datastore.go

package libdatastore

import (
	"fmt"
	"log"
	"strings"
	"sync"

	"github.com/docker/libkv"
	"github.com/docker/libkv/store"
	"github.com/docker/libkv/store/boltdb"
	"github.com/docker/libkv/store/consul"
	"github.com/docker/libkv/store/etcd"
	"github.com/docker/libkv/store/zookeeper"
)

//DataStore exported
type DataStore interface {
	// GetObject gets data from datastore and unmarshals to the specified object
	GetObject(key string, o KVObject) error
	// PutObject adds a new Record based on an object into the datastore
	PutObject(kvObject KVObject) error
	// PutObjectAtomic provides an atomic add and update operation for a Record
	PutObjectAtomic(kvObject KVObject) error
	// DeleteObject deletes a record
	DeleteObject(kvObject KVObject) error
	// DeleteObjectAtomic performs an atomic delete operation
	DeleteObjectAtomic(kvObject KVObject) error
	// DeleteTree deletes a record
	DeleteTree(kvObject KVObject) error
	// Watchable returns whether the store is watchable are not
	Watchable() bool
	// Watch for changes on a KVObject
	Watch(kvObject KVObject, stopCh <-chan struct{}) (<-chan KVObject, error)
	// RestartWatch retriggers stopped Watches
	RestartWatch()
	// Active returns if the store is active
	Active() bool
	// List returns of a list of KVObjects belonging to the parent
	// key. The caller must pass a KVObject of the same type as
	// the objects that need to be listed
	List(string, KVObject) ([]KVObject, error)
	// Scope returns the scope of the store
	Scope() string
	// KVStore returns access to the KV Store
	KVStore() store.Store
	// Close closes the data store
	Close()
}

var ErrKeyNotFound = store.ErrKeyNotFound

type datastore struct {
	scope      string
	store      store.Store
	cache      *cache
	watchCh    chan struct{}
	active     bool
	rootchains []string
	sync.Mutex
}

// KVObject is  Key/Value interface used by objects to be part of the DataStore
type KVObject interface {
	// Key method lets an object to provide the Key to be used in KV Store
	Key() []string
	// KeyPrefix method lets an object to return immediate parent key that can be used for tree walk
	KeyPrefix() []string
	// Value method lets an object to marshal its content to be stored in the KV store
	Value() []byte
	// SetValue is used by the datastore to set the object's value when loaded from the data store.
	SetValue([]byte) error
	// Index method returns the latest DB Index as seen by the object
	Index() uint64
	// SetIndex method allows the datastore to store the latest DB Index into the object
	SetIndex(uint64)
	// True if the object exists in the datastore, false if it hasn't been stored yet.
	// When SetIndex() is called, the object has been stored.
	Exists() bool
	// DataScope indicates the storage scope of the KV object
	DataScope() string
	// Skip provides a way for a KV Object to avoid persisting it in the KV Store
	Skip() bool
}

// KVConstructor interface defines methods which can construct a KVObject from another.
type KVConstructor interface {
	// New returns a new object which is created based on the
	// source object
	New() KVObject
	// CopyTo deep copies the contents of the implementing object
	// to the passed destination object
	CopyTo(KVObject) error
}

// ScopeCfg represents Datastore configuration.
type ScopeCfg struct {
	Client ScopeClientCfg
}

// ScopeClientCfg represents Datastore Client-only mode configuration
type ScopeClientCfg struct {
	Provider string
	Address  string
	Config   *store.Config
}

const (
// LocalScope indicates to store the KV object in local datastore such as boltdb
	LocalScope = "local"
// GlobalScope indicates to store the KV object in global datastore such as consul/etcd/zookeeper
	GlobalScope = "global"
)

func init() {
	consul.Register()
	zookeeper.Register()
	etcd.Register()
	boltdb.Register()
}

// IsValid checks if the scope config has valid configuration.
func (cfg *ScopeCfg) IsValid() bool {
	if cfg == nil ||
	strings.TrimSpace(cfg.Client.Provider) == "" ||
	strings.TrimSpace(cfg.Client.Address) == "" {
		return false
	}

	return true
}

// newClient used to connect to KV Store
func newClient(scope string, kv string, addr string, config *store.Config, cached bool) (DataStore, error) {
	if cached && scope != LocalScope {
		return nil, fmt.Errorf("caching supported only for scope %s", LocalScope)
	}

	if config == nil {
		config = &store.Config{}
	}

	var (
		addrs []string
		rootchains []string
	)

	if kv == string(store.BOLTDB) {
		// Parse file path
		addrs = strings.Split(addr, ",")
	} else {
		// Parse URI
		parts := strings.SplitN(addr, "/", 2)
		addrs = strings.Split(parts[0], ",")

