Clarify mediaType and artifactType syntax

Signed-off-by: Brandon Mitchell <[email protected]>

descriptor.md

@@ -19,7 +19,7 @@ The following fields contain the primary properties that constitute a Descriptor
 - **`mediaType`** *string*
 
   This REQUIRED property contains the media type of the referenced content.
-  Values MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2].
+  Values MUST comply with the [media type syntax](media-types.md#media-type-syntax).
 
   The OCI image specification defines [several of its own MIME types](media-types.md) for resources defined in the specification.
 
@@ -56,7 +56,7 @@ The following fields contain the primary properties that constitute a Descriptor
 
   This OPTIONAL property contains the type of an artifact when the descriptor points to an artifact.
   This is the value of the config descriptor `mediaType` when the descriptor references an [image manifest](manifest.md).
-  If defined, the value MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2], and MAY be registered with [IANA][iana].
+  If defined, the value MUST comply with the [media type syntax](media-types.md#media-type-syntax).
 
 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.
 
@@ -214,8 +214,5 @@ In the following example, the descriptor indicates the type of artifact it is re
 [rfc4634-s4.1]: https://tools.ietf.org/html/rfc4634#section-4.1
 [rfc4634-s4.2]: https://tools.ietf.org/html/rfc4634#section-4.2
 [rfc4648-s4]: https://tools.ietf.org/html/rfc4648#section-4
-[rfc6838]: https://tools.ietf.org/html/rfc6838
-[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

image-index.md

@@ -25,7 +25,7 @@ For the media type(s) that this document is compatible with, see the [matrix][ma
 - **`artifactType`** *string*
 
   This OPTIONAL property contains the type of an artifact when the manifest is used for an artifact.
-  If defined, the value MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2], and MAY be registered with [IANA][iana].
+  If defined, the value MUST comply with the [media type syntax](media-types.md#media-type-syntax).
 
 - **`manifests`** *array of objects*
 
@@ -183,8 +183,5 @@ These values SHOULD match (or be similar to) their analog listed in [the Go Lang
 
 [dag]:             https://en.wikipedia.org/wiki/Merkle_tree
 [go-environment2]: https://golang.org/doc/install/source#environment
-[iana]:            https://www.iana.org/assignments/media-types/media-types.xhtml
 [matrix]:          media-types.md#compatibility-matrix
 [referrers-api]:   https://github.com/opencontainers/distribution-spec/blob/main/spec.md#listing-referrers
-[rfc6838]:         https://tools.ietf.org/html/rfc6838
-[rfc6838-s4.2]:    https://tools.ietf.org/html/rfc6838#section-4.2

manifest.md

@@ -30,7 +30,7 @@ Unlike the [image index](image-index.md), which contains information about a set
 
   This OPTIONAL property contains the type of an artifact when the manifest is used for an artifact.
   This MUST be set when `config.mediaType` is set to the [empty value](#guidance-for-an-empty-descriptor).
-  If defined, the value MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2], and MAY be registered with [IANA][iana].
+  If defined, the value MUST comply with the [media type syntax](media-types.md#media-type-syntax).
   Implementations storing or copying image manifests MUST NOT error on encountering an `artifactType` that is unknown to the implementation.
 
 - **`config`** *[descriptor](descriptor.md)*
@@ -53,7 +53,7 @@ Unlike the [image index](image-index.md), which contains information about a set
     Manifests for container images concerned with portability SHOULD use one of the above media types.
     Manifests for artifacts concerned with portability SHOULD use `config.mediaType` as described in [Guidelines for Artifact Usage](#guidelines-for-artifact-usage).
 
-    If the manifest uses a different media type than the above, it MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2], and MAY be registered with [IANA][iana].
+    If the manifest uses a different media type than the above, it MUST comply with the [media type syntax](media-types.md#media-type-syntax).
 
   To set an effectively null or empty config and maintain portability see the [guidance for an empty descriptor](#guidance-for-an-empty-descriptor) below, and `DescriptorEmptyJSON` of the reference code.
 
@@ -89,7 +89,7 @@ Unlike the [image index](image-index.md), which contains information about a set
 
     Entries in this field will frequently use the `+gzip` types.
 
