new command: crane size

[imjasonh]

This adds crane size which returns the total compressed size of blobs referenced by a manifest. This can be useful to roughly determine the relative size of two images in a registry, and over the wire.

This won't tell you how many uncompressed bytes the image might take up if you pull it locally.

go run ./cmd/crane size ubuntu                               
146051085

go run ./cmd/crane size ubuntu --human                       
139 MiB

go run ./cmd/crane size ubuntu --platform=linux/arm64
27361037

go run ./cmd/crane size ubuntu --platform=linux/ppc64le
34496056

go run ./cmd/crane size ubuntu --platform=linux/s390x --human
27 MiB

It forks some code from https://github.com/dustin/go-humanize/blob/master/bytes.go which hasn't been changed in 7 years, so it's expected to be pretty stable. This avoids taking a full dependency on the package, which overall does get occasional updates.

Open to ideas about other things we may want to support with this. This is a Go port of this one-liner that I use pretty often:

function imgsize() {
  crane manifest $1 --platform ${2:-linux/amd64} | jq '.config.size + ([.layers[].size] | add)' | numfmt --to=iec
}

[github-actions]

This Pull Request is stale because it has been open for 90 days with
no activity. It will automatically close after 30 more days of
inactivity. Keep fresh with the 'lifecycle/frozen' label.