		// Add the custom prefix to the root chain
		if len(parts) == 2 {
			rootchains = strings.Split(parts[1], "/")
		}
	}

	store, err := libkv.NewStore(store.Backend(kv), addrs, config)
	if err != nil {
		return nil, err
	}

	ds := &datastore{scope: scope, store: store, active: true, watchCh: make(chan struct{}), rootchains: rootchains}
	if cached {
		ds.cache = newCache(ds)
	}

	return ds, nil
}

// NewDataStore creates a new instance of LibKV data store
func NewDataStore(scope string, cfg *ScopeCfg) (DataStore, error) {
	if cfg == nil || cfg.Client.Provider == "" || cfg.Client.Address == "" {
		return nil, fmt.Errorf("unexpected scope %s without configuration passed", scope)
	}

	var cached bool
	if scope == LocalScope {
		cached = true
	}

	return newClient(scope, cfg.Client.Provider, cfg.Client.Address, cfg.Client.Config, cached)
}

func (ds *datastore) Close() {
	ds.store.Close()
}

func (ds *datastore) Scope() string {
	return ds.scope
}

func (ds *datastore) Active() bool {
	return ds.active
}

func (ds *datastore) Watchable() bool {
	return ds.scope != LocalScope
}

func (ds *datastore) key(key ...string) string {
	keychain := append(ds.rootchains, key...)
	str := strings.Join(keychain, "/")
	return str + "/"
}

func (ds *datastore) Watch(kvObject KVObject, stopCh <-chan struct{}) (<-chan KVObject, error) {
	sCh := make(chan struct{})

	ctor, ok := kvObject.(KVConstructor)
	if !ok {
		return nil, fmt.Errorf("error watching object type %T, object does not implement KVConstructor interface", kvObject)
	}

	kvpCh, err := ds.store.Watch(ds.key(kvObject.Key()...), sCh)
	if err != nil {
		return nil, err
	}

	kvoCh := make(chan KVObject)

	go func() {
		retry_watch:
		var err error

		// Make sure to get a new instance of watch channel
		ds.Lock()
		watchCh := ds.watchCh
		ds.Unlock()

		loop:
		for {
			select {
			case <-stopCh:
				close(sCh)
				return
			case kvPair := <-kvpCh:
			// If the backend KV store gets reset libkv's go routine
			// for the watch can exit resulting in a nil value in
			// channel.
				if kvPair == nil {
					ds.Lock()
					ds.active = false
					ds.Unlock()
					break loop
				}

				dstO := ctor.New()

				if err = dstO.SetValue(kvPair.Value); err != nil {
					log.Printf("Could not unmarshal kvpair value = %s", string(kvPair.Value))
					break
				}

				dstO.SetIndex(kvPair.LastIndex)
				kvoCh <- dstO
			}
		}

		// Wait on watch channel for a re-trigger when datastore becomes active
		<-watchCh

		kvpCh, err = ds.store.Watch(ds.key(kvObject.Key()...), sCh)
		if err != nil {
			log.Printf("Could not watch the key %s in store: %v", ds.key(kvObject.Key()...), err)
		}

		goto retry_watch
	}()

	return kvoCh, nil
}

func (ds *datastore) RestartWatch() {
	ds.Lock()
	defer ds.Unlock()

	ds.active = true
	watchCh := ds.watchCh
	ds.watchCh = make(chan struct{})
	close(watchCh)
}

func (ds *datastore) KVStore() store.Store {
	return ds.store
}

// PutObjectAtomic adds a new Record based on an object into the datastore
func (ds *datastore) PutObjectAtomic(kvObject KVObject) error {
	var (
		previous *store.KVPair
		pair     *store.KVPair
		err error
	)
	ds.Lock()
	defer ds.Unlock()

	if kvObject == nil {
		return fmt.Errorf("invalid KV Object : nil")
	}

	kvObjValue := kvObject.Value()

	if kvObjValue == nil {
		return fmt.Errorf("invalid KV Object with a nil Value for key %s", ds.key(kvObject.Key()...))
	}

	if kvObject.Skip() {
		goto add_cache
	}

	if kvObject.Exists() {
		previous = &store.KVPair{Key: ds.key(kvObject.Key()...), LastIndex: kvObject.Index()}
	} else {
		previous = nil
	}

