pull manifest + layers from a docker image with curl with progress meter visible

get-docker-layers.sh

#! /usr/bin/env bash

set -euo pipefail

api() {
  local type endpoint registry image arg url
  type=$1 endpoint=$2 registry=$3 image=$4 arg=$5
  url="https://$registry/v2/$image/$endpoint/$arg"
  curl --config - <<<"-u $ARTIFACTORY_CREDS" -H "Accept: $type" "$url"
}

get-manifest() {
  local registry image label
  IFS=$'\t' read -r registry image label < <(split-docker-url "$1" $'\t')
  api application/vnd.docker.distribution.manifest.v2+json manifests "$registry" "$image" "$label"
}

get-blob() {
  local registry image label
  IFS=$'\t' read -r registry image label < <(split-docker-url "$1" $'\t')
  api application/vnd.docker.image.rootfs.diff.tar.gzip blobs "$registry" "$image" "$2"
}

get-image() {
  local image manifest layers
  image=$1
  echo >&2 "fetching manifest for $image"
  manifest=$(get-manifest "$image")
  counter=0
  while IFS=$'\t' read -r size digest; do
    counter=$((counter+1))
    echo >&2 "fetching layer $counter, $digest, size $size"
    get-blob "$image" "$digest" > "${digest#sha256:}.tar"
  done < <(jq <<<"$manifest" --raw-output '.layers | .[] | "\(.size)\t\(.digest)"')
}

split-docker-url() {
  local s sep image label registry
  s=$1 sep=$2

  registry=${s%%/*} s=${s#*/}
  if [[ "$s" == "$registry" ]]; then echo >&2 "no registry?"; return 1; fi
  label=${s##*:} s=${s%:*}
  if [[ "$s" == "$label" ]]; then label=latest; fi
  image=$s

  echo "$registry$sep$image$sep$label$sep"
}

main() {
  for image in "$@"; do
    get-image "$image"
  done
}

main "$@"