contrib/download-frozen-image-v2.sh
#!/usr/bin/env bash
set -eo pipefail
# This script was developed for use in Moby's CI, and as such the use cases and
# usability are (intentionally) limited. You may find this script useful for
# educational purposes, for example, to learn how pulling images works "under
# the hood", and you may be able to use it for other purposes, but it should not
# be considered a "general purpose" tool for pulling images.
#
# The project maintainers accept contributions to this script within its intended
# scope, but may not accept contributions beyond that.
#
# For users who have a similar need but require more flexibility/functionality,
# refer to the discussion on GitHub, which mentions various alternatives that
# are more suitable for other uses: https://github.com/moby/moby/issues/40857
# 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 jq; do
if ! command -v $cmd &> /dev/null; then
echo >&2 "error: \"$cmd\" not found!"
exit 1
fi
done
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
if ! [ $# -gt 0 ] && [ "$dir" ]; then
usage 2 >&2
fi
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... and linux doesn't seem to care either way
newlineIFS=$'\n'
major=$(echo "${BASH_VERSION%%[^0.9]}" | cut -d. -f1)
if [ "$major" -ge 4 ]; then
newlineIFS=$'\r\n'
fi
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
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 "$targetFile"
local blobRedirect
blobRedirect="$(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="$1"
shift
local configDigest
configDigest="$(echo "$manifestJson" | jq --raw-output '.config.digest')"
local imageId="${configDigest#*:}" # strip off "sha256:"
local configFile="$imageId.json"
fetch_blob "$token" "$image" "$configDigest" "$dir/$configFile" -s
local layersFs
layersFs="$(echo "$manifestJson" | jq --raw-output --compact-output '.layers[]')"
local IFS="$newlineIFS"
local layers
mapfile -t layers <<< "$layersFs"
unset IFS
echo "Downloading '$imageIdentifier' (${#layers[@]} layers)..."
local layerId=
local layerFiles=()
for i in "${!layers[@]}"; do
local layerMeta="${layers[$i]}"
local layerMediaType
layerMediaType="$(echo "$layerMeta" | jq --raw-output '.mediaType')"
local layerDigest
layerDigest="$(echo "$layerMeta" | jq --raw-output '.digest')"
# save the previous layer's ID
local parentId="$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
local parentJson
parentJson="$(printf ', parent: "%s"' "$parentId")"
local addJson
addJson="$(printf '{ id: "%s"%s }' "$layerId" "${parentId:+$parentJson}")"
# this starter JSON is taken directly from Docker's own "docker save" output for unimportant layers
jq "$addJson + ." > "$dir/$layerId/json" <<- 'EOJSON'
{
"created": "0001-01-01T00:00:00Z",
"container_config": {
"Hostname": "",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": null,
"Cmd": null,
"Image": "",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": null
}
}
EOJSON
fi
case "$layerMediaType" in
application/vnd.oci.image.layer.v1.tar+gzip | 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 ${layerId:0:12}"
continue
fi
local token
token="$(curl -fsSL "$authBase/token?service=$authService&scope=repository:$image:pull" | jq --raw-output '.token')"
fetch_blob "$token" "$image" "$layerDigest" "$dir/$layerTar" --progress-bar
;;
*)
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
imageOldConfig="$(jq --raw-output --compact-output '{ id: .id } + if .parent then { parent: .parent } else {} end' "$dir/$imageId/json")"
jq --raw-output "$imageOldConfig + del(.history, .rootfs)" "$dir/$configFile" > "$dir/$imageId/json"
local manifestJsonEntry
manifestJsonEntry="$(
echo '{}' | jq --raw-output --compact-output '. + {
Config: "'"$configFile"'",
RepoTags: ["'"${image#library\/}:$tag"'"],
Layers: '"$(echo '[]' | jq --raw-output --compact-output ".$(for layerFile in "${layerFiles[@]}"; do echo " + [ \"$layerFile\" ]"; done)")"'
}'
)"
manifestJsonEntries=("${manifestJsonEntries[@]}" "$manifestJsonEntry")
}
get_target_arch() {
if [ -n "${TARGETARCH:-}" ]; then
echo "${TARGETARCH}"
return 0
fi
if type go > /dev/null; then
go env GOARCH
return 0
fi
if type dpkg > /dev/null; then
debArch="$(dpkg --print-architecture)"
case "${debArch}" in
armel | armhf)
echo "arm"
return 0
;;
*64el)
echo "${debArch%el}le"
return 0
;;
*)
echo "${debArch}"
return 0
;;
esac
fi
if type uname > /dev/null; then
uArch="$(uname -m)"
case "${uArch}" in
x86_64)
echo amd64
return 0
;;
arm | armv[0-9]*)
echo arm
return 0
;;
aarch64)
echo arm64
return 0
;;
mips*)
echo >&2 "I see you are running on mips but I don't know how to determine endianness yet, so I cannot select a correct arch to fetch."
