92 lines
3.7 KiB
Markdown
92 lines
3.7 KiB
Markdown
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This package parses [SPDX license expression](https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60) strings describing license terms, like [package.json license strings](https://docs.npmjs.com/files/package.json#license), into consistently structured ECMAScript objects. The npm command-line interface depends on this package, as do many automatic license-audit tools.
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In a nutshell:
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```javascript
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var parse = require('spdx-expression-parse')
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var assert = require('assert')
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assert.deepEqual(
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// Licensed under the terms of the Two-Clause BSD License.
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parse('BSD-2-Clause'),
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{license: 'BSD-2-Clause'}
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)
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assert.throws(function () {
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// An invalid SPDX license expression.
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// Should be `Apache-2.0`.
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parse('Apache 2')
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})
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assert.deepEqual(
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// Dual licensed under either:
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// - LGPL 2.1
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// - a combination of Three-Clause BSD and MIT
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parse('(LGPL-2.1 OR BSD-3-Clause AND MIT)'),
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{
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left: {license: 'LGPL-2.1'},
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conjunction: 'or',
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right: {
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left: {license: 'BSD-3-Clause'},
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conjunction: 'and',
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right: {license: 'MIT'}
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}
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}
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)
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```
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The syntax comes from the [Software Package Data eXchange (SPDX)](https://spdx.org/), a standard from the [Linux Foundation](https://www.linuxfoundation.org) 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.
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The bulk of the SPDX standard describes syntax and semantics of XML metadata files. This package implements two lightweight, plain-text components of that larger standard:
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1. The [license list](https://spdx.org/licenses), a mapping from specific string identifiers, like `Apache-2.0`, to standard form license texts and bolt-on license exceptions. The [spdx-license-ids](https://www.npmjs.com/package/spdx-license-ids) and [spdx-exceptions](https://www.npmjs.com/package/spdx-exceptions) packages implement the license list. `spdx-expression-parse` depends on and `require()`s them.
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Any license identifier from the license list is a valid license expression:
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```javascript
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var identifiers = []
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.concat(require('spdx-license-ids'))
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.concat(require('spdx-license-ids/deprecated'))
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identifiers.forEach(function (id) {
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assert.deepEqual(parse(id), {license: id})
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})
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```
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So is any license identifier `WITH` a standardized license exception:
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```javascript
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identifiers.forEach(function (id) {
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require('spdx-exceptions').forEach(function (e) {
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assert.deepEqual(
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parse(id + ' WITH ' + e),
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{license: id, exception: e}
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)
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})
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})
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```
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2. The license expression language, for describing simple and complex license terms, like `MIT` for MIT-licensed and `(GPL-2.0 OR Apache-2.0)` for dual-licensing under GPL 2.0 and Apache 2.0. `spdx-expression-parse` itself implements license expression language, exporting a parser.
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```javascript
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assert.deepEqual(
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// Licensed under a combination of:
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// - the MIT License AND
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// - a combination of:
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// - LGPL 2.1 (or a later version) AND
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// - Three-Clause BSD
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parse('(MIT AND (LGPL-2.1+ AND BSD-3-Clause))'),
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{
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left: {license: 'MIT'},
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conjunction: 'and',
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right: {
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left: {license: 'LGPL-2.1', plus: true},
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conjunction: 'and',
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right: {license: 'BSD-3-Clause'}
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}
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}
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)
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```
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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")](http://spdx.org/licenses/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.
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