mirror of
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254 lines
8.9 KiB
Bash
254 lines
8.9 KiB
Bash
#!/bin/sh
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#
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# This script pulls and extracts all files from an image in Docker Hub.
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#
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# Copyright (c) 2020-2022, Jeremy Lin
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#
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# Permission is hereby granted, free of charge, to any person obtaining a
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# copy of this software and associated documentation files (the "Software"),
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# to deal in the Software without restriction, including without limitation
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# the rights to use, copy, modify, merge, publish, distribute, sublicense,
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# and/or sell copies of the Software, and to permit persons to whom the
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# Software is furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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# DEALINGS IN THE SOFTWARE.
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PLATFORM_DEFAULT="linux/amd64"
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PLATFORM="${PLATFORM_DEFAULT}"
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OUT_DIR="./output"
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usage() {
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echo "This script pulls and extracts all files from an image in Docker Hub."
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echo
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echo "$0 [OPTIONS...] IMAGE[:REF]"
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echo
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echo "IMAGE can be a community user image (like 'some-user/some-image') or a"
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echo "Docker official image (like 'hello-world', which contains no '/')."
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echo
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echo "REF is either a tag name or a full SHA-256 image digest (with a 'sha256:' prefix)."
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echo
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echo "Options:"
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echo
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echo " -p PLATFORM Pull image for the specified platform (default: ${PLATFORM})"
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echo " For a given image on Docker Hub, the 'Tags' tab lists the"
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echo " platforms supported for that image."
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echo " -o OUT_DIR Extract image to the specified output dir (default: ${OUT_DIR})"
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echo " -h Show help with usage examples"
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}
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usage_detailed() {
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usage
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echo
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echo "Examples:"
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echo
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echo "# Pull and extract all files in the 'hello-world' image tagged 'latest'."
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echo "\$ $0 hello-world:latest"
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echo
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echo "# Same as above; ref defaults to the 'latest' tag."
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echo "\$ $0 hello-world"
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echo
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echo "# Pull the 'hello-world' image for the 'linux/arm64/v8' platform."
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echo "\$ $0 -p linux/arm64/v8 hello-world"
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echo
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echo "# Pull an image by digest."
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echo "\$ $0 hello-world:sha256:90659bf80b44ce6be8234e6ff90a1ac34acbeb826903b02cfa0da11c82cbc042"
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}
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if [ $# -eq 0 ]; then
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usage_detailed
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exit 0
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fi
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while getopts ':ho:p:' opt; do
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case $opt in
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o)
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OUT_DIR="${OPTARG}"
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;;
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p)
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PLATFORM="${OPTARG}"
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;;
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h)
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usage_detailed
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exit 0
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;;
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\?)
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echo "ERROR: Invalid option '-$OPTARG'"
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echo
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usage
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exit 1
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;;
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\:) echo "ERROR: Argument required for option '-$OPTARG'"
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echo
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usage
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exit 1
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;;
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esac
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done
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shift $(($OPTIND - 1))
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have_curl() {
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command -v curl >/dev/null
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}
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have_wget() {
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command -v wget >/dev/null
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}
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if ! have_curl && ! have_wget; then
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echo "This script requires either curl or wget."
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exit 1
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fi
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image_spec="$1"
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image="${image_spec%%:*}"
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if [ "${image#*/}" = "${image}" ]; then
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# Docker official images are in the 'library' namespace.
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image="library/${image}"
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fi
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ref="${image_spec#*:}"
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if [ "${ref}" = "${image_spec}" ]; then
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echo "Defaulting ref to tag 'latest'..."
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ref=latest
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fi
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# Split platform (OS/arch/variant) into separate variables.
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# A platform specifier doesn't always include the `variant` component.
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OLD_IFS="${IFS}"
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IFS=/ read -r OS ARCH VARIANT <<EOF
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${PLATFORM}
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EOF
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IFS="${OLD_IFS}"
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# Given a JSON input on stdin, extract the string value associated with the
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# specified key. This avoids an extra dependency on a tool like `jq`.
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extract() {
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local key="$1"
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# Extract "<key>":"<val>" (assumes key/val won't contain double quotes).
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# The colon may have whitespace on either side.
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grep -o "\"${key}\"[[:space:]]*:[[:space:]]*\"[^\"]\+\"" |
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# Extract just <val> by deleting the last '"', and then greedily deleting
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# everything up to '"'.
