Add intelligent type marshalling/unmarshalling

pkg/api/helper.go

@@ -0,0 +1,111 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package api
+
+import (
+	"encoding/json"
+	"fmt"
+	"reflect"
+)
+
+var knownTypes = map[string]reflect.Type{}
+
+func init() {
+	types := []interface{}{
+		PodList{}, Pod{}, ReplicationControllerList{},
+		ReplicationController{}, ServiceList{}, Service{},
+	}
+	for _, obj := range types {
+		t := reflect.TypeOf(obj)
+		knownTypes[t.Name()] = t
+	}
+}
+
+// Returns the name of the type (sans pointer), and its kind field. Takes pointer-to-struct..
+func nameAndJSONBase(obj interface{}) (string, reflect.Value, error) {
+	v := reflect.ValueOf(obj)
+	if v.Kind() != reflect.Ptr {
+		return "", reflect.Value{}, fmt.Errorf("expected pointer, but got %v", v.Type().Name())
+	}
+	v = v.Elem()
+	name := v.Type().Name()
+	if v.Kind() != reflect.Struct {
+		return "", reflect.Value{}, fmt.Errorf("expected struct, but got %v", name)
+	}
+	jsonBase := v.FieldByName("JSONBase")
+	if !jsonBase.IsValid() {
+		return "", reflect.Value{}, fmt.Errorf("struct %v lacks embedded JSON type", name)
+	}
+	return name, jsonBase, nil
+}
+
+// Encode turns the given api object into an appropriate JSON string.
+// Will return an error if the object doesn't have an embedded JSONBase.
+// Obj must be a pointer to a struct. Note, this sets the object's Kind
+// field.
+func Encode(obj interface{}) (data []byte, err error) {
+	name, jsonBase, err := nameAndJSONBase(obj)
+	if err != nil {
+		return nil, err
+	}
+	if _, contains := knownTypes[name]; !contains {
+		return nil, fmt.Errorf("struct %v can't be unmarshalled because it's not in knownTypes", name)
+	}
+	jsonBase.FieldByName("Kind").Set(reflect.ValueOf(name))
+	return json.Marshal(obj)
+}
+
+// Decode converts a JSON string back into a pointer to an api object. Deduces the type
+// based upon the Kind field (set by encode).
+func Decode(data []byte) (interface{}, error) {
+	findKind := struct {
+		Kind string `json:"kind,omitempty" yaml:"kind,omitempty"`
+	}{}
+	err := json.Unmarshal(data, &findKind)
+	if err != nil {
+		return nil, fmt.Errorf("Couldn't get kind: %#v", err)
+	}
+	objType, found := knownTypes[findKind.Kind]
+	if !found {
+		return nil, fmt.Errorf("%v is not a known type", findKind.Kind)
+	}
+	obj := reflect.New(objType).Interface()
+	err = json.Unmarshal(data, obj)
+	if err != nil {
+		return nil, err
+	}
+	return obj, nil
+}
+
+// DecodeInto parses a JSON string and stores it in obj. Returns an error
+// if data.Kind is set and doesn't match the type of obj. Obj should be a
+// pointer to an api type.
+func DecodeInto(data []byte, obj interface{}) error {
+	err := json.Unmarshal(data, obj)
+	if err != nil {
+		return err
+	}
+	name, jsonBase, err := nameAndJSONBase(obj)
+	if err != nil {
+		return err
+	}
+	foundName := jsonBase.FieldByName("Kind").Interface().(string)
+	if foundName != "" && foundName != name {
+		return fmt.Errorf("data had kind %v, but passed object was of type %v", foundName, name)
+	}
+	return nil
+}

pkg/api/helper_test.go

@@ -0,0 +1,74 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package api
+
+import (
+	"reflect"
+	"testing"
+)
+
+func runTest(t *testing.T, source interface{}) {
+	name := reflect.TypeOf(source).Name()
+	data, err := Encode(source)
+	if err != nil {
+		t.Errorf("%v: %v", name, err)
+		return
+	}
+	obj2, err := Decode(data)
+	if err != nil {
+		t.Errorf("%v: %v", name, err)
+		return
+	}
+	if !reflect.DeepEqual(source, obj2) {
+		t.Errorf("%v: wanted %#v, got %#v", name, source, obj2)
+		return
+	}
+	obj3 := reflect.New(reflect.TypeOf(source).Elem()).Interface()
+	err = DecodeInto(data, obj3)
+	if err != nil {
+		t.Errorf("%v: %v", name, err)
+		return
+	}
+	if !reflect.DeepEqual(source, obj3) {
+		t.Errorf("%v: wanted %#v, got %#v", name, source, obj3)
+		return
+	}
+}
+
+func TestTypes(t *testing.T) {
+	// TODO: auto-fill all fields.
+	table := []interface{}{
+		&Pod{
+			JSONBase: JSONBase{
+				ID: "mylittlepod",
+			},
+			Labels: map[string]string{
+				"name": "pinky",
+			},
+		},
+		&Service{},
+		&ServiceList{},
+		&ReplicationControllerList{},
+		&ReplicationController{},
+		&PodList{},
+	}
+	for _, item := range table {
+		runTest(t, item)
+	}
+}
+
+// TODO: test rejection of bad JSON.