// k8s.io/apiserver/pkg/server/config.go

func DefaultBuildHandlerChain(apiHandler http.Handler, c *Config) http.Handler {
    handler := filterlatency.TrackCompleted(apiHandler)
  // 構造權限檢查filter
    handler = genericapifilters.WithAuthorization(handler, c.Authorization.Authorizer, c.Serializer)
    ...
  // 構造認證filter
    handler = genericapifilters.WithAuthentication(handler, c.Authentication.Authenticator, failedHandler, c.Authentication.APIAudiences)
  ...
  // 構造請求超時filter, LongRunningFunc會判斷該請求是否是需要LongRunning的，比如watch的請求，如果是，該filter不會對這類請求生效
    // WithTimeoutForNonLongRunningRequests will call the rest of the request handling in a go-routine with the
    // context with deadline. The go-routine can keep running, while the timeout logic will return a timeout to the client.
    handler = genericfilters.WithTimeoutForNonLongRunningRequests(handler, c.LongRunningFunc)
    handler = genericapifilters.WithRequestDeadline(handler, c.AuditBackend, c.AuditPolicyRuleEvaluator,
        c.LongRunningFunc, c.Serializer, c.RequestTimeout)
  
    handler = genericfilters.WithWaitGroup(handler, c.LongRunningFunc, c.HandlerChainWaitGroup)
  ...
  // 初始化RequestInfo的filter并將其放入context中，后續的處理邏輯可以從context直接獲取RequestInfo
    handler = genericapifilters.WithRequestInfo(handler, c.RequestInfoResolver)
  ....
    return handler
}

//pkg/controlplane/instance.go

func (c completedConfig) New(delegationTarget genericapiserver.DelegationTarget) (*Instance, error) {
  ...
  // 構造內置資源的RESTStorageProvider
    restStorageProviders := []RESTStorageProvider{
        apiserverinternalrest.StorageProvider{},
        authenticationrest.RESTStorageProvider{Authenticator: c.GenericConfig.Authentication.Authenticator, APIAudiences: c.GenericConfig.Authentication.APIAudiences},
        authorizationrest.RESTStorageProvider{Authorizer: c.GenericConfig.Authorization.Authorizer, RuleResolver: c.GenericConfig.RuleResolver},
        autoscalingrest.RESTStorageProvider{},
        batchrest.RESTStorageProvider{},
        certificatesrest.RESTStorageProvider{},
        coordinationrest.RESTStorageProvider{},
        discoveryrest.StorageProvider{},
        networkingrest.RESTStorageProvider{},
        noderest.RESTStorageProvider{},
        policyrest.RESTStorageProvider{},
        rbacrest.RESTStorageProvider{Authorizer: c.GenericConfig.Authorization.Authorizer},
        schedulingrest.RESTStorageProvider{},
        storagerest.RESTStorageProvider{},
        flowcontrolrest.RESTStorageProvider{InformerFactory: c.GenericConfig.SharedInformerFactory},
        // keep apps after extensions so legacy clients resolve the extensions versions of shared resource names.
        // See https://github.com/kubernetes/kubernetes/issues/42392
        appsrest.StorageProvider{},
        admissionregistrationrest.RESTStorageProvider{},
        eventsrest.RESTStorageProvider{TTL: c.ExtraConfig.EventTTL},
    }
    if err := m.InstallAPIs(c.ExtraConfig.APIResourceConfigSource, c.GenericConfig.RESTOptionsGetter, restStorageProviders...); err != nil {
        return nil, err
    }
  ...
}

//k8s.io/apiserver/pkg/server/genericapiserver.go

// Info about an API group.
type APIGroupInfo struct {
    PrioritizedVersions []schema.GroupVersion
    // Info about the resources in this group. It's a map from version to resource to the storage.
    VersionedResourcesStorageMap map[string]map[string]rest.Storage
  ...
    // NegotiatedSerializer controls how this group encodes and decodes data
    NegotiatedSerializer runtime.NegotiatedSerializer
    // ParameterCodec performs conversions for query parameters passed to API calls
    ParameterCodec runtime.ParameterCodec
    ...
}

