docker_image_downloader.sh

#!/usr/bin/env bash
set -eo pipefail
# from moby project - w/o go dependency (nailing amd64) and w/o jq dep (using
# python)

# hello-world                      latest              ef872312fe1b        3 months ago        910 B
# hello-world                      latest              ef872312fe1bbc5e05aae626791a47ee9b032efa8f3bda39cc0be7b56bfe59b9   3 months ago        910 B

# debian                           latest              f6fab3b798be        10 weeks ago        85.1 MB
# debian                           latest              f6fab3b798be3174f45aa1eb731f8182705555f89c9026d8c1ef230cbf8301dd   10 weeks ago        85.1 MB

# check if essential commands are in our PATH
for cmd in curl; do
	if ! command -v $cmd &> /dev/null; then
		echo >&2 "error: \"$cmd\" not found!"
		exit 1
	fi
done

#set -x
py_jq () {
    python -Ssc 'if 1:
    #log = lambda s: open("/tmp/arg", "a").write("\n----" + str(s))
    # from time import sleep # debugging in pipes, make it stop, watch log
    import json as j, sys; jl=j.loads; jd=j.dumps
    r=sys.stdin.read; w=sys.stdout.write
    a=sys.argv[1:]; ra="--raw-output"; co="--compact-output"
    if a[0] == "id_and_parent":
        s, m = jl(open(a[1]).read()), {}
        m["id"] = s["id"]
        p = s.get("parent")
        if p is not None:
            m["parent"] = p
        w(jd(m))
    elif a[0] == "make_mani":
        w(jd("".join(a[1:])))
        sys.exit(0)
    elif a[0] == "del_hist_and_root":
        fn = a[-1]
        j = jl(open(a[-1]).read())
        j.update(jl("".join(a[1:5])))
        j.pop("history")
        j.pop("rootfs")
        w(jd(j, indent=4))
    elif len(a) == 2 and ra in a and a[-1].startswith("."):
        js_in = jl(r())
        p = a[-1][1:].split(".")
        while p:
            js_in = js_in[p.pop(0)]
        w(str(js_in))
    elif a and a[-1] in (".manifests[]", ".layers[]"):
        js_in = jl(r())
        for m in js_in[a[-1][1:-2]]:
            print(jd(m))
    else:
        raise Exception("not implemented: %s" % str(a))
    ' $* || exit 1
}

usage() {
	echo "usage: $0 dir image[:tag][@digest] ..."
	echo "       $0 /tmp/old-hello-world hello-world:latest@sha256:8be990ef2aeb16dbcb9271ddfe2610fa6658d13f6dfb8bc72074cc1ca36966a7"
	[ -z "$1" ] || exit "$1"
}


dir="$1" # dir for building tar in
shift || usage 1 >&2

[ $# -gt 0 -a "$dir" ] || usage 2 >&2
mkdir -p "$dir"

# hacky workarounds for Bash 3 support (no associative arrays)
images=()
rm -f "$dir"/tags-*.tmp
manifestJsonEntries=()
doNotGenerateManifestJson=
# repositories[busybox]='"latest": "...", "ubuntu-14.04": "..."'

# bash v4 on Windows CI requires CRLF separator
newlineIFS=$'\n'

registryBase='https://registry-1.docker.io'
authBase='https://auth.docker.io'
authService='registry.docker.io'

# https://github.com/moby/moby/issues/33700
fetch_blob() {
	local token="$1"; shift
	local image="$1"; shift
	local digest="$1"; shift
	local targetFile="$1"; shift
	local curlArgs=( "$@" )

	local curlHeaders="$(
		curl -S "${curlArgs[@]}" \
			-H "Authorization: Bearer $token" \
			"$registryBase/v2/$image/blobs/$digest" \
			-o "$targetFile" \
			-D-
	)"
	curlHeaders="$(echo "$curlHeaders" | tr -d '\r')"
	if grep -qE "^HTTP/[0-9].[0-9] 3" <<<"$curlHeaders"; then
		rm -f "$targetFile"

