add go specs for artifact manifest (#17)

* add go specs for artifact manifest
* update mediaType
* define artifact descriptor
* remove dependency on opencontainers/image-spec by referencing the artifact-descriptor
Signed-off-by: Aviral Takkar <[email protected]>

Author: aviral26

go.mod

@@ -0,0 +1,5 @@
+module github.com/oras-project/artifacts-spec
+
+go 1.17
+
+require github.com/opencontainers/go-digest v1.0.0

go.sum

@@ -0,0 +1,2 @@
+github.com/opencontainers/go-digest v1.0.0 h1:apOUWs51W5PlhuyGyz9FCeeBIOUDA/6nW8Oi/yOhh5U=
+github.com/opencontainers/go-digest v1.0.0/go.mod h1:0JzlMkj0TRzQZfJkVvzbP0HBR3IKzErnv2BNG4W4MAM=

specs-go/v1/descriptor.go

@@ -0,0 +1,40 @@
+// Copyright 2021 ORAS Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package v1
+
+import digest "github.com/opencontainers/go-digest"
+
+// Descriptor describes the disposition of targeted content.
+type Descriptor struct {
+	// MediaType is the media type of the object this schema refers to.
+	MediaType string `json:"mediaType,omitempty"`
+
+	// ArtifactType is the artifact type of the object this schema refers to.
+	//
+	// When the descriptor is used for blobs, this property must be empty.
+	ArtifactType string `json:"artifactType"`
+
+	// Digest is the digest of the targeted content.
+	Digest digest.Digest `json:"digest"`
+
+	// Size specifies the size in bytes of the blob.
+	Size int64 `json:"size"`
+
+	// URLs specifies a list of URLs from which this object MAY be downloaded
+	URLs []string `json:"urls,omitempty"`
+
+	// Annotations contains arbitrary metadata relating to the targeted content.
+	Annotations map[string]string `json:"annotations,omitempty"`
+}

specs-go/v1/manifest.go

@@ -0,0 +1,35 @@
+// Copyright 2021 ORAS Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package v1
+
+// Manifest describes an ORAS artifact.
+// This structure provides `application/vnd.oras.artifact.manifest.v1+json` mediatype when marshalled to JSON.
+type Manifest struct {
+	// MediaType is the media type of the object this schema refers to.
+	MediaType string `json:"mediaType"`
+
+	// ArtifactType is the artifact type of the object this schema refers to.
+	ArtifactType string `json:"artifactType"`
+
+	// Blobs is a collection of blobs referenced by this manifest.
+	Blobs []Descriptor `json:"blobs"`
+
+	// SubjectManifest is an optional reference to any existing manifest within the repository.
+	// When specified, the artifact is said to be dependent upon the referenced subjectManifest.
+	SubjectManifest Descriptor `json:"subjectManifest"`
+
+	// Annotations contains arbitrary metadata for the artifact manifest.
+	Annotations map[string]string `json:"annotations,omitempty"`
+}

specs-go/v1/mediatype.go

@@ -0,0 +1,20 @@
+// Copyright 2021 ORAS Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package v1
+
+const (
+	// MediaTypeArtifactManifest specifies the media type for an ORAS artifact reference type manifest.
+	MediaTypeArtifactManifest = "application/vnd.cncf.oras.artifact.manifest.v1+json"
+)