over callbacks, and for
`async/await` over `.then()`.

## Updating upstream dependencies

In order to get proper nested changelogs, when updating upstream modules that are in the repo.yml
(like the balena-sdk), the commit body has to contain a line with the following format:
```
Update balena-sdk from 12.0.0 to 12.1.0
```

Since this is error prone, it's suggested to use the following npm script:
```
npm run update balena-sdk ^12.1.0
```

This will create a new branch (only if you are currently on master), run `npm update` with the
version you provided as a target and commit the package.json & npm-shrinkwrap.json. The script by
default will set the `Change-type` to `patch` or `minor`, depending on the semver change of the
updated dependency, but if you need to use a different one (eg `major`) you can specify it as an
extra argument:
```
npm run update balena-sdk ^12.14.0 patch
npm run update balena-sdk ^13.0.0 major
```

## Common gotchas

One thing that most CLI bugs have in common is the absence of test cases exercising the broken
code, so writing some test code is a great idea. Having said that, there are also some common
gotchas to bear in mind:

* Forward slashes ('/') _vs._ backslashes ('\') in file paths. The Node.js
  [path.sep](https://nodejs.org/docs/latest-v12.x/api/path.html#path_path_sep) variable stores a
  platform-specific path separator character: the backslash on Windows and the forward slash on
  Linux and macOS. The
  [path.join](https://nodejs.org/docs/latest-v12.x/api/path.html#path_path_join_paths) function
  builds paths using such platform-specific path separator. However:
  * Note that Windows (kernel, cmd.exe, PowerShell, many applications) accepts ***both*** forward
    slashes and backslashes as path separators (including mixing them in a path string), so code
    like `mypath.split(path.sep)` may fail on Windows if `mypath` contains forward slashes. The
    [path.parse](https://nodejs.org/docs/latest-v12.x/api/path.html#path_path_parse_path) function
    understands both forward slashes and backslashes on Windows, and the
    [path.normalize](https://nodejs.org/docs/latest-v12.x/api/path.html#path_path_normalize_path)
    function will _replace_ forward slashes with backslashes.
  * In [tar](https://en.wikipedia.org/wiki/Tar_(computing)#File_format) streams sent to the Docker
    daemon and to balenaCloud, the forward slash is the only acceptable path separator, regardless
    of the OS where the CLI is running. Therefore, `path.sep` and `path.join` should never be used
    when handling paths in tar streams! `path.posix.join` may be used instead of `path.join`.

* Avoid using the system shell to execute external commands, for example:  
  `child_process.exec('ssh "arg1" "arg2"');`  
  `child_process.spawn('ssh "arg1" "arg2"', { shell: true });`  
  Besides the usual security concerns of unsanitized strings, another problem is to get argument
  escaping right because of the differences between the Windows 'cmd.exe' shell and the Unix
  '/bin/sh'. For example, 'cmd.exe' doesn't recognize single quotes like '/bin/sh', and uses the
  caret (^) instead of the backslash as the escape character. Bug territory! Most of the time,
  it is possible to avoid relying on the shell altogether by providing a Javascript array of
  arguments:  
  `spawn('ssh', ['arg1', 'arg2'], { shell: false});`  
  To allow for logging and debugging, the [which](https://www.npmjs.com/package/which) package may
  be used to get the full path of a command before executing it, without relying on any shell:  
  `const fullPath = await which('ssh');`  
  `console.log(fullPath);  # 'C:\WINDOWS\System32\OpenSSH\ssh.EXE'`  
  `spawn(fullPath, ['arg1', 'arg2'], { shell: false });`

* Avoid the `instanceof` operator when testing against classes/types from external packages
  (including base classes), because `npm install` may result in multiple versions of the same
  package being installed (to satisfy declared dependencies) and a false negative may result when
  comparing an object instance from one package version with a class of another package version
  (even if the implementations are identical in both packages). For example, once we fixed a bug
  where the test:  
  `error instanceof BalenaApplicationNotFound`  
  changed from true to false because `npm install` added an additional copy of the `balena-errors`
  package to satisfy a minor `balena-sdk` version update:  
  `$ find node_modules -name balena-errors`  
  `node_modules/balena-errors`  
  `node_modules/balena-sdk/node_modules/balena-errors`  
  In the case of subclasses of `TypedError`, a string comparison may be used instead:  
  `error.name === 'BalenaApplicationNotFound'`