Ensure New Layers Match Image Media Type

[loganprice]

Fixes #1836 in case of a bug fix, this should point to a bug and any other related issue(s)

Description

Before adding a layer to an image check the images manifest media type and then add the layer with the corresponding media type.

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Adds integration tests if needed.

See the contribution guide for more details.

Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

Release Notes

Describe any changes here so maintainer can include it in the release notes, or delete this block.

[aaron-prindle]

Thanks for the PR here @loganprice! Just tested this using the repro identified in #1836 and looks like it’s working great! Adding my testing results below for others who might be looking at this:

Build an OCI base image named [gcr.io/<repo-name>/base-image:latest](http://gcr.io/<repo-name>/base-image:latest) using podman with the below Containerfile:

Containerfile

FROM docker.io/alpine
RUN touch file.txt
RUN echo "hello world"

Results in the following layers[i].mediaType: application/vnd.oci.image.layer.v1.tar+gzip

$ skopeo inspect --raw docker://gcr.io/<repo-name>/base-image:latest | jq .
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.oci.image.config.v1+json",
    "digest": "sha256:082ee62d11b7c4331131e2cd1b522b72b5904511112a0f3087785100428cd9e8",
    "size": 1030
  },
  "layers": [
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "digest": "sha256:97d7b294855ea22919bd873ce14c0bde0ba6702a2324133153d589153d96bd93",
      "size": 3494996
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "digest": "sha256:74acd493e8f8a8c3228561a31428b7cb0960e5dbc2abce49fa7e46f4a63b721e",
      "size": 164
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "digest": "sha256:bd9ddc54bea929a22b334e73e026d4136e5b73f5cc29942896c72e4ece69b13d",
      "size": 34
    }
  ],
  "annotations": {
    "org.opencontainers.image.base.digest": "sha256:17e69582475dc2e805ddda4d09c2c089349a6f8d5cb11b2ff632edcd6587b981",
    "org.opencontainers.image.base.name": "docker.io/library/alpine:latest"
  }
}

Then an image is built FROM that OCI image using kaniko w/ the following Dockerfile:

Dockerfile

FROM ubuntu:20.04 as installer
ADD installer.sh .
RUN bash installer.sh
######################
FROM gcr.io/<repo-name>/base-image:latest
COPY --from=installer /opt/application /opt/application
RUN ln -s /opt/application/1.0.0 /opt/application/stable
CMD ["/bin/bash"]

Where [installer.sh](http://installer.sh/) is

mkdir -p /opt/application/1.0.0
touch /opt/application/1.0.0/file.txt
touch /opt/application/1.0.0/file2.txt
touch /opt/application/1.0.0/file3.txt

Using kaniko @ HEAD (w/o this PR) the results incorrectly have layers[i].mediaType values of both application/vnd.oci.image.layer.v1.tar+gzip and application/vnd.docker.image.rootfs.diff.tar.gzip

$ skopeo inspect --raw docker://gcr.io/<repo-name>/kaniko-test:latest | jq .
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.oci.image.config.v1+json",
    "size": 1429,
    "digest": "sha256:84e146bb9a534436347a6d049fc9cfeac220953643eb4129ab6b9f483c370b9d"
  },
  "layers": [
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 3494996,
      "digest": "sha256:97d7b294855ea22919bd873ce14c0bde0ba6702a2324133153d589153d96bd93"
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 164,
      "digest": "sha256:74acd493e8f8a8c3228561a31428b7cb0960e5dbc2abce49fa7e46f4a63b721e"
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 34,
      "digest": "sha256:bd9ddc54bea929a22b334e73e026d4136e5b73f5cc29942896c72e4ece69b13d"
    },
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 496,
      "digest": "sha256:7a82e9349afca5356b19dee04d8e277cf6170b43db5582e373f40adfc6ad80a2"
    },
    {
      "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip",
      "size": 437,
      "digest": "sha256:f540484ad5d323a207c600052483ac30177ed3ad08620b249c6e8b5981897d4c"
    }
  ],
  "annotations": {
    "org.opencontainers.image.base.digest": "sha256:17e69582475dc2e805ddda4d09c2c089349a6f8d5cb11b2ff632edcd6587b981",
    "org.opencontainers.image.base.name": "docker.io/library/alpine:latest"
  }
}

Using kaniko w/ this PR the results corretly have a layers[i].mediaType of application/vnd.oci.image.layer.v1.tar+gzip

$ skopeo inspect --raw docker://gcr.io/<repo-name>/kaniko-test:latest | jq .
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.manifest.v1+json",
  "config": {
    "mediaType": "application/vnd.oci.image.config.v1+json",
    "size": 1429,
    "digest": "sha256:9600df3e927f23d9bb1fd158be7051a5b0949b89010ced63100b9b52738f337a"
  },
  "layers": [
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 3494996,
      "digest": "sha256:97d7b294855ea22919bd873ce14c0bde0ba6702a2324133153d589153d96bd93"
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 164,
      "digest": "sha256:74acd493e8f8a8c3228561a31428b7cb0960e5dbc2abce49fa7e46f4a63b721e"
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 34,
      "digest": "sha256:bd9ddc54bea929a22b334e73e026d4136e5b73f5cc29942896c72e4ece69b13d"
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 501,
      "digest": "sha256:aa79049a3805626f7d09dc2acef48525fc0e4922df5f953377c7b083043ab9bb"
    },
    {
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 433,
      "digest": "sha256:b59c2d0b1062f64dc3f00ef2ebf9d6691ff4d6139a649ecd75f95fc2235d8e4c"
    }
  ],
  "annotations": {
    "org.opencontainers.image.base.digest": "sha256:17e69582475dc2e805ddda4d09c2c089349a6f8d5cb11b2ff632edcd6587b981",
    "org.opencontainers.image.base.name": "docker.io/library/alpine:latest"
  }
}

[aaron-prindle]

LGTM, thanks for the PR here @loganprice!