kubernetes/pkg/client/cache/store.go

/*
Copyright 2014 The Kubernetes Authors 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 cache

import (
	"fmt"
	"strings"

	"k8s.io/kubernetes/pkg/api/meta"
)

// Store is a generic object storage interface. Reflector knows how to watch a server
// and update a store. A generic store is provided, which allows Reflector to be used
// as a local caching system, and an LRU store, which allows Reflector to work like a
// queue of items yet to be processed.
//
// Store makes no assumptions about stored object identity; it is the responsibility
// of a Store implementation to provide a mechanism to correctly key objects and to
// define the contract for obtaining objects by some arbitrary key type.
type Store interface {
	Add(obj interface{}) error
	Update(obj interface{}) error
	Delete(obj interface{}) error
	List() []interface{}
	ListKeys() []string
	Get(obj interface{}) (item interface{}, exists bool, err error)
	GetByKey(key string) (item interface{}, exists bool, err error)

	// Replace will delete the contents of the store, using instead the
	// given list. Store takes ownership of the list, you should not reference
	// it after calling this function.
	Replace([]interface{}, string) error
}

// KeyFunc knows how to make a key from an object. Implementations should be deterministic.
type KeyFunc func(obj interface{}) (string, error)

// KeyError will be returned any time a KeyFunc gives an error; it includes the object
// at fault.
type KeyError struct {
	Obj interface{}
	Err error
}

// Error gives a human-readable description of the error.
func (k KeyError) Error() string {
	return fmt.Sprintf("couldn't create key for object %+v: %v", k.Obj, k.Err)
}

// ExplicitKey can be passed to MetaNamespaceKeyFunc if you have the key for
// the object but not the object itself.
type ExplicitKey string

// MetaNamespaceKeyFunc is a convenient default KeyFunc which knows how to make
// keys for API objects which implement meta.Interface.
// The key uses the format <namespace>/<name> unless <namespace> is empty, then
// it's just <name>.
//
// TODO: replace key-as-string with a key-as-struct so that this
// packing/unpacking won't be necessary.
func MetaNamespaceKeyFunc(obj interface{}) (string, error) {
	if key, ok := obj.(ExplicitKey); ok {
		return string(key), nil
	}
	meta, err := meta.Accessor(obj)
	if err != nil {
		return "", fmt.Errorf("object has no meta: %v", err)
	}
	if len(meta.Namespace()) > 0 {
		return meta.Namespace() + "/" + meta.Name(), nil
	}
	return meta.Name(), nil
}

// SplitMetaNamespaceKey returns the namespace and name that
// MetaNamespaceKeyFunc encoded into key.
//
// TODO: replace key-as-string with a key-as-struct so that this
// packing/unpacking won't be necessary.
func SplitMetaNamespaceKey(key string) (namespace, name string, err error) {
	parts := strings.Split(key, "/")
	switch len(parts) {
	case 1:
		// name only, no namespace
		return "", parts[0], nil
	case 2:
		// name and namespace
		return parts[0], parts[1], nil
	}

	return "", "", fmt.Errorf("unexpected key format: %q", key)
}

// cache responsibilities are limited to:
//	1. Computing keys for objects via keyFunc
//  2. Invoking methods of a ThreadSafeStorage interface
type cache struct {
	// cacheStorage bears the burden of thread safety for the cache
	cacheStorage ThreadSafeStore
	// keyFunc is used to make the key for objects stored in and retrieved from items, and
	// should be deterministic.
	keyFunc KeyFunc
}

// Add inserts an item into the cache.
func (c *cache) Add(obj interface{}) error {
	key, err := c.keyFunc(obj)
	if err != nil {
		return KeyError{obj, err}
	}
	c.cacheStorage.Add(key, obj)
	return nil
}

// Update sets an item in the cache to its updated state.
func (c *cache) Update(obj interface{}) error {
	key, err := c.keyFunc(obj)
	if err != nil {
		return KeyError{obj, err}
	}
	c.cacheStorage.Update(key, obj)
	return nil
}

// Delete removes an item from the cache.
func (c *cache) Delete(obj interface{}) error {
	key, err := c.keyFunc(obj)
	if err != nil {
		return KeyError{obj, err}
	}
	c.cacheStorage.Delete(key)
	return nil
}

// List returns a list of all the items.
// List is completely threadsafe as long as you treat all items as immutable.
func (c *cache) List() []interface{} {
	return c.cacheStorage.List()
}

// ListKeys returns a list of all the keys of the objects currently
// in the cache.
func (c *cache) ListKeys() []string {
	return c.cacheStorage.ListKeys()
}

// Index returns a list of items that match on the index function
// Index is thread-safe so long as you treat all items as immutable
func (c *cache) Index(indexName string, obj interface{}) ([]interface{}, error) {
	return c.cacheStorage.Index(indexName, obj)
}

// ListIndexFuncValues returns the list of generated values of an Index func
func (c *cache) ListIndexFuncValues(indexName string) []string {
	return c.cacheStorage.ListIndexFuncValues(indexName)
}

func (c *cache) ByIndex(indexName, indexKey string) ([]interface{}, error) {
	return c.cacheStorage.ByIndex(indexName, indexKey)
}

// Get returns the requested item, or sets exists=false.
// Get is completely threadsafe as long as you treat all items as immutable.
func (c *cache) Get(obj interface{}) (item interface{}, exists bool, err error) {
	key, err := c.keyFunc(obj)
	if err != nil {
		return nil, false, KeyError{obj, err}
	}
	return c.GetByKey(key)
}

// GetByKey returns the request item, or exists=false.
// GetByKey is completely threadsafe as long as you treat all items as immutable.
func (c *cache) GetByKey(key string) (item interface{}, exists bool, err error) {
	item, exists = c.cacheStorage.Get(key)
	return item, exists, nil
}

// Replace will delete the contents of 'c', using instead the given list.
// 'c' takes ownership of the list, you should not reference the list again
// after calling this function.
func (c *cache) Replace(list []interface{}, resourceVersion string) error {
	items := map[string]interface{}{}
	for _, item := range list {
		key, err := c.keyFunc(item)
		if err != nil {
			return KeyError{item, err}
		}
		items[key] = item
	}
	c.cacheStorage.Replace(items, resourceVersion)
	return nil
}

// NewStore returns a Store implemented simply with a map and a lock.
func NewStore(keyFunc KeyFunc) Store {
	return &cache{
		cacheStorage: NewThreadSafeStore(Indexers{}, Indices{}),
		keyFunc:      keyFunc,
	}
}

// NewIndexer returns an Indexer implemented simply with a map and a lock.
func NewIndexer(keyFunc KeyFunc, indexers Indexers) Indexer {
	return &cache{
		cacheStorage: NewThreadSafeStore(indexers, Indices{}),
		keyFunc:      keyFunc,
	}
}