render::unpack fails for some images.

[akhramov]

Hi, thanks for your awesome library! I think I found a little bug, described below. Aside from that -- great overall experience, thanks!

Description
Alpine-based images make a heavy use of symlinks.
As it stands now, tar-rs overwrites files and not symlinks. (alexcrichton/tar-rs/pull/217)
If layers create a symlink in the same location, render::unpack will fail.

Steps to reproduce:

1. Run cargo run --example image registry-1.docker.io nginxdemos/hello

Expected result:

1. Layers are downloaded and unpacked

Actual result:

1. The command fails with

[registry-1.docker.io] failed to unpack `/usr/home/akhramov/dkregistry-rs/nginxdemos_hello:latest/usr/bin/strings`

Known workaround:

None yet, shall tar-rs be fixed?

[steveej]

Thanks for reporting this. I would expect render::unpack to overwrite the previous layers' contents, so I agree this is a bug.

None yet, shall tar-rs be fixed?

I think this should be the goal, yes. It seems that the PR you linked has a larger scope than this and it would probably be better to separate that.

[lucab]

Cross-referencing: alexcrichton/tar-rs#132.

[steveej]

Cross-referencing: alexcrichton/tar-rs#132.

Thanks, but what if just the symlink is changed to point to a different path? That's not the same as following a link and overwriting the target file.

[akhramov]

JFYI, I am implementing an application which partially overlaps this crate's functionality. I ended up replacing tar-rs with libarchive.

There are existing libarchive bindings, yet those are poorly maintained, so I created my own.

Unpacker:
https://github.com/akhramov/werft/blob/master/baustelle/src/unpacker.rs

libarchive glue code:
https://github.com/akhramov/werft/blob/master/baustelle/src/archive.rs - Provides Rust-y API for unpacker.

https://github.com/akhramov/werft/blob/master/baustelle/src/archive/resource.rs -- reads & extracts archives
https://github.com/akhramov/werft/blob/master/baustelle/src/archive/entry.rs -- reads & sets entries path.

[moschroe]

I ended up replacing tar-rs with libarchive.

Shame, since it's a public holiday here, I just got around to tackling this. Still created a more focused PR. (alexcrichton/tar-rs#229)

All the best!

[steveej]

@moschroe thanks! That PR has landed by now so we'll have this in the next tar-rs release 🎉