Downloader for "wrapped" tarbar?

[Hartmut Goebel <h.goebel@crazy-compilers.com>]

Hi,

was just written in another mail, I'm currently working on a
erlang/rebar build system. This includes an importer from hex.pm, a
package repository for elixir and erlang packages. (Since this is build
into rebar3 I assume it what PyPI is for Python and CPAN for Perl.)

At hex.pm, packages are provided in a tarfile [1] wrapping the source
tar-file:

-rw-r--r-- 0/0               1 2017-06-14 21:57 VERSION
-rw-r--r-- 0/0              64 2017-06-14 21:57 CHECKSUM
-rw-r--r-- 0/0             532 2017-06-14 21:57 metadata.config
-rw-r--r-- 0/0            4744 2017-06-14 21:57 contents.tar.gz

IMHO it does not make sense to keep this wrapping tar-file in the store.

So my idea is to create a "hexpm-fetch" method, which downloads the
tar-file and only stores the "content.tar.gz" in the store (using a
proper name, of course).

How can this be done?

[1] https://github.com/hexpm/specifications/blob/master/package_tarball.md

-- 
Regards
Hartmut Goebel

| Hartmut Goebel          | h.goebel@crazy-compilers.com               |
| www.crazy-compilers.com | compilers which you thought are impossible |