Kubernetes类型系统

// k8s.io/apimachinery/pkg/runtime/schema/group_version.go
// 对应一个 http 路径
type GroupVersionResource struct {
	Group    string
	Version  string
	Resource string
}
// 对应一个golang struct
type GroupVersionKind struct {
	Group   string
	Version string
	Kind    string
}

// 生成的 golang 结构体
type EchoRequest struct {
    A  string   `protobuf:"bytes,1,opt,name=A,proto3" json:"A,omitempty"`
}
// 收到请求，在 Unmarshal 过程中会调用这个函数
func (m *EchoRequest) XXX_Unmarshal(b []byte) error {
    return xxx_messageInfo_EchoRequest.Unmarshal(m, b)
}
var xxx_messageInfo_EchoRequest proto.InternalMessageInfo
// InternalMessageInfo 是 Unmarshal 相关信息的存储位置
// b 是 protocol buffer raw 数据，而a 是要 unmarshal 到的结构
// 基础库不关心具体 unmarshal 类型，始终 unmarshal 到一个 interface Message
// 实际上面到结构调用到时候 会是 EchoRequest 类型
func (a *InternalMessageInfo) Unmarshal(msg Message, b []byte) error {
    // ... 略
    err := u.unmarshal(toPointer(&msg), b)
    return err
}
func (u *unmarshalInfo) unmarshal(m pointer, b []byte) error{
    if atomic.LoadInt32(&u.initialized) == 0 {
        // 保存 unmarshal 这个类型的函数、信息到一个结构里面，加速重复的 unmarshal
		u.computeUnmarshalInfo()
	}
	// .... 略
	if fn := f.unmarshal; fn != nil {
		var err error
		// unmarshal 这个 field 这里的关键是 unmarshal 到原始 bytes 设置到对应字段的
		// offset上面去，里面比较关键的是用了 golang reflect的 StructField 
		// StructField 的 Offset 是固定的，根据 一个结构的指针的 pointer 以及 Field的
		// offset 就可以直接用指针设置 结构的某个字段内容了
		b, err = fn(b, m.offset(f.field), wire)
		// ....
	}
}

gvk := schema.GroupVersionKind{Group: "batch", Version: "v2alpha1", Kind: "Job"} 
obj := api.Scheme.New(gvk)
codec := api.Codecs.LegacyCodec(gvk.GroupVersion())
codec.Decode(reqBody, gvk, obj)
type Job struct {  
    metav1.TypeMeta     ---> type TypeMeta struct { Kind string; APIVersion string }
    metav1.ObjectMeta   ---> type ObjectMeta struct { Name string...}
    Spec JobSpec
    Status JobStatus 
}

// k8s.io/apimachinery/pkg/api/meta/interface.go
type RESTMapper interface {
	KindFor(resource schema.GroupVersionResource) (schema.GroupVersionKind, error)
    ResourceFor(input schema.GroupVersionResource) (schema.GroupVersionResource, error)
    ...
}
// k8s.io/apimachinery/pkg/runtime/scheme.go
type Scheme struct {
    // a Type is a particular Go struct，比如k8s.io/api/apps/v1.StatefulSet
	gvkToType map[schema.GroupVersionKind]reflect.Type
    typeToGVK map[reflect.Type][]schema.GroupVersionKind
    ...
}
func (s *Scheme) ObjectKinds(obj Object) ([]schema.GroupVersionKind, bool, error) {...}
func (s *Scheme) New(kind schema.GroupVersionKind) (Object, error) {
	if t, exists := s.gvkToType[kind]; exists {
		return reflect.New(t).Interface().(Object), nil
	}
    ...
	return nil, NewNotRegisteredErrForKind(s.schemeName, kind)
}

// k8s.io/client-go/kubernetes/scheme/register.go
var Scheme = runtime.NewScheme()
var AddToScheme = localSchemeBuilder.AddToScheme
func init(){
    v1.AddToGroupVersion(Scheme, schema.GroupVersion{Version: "v1"})
    utilruntime.Must(AddToScheme(Scheme))
}
var localSchemeBuilder = runtime.SchemeBuilder{
    corev1.AddToScheme,
    appsv1.AddToScheme,
}
// k8s.io/api/core/v1/register.go
var (
	SchemeBuilder = runtime.NewSchemeBuilder(addKnownTypes)
	AddToScheme   = SchemeBuilder.AddToScheme
)
func addKnownTypes(scheme *runtime.Scheme) error {
	scheme.AddKnownTypes(SchemeGroupVersion,
		&Pod{},
        &PodList{},
        &Service{},
    )
    ...
}

// k8s.io/apimachinery/pkg/runtime/interface.go
type Object interface{
    GetObjectKind() schema.ObjectKind
    DeepCopyObject() Object
}
type ObjectKind interface{
    SetGroupVersionKind(kind GroupVersionKind)
    GroupVersionKind() GroupVersionKind
}
// k8s.io/apimachinery/pkg/apis/meta/v1/types.go
// 实现 ObjectKind
type TypeMeta struct{
    Kind string             `json:"kind"`
    APIVersion string       `json:"apiVersion"`
}
type ObjectMeta struct{
    Name string
    Namespace string
    UID types.UID
    ResourceVersion string
    CreationTimestamp Time
    DeletionTimestamp Time
    Labels map[string]string
    Annotations map[string]string
}

// k8s.io/api/core/v1/types.go
type Pod struct{
    metav1.TypeMeta 
    metav1.ObjectMeta   `json:"metadata"`
    Spec PodSpec        `json:"spec"`
    Status PodStatus    `json:"status"`
}

type Deployment struct { 
    metav1.TypeMeta `json:",inline"` 
    metav1.ObjectMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"` 
    Spec DeploymentSpec `json:"spec,omitempty" protobuf:"bytes,2,opt,name=spec"` 
    Status DeploymentStatus `json:"status,omitempty" protobuf:"bytes,3,opt,name=status"` 
} 

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: mpijobs.kubeflow.org
spec:
  group: kubeflow.org
  names:
    kind: MPIJob
    plural: mpijobs
    shortNames:
    - mj
    - mpij
    singular: mpijob
  scope: Namespaced
  versions:
  - name: v1alpha2
    schema: ...
    served: true
    storage: false
  - name: v1
    schema: ...
    served: true
    storage: false
  - name: v2beta1
    schema: ...
    served: true
    storage: true