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 section of the INSTALL.md file. Check the section 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!

Semantic versioning and commit messages

The CLI version numbering adheres to Semantic Versioning. 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 GitHub repo for publishing at the CLI Documentation page.

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.

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 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.

TypeScript vs CoffeeScript, and Capitano vs oclif

The CLI was originally written in CoffeeScript, but we decided to migrate to TypeScript 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.

Similarly, Capitano was originally adopted as the CLI's framework, but later we decided to take advantage of oclif'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 prettier, which automatically reformats the code (based on configuration in the node_modules/resin-lint/config/.prettierrc file). Beyond that, we have a preference for Javascript promises over callbacks, and for async/await over .then().

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. Most developers are aware that they should use Node.js functions like path.join, which will automatically use backslashes on Windows and forward slashes on Linux and macOS. Where people get caught is actually when handling paths in tar streams, which are sent to the Docker daemon and to balenaCloud. Tar streams use forward slashes regardless of whether the CLI runs on Linux or Windows, and for those paths the ideal is to use path.posix.join instead of path.join. Or, simply hardcode those forward slashes!

• When executing external commands, for example 'ssh', developers often rely on the shell and write something like spawn('command "arg1" "arg2"', { shell: true }). Besides the usual security concerns, another problem is to get argument escaping right (single quote, double quote, backslashes...) because of the differences between the Windows 'cmd.exe' shell and the unix '/bin/sh'. Most of the time, it turns out that it is possible to avoid relying on the shell altogether. The which package can be used to get the full path of a command, resolving 'ssh' to, say, 'C:\WINDOWS\System32\OpenSSH\ssh.EXE', and then the command can be executed directly with spawn(fullPath, argArray, { shell: false}). It's a rare combination of more secure and more interoperable with less development effort (as it avoids time-consuming cross-platform trial and error with argument escaping).