DownloadRequest implements the download request for a specific module version.

DownloadResponse implements the download response of a specific module version.

Module implements the available module versions.

Version implements a specific version.

VersionsRequest implements the versions request for available module versions.

VersionsResponse implements the versions response of available module version.

Backend is the interface for module backends https://www.terraform.io/docs/internals/module-registry-protocol.html.