@balena/contrato

Contrato

The official contracts implementation

Quickstart

import { Contract } from 'contrato';

const osContract = new Contract({
	type: 'sw.os',
	slug: 'balenaos',
	version: '6.1.2',
	children: [
		{ type: 'sw.service', slug: 'balena-engine', version: '20.10.43' },
		{ type: 'sw.service', slug: 'NetworkManager', version: '0.6.0' },
	],
	provides: [{ type: 'sw.feature', slug: 'secureboot' }],
});

const serviceContract = new Contract({
	type: 'sw.application',
	slug: 'myapp',
	requires: [
		{ type: 'sw.service', slug: 'balena-engine', version: '>20' },
		{ type: 'sw.feature', slug: 'secureboot' },
	],
});

if (osContract.satisfiesChildContract(serviceContract)) {
	console.log('myapp can be installed!');
}

About contracts

What is a contract?

Is a specification for describing things. A thing can be pretty much anything, a software library, a feature, an API, etc. Relationships between things can be established via composition and referencing (requires and provides). Through this library, contracts can be validated, composed and combined.

Why build this?

balena.io is a complex product with a great number of inter-conecting components. Each of the components have their own requisites, capabilities, and incompatibilities. Contracts are an effort to formally document those interfaces, and a foundation on which we can build advanced tooling to ultimately automate the process of the team, increase productivity, and remove the human element from tasks that can be performed better by a machine.

The concept of contracts is generic enough that it can be applied to seemingly unrelated scenarios, from base images and OS images, to device types and backend components. Re-using the same contract "format" between them allows us to multiply the gains we get by developing complex contract-related programming modules.

What can I do with contracts? Give me some examples

Describe a thing via a contract

{
	"type": "sw.library",
	"slug": "glibc",
	"version": "2.40",
	"assets": {
		"license": {
			"name": "GNU Lesser General Public License",
			"url": "https://www.gnu.org/licenses/lgpl-3.0.html#license-text"
		}
	}
}

Describe a thing that requires a thing

{
	"type": "sw.utility",
	"slug": "curl",
	"version": "8.11.1",
	"requires": [{ "type": "sw.library", "slug": "glibc", "version": ">=2.17" }],
	"data": {
		"protocols": ["HTTP", "HTTPS", "FTP"]
	}
}

Describe a complex thing via a composite contract

{
	"type": "sw.os",
	"slug": "balenaos",
	"version": "4.1.5",
	"children": [
		{
			"type": "sw.library",
			"slug": "glibc",
			"version": "2.16",
			"assets": {
				"license": {
					"name": "GNU Lesser General Public License",
					"url": "https://www.gnu.org/licenses/lgpl-3.0.html#license-text"
				}
			}
		}
	]
}

Validate requirements of a contract via contrato

import { Contract } from 'contrato';

const osContract = new Contract({
	type: 'sw.os',
	slug: 'balenaos',
	version: '4.1.5',
	children: [
		{
			type: 'sw.library',
			slug: 'glibc',
			version: '2.16',
		},
	],
});

const curlContract = new Contract({
	type: 'sw.utility',
	slug: 'curl',
	version: '8.11.1',
	requires: [{ type: 'sw.library', slug: 'glibc', version: '>=2.17' }],
});

if (osContract.satisfiesChildContract(curlContract)) {
	console.log('cURL requirements are met and it can be installed!');
} else {
	// cannot install cURL, missing requirements: { type: 'sw.library', slug: 'glibc', version: '>=2.17' }
	console.log(
		'cannot install cURL, missing requirements: ',
		osContract.getNotSatisfiedChildRequirements(curlContract),
	);
}

Describe a universe of things

import { Contract, Universe } from 'contrato';

const universe = new Universe();
universe.addChildren([
	new Contract({ type: 'sw.os', slug: 'debian' }),
	new Contract({ type: 'sw.os', slug: 'fedora' }),
	new Contract({
		type: 'arch.sw',
		slug: 'armv7hf',
		requires: [{ type: 'hw.device-type', data: { arch: 'armv7hf' } }],
	}),
	new Contract({
		type: 'arch.sw',
		slug: 'amd64',
		requires: [{ type: 'hw.device-type', data: { arch: 'amd64' } }],
	}),
	new Contract({
		type: 'hw.device-type',
		slug: 'raspberrypi3',
		data: { arch: 'armv7hf' /* ... */ },
	}),
	new Contract({
		type: 'hw.device-type',
		slug: 'intel-nuc',
		data: { arch: 'amd64' /* ... */ },
	}),
]);

Generate combinations of things with a Blueprint

import { Contract, Universe, Blueprint } from 'contrato';

const universe = new Universe();
universe.addChildren([
	/* ... */
]);

const blueprint = new Blueprint(
	{ 'hw.device-type': 1, 'arch.sw': 1, 'sw.os': 1 },
	{ type: 'meta.context' },
);

// Generate contexts with valid combinations of the given types
const contexts = blueprint.reproduce(universe);

Build templates using the metadata from a combination

import { Contract, Universe, Blueprint, buildTemplate } from 'contrato';

/* ... */

// Generate contexts with valid combinations of the given types
const contexts = blueprint.reproduce(universe);
const template = ```
Welcome to {{this.sw.os.slug}}OS for {{this.hw.device-type.slug}}!

This build supports the architecture {{this.arch.sw.slug}}
```;

for (const context of contexts) {
	// Welcome to OS fedoraOS for intel-nuc
	// ...
	console.log(buildTemplate(template, context));
}

Additional information

See contracts specification for additional documentation on the contract format.

Tests

Run the test npm script:

npm test

Contribute

• Issue Tracker: github.com/product-os/contrato/issues
• Source Code: github.com/product-os/contrato

Before submitting a PR, please make sure that you include tests, and that the linter runs without any warning:

npm run lint

Support

If you're having any problem, please raise an issue on GitHub.

License

The project is licensed under the Apache 2.0 license.