write history as part of layer meta data.

[loosebazooka]

History might be necessary for some tools to work.

• add history fields to manifest object
• passthrough original history
• write jib layer history
• allow custom "created_by" field

expected format:

{
  "author": "Jib",
  "created": "1970-01-01T00:00:00Z", # or useCurrentTimeStamp
  "created_by": "jib" # or jib-gradle-plugin jib-maven-plugin (tool identifier)
}

[mattmoor]

$ crane config gcr.io/distroless/java/jetty@sha256:4bec71e275183f6306ea1bfe490dcf54732fcc7e37c137129ad30ed9dc62b99d | python -mjson.tool
{
    "architecture": "amd64",
    "author": "Bazel",
    "config": {
        "Cmd": [
            "/jetty/start.jar"
        ],
        "Entrypoint": [
            "/usr/bin/java",
            "-jar"
        ],
        "Env": [
            "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/busybox",
            "SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt"
        ],
        "ExposedPorts": {
            "8080/tcp": {}
        },
        "WorkingDir": "/jetty"
    },
    "created": "1970-01-01T00:00:00Z",
    "history": [
        {
            "author": "Bazel",
            "created": "1970-01-01T00:00:00Z",
            "created_by": "bazel build ..."
        },
        {
            "author": "Bazel",
            "created": "1970-01-01T00:00:00Z",
            "created_by": "bazel build ..."
        },
        {
            "author": "Bazel",
            "created": "1970-01-01T00:00:00Z",
            "created_by": "bazel build ..."
        },
        {
            "author": "Bazel",
            "created": "1970-01-01T00:00:00Z",
            "created_by": "bazel build ..."
        },
        {
            "author": "Bazel",
            "created": "1970-01-01T00:00:00Z",
            "created_by": "bazel build ..."
        }
    ],
    "os": "linux",
    "rootfs": {
        "diff_ids": [
            "sha256:c09300da45505100cbbad5ae5cd8f80389ed86a162e60f6fa211828ff3f80268",
            "sha256:6f1db24e440882e47a86c6cbad091e98fda9e57cbbcb0ff8e34b46e6a435b20a",
            "sha256:6189abe095d53c1c9f2bfc8f50128ee876b9a5d10f9eda1564e5f5357d6ffe61",
            "sha256:60a2d5e902b42d2ecece89489c92e17b417b93ec672c347a115f086b88e2e403",
            "sha256:08ab7965197fe6957bf795e2d6ee4d58d8402e02dc6771e814ab57a5597b707c"
        ],
        "type": "layers"
    }
}

Note that you can add history entries for empty layers (e.g. USER foo), but must add "empty_layer": true IIRC. The length of this list w/o empty_layers must match the diff_ids length and the length of layers in the manifest.

[coollog]

For created_by, perhaps we should use the tool identifier like we pass for the user agent, so it could be jib-maven-plugin, jib-gradle-plugin, jib-sbt-plugin, or jib for no identifier set.

For created (the time), it should probably respect the useCurrentTimestamp flag.