podman load doesn't work on xz compressed files

[vrothberg]

/kind bug

Description

podman load on xz compressed files fails.

Steps to reproduce the issue:

1. Perform a podman load on an xz compressed file.

Describe the results you received:
open container-feeder471485113/manifest.json: not a directory

There are two things related to this issue. The first one is that the fall-through logic in PullImage is masking the actual bug, which made debugging the issue harder. I guess we could improve the situation by being more verbose when falling through the various transports. The second one is that containers/image currently doesn't support xz compressed images and compressed layers. @cyphar has fixed the latter with containers/image#427. I tested containers/image#427 locally with libpod by updating the vendored image library, which required just a minor tweak in the code to reflect the new tar API.

Describe the results you expected:
A successful image load.

[mheon]

Sounds like a nice, easy improvement. We can track the PR in c/image and merge once that's ready.

[baude]

@umohnani8 you did the gz, how hard would it be to add this ?

[umohnani8]

@baude If it is fixed in containers/image, just a matter of vendoring it in.

[cyphar]

I've implemented it in containers/image#427. Just going through review now.

[rhatdan]

@umohnani8 Could you follow up on this one?

[umohnani8]

@rhatdan ACK. Will keep an eye on the containers/image PR for this.

[umohnani8]

Fixed in #1137.