	_, pair, err = ds.store.AtomicPut(ds.key(kvObject.Key()...), kvObjValue, previous, nil)
	if err != nil {
		return err
	}

	kvObject.SetIndex(pair.LastIndex)

	add_cache:
	if ds.cache != nil {
		return ds.cache.add(kvObject)
	}

	return nil
}

// PutObject adds a new Record based on an object into the datastore
func (ds *datastore) PutObject(kvObject KVObject) error {
	ds.Lock()
	defer ds.Unlock()

	if kvObject == nil {
		return fmt.Errorf("invalid KV Object : nil")
	}

	if kvObject.Skip() {
		goto add_cache
	}

	if err := ds.putObjectWithKey(kvObject, kvObject.Key()...); err != nil {
		return err
	}

	add_cache:
	if ds.cache != nil {
		return ds.cache.add(kvObject)
	}

	return nil
}

func (ds *datastore) putObjectWithKey(kvObject KVObject, key ...string) error {
	kvObjValue := kvObject.Value()

	if kvObjValue == nil {
		return fmt.Errorf("invalid KV Object with a nil Value for key %s", ds.key(kvObject.Key()...))
	}
	return ds.store.Put(ds.key(key...), kvObjValue, nil)
}

// GetObject returns a record matching the key
func (ds *datastore) GetObject(key string, o KVObject) error {
	ds.Lock()
	defer ds.Unlock()

	if ds.cache != nil {
		return ds.cache.get(key, o)
	}

	kvPair, err := ds.store.Get(key)
	if err != nil {
		return err
	}

	if err := o.SetValue(kvPair.Value); err != nil {
		return err
	}

	// Make sure the object has a correct view of the DB index in
	// case we need to modify it and update the DB.
	o.SetIndex(kvPair.LastIndex)
	return nil
}

func (ds *datastore) ensureParent(parent string) error {
	exists, err := ds.store.Exists(parent)
	if err != nil {
		return err
	}
	if exists {
		return nil
	}
	return ds.store.Put(parent, []byte{}, &store.WriteOptions{IsDir: true})
}

func (ds *datastore) List(key string, kvObject KVObject) ([]KVObject, error) {
	ds.Lock()
	defer ds.Unlock()

	if ds.cache != nil {
		return ds.cache.list(kvObject)
	}

	// Bail out right away if the kvObject does not implement KVConstructor
	ctor, ok := kvObject.(KVConstructor)
	if !ok {
		return nil, fmt.Errorf("error listing objects, object does not implement KVConstructor interface")
	}

	// Make sure the parent key exists
	if err := ds.ensureParent(key); err != nil {
		return nil, err
	}

	kvList, err := ds.store.List(key)
	if err != nil {
		return nil, err
	}

	var kvol []KVObject
	for _, kvPair := range kvList {
		if len(kvPair.Value) == 0 {
			continue
		}

		dstO := ctor.New()
		if err := dstO.SetValue(kvPair.Value); err != nil {
			return nil, err
		}

		// Make sure the object has a correct view of the DB index in
		// case we need to modify it and update the DB.
		dstO.SetIndex(kvPair.LastIndex)

		kvol = append(kvol, dstO)
	}

	return kvol, nil
}

// DeleteObject unconditionally deletes a record from the store
func (ds *datastore) DeleteObject(kvObject KVObject) error {
	ds.Lock()
	defer ds.Unlock()

	// cleaup the cache first
	if ds.cache != nil {
		ds.cache.del(kvObject)
	}

	if kvObject.Skip() {
		return nil
	}

	return ds.store.Delete(ds.key(kvObject.Key()...))
}

// DeleteObjectAtomic performs atomic delete on a record
func (ds *datastore) DeleteObjectAtomic(kvObject KVObject) error {
	ds.Lock()
	defer ds.Unlock()

	if kvObject == nil {
		return fmt.Errorf("invalid KV Object : nil")
	}

	previous := &store.KVPair{Key: ds.key(kvObject.Key()...), LastIndex: kvObject.Index()}

	if kvObject.Skip() {
		goto del_cache
	}

	if _, err := ds.store.AtomicDelete(ds.key(kvObject.Key()...), previous); err != nil {
		return err
	}

	del_cache:
	// cleanup the cache only if AtomicDelete went through successfully
	if ds.cache != nil {
		return ds.cache.del(kvObject)
	}

	return nil
}

// DeleteTree unconditionally deletes a record from the store
func (ds *datastore) DeleteTree(kvObject KVObject) error {
	ds.Lock()
	defer ds.Unlock()

	// cleaup the cache first
	if ds.cache != nil {
		ds.cache.del(kvObject)
	}

	if kvObject.Skip() {
		return nil
	}

	return ds.store.DeleteTree(ds.key(kvObject.KeyPrefix()...))
}