created_at2021-04-29 07:09:09.872866
updated_at2023-01-06 08:53:32.081185
descriptionHelp in automatically downloading dependencies license files (using the cargo-license json output). Motivation: help in building conda-forge recipes.
Fran├žois-Xavier Pineau (fxpineau)



Get Licenses Helper

Uses the JSON output of cargo-license (cargo license --json) to try to find and automatically download your Rust project dependencies license files.

It is based on an heuristic approach, so you may have to download manually licenses not found automatically (especially if a crate does not come from

Use case

Help in bundling licenses when creating a conda-forge recipe.
See e.g. the license_file section of meta.yaml and the library_licenses directory in cdshealpix-feedstock, (supposedly) mimicking wasmer-feedstock.


First, requires cargo-license :

cargo install cargo-license

Then, install either from a local clone of the repository:

cargo install --path .

or direclty from

cargo install get-license-helper


Result of get-license-helper --help:

get-license-helper 0.1.0
Help in downloading license files from the cargo-license --json output.

    get-license-helper [OPTIONS] [input]

    -h, --help       Prints help information
    -V, --version    Prints version information

    -l <license-dir>        Directory storing the licenses [default: library_licenses]

    <input>    Input file (result of cargo-license --json), stdin if not present

Remark: using twice the same command is faster since already downloaded licenses are not re-downloaded.


In your project directory type:

cargo license --json | get-license-helper

and check the content of the library_licenses directory.

You can obviously re-direct the output:

cargo license --json | get-license-helper > list.yaml

Change the downloaded licenses output directory:

cargo license --json | get-license-helper -l my_licenses > list.yaml

Or use the saved result of cargo-license:

cargo license --json > licenses.json
get-license-helper licenses.json -l my_licenses > list.yaml

Heuristic approach

Ideally, the heuristic should first search in${name}/${version}/source/, but I don't know if one can download the raw files instead of HTML pages.
So far, we rely on the repositories:

  • look at the cargo-license provided repository:
    • if github: look for license(s) in${repo}
      • with ${repo} = ${repository} removing starting and possible ending .git
    • if gitlab: look for license(s) in ${repository}/-/raw removing possible ending .git to ${repository}
    • else, emits a warning
  • for the name of the license file(s):
    • look for the cargo-license provided license (split on ' OR ' in case of multiple licenses):
      • "MIT": look for LICENSE-MIT(.txt|.md) or LICENSE(.txt|.md)
      • "Apache-2.0": look for LICENSE-APACHE(.txt|.md), LICENSE-Apache(.txt|.md) or LICENSE(.txt|.md)
      • "BSD-3-Clause": look for LICENSE-BSD(.txt|.md) or LICENSE(.txt|.md)
      • "BSD-2-Clause": look for LICENSE-BSD(.txt|.md) or LICENSE(.txt|.md)
      • "ISC": look for LICENSE-ISC(.txt|.md) or LICENSE(.txt|.md)
      • "CC0-1.0": look for LICENSE(.txt|.md) or LICENCE(.txt|.md)
      • "MPL-2.0": look for LICENSE(.txt|.md) or LICENCE(.txt|.md)
      • "0BSD": look for LICENSE-0BSD(.txt|.md) or LICENCE-0BSD(.txt|.md)
      • "Zlib": look for LICENSE-ZLIB(.txt|.md) or LICENCE-ZLIB(.txt|.md)
      • "BSL-1.0": look for LICENSE-BOOST(.txt|.md), LICENSE-BST(.txt|.md) or LICENSE(.txt|.md)
      • "Unlicense": do nothing
    • if no license, look at the cargo-license provided license-file
      • if not found, still look for LICENSE(.txt|.md)

To Be Impoved

  • Performances: implement a pool of async workers to explore (HTTP queries) n crates at the same time.
  • Add more licenses: to be done when new cases shows up.
  • ? Feature: check that license files are not empty and are in agreement with the declared license type
  • ? Feature: automatically create a LICENSE file (from a given templates) if license not found
  • ...


  • Using sequential blocking HTTP requests, this is slow.
  • Create duplicate output lines if the same crate (with a different versions) is use multiple times
  • Do not check that the license text is in agreement with the declared license


Like most projects in Rust, this project is licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Commit count: 9

cargo fmt