Convert Docker 25.1.x+ image export from OCI format to legacy format.

[romaincabassot]

Since Docker 25.1.x image export is done in OCI format which is not supported by the clair-local-scan image which bundles an old CLAIR version.

It requires you to have skopeo binary somewhere in your system and the this tool has a recent version. If skopeo is not in the PATH, use SKOPEO_BIN_PATH environment variable to point to the executable.

Skopeo is used to transform the docker image to legacy format.

Dev has been tested with old and new Docker versions.

[cpuguy83]

I assume the old scanner is assuming that things are in specific paths in the tarball?
Why not update the scanner image to read the tarball based on manifest.json?

[romaincabassot]

Because I don't know the internals of clair server and the in-use version is very old so I though it would have been a too big step for me but I'm certain it would have been a better option.