		local blobRedirect="$(echo "$curlHeaders" | awk -F ': ' 'tolower($1) == "location" { print $2; exit }')"
		if [ -z "$blobRedirect" ]; then
			echo >&2 "error: failed fetching '$image' blob '$digest'"
			echo "$curlHeaders" | head -1 >&2
			return 1
		fi

		curl -fSL "${curlArgs[@]}" \
			"$blobRedirect" \
			-o "$targetFile"
	fi
}

# handle 'application/vnd.docker.distribution.manifest.v2+json' manifest
handle_single_manifest_v2() {
	local manifestJson="$1"; shift

	local configDigest="$(echo "$manifestJson" | py_jq --raw-output '.config.digest')"
	local imageId="${configDigest#*:}" # strip off "sha256:"

	local configFile="$imageId.json"
	fetch_blob "$token" "$image" "$configDigest" "$dir/$configFile" -s

	local layersFs="$(echo "$manifestJson" | py_jq --raw-output --compact-output '.layers[]')"
	local IFS="$newlineIFS"
	local layers=( $layersFs )
	unset IFS

	echo "Downloading '$imageIdentifier' (${#layers[@]} layers)..."
	local layerId=
	local layerFiles=()
	for i in "${!layers[@]}"; do
		local layerMeta="${layers[$i]}"

		local layerMediaType="$(echo "$layerMeta" | py_jq --raw-output '.mediaType')"
		local layerDigest="$(echo "$layerMeta" | py_jq --raw-output '.digest')"

		# save the previous layer's ID
		local parentId="$layerId"
		# create a new fake layer ID based on this layer's digest and the previous layer's fake ID
		layerId="$(echo "$parentId"$'\n'"$layerDigest" | sha256sum | cut -d' ' -f1)"
		# this accounts for the possibility that an image contains the same layer twice (and thus has a duplicate digest value)

		mkdir -p "$dir/$layerId"
		echo '1.0' > "$dir/$layerId/VERSION"

		if [ ! -s "$dir/$layerId/json" ]; then
			# this starter JSON is taken directly from Docker's own "docker save" output for unimportant layers
            echo -e '
                {
                    "id": "'$parentId'",
                    "parent": "'$layerId'",
					"created": "0001-01-01T00:00:00Z",
					"container_config": {
						"Hostname": "",
						"Domainname": "",
						"User": "",
						"AttachStdin": false,
						"AttachStdout": false,
						"AttachStderr": false,
						"Tty": false,
						"OpenStdin": false,
						"StdinOnce": false,
						"Env": null,
						"Cmd": null,
						"Image": "",
						"Volumes": null,
						"WorkingDir": "",
						"Entrypoint": null,
						"OnBuild": null,
						"Labels": null
					}
				}' > "$dir/$layerId/json"
		fi

		case "$layerMediaType" in
			application/vnd.docker.image.rootfs.diff.tar.gzip)
				local layerTar="$layerId/layer.tar"
				layerFiles=( "${layerFiles[@]}" "$layerTar" )
				# TODO figure out why "-C -" doesn't work here
				# "curl: (33) HTTP server doesn't seem to support byte ranges. Cannot resume."
				# "HTTP/1.1 416 Requested Range Not Satisfiable"
				if [ -f "$dir/$layerTar" ]; then
					# TODO hackpatch for no -C support :'(
					echo "skipping existing ${layerId:0:12}"
					continue
				fi
				local token="$(curl -fsSL "$authBase/token?service=$authService&scope=repository:$image:pull" | py_jq --raw-output '.token')"
				fetch_blob "$token" "$image" "$layerDigest" "$dir/$layerTar" --progress
				;;

			*)
				echo >&2 "error: unknown layer mediaType ($imageIdentifier, $layerDigest): '$layerMediaType'"
				exit 1
				;;
		esac
	done

