Find out the JRE version for a specific builder image version when using Cloud Native Buildpacks

jdk-version-from-builder.sh

BUILDER_VERSION=base-platform-api-0.3
JDK_MAJOR_VERSION=11

BUILDPACK=paketo-buildpacks/bellsoft-liberica
BUILDER_IMAGE="gcr.io/paketo-buildpacks/builder:${BUILDER_VERSION}"

JQ_PARSE_BUILDPACK_VERSION=".Labels[\"io.buildpacks.buildpack.layers\"] | fromjson | .[\"${BUILDPACK}\"] | keys[0]"

if command -v skopeo; then
  # Skopeo does not need to pull the image, so its much faster when the image is not present locally
  BUILD_PACK_VERSION=$(skopeo inspect "docker://${BUILDER_IMAGE}" | jq -r "${JQ_PARSE_BUILDPACK_VERSION}")
else
  # docker inspect is faster when the image is present locally
  docker pull "${BUILDER_IMAGE}" >/dev/null
  BUILD_PACK_VERSION=$(docker image inspect gcr.io/paketo-buildpacks/builder:base-platform-api-0.3 | jq -r ".[0].Config${JQ_PARSE_BUILDPACK_VERSION}")
fi

# shellcheck disable=SC2016
curl -s \
  -H "Accept: application/vnd.github.v3+json" \
  "https://api.github.com/repos/paketo-buildpacks/bellsoft-liberica/releases/tags/v${BUILD_PACK_VERSION}" |
  jq -r '.body' |
  grep "BellSoft Liberica JRE | \`${JDK_MAJOR_VERSION}" |
  sed 's/BellSoft Liberica JRE | `\([^`]*\).*/\1/'