feat(storage): add ComponentCount as part of ObjectAttrs

storage/integration_test.go

@@ -1659,18 +1659,26 @@ func TestIntegration_Compose(t *testing.T) {
 		// Compose should work even if the user sets no destination attributes.
 		compDst := b.Object("composed1")
 		c := compDst.ComposerFrom(compSrcs...)
-		if _, err := c.Run(ctx); err != nil {
+		attrs, err := c.Run(ctx)
+		if err != nil {
 			t.Fatalf("ComposeFrom error: %v", err)
 		}
+		if attrs.ComponentCount != int64(len(objects)) {
+			t.Errorf("mismatching ComponentCount: got %v, want %v", attrs.ComponentCount, int64(len(objects)))
+		}
 		checkCompose(compDst, "application/octet-stream")
 
 		// It should also work if we do.
 		compDst = b.Object("composed2")
 		c = compDst.ComposerFrom(compSrcs...)
 		c.ContentType = "text/json"
-		if _, err := c.Run(ctx); err != nil {
+		attrs, err = c.Run(ctx)
+		if err != nil {
 			t.Fatalf("ComposeFrom error: %v", err)
 		}
+		if attrs.ComponentCount != int64(len(objects)) {
+			t.Errorf("mismatching ComponentCount: got %v, want %v", attrs.ComponentCount, int64(len(objects)))
+		}
 		checkCompose(compDst, "text/json")
 	})
 }

storage/storage.go

@@ -1315,6 +1315,11 @@ type ObjectAttrs struct {
 	// later value but not to an earlier one. For more information see
 	// https://cloud.google.com/storage/docs/metadata#custom-time .
 	CustomTime time.Time
+
+	// ComponentCount is the number of objects contained within a composite object.
+	// For non-composite objects, the value will be zero.
+	// This field is read-only.
+	ComponentCount int64
 }
 
 // convertTime converts a time in RFC3339 format to time.Time.
@@ -1385,6 +1390,7 @@ func newObject(o *raw.Object) *ObjectAttrs {
 		Updated:                 convertTime(o.Updated),
 		Etag:                    o.Etag,
 		CustomTime:              convertTime(o.CustomTime),
+		ComponentCount:          o.ComponentCount,
 	}
 }
 
@@ -1419,6 +1425,7 @@ func newObjectFromProto(o *storagepb.Object) *ObjectAttrs {
 		Deleted:           convertProtoTime(o.GetDeleteTime()),
 		Updated:           convertProtoTime(o.GetUpdateTime()),
 		CustomTime:        convertProtoTime(o.GetCustomTime()),
+		ComponentCount:    int64(o.ComponentCount),
 	}
 }
 
@@ -1547,6 +1554,7 @@ var attrToFieldMap = map[string]string{
 	"Updated":                 "updated",
 	"Etag":                    "etag",
 	"CustomTime":              "customTime",
+	"ComponentCount":          "componentCount",
 }
 
 // attrToProtoFieldMap maps the field names of ObjectAttrs to the underlying field
@@ -1578,6 +1586,7 @@ var attrToProtoFieldMap = map[string]string{
 	"Owner":                   "owner",
 	"CustomerKeySHA256":       "customer_encryption",
 	"CustomTime":              "custom_time",
+	"ComponentCount":          "component_count",
 	// MediaLink was explicitly excluded from the proto as it is an HTTP-ism.
 	// "MediaLink":               "mediaLink",
 }

storage/storage_test.go

@@ -1747,6 +1747,7 @@ func TestRawObjectToObjectAttrs(t *testing.T) {
 				TimeCreated:             "2019-03-31T19:32:10Z",
 				TimeDeleted:             "2019-03-31T19:33:39Z",
 				TemporaryHold:           true,
+				ComponentCount:          2,
 			},
 			want: &ObjectAttrs{
 				Bucket:                  "Test",
@@ -1763,6 +1764,7 @@ func TestRawObjectToObjectAttrs(t *testing.T) {
 				RetentionExpirationTime: time.Date(2019, 3, 31, 19, 33, 36, 0, time.UTC),
 				Size:                    1 << 20,
 				TemporaryHold:           true,
+				ComponentCount:          2,
 			},
 		},
 	}
@@ -1833,6 +1835,7 @@ func TestProtoObjectToObjectAttrs(t *testing.T) {
 				CreateTime:          timestamppb.New(now),
 				DeleteTime:          timestamppb.New(now),
 				TemporaryHold:       true,
+				ComponentCount:      2,
 			},
 			want: &ObjectAttrs{
 				Bucket:                  "Test",
@@ -1848,6 +1851,7 @@ func TestProtoObjectToObjectAttrs(t *testing.T) {
 				RetentionExpirationTime: now,
 				Size:                    1 << 20,
 				TemporaryHold:           true,
+				ComponentCount:          2,
 			},
 		},
 	}