k8s源码设计模式之Adapter

发表于
什么是Adapter

Adapter也就是适配器模式

适配器模式是一种结构型设计模式，它将一个接口转换成另一个客户端所期望的接口，从而使得原本不兼容的接口能够协同工作。适配器模式常常用于将一个旧接口适配成新接口，或将一个外部库的接口适配成当前应用程序所需的接口

适配器模式由三个主要角色组成：客户端、适配器和被适配者。其中，客户端使用目标接口来与适配器交互，适配器将客户端的请求转换为被适配者的请求并进行处理，被适配者则是适配器所需要的接口。

k8s中适配器模式

k8s中有很多不同的资源，对于创建资源，k8s实现了createHandler方法来处理

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// staging/src/k8s.io/apiserver/pkg/endpoints/handlers/create.go
// 这里返回http.HandlerFunc
func createHandler(r rest.NamedCreater, scope *RequestScope, admit admission.Interface, includeName bool) http.HandlerFunc {
	return func(w http.ResponseWriter, req *http.Request) {
		ctx := req.Context()
		// For performance tracking purposes.
		ctx, span := tracing.Start(ctx, "Create", traceFields(req)...)
		defer span.End(500 * time.Millisecond)
        ...
		namespace, name, err := scope.Namer.Name(req)
		requestFunc := func() (runtime.Object, error) {
            // 调用r实现的Create方法，上层可以实现这个接口实现适配
			return r.Create(
				ctx,
				name,
				obj,
				rest.AdmissionToValidateObjectFunc(admit, admissionAttributes, scope),
				options,
			)
		}
        ...
	}
}


// CreateNamedResource returns a function that will handle a resource creation with name.
func CreateNamedResource(r rest.NamedCreater, scope *RequestScope, admission admission.Interface) http.HandlerFunc {
	return createHandler(r, scope, admission, true)
}

// CreateResource returns a function that will handle a resource creation.
func CreateResource(r rest.Creater, scope *RequestScope, admission admission.Interface) http.HandlerFunc {
	return createHandler(&namedCreaterAdapter{r}, scope, admission, false)
}

// 通过namedCreaterAdapter实现Create方法，适配createHandler. createHandler将调用对应的Create方法
type namedCreaterAdapter struct {
	rest.Creater
}

func (c *namedCreaterAdapter) Create(ctx context.Context, name string, obj runtime.Object, createValidatingAdmission rest.ValidateObjectFunc, options *metav1.CreateOptions) (runtime.Object, error) {
	return c.Creater.Create(ctx, obj, createValidatingAdmission, options)
}

REF:
1.staging/src/k8s.io/apiserver/pkg/endpoints/handlers/create.go