	# change "$imageId" to be the ID of the last layer we added (needed for old-style "repositories" file which is created later -- specifically for older Docker daemons)
	imageId="$layerId"

	# munge the top layer image manifest to have the appropriate image configuration for older daemons
	#local imageOldConfig="$(py_jq --raw-output --compact-output '{ id: .id } + if .parent then { parent: .parent } else {} end' "$dir/$imageId/json")"
	local imageOldConfig="$(py_jq id_and_parent "$dir/$imageId/json")"
	py_jq del_hist_and_root "$imageOldConfig" "$dir/$configFile" > "$dir/$imageId/json"
    local ll=""
    for layerFile in "${layerFiles[@]}"; do ll="$ll\"$layerFile\","; done

	local manifestJsonEntry="$(
		py_jq make_mani '{
			"Config": "'"$configFile"'",
			"RepoTags": ["'"${image#library\/}:$tag"'"],
			"Layers": ['${ll%?}']
		}'
	)"
	manifestJsonEntries=( "${manifestJsonEntries[@]}" "$manifestJsonEntry" )
}

while [ $# -gt 0 ]; do
	imageTag="$1"
	shift
	image="${imageTag%%[:@]*}"
	imageTag="${imageTag#*:}"
	digest="${imageTag##*@}"
	tag="${imageTag%%@*}"

	# add prefix library if passed official image
	if [[ "$image" != *"/"* ]]; then
		image="library/$image"
	fi

	imageFile="${image//\//_}" # "/" can't be in filenames :)

	token="$(curl -fsSL "$authBase/token?service=$authService&scope=repository:$image:pull" | py_jq --raw-output '.token')"

	manifestJson="$(
		curl -fsSL \
			-H "Authorization: Bearer $token" \
			-H 'Accept: application/vnd.docker.distribution.manifest.v2+json' \
			-H 'Accept: application/vnd.docker.distribution.manifest.list.v2+json' \
			-H 'Accept: application/vnd.docker.distribution.manifest.v1+json' \
			"$registryBase/v2/$image/manifests/$digest"
	)"
	if [ "${manifestJson:0:1}" != '{' ]; then
		echo >&2 "error: /v2/$image/manifests/$digest returned something unexpected:"
		echo >&2 "  $manifestJson"
		exit 1
	fi

	imageIdentifier="$image:$tag@$digest"

	schemaVersion="$(echo "$manifestJson" | py_jq --raw-output '.schemaVersion')"
	case "$schemaVersion" in
		2)
			mediaType="$(echo "$manifestJson" | py_jq --raw-output '.mediaType')"

			case "$mediaType" in
				application/vnd.docker.distribution.manifest.v2+json)
					handle_single_manifest_v2 "$manifestJson"
					;;
				application/vnd.docker.distribution.manifest.list.v2+json)
					layersFs="$(echo "$manifestJson" | py_jq --raw-output --compact-output '.manifests[]')"
					IFS="$newlineIFS"
					layers=( $layersFs )
					unset IFS

					found=""
					# parse first level multi-arch manifest
					for i in "${!layers[@]}"; do
						layerMeta="${layers[$i]}"
						maniArch="$(echo "$layerMeta" | py_jq --raw-output '.platform.architecture')"
						if [ "$maniArch" = "amd64" ]; then
							digest="$(echo "$layerMeta" | py_jq --raw-output '.digest')"
							# get second level single manifest
							submanifestJson="$(
								curl -fsSL \
									-H "Authorization: Bearer $token" \
									-H 'Accept: application/vnd.docker.distribution.manifest.v2+json' \
									-H 'Accept: application/vnd.docker.distribution.manifest.list.v2+json' \
									-H 'Accept: application/vnd.docker.distribution.manifest.v1+json' \
									"$registryBase/v2/$image/manifests/$digest"
							)"
							handle_single_manifest_v2 "$submanifestJson"
							found="found"
							break
						fi
					done
					if [ -z "$found" ]; then
						echo >&2 "error: manifest for $maniArch is not found"
						exit 1
					fi
					;;
				*)
					echo >&2 "error: unknown manifest mediaType ($imageIdentifier): '$mediaType'"
					exit 1
					;;
			esac
			;;

