imagetools: fix merging JSON descriptor with old one

commands/imagetools/create.go

@@ -118,7 +118,15 @@ func runCreate(dockerCli command.Cli, in createOptions, args []string) error {
 						return err
 					}
 					srcs[i].Ref = nil
-					srcs[i].Desc = desc
+					if srcs[i].Desc.Digest == "" {
+						srcs[i].Desc = desc
+					} else {
+						var err error
+						srcs[i].Desc, err = mergeDesc(desc, srcs[i].Desc)
+						if err != nil {
+							return err
+						}
+					}
 					return nil
 				})
 			}(i)
@@ -238,3 +246,19 @@ func createCmd(dockerCli command.Cli) *cobra.Command {
 
 	return cmd
 }
+
+func mergeDesc(d1, d2 ocispec.Descriptor) (ocispec.Descriptor, error) {
+	if d2.Size != 0 && d1.Size != d2.Size {
+		return ocispec.Descriptor{}, errors.Errorf("invalid size mismatch for %s, %d != %d", d1.Digest, d2.Size, d1.Size)
+	}
+	if d2.MediaType != "" {
+		d1.MediaType = d2.MediaType
+	}
+	if len(d2.Annotations) != 0 {
+		d1.Annotations = d2.Annotations // no merge so support removes
+	}
+	if d2.Platform != nil {
+		d1.Platform = d2.Platform // missing items filled in later from image config
+	}
+	return d1, nil
+}

docs/reference/buildx_imagetools_create.md

@@ -50,6 +50,19 @@ Use the `--dry-run` flag to not push the image, just show it.
 Reads source from files. A source can be a manifest digest, manifest reference,
 or a JSON of OCI descriptor object.
 
+In order to define annotations or additional platform properties like `os.version` and
+`os.features` you need to add them in the OCI descriptor object encoded in JSON.
+
+```
+docker buildx imagetools inspect --raw alpine | jq '.manifests[0] | .platform."os.version"="10.1"' > descr.json
+docker buildx imagetools create -f descr.json myuser/image
+```
+
+The descriptor in the file is merged with existing descriptor in the registry if it exists.
+
+The supported fields for the descriptor are defined in [OCI spec](https://github.com/opencontainers/image-spec/blob/master/descriptor.md#properties) .
+
+
 ### <a name="tag"></a> Set reference for new image  (-t, --tag)
 
 ```

util/imagetools/create.go

@@ -47,13 +47,16 @@ func (r *Resolver) Combine(ctx context.Context, in string, descs []ocispec.Descr
 
 				switch mt {
 				case images.MediaTypeDockerSchema2Manifest, ocispec.MediaTypeImageManifest:
+					p := descs[i].Platform
 					if descs[i].Platform == nil {
-						p, err := r.loadPlatform(ctx, in, dt)
-						if err != nil {
+						p = &ocispec.Platform{}
+					}
+					if p.OS == "" || p.Architecture == "" {
+						if err := r.loadPlatform(ctx, p, in, dt); err != nil {
 							return err
 						}
-						descs[i].Platform = p
 					}
+					descs[i].Platform = p
 				case images.MediaTypeDockerSchema1Manifest:
 					return errors.Errorf("schema1 manifests are not allowed in manifest lists")
 				}
@@ -166,24 +169,35 @@ func (r *Resolver) Push(ctx context.Context, ref reference.Named, desc ocispec.D
 	return err
 }
 
-func (r *Resolver) loadPlatform(ctx context.Context, in string, dt []byte) (*ocispec.Platform, error) {
+func (r *Resolver) loadPlatform(ctx context.Context, p2 *ocispec.Platform, in string, dt []byte) error {
 	var manifest ocispec.Manifest
 	if err := json.Unmarshal(dt, &manifest); err != nil {
-		return nil, errors.WithStack(err)
+		return errors.WithStack(err)
 	}
 
 	dt, err := r.GetDescriptor(ctx, in, manifest.Config)
 	if err != nil {
-		return nil, err
+		return err
 	}
 
 	var p ocispec.Platform
 	if err := json.Unmarshal(dt, &p); err != nil {
-		return nil, errors.WithStack(err)
+		return errors.WithStack(err)
 	}
 
 	p = platforms.Normalize(p)
-	return &p, nil
+
+	if p2.Architecture == "" {
+		p2.Architecture = p.Architecture
+		if p2.Variant == "" {
+			p2.Variant = p.Variant
+		}
+	}
+	if p2.OS == "" {
+		p2.OS = p.OS
+	}
+
+	return nil
 }
 
 func detectMediaType(dt []byte) (string, error) {