add missing functionality to build_tar

[ixdy]

Our Go implementation of build_tar has fallen behind some of the features in the upstream Python implementation of build_tar:

• --manifest: JSON manifest of contents to add to the layer
• --empty_file: add an empty file
• --empty_dir: add an empty dir (Kubernetes would use this, currently we create a dummy archive instead)
• --empty_root_dir: this defaults to "./" upstream; we currently don't support this, but could add it for compatibility (and then set to "kubernetes/" or "" for our usage, similar to what's being discussed in https://github.com/bazelbuild/bazel/issues/7293)
• --mtime: "Set mtime on tar file entries. May be an integer or the value "portable", to get the value 2000-01-01, which is usable with non *nix OSes" (bazelbuild/bazel@25d202f)
• deb support - tracked in support debs in tools/build_tar #61

cc @mikedanese

[ixdy]

It'd also be good if we could reuse some of the tests for upstream build_tar and pkg_tar, or at least add some kind of testing.

[mikedanese]

@ixdy is bazel_tools open to using go based tools for core rules? what are the roadblocks for getting our build_tar to replace build_tar.py?

[ixdy]

I haven't asked, but I don't think there's any precedent of having go in core bazelbuild/bazel. Maybe if pkg_tar were moved into bazelbuild/rules_pkg? Or at least we could see about hosting this binary there instead.

[fejta]

we should kill this tool and use the built-in one

there is no reason for us to spend our time competing with bazel here. If we are unhappy the performance we should get them to improve the performance, not roll our own replacement

[ixdy]

@fejta the built-in python one is slooooow

[fejta]

I know, and I'll take slow and functional over high maintenance costs every day of the week

[ixdy]

If I use the python implementation and bazel build //build/release-tars, then make a change to CONTRIBUTING.md and rebuild //build/release-tars, it takes 225s just to rebuild kubernetes-src.tar.gz and kubernetes-server-linux-amd64.tar.gz (with no compilation). That seems pretty unacceptable to me.

Another issue is that our implementation is intentionally not quite identical - we don't prepend ./ to the filenames in the tarfile. I attempted to fix this issue upstream in bazelbuild/bazel@72ab932, but it ended up breaking other users, because pkg_tar is used in a lot of places, and it's hard to track them down (especially since Google's uses are more opaque).

https://github.com/bazelbuild/bazel/issues/2380 and https://github.com/bazelbuild/bazel/issues/7293 are relevant issues which might solve our problems if addressed, but neither seem to be getting any traction.

[fejta-bot]

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