Add artifactType to descriptor (#11)

Signed-off-by: Sajay Antony <sajaya@microsoft.com>

artifact.md

@@ -15,6 +15,10 @@ For the media type(s) that this is compatible with see the [matrix](media-types.
 
   This property MUST be used and contain the media type `application/vnd.oci.artifact.manifest.v1+json`.
 
+- **`artifactType`** *string*
+
+  This property SHOULD specify the mediaType of the referenced content and MAY be registered with [IANA][iana].
+
 - **`blobs`** *string*
 
   This OPTIONAL property contains a list of [descriptors](descriptor.md).
@@ -35,7 +39,7 @@ For the media type(s) that this is compatible with see the [matrix](media-types.
   The following annotations MAY be used:
 
   - `org.opencontainers.artifact.description`: human readable description for the artifact
-  - `org.opencontainers.artifact.created`: creation time of the artifact
+  - `org.opencontainers.artifact.created`: creation time of the artifact expressed as string defined by [RFC 3339][rfc-3339]
 
   Additionally, the following annotations SHOULD be used when deploying multi-arch container images:
 
@@ -56,6 +60,7 @@ For the media type(s) that this is compatible with see the [matrix](media-types.
 {
   "schemaVersion": 2,
   "mediaType": "application/vnd.oci.artifact.manifest.v1+json",
+  "artifactType" "application/example"
   "blobs": [
     {
       "mediaType": "application/vnd.icecream.flavor",
@@ -74,3 +79,6 @@ For the media type(s) that this is compatible with see the [matrix](media-types.
   ]
 }
 ```
+
+[iana]:         https://www.iana.org/assignments/media-types/media-types.xhtml
+[rfc-3339]:     https://tools.ietf.org/html/rfc3339#section-5.6

descriptor.md

@@ -56,8 +56,14 @@ The following fields contain the primary properties that constitute a Descriptor
   The decoded data MUST be identical to the referenced content and SHOULD be verified against the [`digest`](#digests) and `size` fields by content consumers.
   See [Embedded Content](#embedded-content) for when this is appropriate.
 
+- **`artifactType`** *string*
+
+  This OPTIONAL property contains the [IANA][iana] mediaType of the object when the descriptor is pointing to an [artifact manifest](artifact.md).
+
 Descriptors pointing to [`application/vnd.oci.image.manifest.v1+json`](manifest.md) SHOULD include the extended field `platform`, see [Image Index Property Descriptions](image-index.md#image-index-property-descriptions) for details.
 
+Descriptors pointing to [`application/vnd.oci.artifact.manifest.v1+json`](artifact.md) SHOULD include the extended field `artifactType`.
+
 ### Reserved
 
 Extended _Descriptor_ field additions proposed in other OCI specifications SHOULD first be considered for addition into this specification.
@@ -216,3 +222,4 @@ In the following example, the descriptor indicates the type of artifact it is re
 [rfc6838-s4.2]: https://tools.ietf.org/html/rfc6838#section-4.2
 [rfc7230-s2.7]: https://tools.ietf.org/html/rfc7230#section-2.7
 [sha256-vs-sha512]: https://groups.google.com/a/opencontainers.org/forum/#!topic/dev/hsMw7cAwrZE
+[iana]: https://www.iana.org/assignments/media-types/media-types.xhtml

media-types.md

@@ -13,6 +13,7 @@ The following media types identify the formats described here and their referenc
 - `application/vnd.oci.image.layer.nondistributable.v1.tar`: ["Layer", as a tar archive with distribution restrictions](layer.md#non-distributable-layers)
 - `application/vnd.oci.image.layer.nondistributable.v1.tar+gzip`: ["Layer", as a tar archive with distribution restrictions](layer.md#gzip-media-types) compressed with [gzip][rfc1952]
 - `application/vnd.oci.image.layer.nondistributable.v1.tar+zstd`: ["Layer", as a tar archive with distribution restrictions](layer.md#zstd-media-types) compressed with [zstd][rfc8478]
+- `application/vnd.oci.artifact.manifest.v1+json`: [Artifact manifest](artifact.md)
 
 ## Media Type Conflicts
 

specs-go/v1/descriptor.go

@@ -29,9 +29,6 @@ type Descriptor struct {
 	// Size specifies the size in bytes of the blob.
 	Size int64 `json:"size"`
 
-	// ArtifactType is the type of artifact this schema refers to.
-	ArtifactType string `json:"artifactType,omitempty"`
-
 	// URLs specifies a list of URLs from which this object MAY be downloaded
 	URLs []string `json:"urls,omitempty"`
 
@@ -47,6 +44,9 @@ type Descriptor struct {
 	//
 	// This should only be used when referring to a manifest.
 	Platform *Platform `json:"platform,omitempty"`
+
+	// ArtifactType is the IANA media type of this artifact.
+	ArtifactType string `json:"artifactType,omitempty"`
 }
 
 // Platform describes the platform which the image in the manifest runs on.