Download and install missing plugins

[Andrew-Morozko]

Background

The templates might use the plugins that are not installed on the local FS. In this case, fabric should be able to download and install the plugins of the specified versions.

Design

• when fabric executes, before the template execution, it populates the in-memory registry of available plugins from the plugins present in the FS cache (cache_local_path path set in global settings)
  • the local cache directory structure is <cache_local_path>/plugins/<data|content>/<name>/<version>/
• if the template uses the data / content plugins not present in the cache, download and install the missing plugins:
  • read the list of plugins from plugin_versions from the global configuration (Support global configuration #5)
    • try fetching the appropriate (latest up to the ceiling) version of the plugin from the local mirror, if mirror_local_path is provided in the global settings. The path schema is <mirror_local_path>/<data|content>/<name>/<version>.zip
    • try fetching the appropriate (latest up to the ceiling) version of the plugin from the registry using base_url from the global config in the URL schema -- <base_url>/<data|content>/<name>/<version>.zip
  • if the archive is downloaded, unpack it into <cache_local_path>/plugins/<data|content>/<name>/<version>/ and update the in-memory plugins registry.
  • if no plugin found, error out and die

Some of the plugins must be built-in -- #13

References

• Support global configuration #5

[traut]

there might be a way here to use GitHub releases as a poor-man's plugin registry. Since we control fabric repo, we can pack / release various plugins under different tags (name + version?).

• pros:
  • no need to manage additional infrastructure
  • release notes are built-in per release
• cons:
  • releases page for the github project might get messy
  • plugin release process is a bit more complicated

Something to look into!

[traut]

another note: I think the implicit automatic download of the latest version is a bad idea. I've updated the issue body with the step of explicitly defining the plugins used