-    If the manifest uses a different media type than the above, it MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2], and MAY be registered with [IANA][iana].
+    If the manifest uses a different media type than the above, it MUST comply with the [media type syntax](media-types.md#media-type-syntax).
 
   See [Guidelines for Artifact Usage](#guidelines-for-artifact-usage) for other uses of the `layers`.
 
@@ -260,7 +260,4 @@ The decision tree below and the associated examples MAY be used to design new ar
 _Implementers note:_ artifacts have historically been created without an `artifactType` field, and tooling to work with artifacts should fallback to the `config.mediaType` value.
 
 [dag]:           https://en.wikipedia.org/wiki/Merkle_tree
-[iana]:          https://www.iana.org/assignments/media-types/media-types.xhtml
 [referrers-api]: https://github.com/opencontainers/distribution-spec/blob/main/spec.md#listing-referrers
-[rfc6838]:       https://tools.ietf.org/html/rfc6838
-[rfc6838-s4.2]:  https://tools.ietf.org/html/rfc6838#section-4.2

media-types.md

@@ -18,6 +18,17 @@ The following media types identify a ["Layer" with distribution restrictions](la
 - `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]
 
+## Media Type Syntax
+
+Media types values MUST comply with [RFC 6838][rfc6838], including the [naming requirements in its section 4.2][rfc6838-s4.2], and MAY be registered with [IANA][iana].
+Media types values MUST have a top-level type and subtype name, separated by a `/`, without any parameters.
+
+The following regular expression may be used to validate media types:
+
+```regexp
+^[A-Za-z0-9][A-Za-z0-9!#$&^_.+-]{0,126}/[A-Za-z0-9][A-Za-z0-9!#$&^_.+-]{0,126}$
+```
+
 ## Media Type Conflicts
 
 [Blob](image-layout.md) retrieval methods MAY return media type metadata.
@@ -86,5 +97,8 @@ The following figure shows how the above media types reference each other:
 [Descriptors](descriptor.md) are used for all references.
 The image-index being a "fat manifest" references a list of image manifests per target platform. An image manifest references exactly one target configuration and possibly many layers.
 
-[rfc1952]: https://tools.ietf.org/html/rfc1952
-[rfc8478]: https://tools.ietf.org/html/rfc8478
+[iana]:          https://www.iana.org/assignments/media-types/media-types.xhtml
+[rfc1952]:       https://tools.ietf.org/html/rfc1952
+[rfc6838]:       https://tools.ietf.org/html/rfc6838
+[rfc6838-s4.2]:  https://tools.ietf.org/html/rfc6838#section-4.2
+[rfc8478]:       https://tools.ietf.org/html/rfc8478

schema/descriptor_test.go

@@ -259,6 +259,19 @@ func TestDescriptor(t *testing.T) {
 			fail: true,
 		},
 
+		// expected failure: artifactType does not match pattern (parameters not allowed)
+		{
+			descriptor: `
+		{
+			"mediaType": "application/vnd.oci.image.manifest.v1+json",
+			"artifactType": "foo/star.bar;version=1.0",
+			"size": 7682,
+			"digest": "sha256:5b0bcabd1ed22e9fb1310cf6c2dec7cdef19f0ad69efa1f392e94a4333501270"
+		}
+		`,
+			fail: true,
+		},
+
 		// expected success: data field is present and has base64 content
 		{
 			descriptor: `

schema/manifest_test.go

@@ -336,6 +336,30 @@ func TestManifest(t *testing.T) {
 `,
 			fail: false,
 		},
+
+		// invalid artifactType value
+		{
+			manifest: `
+{
+  "schemaVersion": 2,
+  "mediaType" : "application/vnd.oci.image.manifest.v1+json",
+  "artifactType": "application/vnd.example+type;revision=1.5",
+  "config": {
+    "mediaType": "application/vnd.oci.empty.v1+json",
+    "size": 2,
+    "digest": "sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a"
+  },
+  "layers": [
+    {
+      "mediaType": "application/vnd.example+type;revision=1.5",
+      "size": 675598,
+      "digest": "sha256:9d3dd9504c685a304985025df4ed0283e47ac9ffa9bd0326fddf4d59513f0827"
+    }
+  ]
+}
+`,
+			fail: true,
+		},
 	} {
 		r := strings.NewReader(tt.manifest)
 		err := schema.ValidatorMediaTypeManifest.Validate(r)