echo >&2 "Consider installing \"go\" on the system which I can use to determine the correct arch or specify it explicitly by setting TARGETARCH"
exit 1
;;
*)
echo "${uArch}"
return 0
;;
esac
fi
# default value
echo >&2 "Unable to determine CPU arch, falling back to amd64. You can specify a target arch by setting TARGETARCH"
echo amd64
}
get_target_variant() {
echo "${TARGETVARIANT:-}"
}
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" | jq --raw-output '.token')"
manifestJson="$(
curl -fsSL \
-H "Authorization: Bearer $token" \
-H 'Accept: application/vnd.oci.image.manifest.v1+json' \
-H 'Accept: application/vnd.oci.image.index.v1+json' \
-H 'Accept: application/vnd.docker.distribution.manifest.v2+json' \
-H 'Accept: application/vnd.docker.distribution.manifest.list.v2+json' \
-H 'Accept: application/vnd.docker.distribution.manifest.v1+json' \
"$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" | jq --raw-output '.schemaVersion')"
case "$schemaVersion" in
2)
mediaType="$(echo "$manifestJson" | jq --raw-output '.mediaType')"
case "$mediaType" in
application/vnd.oci.image.manifest.v1+json | application/vnd.docker.distribution.manifest.v2+json)
handle_single_manifest_v2 "$manifestJson"
;;
application/vnd.oci.image.index.v1+json | application/vnd.docker.distribution.manifest.list.v2+json)
layersFs="$(echo "$manifestJson" | jq --raw-output --compact-output '.manifests[]')"
IFS="$newlineIFS"
mapfile -t layers <<< "$layersFs"
unset IFS
found=""
targetArch="$(get_target_arch)"
targetVariant="$(get_target_variant)"
# parse first level multi-arch manifest
for i in "${!layers[@]}"; do
layerMeta="${layers[$i]}"
maniArch="$(echo "$layerMeta" | jq --raw-output '.platform.architecture')"
maniVariant="$(echo "$layerMeta" | jq --raw-output '.platform.variant')"
if [[ "$maniArch" = "${targetArch}" ]] && [[ -z "${targetVariant}" || "$maniVariant" = "${targetVariant}" ]]; then
digest="$(echo "$layerMeta" | jq --raw-output '.digest')"
# get second level single manifest
submanifestJson="$(
curl -fsSL \
-H "Authorization: Bearer $token" \
-H 'Accept: application/vnd.oci.image.manifest.v1+json' \
-H 'Accept: application/vnd.oci.image.index.v1+json' \
-H 'Accept: application/vnd.docker.distribution.manifest.v2+json' \
-H 'Accept: application/vnd.docker.distribution.manifest.list.v2+json' \
-H 'Accept: application/vnd.docker.distribution.manifest.v1+json' \
"$registryBase/v2/$image/manifests/$digest"
)"
handle_single_manifest_v2 "$submanifestJson"
found="found"
break
fi
done
if [ -z "$found" ]; then
echo >&2 "error: manifest for ${targetArch}${targetVariant:+/${targetVariant}} is not found"
exit 1
fi
;;
*)
echo >&2 "error: unknown manifest mediaType ($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" | jq --raw-output '.fsLayers | .[] | .blobSum')"
IFS="$newlineIFS"
mapfile -t layers <<< "$layersFs"
unset IFS
history="$(echo "$manifestJson" | jq '.history | [.[] | .v1Compatibility]')"
imageId="$(echo "$history" | jq --raw-output '.[0]' | jq --raw-output '.id')"
echo "Downloading '$imageIdentifier' (${#layers[@]} layers)..."
for i in "${!layers[@]}"; do
imageJson="$(echo "$history" | jq --raw-output ".[${i}]")"
layerId="$(echo "$imageJson" | 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:$image:pull" | jq --raw-output '.token')"
fetch_blob "$token" "$image" "$imageLayer" "$dir/$layerId/layer.tar" --progress-bar
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" ] && [ "${#manifestJsonEntries[@]}" -gt 0 ]; then
echo '[]' | jq --raw-output ".$(for entry in "${manifestJsonEntries[@]}"; do echo " + [ $entry ]"; done)" > "$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"