fix: generate unique config when build model artifact (#20)

Author: chlins

pkg/backend/build/build.go

@@ -21,6 +21,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"time"
 
 	modelspec "github.com/CloudNativeAI/modctl/pkg/spec"
 	"github.com/CloudNativeAI/modctl/pkg/storage"
@@ -30,12 +31,10 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
-// DescriptorEmptyJSON is the descriptor of a blob with content of `{}`.
-var DescriptorEmptyJSON = ocispec.Descriptor{
-	MediaType: ocispec.MediaTypeImageConfig,
-	Digest:    `sha256:44136fa355b3678a1146ad16f7e8649e94fb4fc21fe77e8310c060f61caaff8a`,
-	Size:      2,
-	Data:      []byte(`{}`),
+// ModelConfig is a configuration that corresponds to the image config in the image spec.
+type ModelConfig struct {
+	// Created is the time when the model image is created.
+	Created string `json:"Created"`
 }
 
 // BuildLayer converts the file to the image blob and push it to the storage.
@@ -60,13 +59,25 @@ func BuildLayer(ctx context.Context, store storage.Storage, repo, path string) (
 
 // BuildConfig builds the image config and push it to the storage.
 func BuildConfig(ctx context.Context, store storage.Storage, repo string) (ocispec.Descriptor, error) {
-	// by default using the empty JSON config.
-	_, _, err := store.PushBlob(ctx, repo, bytes.NewReader(DescriptorEmptyJSON.Data))
+	config := &ModelConfig{
+		Created: time.Now().Format(time.RFC3339Nano),
+	}
+	configJSON, err := json.Marshal(config)
+	if err != nil {
+		return ocispec.Descriptor{}, fmt.Errorf("failed to marshal config: %w", err)
+	}
+
+	digest, size, err := store.PushBlob(ctx, repo, bytes.NewReader(configJSON))
 	if err != nil {
 		return ocispec.Descriptor{}, fmt.Errorf("failed to push config to storage: %w", err)
 	}
 
-	return DescriptorEmptyJSON, nil
+	return ocispec.Descriptor{
+		// reuse the image config media type for runtime compatibility.
+		MediaType: ocispec.MediaTypeImageConfig,
+		Size:      size,
+		Digest:    godigest.Digest(digest),
+	}, nil
 }
 
 // BuildManifest builds the manifest and push it to the storage.