Get labels of remote docker image

user_806963 0
Viewed 3997

I'm trying to get the labels of an image without pulling it.

For example: in docker-hub, on my username (stavalfi), in repo: projecty: https://hub.docker.com/v2/repositories/stavalfi/projecty/tags

I want to get all the labels of this image.

Following this guide: https://hackernoon.com/inspecting-docker-images-without-pulling-them-4de53d34a604

and this: https://docs.docker.com/registry/spec/api/#pulling-a-layer

I tried to reach to: http://$REGISTRY_ADDRESS/v2/$image/blobs/$digest:

https://hub.docker.com/v2/stavalfi/projecty/blobs/sha256:7701c1411c0e438c5bfb1d7b4c1f337ee75b4a3a1d8492fc3b608cdc2b320a9d

but the result is a 404.

What is the problem?

I can't use skopeo because it can't inspect registries with an HTTP connection (insecure).

docker-registry docker
2 Answers

You can find the labels in the first layer of the docker manifest:

$ repo=stavalfi/k8test-monitoring                                                                                                                                                                                 

$ token=$(curl -s "https://auth.docker.io/token?service=registry.docker.io&scope=repository:${repo}:pull" \
  | jq -r '.token')

$ curl -s -H "Authorization: Bearer $token" "https://registry-1.docker.io/v2/${repo}/manifests/latest" \
  | jq ".history[0].v1Compatibility" -r | jq .config.Labels
{
  "latest-hash": "dc971f310bd0b172fd0379cc9a1810f209c9a9604a28da14cef36457",
  "latest-tag": "1.3.4"
}

Update: the v2 registry API is a bit cleaner, but needs one more curl:

$ repo=stavalfi/k8test-monitoring                                                                                                                                                                                 

$ token=$(curl -s "https://auth.docker.io/token?service=registry.docker.io&scope=repository:${repo}:pull" \
        | jq -r '.token')

$ digest=$(curl -s -H "Accept: application/vnd.docker.distribution.manifest.v2+json" -H "Authorization: Bearer $token" "https://registry-1.docker.io/v2/${repo}/manifests/latest" \
  | jq .config.digest -r)

$ curl -s -L -H "Accept: application/vnd.docker.distribution.manifest.v2+json" -H "Authorization: Bearer $token" "https://registry-1.docker.io/v2/${repo}/blobs/$digest" \
  | jq .config.Labels
{
  "latest-hash": "dc971f310bd0b172fd0379cc9a1810f209c9a9604a28da14cef36457",
  "latest-tag": "1.3.4"
}

For a more generic use case, here's a script to pull the config of any public image on docker hub without downloading the full image:

#!/bin/sh

repo=${1:-library/ubuntu}
tag=${2:-latest}
token=$(curl -s "https://auth.docker.io/token?service=registry.docker.io&scope=repository:${repo}:pull" \
        | jq -r '.token')
digest=$(curl -H "Accept: application/vnd.docker.distribution.manifest.v2+json" \
              -H "Authorization: Bearer $token" \
              -s "https://registry-1.docker.io/v2/${repo}/manifests/${tag}" | jq -r .config.digest)
curl -H "Accept: application/vnd.docker.distribution.manifest.v2+json" \
     -H "Authorization: Bearer $token" \
     -s -L "https://registry-1.docker.io/v2/${repo}/blobs/${digest}" | jq .

Just make sure to include the "library" prefix for official images:

$ ./get-config-v2.sh library/alpine 3.9
{
  "architecture": "amd64",
  "config": {
    "Hostname": "",
    "Domainname": "",
    "User": "",
    "AttachStdin": false,
    "AttachStdout": false,
    "AttachStderr": false,
    "Tty": false,
    "OpenStdin": false,
    "StdinOnce": false,
    "Env": [
      "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    ],
    "Cmd": [
      "/bin/sh"
    ],
    "ArgsEscaped": true,
    "Image": "sha256:186eda4636e895d982896312666e472a2d62aab1490608701e1b3438ac6649e7",
    "Volumes": null,
    "WorkingDir": "",
    "Entrypoint": null,
    "OnBuild": null,
    "Labels": null
  },
  ....

Since this answer was first posted, I've also created regclient which includes the command regctl. This handles authentication, allows you to configure a registry without TLS or with a self signed certificate, resolves multi-platform images, and includes support for Go templates to extract the specific fields you want:

$ regctl image config regclient/regsync:latest --format '{{ jsonPretty .Config.Labels }}'
{
  "maintainer": "",
  "org.opencontainers.image.authors": "Regclient contributors",
  "org.opencontainers.image.created": "2021-04-02T18:55:09Z",
  "org.opencontainers.image.description": "",
  "org.opencontainers.image.documentation": "https://github.com/regclient/regclient",
  "org.opencontainers.image.licenses": "Apache 2.0",
  "org.opencontainers.image.revision": "5a6a1d95524b9c1c2d38a5af7ab744742f8d55e9",
  "org.opencontainers.image.source": "git://github.com/regclient/regclient.git",
  "org.opencontainers.image.title": "regsync",
  "org.opencontainers.image.url": "https://github.com/regclient/regclient",
  "org.opencontainers.image.vendor": "",
  "org.opencontainers.image.version": "v0.3.0"
}
user_5962850

this worked for me, you can try this

curl 'https://registry.hub.docker.com/v2/repositories/< username>/<repo>/tags/'|jq '."results"[]["name"]'

regarding blob, token need to be generated then use this token for blob

export TOKEN=\
"$(curl \
--silent \
--header 'GET' \
"https://auth.docker.io/token? 
service=registry.docker.io&scope=repository:<username>/<repo>:pull,push" \
| jq -r '.token' \
)"

now get the manifest of the image

curl \
--silent \
--request 'GET' \
--header "Authorization: Bearer ${TOKEN}" \
'https://registry-1.docker.io/v2/<username>/<repo>/manifests/<latest>' \
| jq '.'

now get the blob for that image

curl \
--silent \
--request 'GET' \
--header "Authorization: Bearer ${TOKEN}" \
"https://registry-1.docker.io/v2/<username>/<repo>/manifests/19" \
| jq -r '.fsLayers[].blobSum'

the above command gives the list of digests which can be used to fetch the image
set the following variable

DIGEST=<SHA:somevalue>  

curl \
--silent \
--location \
--request GET \
--header "Authorization: Bearer ${TOKEN}" \
"https://registry-1.docker.io/v2/<username>/<repo>/blobs/${DIGEST}" > 
"${DIGEST/*:/}.gz"
user_73034150
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