Add a label to a Docker image tarball.

add-label

#!/bin/bash
#
# Add a label to an image tarball (manifest v1).
#
# $ docker save alpine -o alpine.tar
# $ add-label alpine.tar org.mine.key foobar
# $ docker load -i alpine.tar
# $ docker inspect alpine | jq '.[].Config.Labels'
# {
#   "org.mine.key": "foobar"
# }

set -euf -o pipefail

tarball=${1:-''}
key=${2:-''}
val=${3:-''}

if [[ -z "${tarball}" || -z "${key}" || -z "${val}" ]]; then
  echo "Usage: add-label image.tar key value" && exit 1
fi

workdir=$(mktemp -d)
imagedir=${workdir}/image
mkdir "${imagedir}"

cleanup() {
  rc=${1:-0}
  rm -rf "${workdir}"
  exit "${rc}"
}

trap cleanup EXIT

tar -C "${imagedir}" -xf "${tarball}"

# Figure out which file is the config json.
config=$(jq -r '.[].Config' "${imagedir}/manifest.json")

# modify config.Labels to a tempfile
jq -c \
  --arg key "${key}" \
  --arg val "${val}" \
  '. * {config: { Labels: { ($key): $val }}}' "${imagedir}/${config}" \
  >"${workdir}/config.json"

# modify container_config.Labels and overwrite original file.
jq -c \
  --arg key "${key}" \
  --arg val "${val}" \
  '. * {container_config: { Labels: { ($key): $val }}}' "${workdir}/config.json" \
  >"${imagedir}/${config}"

mv -f "${tarball}" "${tarball}.orig"
pushd "${imagedir}" >/dev/null

# shellcheck disable=SC2046
tar -cf "${workdir}/out.tar" $(ls)

popd >/dev/null

mv "${workdir}/out.tar" "${tarball}"