Question: diffs_ids and history

[jpetazzo]

In the example in the spec, the rootfs field has a list of two diff_ids, but the history field has only one non-empty layer:

    "rootfs": {
      "diff_ids": [
        "sha256:c6f988f4874bb0add23a778f753c65efe992244e148a1d2ec2a8b664fb66bbd1",
        "sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef"
      ],
      "type": "layers"
    },
    "history": [
      {
        "created": "2015-10-31T22:22:54.690851953Z",
        "created_by": "/bin/sh -c #(nop) ADD file:a3bc1e842b69636f9df5256c49c5374fb4eef1e281fe3f282c65fb853ee171c5 in /"
      },
      {
        "created": "2015-10-31T22:22:55.613815829Z",
        "created_by": "/bin/sh -c #(nop) CMD [\"sh\"]",
        "empty_layer": true
      }

I had the impression that we would have diff_ids (content hashes) only for non-empty layers. Is this a small typo/mistake in the example, or did I miss something?

Thank you! ♥

[cyphar]

Yeah I think that's a mistake in the example. empty_layer means there's no associated layer (so no diff_id). Maybe there should be another history entry afterwards in the example to make it (more) valid.