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sed -e 's/"$//' -e 's/.*"//'
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}
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# Fetch a URL to stdout. Up to two header arguments may be specified:
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#
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# fetch <url> [name1: value1] [name2: value2]
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#
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fetch() {
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if have_curl; then
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if [ $# -eq 2 ]; then
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set -- -H "$2" "$1"
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elif [ $# -eq 3 ]; then
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set -- -H "$2" -H "$3" "$1"
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fi
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curl -sSL "$@"
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else
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if [ $# -eq 2 ]; then
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set -- --header "$2" "$1"
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elif [ $# -eq 3 ]; then
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set -- --header "$2" --header "$3" "$1"
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fi
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wget -qO- "$@"
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fi
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}
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# https://docs.docker.com/docker-hub/api/latest/#tag/repositories
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manifest_list_url="https://hub.docker.com/v2/repositories/${image}/tags/${ref}"
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# If we're pulling the image for the default platform, or the ref is already
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# a SHA-256 image digest, then we don't need to look up anything.
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if [ "${PLATFORM}" = "${PLATFORM_DEFAULT}" ] || [ -z "${ref##sha256:*}" ]; then
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digest="${ref}"
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else
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echo "Getting multi-arch manifest list..."
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digest=$(fetch "${manifest_list_url}" |
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# Break up the single-line JSON output into separate lines by adding
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# newlines before and after the chars '[', ']', '{', and '}'.
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sed -e 's/\([][{}]\)/\n\1\n/g' |
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# Extract the "images":[...] list.
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sed -n '/"images":/,/]/ p' |
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# Each image's details are now on a separate line, e.g.
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# "architecture":"arm64","features":"","variant":"v8","digest":"sha256:054c85801c4cb41511b176eb0bf13a2c4bbd41611ddd70594ec3315e88813524","os":"linux","os_features":"","os_version":null,"size":828724,"status":"active","last_pulled":"2022-09-02T22:46:48.240632Z","last_pushed":"2022-09-02T00:42:45.69226Z"
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# The image details are interspersed with lines of stray punctuation,
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# so grep for an arbitrary string that must be in these lines.
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grep architecture |
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# Search for an image that matches the platform.
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while read -r image; do
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# Arch is probably most likely to be unique, so check that first.
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arch="$(echo ${image} | extract 'architecture')"
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if [ "${arch}" != "${ARCH}" ]; then continue; fi
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os="$(echo ${image} | extract 'os')"
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if [ "${os}" != "${OS}" ]; then continue; fi
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variant="$(echo ${image} | extract 'variant')"
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if [ "${variant}" = "${VARIANT}" ]; then
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echo ${image} | extract 'digest'
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break
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fi
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done)
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fi
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if [ -n "${digest}" ]; then
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echo "Platform ${PLATFORM} resolved to '${digest}'..."
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else
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echo "No image digest found. Verify that the image, ref, and platform are valid."
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exit 1
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fi
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# https://docs.docker.com/registry/spec/auth/token/#how-to-authenticate
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api_token_url="https://auth.docker.io/token?service=registry.docker.io&scope=repository:$image:pull"
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# https://github.com/docker/distribution/blob/master/docs/spec/api.md#pulling-an-image-manifest
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manifest_url="https://registry-1.docker.io/v2/${image}/manifests/${digest}"
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# https://github.com/docker/distribution/blob/master/docs/spec/api.md#pulling-a-layer
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blobs_base_url="https://registry-1.docker.io/v2/${image}/blobs"
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echo "Getting API token..."
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token=$(fetch "${api_token_url}" | extract 'token')
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auth_header="Authorization: Bearer $token"
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v2_header="Accept: application/vnd.docker.distribution.manifest.v2+json"
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echo "Getting image manifest for $image:$ref..."
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layers=$(fetch "${manifest_url}" "${auth_header}" "${v2_header}" |
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# Extract `digest` values only after the `layers` section appears.
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sed -n '/"layers":/,$ p' |
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extract 'digest')
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if [ -z "${layers}" ]; then
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echo "No layers returned. Verify that the image and ref are valid."
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exit 1
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fi
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mkdir -p "${OUT_DIR}"
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for layer in $layers; do
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hash="${layer#sha256:}"
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echo "Fetching and extracting layer ${hash}..."
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fetch "${blobs_base_url}/${layer}" "${auth_header}" | gzip -d | tar -C "${OUT_DIR}" -xf -
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# Ref: https://github.com/moby/moby/blob/master/image/spec/v1.2.md#creating-an-image-filesystem-changeset
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# https://github.com/moby/moby/blob/master/pkg/archive/whiteouts.go
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# Search for "whiteout" files to indicate files deleted in this layer.
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OLD_IFS="${IFS}"
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find "${OUT_DIR}" -name '.wh.*' | while IFS= read -r f; do
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dir="${f%/*}"
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wh_file="${f##*/}"
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file="${wh_file#.wh.}"
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# Delete both the whiteout file and the whited-out file.
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rm -rf "${dir}/${wh_file}" "${dir}/${file}"
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done
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IFS="${OLD_IFS}"
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done
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echo "Image contents extracted into ${OUT_DIR}."
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