Question: list vs YAML array for inputs

[tpolekhin]

Hello!
I was wondering why use multi-line string list instead of YAML array for inputs?
Maybe it's a technical limitation and it's okay if so I just wanted to check.

I'm trying to pass build args to the docker build with meta information and having difficulties because of this list type.
https://github.com/docker/metadata-action provides an easy way to inject meta labels for the container,
exporting a list of OCI labels that you can then use for labels: input. I guess they used a list type for their output to match this action input type.

I'm trying to reuse some of them as build args to also inject this information into the app binary, but it doesn't work because steps.meta.outputs.labels is not an array. I was looking around for a conversion function or tool that would help me to get this values out of labels, but couldn't find anything.

      - name: Prepare image metadata
        uses: docker/metadata-action@v3
        id: meta
        with:
          images: repo/app

      - name: Build and push docker image
        uses: docker/build-push-action@v2
        with:
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          build-args: |
            BUILDTIME=${{ steps.meta.outputs.labels['org.opencontainers.image.created'] }}
            VERSION=${{ steps.meta.outputs.labels['org.opencontainers.image.version'] }}
            REVISION=${{ steps.meta.outputs.labels['org.opencontainers.image.revision'] }}

I think it would be more convenient to work with JSON/YAML Arrays, just because there's a lot more supported tooling and operations than for just a list of strings.

Curious to get your opinion on this

[crazy-max]

@tpolekhin

I was wondering why use multi-line string list instead of YAML array for inputs?
Maybe it's a technical limitation and it's okay if so I just wanted to check.

This is a limitation with the GitHub Actions toolkit itself yes (actions/toolkit#184).

I guess they used a list type for their output to match this action input type.

The separator used by the metadata action for tags or labels output is lf (\n).

I'm trying to reuse some of them as build args to also inject this information into the app binary, but it doesn't work because steps.meta.outputs.labels is not an array.

We could output labels, tags and other info using a JSON representation with a new output for this purpose:

{
  "tags": [
    "name/app:1.2.3",
    "name/app:1.2",
    "name/app:sha-90dd603",
    "name/app:latest"
  ],
  "labels": {
    "org.opencontainers.image.title": "Hello-World",
    "org.opencontainers.image.description": "This your first repo!",
    "org.opencontainers.image.url": "https://github.com/octocat/Hello-World",
    "org.opencontainers.image.source": "https://github.com/octocat/Hello-World",
    "org.opencontainers.image.version": "1.2.3",
    "org.opencontainers.image.created": "2020-01-10T00:30:00.000Z",
    "org.opencontainers.image.revision": "90dd6032fac8bda1b6c4436a2e65de27961ed071",
    "org.opencontainers.image.licenses": "MIT"
  }
}

This way you could use the fromJSON function expression to handle that:

      - name: Prepare image metadata
        uses: docker/metadata-action@v3
        id: meta
        with:
          images: repo/app

      - name: Build and push docker image
        uses: docker/build-push-action@v2
        with:
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          build-args: |
            BUILDTIME=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.created'] }}
            VERSION=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.version'] }}
            REVISION=${{ fromJSON(steps.meta.outputs.json).labels['org.opencontainers.image.revision'] }}

[tpolekhin]

Thank you for a quick response on that!
Currently I use workaround, pretty similar to what you proposed actually :)

      - name: Extract meta image labels
        id: extract
        run: echo ::set-output name=labels::$(jq -r -c '.target."docker-metadata-action".labels' ${{ steps.meta.outputs.bake-file }})

      - name: Build and push operator image
        uses: docker/build-push-action@v2
        with:
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          build-args: |
            BUILDTIME=${{ fromJSON(steps.extract.outputs.labels)['org.opencontainers.image.created'] }}
            VERSION=${{ fromJSON(steps.extract.outputs.labels)['org.opencontainers.image.version'] }}
            REVISION=${{ fromJSON(steps.extract.outputs.labels)['org.opencontainers.image.revision'] }}

I would definitely appreciate if you can add json format output so I can throw away this intermediate step

[crazy-max]

@tpolekhin Ok thanks for your feedback. I move this issue to the metadata repo.

[crazy-max]

@tpolekhin You can try with docker/metadata-action@master.

[tpolekhin]

@crazy-max Works perfectly! Thanks!
https://github.com/tpolekhin/actions-playground/runs/2650265161

Are you planning to release a new version?
I'm a little concerned to use @master in the real pipeline

[crazy-max]

@tpolekhin Yes in few minutes