// k8s.io/apiserver/pkg/registry/rest/rest.go

// Storage is a generic interface for RESTful storage services.
// Resources which are exported to the RESTful API of apiserver need to implement this interface. It is expected
// that objects may implement any of the below interfaces.
type Storage interface {
    // New returns an empty object that can be used with Create and Update after request data has been put into it.
    // This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
    New() runtime.Object

    // Destroy cleans up its resources on shutdown.
    // Destroy has to be implemented in thread-safe way and be prepared
    // for being called more than once.
    Destroy()
}

// k8s.io/apiserver/pkg/registry/rest/rest.go

// 資源對象支持POST請求，例入通過kubectl create一個資源對象。
// Creater is an object that can create an instance of a RESTful object.
type Creater interface {
    // New returns an empty object that can be used with Create after request data has been put into it.
    // This object must be a pointer type for use with Codec.DecodeInto([]byte, runtime.Object)
    New() runtime.Object

    // Create creates a new version of a resource.
    Create(ctx context.Context, obj runtime.Object, createValidation ValidateObjectFunc, options *metav1.CreateOptions) (runtime.Object, error)
}
// 資源對象支持GET請求，例如通過kubectl get 一個資源對象。
// Getter is an object that can retrieve a named RESTful resource.
type Getter interface {
    // Get finds a resource in the storage by name and returns it.
    // Although it can return an arbitrary error value, IsNotFound(err) is true for the
    // returned error value err when the specified resource is not found.
    Get(ctx context.Context, name string, options *metav1.GetOptions) (runtime.Object, error)
}
// 支持對資源對象進行watch操作 例如通過kubectl get 資源對象 -w。
type Watcher interface {
    // 'label' selects on labels; 'field' selects on the object's fields. Not all fields
    // are supported; an error should be returned if 'field' tries to select on a field that
    // isn't supported. 'resourceVersion' allows for continuing/starting a watch at a
    // particular version.
    Watch(ctx context.Context, options *metainternalversion.ListOptions) (watch.Interface, error)
}

// NewREST returns a RESTStorage object that will work against deployments.
func NewREST(optsGetter generic.RESTOptionsGetter) (*REST, *StatusREST, *RollbackREST, error) {
   // 創建一個deployments的genericregistry.Store
    store := &genericregistry.Store{
    // 初始化一個空資源對象，這里使用的是internal的版本，下面定義的各種strategy操作的對象也是internal版本，這樣就不用為每一種版本編寫一個strategy策略
        NewFunc:                  func() runtime.Object { return &apps.Deployment{} },
    // 初始化一個空資源對象列表
        NewListFunc:              func() runtime.Object { return &apps.DeploymentList{} },
    
        DefaultQualifiedResource: apps.Resource("deployments"),
    // 創建更新刪除策略 主要是做校驗及控制那些字段不能被用戶覆蓋用
        CreateStrategy:      deployment.Strategy,
        UpdateStrategy:      deployment.Strategy,
        DeleteStrategy:      deployment.Strategy,
        ResetFieldsStrategy: deployment.Strategy,
 
        TableConvertor: printerstorage.TableConvertor{TableGenerator: printers.NewTableGenerator().With(printersinternal.AddHandlers)},
    }
    options := &generic.StoreOptions{RESTOptions: optsGetter}
  // 繼續完成store其他屬性的初始化，比如初始化store.Storage屬性。Storage主要用于和底層存儲層交互
    if err := store.CompleteWithOptions(options); err != nil {
        return nil, nil, nil, err
    }
    
    statusStore := *store
  // deployment的status子資源也是使用store, 區別是更新策略不一樣, 即在update時會用舊對象的spec和lable覆蓋新對象的，防止非status字段被用戶意外覆蓋
    statusStore.UpdateStrategy = deployment.StatusStrategy
    statusStore.ResetFieldsStrategy = deployment.StatusStrategy
    return &REST{store}, &StatusREST{store: &statusStore}, &RollbackREST{store: store}, nil
}

