Kubernetes 源码分析 -- API Server之编解码

// Scheme defines methods for serializing and deserializing API objects, a type
// registry for converting group, version, and kind information to and from Go
// schemas, and mappings between Go schemas of different versions. A scheme is the
// foundation for a versioned API and versioned configuration over time.
//
// In a Scheme, a Type is a particular Go struct, a Version is a point-in-time
// identifier for a particular representation of that Type (typically backwards
// compatible), a Kind is the unique name for that Type within the Version, and a
// Group identifies a set of Versions, Kinds, and Types that evolve over time. An
// Unversioned Type is one that is not yet formally bound to a type and is promised
// to be backwards compatible (effectively a "v1" of a Type that does not expect
// to break in the future).
//
// Schemes are not expected to change at runtime and are only threadsafe after
// registration is complete.
type Scheme struct {
	// versionMap allows one to figure out the go type of an object with
	// the given version and name.
	gvkToType map[schema.GroupVersionKind]reflect.Type

	// typeToGroupVersion allows one to find metadata for a given go object.
	// The reflect.Type we index by should *not* be a pointer.
	typeToGVK map[reflect.Type][]schema.GroupVersionKind

	// unversionedTypes are transformed without conversion in ConvertToVersion.
	unversionedTypes map[reflect.Type]schema.GroupVersionKind

	// unversionedKinds are the names of kinds that can be created in the context of any group
	// or version
	// TODO: resolve the status of unversioned types.
	unversionedKinds map[string]reflect.Type

	// Map from version and resource to the corresponding func to convert
	// resource field labels in that version to internal version.
	fieldLabelConversionFuncs map[schema.GroupVersionKind]FieldLabelConversionFunc

	// defaulterFuncs is an array of interfaces to be called with an object to provide defaulting
	// the provided object must be a pointer.
	defaulterFuncs map[reflect.Type]func(interface{})

	// converter stores all registered conversion functions. It also has
	// default converting behavior.
	converter *conversion.Converter

	// versionPriority is a map of groups to ordered lists of versions for those groups indicating the
	// default priorities of these versions as registered in the scheme
	versionPriority map[string][]string

	// observedVersions keeps track of the order we‘ve seen versions during type registration
	observedVersions []schema.GroupVersion

	// schemeName is the name of this scheme.  If you don‘t specify a name, the stack of the NewScheme caller will be used.
	// This is useful for error reporting to indicate the origin of the scheme.
	schemeName string
}

// New returns a new API object of the given version and name, or an error if it hasn‘t
// been registered. The version and kind fields must be specified.
func (s *Scheme) New(kind schema.GroupVersionKind) (Object, error) {
	if t, exists := s.gvkToType[kind]; exists {
		return reflect.New(t).Interface().(Object), nil
	}

	if t, exists := s.unversionedKinds[kind.Kind]; exists {
		return reflect.New(t).Interface().(Object), nil
	}
	return nil, NewNotRegisteredErrForKind(s.schemeName, kind)
}

var (
	// TODO: move SchemeBuilder with zz_generated.deepcopy.go to k8s.io/api.
	// localSchemeBuilder and AddToScheme will stay in k8s.io/kubernetes.
	SchemeBuilder      = runtime.NewSchemeBuilder(addKnownTypes)
	localSchemeBuilder = &SchemeBuilder
	AddToScheme        = localSchemeBuilder.AddToScheme
)