How to list images and tags from the gcr.io Docker

Question

I'm trying to fetch a list of available images and their tags from Google Container Registry (gcr.io) in Node.js.

I first use google-auto-auth to optain a token with scope https://www.googleapis.com/auth/devstorage.read_write, and I exchange that token for a gcr.io token like so:

axios.get('https://gcr.io/v2/token?service=gcr.io', {
  auth: {
    username: '_token',
    password: token // token I got from `google-auto-auth`
  }
})

I then try to use this to call the v2/_catalog endpoint:

axios.get('https://gcr.io/v2/_catalog', {
  headers: {
    Authorization: `Bearer ${gcrToken}`
  }
})

And I get the following error:

{ 
  errors: [ { code: 'DENIED', message: 'Failed to retrieve projects.' } ] 
}

Fair enough, it must require my project ID, but where am I supposed to provide it?

Just to see if I could get anything else working, I tried:

axios.get('https://gcr.io/v2/my-project-id/my-image/tags/list', {
  headers: {
    Authorization: `Bearer ${gcrToken}`
  }
})

And I get the following back:

{ 
  errors: [ 
    { 
      code: 'NAME_INVALID', 
      message: 'Requested repository does not match bearer token resource: my-project-id/my-image' 
    } 
  ] 
}

How can I read image info from gcr.io?

Answer 1

The first error is likely because you're missing one of the scopes for listing projects: https://cloud.google.com/resource-manager/reference/rest/v1/projects/list#authorization

You get the second error because you're missing the scope in your token exchange.

You want something like:

https://gcr.io/v2/token?service=gcr.io&scope=repository:<my-project-id/my-image>:*

See the example here: https://docs.docker.com/registry/spec/auth/token/#requesting-a-token

Answer 2

After extensive communication with Jon Johnson from GCR, we finally figured out what was wrong. If you upvote this answer, please upvote Jon's as well, he went above and beyond to get this issue resolved.

Most of this stuff is undocumented as of this writing.

• need to use the registry:catalog:* scope.
• my images were pushed to us.gcr.io, and they treat them as separate registries — I thought they were mirrors.
• the service account must have the Project Viewer role in Google Cloud IAM.
• you can use a GCR token, as well as a Google Cloud token. However while the GCR token cannot be used with Basic base64(_token:<token>), the Google Cloud token can.

Getting the GCR token

// Updated host
axios.get('https://us.gcr.io/v2/token?service=gcr.io', {
  params: {
    service: 'us.gcr.io',
    scope: `registry:catalog:*`
  },
  auth: {
    username: '_token',
    password: token // token I got from `google-auto-auth`
  },  
})

Using the token to list repositories

const client = axios.create({
  baseURL: `https://us.gcr.io/v2`,
  headers: {
    Authorization: `Bearer ${token}`
  }
})

client.get('/_catalog').then((response) => {
  console.log(response.data.repositories)
})