// k8s.io/apiserver/pkg/endpoints/groupversion.go

func (g *APIGroupVersion) InstallREST(container *restful.Container) ([]*storageversion.ResourceInfo, error) {
  // 從InstallAPI調用鏈下來這里的g.Root為/apis，這樣就可以確定handler的前綴為/apis/{goup}/{version}
    prefix := path.Join(g.Root, g.GroupVersion.Group, g.GroupVersion.Version)
    installer := &APIInstaller{
        group:             g,
        prefix:            prefix,
        minRequestTimeout: g.MinRequestTimeout,
    }

    apiResources, resourceInfos, ws, registrationErrors := installer.Install()
    versionDiscoveryHandler := discovery.NewAPIVersionHandler(g.Serializer, g.GroupVersion, staticLister{apiResources})
    versionDiscoveryHandler.AddToWebService(ws)
    container.Add(ws)
    return removeNonPersistedResources(resourceInfos), utilerrors.NewAggregate(registrationErrors)
}

// Install handlers for API resources.
func (a *APIInstaller) Install() ([]metav1.APIResource, []*storageversion.ResourceInfo, *restful.WebService, []error) {
    var apiResources []metav1.APIResource
    var resourceInfos []*storageversion.ResourceInfo
    var errors []error
    ws := a.newWebService()

    // Register the paths in a deterministic (sorted) order to get a deterministic swagger spec.
    paths := make([]string, len(a.group.Storage))
    var i int = 0
  // a.goup.Storage的簽名是 map[string]Storage, for循環的path是map的key，即資源名稱
    for path := range a.group.Storage {
        paths[i] = path
        i++
    }
    sort.Strings(paths)
    for _, path := range paths {
        apiResource, resourceInfo, err := a.registerResourceHandlers(path, a.group.Storage[path], ws)
        ...
}

// k8s.io/apiserver/pkg/endpoints/installer.go
func (a *APIInstaller) registerResourceHandlers(path string, storage rest.Storage, ws *restful.WebService) (*metav1.APIResource, *storageversion.ResourceInfo, error) {
  ...
  // 初始化rest容器，根目錄是APIInstaller的prefix屬性，從InstallAPI調用鏈下來值為/apis/{goup}/{version}
  ws := a.newWebService()
    ...
  // 進行類型轉換判斷當前的storage支持哪些類型的操作
    creater, isCreater := storage.(rest.Creater)
    namedCreater, isNamedCreater := storage.(rest.NamedCreater)
    lister, isLister := storage.(rest.Lister)
    getter, isGetter := storage.(rest.Getter)
    getterWithOptions, isGetterWithOptions := storage.(rest.GetterWithOptions)
    gracefulDeleter, isGracefulDeleter := storage.(rest.GracefulDeleter)
    collectionDeleter, isCollectionDeleter := storage.(rest.CollectionDeleter)
    updater, isUpdater := storage.(rest.Updater)
    patcher, isPatcher := storage.(rest.Patcher)
    watcher, isWatcher := storage.(rest.Watcher)
    connecter, isConnecter := storage.(rest.Connecter)
    storageMeta, isMetadata := storage.(rest.StorageMetadata)
    storageVersionProvider, isStorageVersionProvider := storage.(rest.StorageVersionProvider)

  // Get the list of actions for the given scope.
    switch {
    case !namespaceScoped:
    // 構造有無namespace資源的action
        // Handle non-namespace scoped resources like nodes.
        ...
    default:
    // 構造有namespace資源的action
    // 構造handler的注冊路徑
      namespaceParamName := "namespaces"
        // Handler for standard REST verbs (GET, PUT, POST and DELETE).
        namespaceParam := ws.PathParameter("namespace", "object name and auth scope, such as for teams and projects").DataType("string")
        namespacedPath := namespaceParamName + "/{namespace}/" + resource
        namespaceParams := []*restful.Parameter{namespaceParam}
   
