This package parses a string representation of an SPDX license describing license terms, like those found in the package.json files' license fields, into consistently structured ECMAScript objects or JSON for programmatic analysis.
Parsing SPDX license expressions in pure JavaScript (TypeScript).
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The SPDX syntax for expressing license terms comes from the Software Package Data eXchange (SPDX), a standard from the Linux Foundation for shareable data about software package license terms. SPDX aims to make sharing and auditing license data easy, especially for users of open-source software.
There are plenty of NPM packages available for dealing with SPDX license expressions, each with their specific scope and objectives – and, conversely, they all make some assumptions that may or may not suit your purposes. Many of these packages also lack support (types) for TypeScript.
The particular challenge that soon gave birth to license-expressions was that libraries such as spdx-expression-parse produce a parse tree but require each license identifier to be a known SPDX license.
The objective of license-expressions is to support building automation tools that deal with license information in bulk or otherwise without ability to correct sloppy or outright invalid license expressions one by one, for example, when processing hundreds or thousands of direct and transitive dependencies of as part of a software audit.
This is an example of how you may give instructions on setting up your project locally. To get a local copy up and running follow these simple example steps.
This is an example of how to list things you need to use the software and how to install them.
- npm
npm install npm@latest -g
With a global install from the NPM registry:
- Install the NPM package globally
$ npm install -g license-expressions
By cloning the Git repository and installing locally:
- Clone the repo
$ git clone https://github.com/lkoskela/license-expressions.git
- Install NPM packages
$ npm install
- Link the CLI entrypoint to your PATH
$ npm link
- Install the
license-expressionspackage as a dependency$ npm install --save license-expressions
- Import the parse function in your code...
const parse = require('license-expressions')
- ...or import the whole set:
import { parse, normalize, validate } from 'license-expressions'
After installing for command-line use, run the spdx command and pass an SPDX expression to it for parsing. The spdx command will print out a JSON representation of the given SPDX expression, or a JSON object describing the error should the parsing fail for some reason.
$ npm install -g license-expressions
$ npm link
# => the executable `spdx` should now be in your PATH
$ spdx "GPL-3.0+"
# => {
# "expression": {
# "license": "GPL-3.0-or-later"
# },
# "errors": []
# }
$ spdx "GPL-3.0"
# => {
# "expression": {
# "license": "GPL-3.0"
# },
# "errors": []
# }
$ spdx --upgrade "GPL-3.0"
# => {
# "expression": {
# "license": "GPL-3.0-only"
# },
# "errors": []
# }
$ spdx "MIT OR (Apache-2.0 AND 0BSD)"
# => {
# "expression": {
# "conjunction": "or",
# "left": {
# "license": "MIT"
# },
# "right": {
# "conjunction": "and",
# "left": {
# "license": "Apache-2.0"
# },
# "right": {
# "license": "0BSD"
# }
# }
# },
# "errors": []
# }
$ spdx "Invalid license expression"
# => {
# "expression": {
# "license": "Invalid license expression"
# },
# "errors": [
# "Unknown SPDX license identifier: \"Invalid license expression\""
# ]
# }Parsing SPDX expressions into a structured object:
import { parse } from 'license-expressions'
const simple = parse("GPL-3.0+")
// => { license: 'GPL-3.0-or-later' }
const compound = parse("MIT OR (Apache-2.0 AND 0BSD)")
// => {
// conjunction: 'or',
// left: { license: 'MIT' },
// right: {
// conjunction: 'and',
// left: { license: 'Apache-2.0' },
// right: { license: '0BSD' }
// }
// }Rendering a normalized string representation of an SPDX expression:
import { normalize } from 'license-expressions'
normalize(' \t ( MIT OR Apache-2.0 )\n')
// => "Apache-2.0 OR MIT"Validating an SPDX expression:
import { validate } from 'license-expressions'
validate('GPL-2.0 OR BSD-3-Clause')
// => { valid: true, errors: [] }
validate('MIT OR Apache-2.0 WITH Autoconf-exception-2.0')
// => { valid: false, errors: [ "Exception associated with unrelated license: \"Apache-2.0 WITH Autoconf-exception-2.0\"" ] }There is currently not much of a roadmap.
The rough idea is to first reach a sufficient level of correctness and robustness within the realm of valid SPDX expressions with valid license identifiers. This is mostly in place already.
The subsequent evolutionary step is to add the ability to correct slightly mistyped or liberal references to valid licenses, i.e. parse an input such as parsing "Apache 2" into { license: Apache-2.0 }, or parsing "Apache2 or MIT" into { conjunction: 'or', left: { license: 'Apache-2.0' }, right: { license: 'MIT } }. The basics for such corrections are in place with the help of a secondary, looser parser grammar, the spdx-correct third-party library, and additional heuristics/corrections implemented in this library.
Right now we're at a phase where all the major functionality is in place and need for change comes primarily from stumbling onto a live example of a license expression that the library doesn't manage to coerce into a valid format while it seems like a feasible thing to do.
See the open issues for a full and up to date list of proposed features (and known issues).
Contributions are what make the open source community such an amazing place to learn, inspire, and create. Any contributions you make are greatly appreciated.
If you have a suggestion that would make this better, please fork the repo and create a pull request. You can also simply open an issue with the tag "enhancement". Don't forget to give the project a star! Thanks again!
- Fork the Project
- Create your Feature Branch (
git checkout -b feature/AmazingFeature) - Commit your Changes (
git commit -m 'Add some AmazingFeature') - Push to the Branch (
git push origin feature/AmazingFeature) - Once you feel good about the contribution, its tests all pass (
npm test) and test coverage looks good, go ahead and open a Pull Request
Distributed under the MIT License. See LICENSE for more information.
The Linux Foundation and its contributors license the SPDX standard under the terms of the Creative Commons Attribution License 3.0 Unported (SPDX: "CC-BY-3.0"). "SPDX" is a United States federally registered trademark of the Linux Foundation. The authors of this package license their work under the terms of the MIT License.
Lasse Koskela - @lassekoskela on Twitter or the same at gmail.com
- Othneil Drew for the Best-README-Template