fix(oci): create blobs dir and define blobs dir name constant (#520)

https://github.com/opencontainers/image-spec/blob/v1.0/image-layout.md#content
specifies that the blobs dir must exist, so the changed ensureDir in
this PR is a bugfix.

The addition and use of the ociBlobsDir constant is more of a cleanup
suggestion, and I can remove it if necessary. I've also asked for it to
be added upstream at
opencontainers/image-spec#1069 but that will
probably take significantly longer.

Signed-off-by: Clarence "Sparr" Risher <clrnc@amazon.com>

Author: sparr

content/oci/oci.go

@@ -43,6 +43,11 @@ import (
 // Reference: https://github.com/opencontainers/image-spec/blob/v1.1.0-rc2/image-layout.md#indexjson-file
 const ociImageIndexFile = "index.json"
 
+// ociBlobsDir is the name of the blobs directory
+// from the OCI Image Layout Specification.
+// Reference: https://github.com/opencontainers/image-spec/blob/v1.1.0-rc2/image-layout.md#content
+const ociBlobsDir = "blobs"
+
 // Store implements `oras.Target`, and represents a content store
 // based on file system with the OCI-Image layout.
 // Reference: https://github.com/opencontainers/image-spec/blob/v1.1.0-rc2/image-layout.md
@@ -90,7 +95,7 @@ func NewWithContext(ctx context.Context, root string) (*Store, error) {
 		graph:         graph.NewMemory(),
 	}
 
-	if err := ensureDir(rootAbs); err != nil {
+	if err := ensureDir(filepath.Join(rootAbs, ociBlobsDir)); err != nil {
 		return nil, err
 	}
 	if err := store.ensureOCILayoutFile(); err != nil {

content/oci/readonlyoci_test.go

@@ -123,7 +123,7 @@ func TestReadOnlyStore(t *testing.T) {
 	// build fs
 	fsys := fstest.MapFS{}
 	for i, desc := range descs {
-		path := strings.Join([]string{"blobs", desc.Digest.Algorithm().String(), desc.Digest.Encoded()}, "/")
+		path := strings.Join([]string{ociBlobsDir, desc.Digest.Algorithm().String(), desc.Digest.Encoded()}, "/")
 		fsys[path] = &fstest.MapFile{Data: blobs[i]}
 	}
 	fsys[ocispec.ImageLayoutFile] = &fstest.MapFile{Data: layoutJSON}
@@ -603,7 +603,7 @@ func TestReadOnlyStore_Copy_OCIToMemory(t *testing.T) {
 	// build fs
 	fsys := fstest.MapFS{}
 	for i, desc := range descs {
-		path := strings.Join([]string{"blobs", desc.Digest.Algorithm().String(), desc.Digest.Encoded()}, "/")
+		path := strings.Join([]string{ociBlobsDir, desc.Digest.Algorithm().String(), desc.Digest.Encoded()}, "/")
 		fsys[path] = &fstest.MapFile{Data: blobs[i]}
 	}
 	fsys[ocispec.ImageLayoutFile] = &fstest.MapFile{Data: layoutJSON}
@@ -717,7 +717,7 @@ func TestReadOnlyStore_Tags(t *testing.T) {
 	// build fs
 	fsys := fstest.MapFS{}
 	for i, desc := range descs {
-		path := strings.Join([]string{"blobs", desc.Digest.Algorithm().String(), desc.Digest.Encoded()}, "/")
+		path := strings.Join([]string{ociBlobsDir, desc.Digest.Algorithm().String(), desc.Digest.Encoded()}, "/")
 		fsys[path] = &fstest.MapFile{Data: blobs[i]}
 	}
 	fsys[ocispec.ImageLayoutFile] = &fstest.MapFile{Data: layoutJSON}

content/oci/readonlystorage.go

@@ -95,5 +95,5 @@ func blobPath(dgst digest.Digest) (string, error) {
 		return "", fmt.Errorf("cannot calculate blob path from invalid digest %s: %w: %v",
 			dgst.String(), errdef.ErrInvalidDigest, err)
 	}
-	return path.Join("blobs", dgst.Algorithm().String(), dgst.Encoded()), nil
+	return path.Join(ociBlobsDir, dgst.Algorithm().String(), dgst.Encoded()), nil
 }

content/oci/readonlystorage_test.go

@@ -38,7 +38,7 @@ func TestReadOnlyStorage_Exists(t *testing.T) {
 	dgst := digest.FromBytes(blob)
 	desc := content.NewDescriptorFromBytes("", blob)
 	fsys := fstest.MapFS{
-		strings.Join([]string{"blobs", dgst.Algorithm().String(), dgst.Encoded()}, "/"): {},
+		strings.Join([]string{ociBlobsDir, dgst.Algorithm().String(), dgst.Encoded()}, "/"): {},
 	}
 	s := NewStorageFromFS(fsys)
 	ctx := context.Background()
@@ -76,7 +76,7 @@ func TestReadOnlyStorage_Fetch(t *testing.T) {
 	dgst := digest.FromBytes(blob)
 	desc := content.NewDescriptorFromBytes("", blob)
 	fsys := fstest.MapFS{
-		strings.Join([]string{"blobs", dgst.Algorithm().String(), dgst.Encoded()}, "/"): {
+		strings.Join([]string{ociBlobsDir, dgst.Algorithm().String(), dgst.Encoded()}, "/"): {
 			Data: blob,
 		},
 	}
@@ -123,7 +123,7 @@ func TestReadOnlyStorage_DirFS(t *testing.T) {
 	dgst := digest.FromBytes(blob)
 	desc := content.NewDescriptorFromBytes("test", blob)
 	// write blob to disk
-	path := filepath.Join(tempDir, "blobs", dgst.Algorithm().String(), dgst.Encoded())
+	path := filepath.Join(tempDir, ociBlobsDir, dgst.Algorithm().String(), dgst.Encoded())
 	if err := os.MkdirAll(filepath.Dir(path), 0777); err != nil {
 		t.Fatal("error calling Mkdir(), error =", err)
 	}

content/oci/storage_test.go

@@ -289,7 +289,7 @@ func TestStorage_Fetch_ExistingBlobs(t *testing.T) {
 	}
 
 	tempDir := t.TempDir()
-	path := filepath.Join(tempDir, "blobs", dgst.Algorithm().String(), dgst.Encoded())
+	path := filepath.Join(tempDir, ociBlobsDir, dgst.Algorithm().String(), dgst.Encoded())
 	if err := os.MkdirAll(filepath.Dir(path), 0777); err != nil {
 		t.Fatal("error calling Mkdir(), error =", err)
 	}