    //resourcePath的值為 /namespaces/{namespace}/{resource}
        resourcePath := namespacedPath
        resourceParams := namespaceParams
    // itemPath： /namespaces/{namespace}/{resource}/{name}
    // name是請求資源對象的名字
        itemPath := namespacedPath + "/{name}"
        nameParams := append(namespaceParams, nameParam)
        proxyParams := append(nameParams, pathParam)
        itemPathSuffix := ""
        if isSubresource {
            itemPathSuffix = "/" + subresource
       // 有子資源等情況下 resourcePath被定義為：/namespaces/{namespace}/{resource}/{name}/{subResource}
            itemPath = itemPath + itemPathSuffix
      // itemPath與resourcePath的值一樣
            resourcePath = itemPath
            resourceParams = nameParams
        }
        apiResource.Name = path
        apiResource.Namespaced = true
        apiResource.Kind = resourceKind
        namer := handlers.ContextBasedNaming{
            Namer:         a.group.Namer,
            ClusterScoped: false,
        }
    // 根據storage實現的接口添加添加相關的action
        actions = appendIf(actions, action{"LIST", resourcePath, resourceParams, namer, false}, isLister)
        actions = appendIf(actions, action{"POST", resourcePath, resourceParams, namer, false}, isCreater)
        actions = appendIf(actions, action{"DELETECOLLECTION", resourcePath, resourceParams, namer, false}, isCollectionDeleter)
        // DEPRECATED in 1.11
        actions = appendIf(actions, action{"WATCHLIST", "watch/" + resourcePath, resourceParams, namer, false}, allowWatchList)

        actions = appendIf(actions, action{"GET", itemPath, nameParams, namer, false}, isGetter)
        if getSubpath {
            actions = appendIf(actions, action{"GET", itemPath + "/{path:*}", proxyParams, namer, false}, isGetter)
        }
        actions = appendIf(actions, action{"PUT", itemPath, nameParams, namer, false}, isUpdater)
        actions = appendIf(actions, action{"PATCH", itemPath, nameParams, namer, false}, isPatcher)
        actions = appendIf(actions, action{"DELETE", itemPath, nameParams, namer, false}, isGracefulDeleter)
        // DEPRECATED in 1.11
        actions = appendIf(actions, action{"WATCH", "watch/" + itemPath, nameParams, namer, false}, isWatcher)
        actions = appendIf(actions, action{"CONNECT", itemPath, nameParams, namer, false}, isConnecter)
        actions = appendIf(actions, action{"CONNECT", itemPath + "/{path:*}", proxyParams, namer, false}, isConnecter && connectSubpath)

        // list or post across namespace.
        // For ex: LIST all pods in all namespaces by sending a LIST request at /api/apiVersion/pods.
        // TODO: more strongly type whether a resource allows these actions on "all namespaces" (bulk delete)
        if !isSubresource {
            actions = appendIf(actions, action{"LIST", resource, params, namer, true}, isLister)
            // DEPRECATED in 1.11
            actions = appendIf(actions, action{"WATCHLIST", "watch/" + resource, params, namer, true}, allowWatchList)
        }
    }
  ...
  for _, action := range actions {
        ...
        switch action.Verb {
    case "GET": // Get a resource.
            var handler restful.RouteFunction
      // 構造get請求的handler
      // restfulGetResourceWithOptions和restfulGetResource將handlers.GetResource函數轉換成restful.RouteFunction，即handler的函數簽名
            if isGetterWithOptions {
                handler = restfulGetResourceWithOptions(getterWithOptions, reqScope, isSubresource)
            } else {
                handler = restfulGetResource(getter, reqScope)
            }
      ...
      // 將handler注冊到rest容器中
      // action.Path是上面定義的itemPath或resourcePath，對于GET來說是itemPath
      // 當前注冊的handler的路徑是ws的根路徑加上ation.Path. 完整的路徑為：/apis/{goup}/{version}/namespaces/{namespace}/{resource}/{name}
            route := ws.GET(action.Path).To(handler).
                Doc(doc).
                Param(ws.QueryParameter("pretty", "If 'true', then the output is pretty printed.")).
                Operation("read"+namespaced+kind+strings.Title(subresource)+operationSuffix).
                Produces(append(storageMeta.ProducesMIMETypes(action.Verb), mediaTypes...)...).
                Returns(http.StatusOK, "OK", producedObject).
                Writes(producedObject)
            if isGetterWithOptions {
                if err := AddObjectParams(ws, route, versionedGetOptions); err != nil {
                    return nil, nil, err
                }
            }
            addParams(route, action.Params)
            routes = append(routes, route)
    }
    case "LIST": // List all resources of a kind.
    ...
    case "PUT": // Update a resource.
    ...
    case "PATCH": // Partially update a resource
    ...
    case "POST": // Create a resource.
    ...
    case "DELETE": // Delete a resource.
    ....
  }
  ...

