license_checker

Dependency license verification tool

This tool allows the verification of information in docs/LICENSE_OF_DEPENDENCIES.md against the linked license information. To do so, the license reported by the user is checked against the license classification of the downloaded license file for each dependency.

Building

make build_tools

Running

The simplest way to run the verification tool is to execute

telegraf$ ./tools/license_checker/license_checker

using the current directory as telegraf's root directory and verifies all licenses. Only errors will be reported by default.

There are multiple options you can use to customize the verification. Take a look at

telegraf$ ./tools/license_checker/license_checker --help

to get an overview.

As the verification tool downloads each license file linked in the dependency license document, you should be careful on not exceeding the access limits of e.g. GitHub by running the tool too frequent.

Some packages change the license for newer versions. As we always link to the latest license text the classification might not match the actual license of our used dependency. Furthermore, some license text might be wrongly classified, or not classified at all. In these cases, you can use a whitelist to explicitly state the license SPDX classifier for those packages. See the whitelist section for more details.

The recommended use in telegraf is to run

telegraf$ ./tools/license_checker/license_checker \
              -whitelist ./tools/license_checker/data/whitelist

using the code-versioned whitelist. This command will report all non-matching entries with an ERR: prefix.

Whitelist

Whitelist entries contain explicit license information for a set of packages to use instead of classification. Each entry in the whitelist is a line of the form

[comparison operator]<package name>[@vX.Y.Z] <license SPDX>

where the comparison operator is one of >, >=, =, <= or < and the license SPDX is a SPDX license identifier. In case no package version is specified, the entry matches all versions of the library. Furthermore, the comparison operator can be omitted which is equivalent to an exact match (=).

The entries are processed in order until the first match is found.

Here is an example of a whitelist. Assume that you have library github.com/foo/bar which started out with the MIT license until version 1.0.0 where it changed to EFL-1.0 until it again changed to EFL-2.0 starting after version 2.3.0. In this case the whitelist should look like this

<github.com/foo/bar@v1.0.0 MIT
<=github.com/foo/bar@v2.3.0 EFL-1.0
github.com/foo/bar EFL-2.0

All versions below 1.0.0 are matched by the first line and are thus classified as MIT. The second line matches everything that is above 1.0.0 (thus not matched by the first line) until (and including) 2.3.0. The last line with catch everything that was passing the first two lines i.e. everything after 2.3.0.