feat(mgmt): added mgmt extension which returns current zot configuration (#1198)

Signed-off-by: Petu Eusebiu <peusebiu@cisco.com>

pkg/common/common.go

@@ -211,3 +211,23 @@ func DirExists(d string) bool {
 
 	return true
 }
+
+// Used to filter a json fields by using an intermediate struct.
+func MarshalThroughStruct(obj interface{}, throughStruct interface{}) ([]byte, error) {
+	toJSON, err := json.Marshal(obj)
+	if err != nil {
+		return []byte{}, err
+	}
+
+	err = json.Unmarshal(toJSON, throughStruct)
+	if err != nil {
+		return []byte{}, err
+	}
+
+	toJSON, err = json.Marshal(throughStruct)
+	if err != nil {
+		return []byte{}, err
+	}
+
+	return toJSON, nil
+}

pkg/common/common_test.go

@@ -24,6 +24,28 @@ func TestCommon(t *testing.T) {
 		So(common.Contains([]string{}, "apple"), ShouldBeFalse)
 	})
 
+	Convey("test MarshalThroughStruct()", t, func() {
+		cfg := config.New()
+
+		newCfg := struct {
+			DistSpecVersion string
+		}{}
+
+		_, err := common.MarshalThroughStruct(cfg, &newCfg)
+		So(err, ShouldBeNil)
+		So(newCfg.DistSpecVersion, ShouldEqual, cfg.DistSpecVersion)
+
+		// negative
+		obj := make(chan int)
+		toObj := config.New()
+
+		_, err = common.MarshalThroughStruct(obj, &toObj)
+		So(err, ShouldNotBeNil)
+
+		_, err = common.MarshalThroughStruct(toObj, &obj)
+		So(err, ShouldNotBeNil)
+	})
+
 	Convey("test getTLSConfig()", t, func() {
 		caCertPool, _ := x509.SystemCertPool()
 		tlsConfig, err := common.GetTLSConfig("wrongPath", caCertPool)