}

// k8s.io/apiserver/pkg/endpoints/handlers/get.go

// GetResource returns a function that handles retrieving a single resource from a rest.Storage object.
func GetResource(r rest.Getter, scope *RequestScope) http.HandlerFunc {
    return getResourceHandler(scope,
        func(ctx context.Context, name string, req *http.Request, trace *utiltrace.Trace) (runtime.Object, error) {
            // check for export
            options := metav1.GetOptions{}
      // 獲取查詢串
            if values := req.URL.Query(); len(values) > 0 {
                ...
        // 將查詢串解碼成metav1.GetOptions
                if err := metainternalversionscheme.ParameterCodec.DecodeParameters(values, scope.MetaGroupVersion, &options); err != nil {
                    err = errors.NewBadRequest(err.Error())
                    return nil, err
                }
            }
            if trace != nil {
                trace.Step("About to Get from storage")
            }
      // 交給Getter接口處理
            return r.Get(ctx, name, &options)
        })
}

// getResourceHandler is an HTTP handler function for get requests. It delegates to the
// passed-in getterFunc to perform the actual get.
func getResourceHandler(scope *RequestScope, getter getterFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, req *http.Request) {
        ...
        namespace, name, err := scope.Namer.Name(req)
        ...
        ctx := req.Context()
        ctx = request.WithNamespace(ctx, namespace)
        ...
        result, err := getter(ctx, name, req, trace)
        ...
    // 對處理結果進行轉化為用戶期望的格式并寫入到response中返回給用戶
        transformResponseObject(ctx, scope, trace, req, w, http.StatusOK, outputMediaType, result)
    }
}

// k8s.io/apiserver/pkg/endpoints/handlers/create.go

// 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)
}

func createHandler(r rest.NamedCreater, scope *RequestScope, admit admission.Interface, includeName bool) http.HandlerFunc {
    return func(w http.ResponseWriter, req *http.Request) {
    ...
    // 從request中取出請求body
    body, err := limitedReadBody(req, scope.MaxRequestBodyBytes)
    ...
    // 對查詢傳進行解碼生成metav1.CreateOptions
        options := &metav1.CreateOptions{}
        values := req.URL.Query()
        if err := metainternalversionscheme.ParameterCodec.DecodeParameters(values, scope.MetaGroupVersion, options); err != nil {
            ...
        }
        // 將請求body解碼成資源對象, defaultGVK是用戶請求的版本，這里decoder解碼出來的對象是internal版本的對象
        obj, gvk, err := decoder.Decode(body, &defaultGVK, original)
        ...
    admissionAttributes := admission.NewAttributesRecord(obj, nil, scope.Kind, namespace, name, scope.Resource, scope.Subresource, admission.Create, options, dryrun.IsDryRun(options.DryRun), userInfo)
        // 構建調用create方法的函數
        requestFunc := func() (runtime.Object, error) {
            return r.Create(
                ctx,
                name,
                obj,
                rest.AdmissionToValidateObjectFunc(admit, admissionAttributes, scope),
                options,
            )
        }
        // Dedup owner references before updating managed fields
        dedupOwnerReferencesAndAddWarning(obj, req.Context(), false)
        result, err := finisher.FinishRequest(ctx, func() (runtime.Object, error) {
      ...
      // 執行mutation的admission操作，即在創建時對象進行修改操作。
      // admin在buildGenericConfig中初始化，通過config傳遞給genericsever，然后傳遞到此處
            if mutatingAdmission, ok := admit.(admission.MutationInterface); ok && mutatingAdmission.Handles(admission.Create) {
                if err := mutatingAdmission.Admit(ctx, admissionAttributes, scope); err != nil {
                    return nil, err
                }
            }
            // Dedup owner references again after mutating admission happens
            dedupOwnerReferencesAndAddWarning(obj, req.Context(), true)
      // 調用創建方法
            result, err := requestFunc()
            ...
            return result, err
        })
        ...
    // resutl也是internal版本的對象，transformResponseObject會轉換為用戶請求的版本并輸出
        transformResponseObject(ctx, scope, trace, req, w, code, outputMediaType, result)
    }