		1)
			if [ -z "$doNotGenerateManifestJson" ]; then
				echo >&2 "warning: '$imageIdentifier' uses schemaVersion '$schemaVersion'"
				echo >&2 "  this script cannot (currently) recreate the 'image config' to put in a 'manifest.json' (thus any schemaVersion 2+ images will be imported in the old way, and their 'docker history' will suffer)"
				echo >&2
				doNotGenerateManifestJson=1
			fi

			layersFs="$(echo "$manifestJson" | py_jq --raw-output '.fsLayers | .[] | .blobSum')"
			IFS="$newlineIFS"
			layers=( $layersFs )
			unset IFS

			history="$(echo "$manifestJson" | py_jq '.history | [.[] | .v1Compatibility]')"
			imageId="$(echo "$history" | py_jq --raw-output '.[0]' | py_jq --raw-output '.id')"

			echo "Downloading '$imageIdentifier' (${#layers[@]} layers)..."
			for i in "${!layers[@]}"; do
				imageJson="$(echo "$history" | py_jq --raw-output ".[${i}]")"
				layerId="$(echo "$imageJson" | py_jq --raw-output '.id')"
				imageLayer="${layers[$i]}"

				mkdir -p "$dir/$layerId"
				echo '1.0' > "$dir/$layerId/VERSION"

				echo "$imageJson" > "$dir/$layerId/json"

				# TODO figure out why "-C -" doesn't work here
				# "curl: (33) HTTP server doesn't seem to support byte ranges. Cannot resume."
				# "HTTP/1.1 416 Requested Range Not Satisfiable"
				if [ -f "$dir/$layerId/layer.tar" ]; then
					# TODO hackpatch for no -C support :'(
					echo "skipping existing ${layerId:0:12}"
					continue
				fi
				token="$(curl -fsSL "$authBase/token?service=$authService&scope=repository:$image:pull" | py_jq --raw-output '.token')"
				fetch_blob "$token" "$image" "$imageLayer" "$dir/$layerId/layer.tar" --progress
			done
			;;

		*)
			echo >&2 "error: unknown manifest schemaVersion ($imageIdentifier): '$schemaVersion'"
			exit 1
			;;
	esac

	echo

	if [ -s "$dir/tags-$imageFile.tmp" ]; then
		echo -n ', ' >> "$dir/tags-$imageFile.tmp"
	else
		images=( "${images[@]}" "$image" )
	fi
	echo -n '"'"$tag"'": "'"$imageId"'"' >> "$dir/tags-$imageFile.tmp"
done

echo -n '{' > "$dir/repositories"
firstImage=1
for image in "${images[@]}"; do
	imageFile="${image//\//_}" # "/" can't be in filenames :)
	image="${image#library\/}"

	[ "$firstImage" ] || echo -n ',' >> "$dir/repositories"
	firstImage=
	echo -n $'\n\t' >> "$dir/repositories"
	echo -n '"'"$image"'": { '"$(cat "$dir/tags-$imageFile.tmp")"' }' >> "$dir/repositories"
done
echo -n $'\n}\n' >> "$dir/repositories"

rm -f "$dir"/tags-*.tmp

if [ -z "$doNotGenerateManifestJson" ] && [ "${#manifestJsonEntries[@]}" -gt 0 ]; then
    ll=""; for e in "${manifestJsonEntries[@]}"; do ll="${ll}$e,"; done
    python -Ssc "import json; import sys; print(json.dumps([json.loads(k) for k in [$ll]], indent=4))"  > "$dir/manifest.json"
else
	rm -f "$dir/manifest.json"
fi

echo "Download of images into '$dir' complete."
echo "Use something like the following to load the result into a Docker daemon:"
echo "  tar -cC '$dir' . | docker load"