Ability to read (tar) stream from stdin

[deitch]

What would you like to be added:

Syft is able to scan directory, as well as a tar file as if it were a directory, so I can do syft packages path/to/file.tar.

It would be helpful if it could read that from stdin:

cat file.tar | syft packages -

Why is this needed:

There are two use cases I have come across:

1. Downloading a very large tar from network
2. Docker container wherein mounting the dir might not work

Thanks!

[tgerla]

Thanks @deitch, we will put this in the backlog for the future. If you're interested in working on it, please let us know and we can help get you started.

[elifarley]

I would expect that the script below would work, but it doesn't:

mkfifo /tmp/image.tar
skopeo >/dev/null 2>&1 copy docker://alpine:latest docker-archive:/tmp/image.tar &
syft -o cyclonedx-json packages docker-archive:/tmp/image.tar

Apparently, Syft needs to seek back in the file, which doesn't work on a named pipe.

[popey]

Duplicate of #569