License Classifier

Introduction

The license classifier is a library and set of tools that can analyze text to
determine what type of license it contains. It searches for license texts in a
file and compares them to an archive of known licenses. These files could be,
e.g., LICENSE files with a single or multiple licenses in it, or source code
files with the license text in a comment.

A "confidence level" is associated with each result indicating how close the
match was. A confidence level of 1.0 indicates an exact match, while a
confidence level of 0.0 indicates that no license was able to match the text.

Adding a new license

Adding a new license is straight-forward:

1. Create a file in licenses/.

   • The filename should be the name of the license or its abbreviation. If
     the license is an Open Source license, use the appropriate identifier
     specified at https://spdx.org/licenses/.
   • If the license is the "header" version of the license, append the suffix
     ".header" to it. See licenses/README.md for more details.

2. Add the license name to the list in license_type.go.

3. Regenerate the licenses.db file by running the license serializer:

   $ license_serializer -output licenseclassifier/licenses
   

4. Create and run appropriate tests to verify that the license is indeed
   present.

Tools

Identify license

identify_license is a command line tool that can identify the license(s)
within a file.

$ identify_license LICENSE
LICENSE: GPL-2.0 (confidence: 1, offset: 0, extent: 14794)
LICENSE: LGPL-2.1 (confidence: 1, offset: 18366, extent: 23829)
LICENSE: MIT (confidence: 1, offset: 17255, extent: 1059)

License serializer

The license_serializer tool regenerates the licenses.db archive. The archive
contains preprocessed license texts for quicker comparisons against unknown
texts.

$ license_serializer -output licenseclassifier/licenses

This is not an official Google product (experimental or otherwise), it is just
code that happens to be owned by Google.