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zookeeper.go
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zookeeper.go
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package zookeeper
import (
"strings"
"time"
"github.com/abronan/valkeyrie"
"github.com/abronan/valkeyrie/store"
"github.com/samuel/go-zookeeper/zk"
)
const (
// SOH control character
SOH = "\x01"
defaultTimeout = 10 * time.Second
syncRetryLimit = 5
)
// Zookeeper is the receiver type for
// the Store interface
type Zookeeper struct {
timeout time.Duration
client *zk.Conn
}
type zookeeperLock struct {
client *zk.Conn
lock *zk.Lock
key string
value []byte
}
// Register registers zookeeper to valkeyrie
func Register() {
valkeyrie.AddStore(store.ZK, New)
}
// New creates a new Zookeeper client given a
// list of endpoints and an optional tls config
func New(endpoints []string, options *store.Config) (store.Store, error) {
s := &Zookeeper{}
s.timeout = defaultTimeout
// Set options
if options != nil {
if options.ConnectionTimeout != 0 {
s.setTimeout(options.ConnectionTimeout)
}
}
// Connect to Zookeeper
conn, _, err := zk.Connect(endpoints, s.timeout)
if err != nil {
return nil, err
}
s.client = conn
return s, nil
}
// setTimeout sets the timeout for connecting to Zookeeper
func (s *Zookeeper) setTimeout(time time.Duration) {
s.timeout = time
}
// Get the value at "key", returns the last modified index
// to use in conjunction to Atomic calls
func (s *Zookeeper) Get(key string, opts *store.ReadOptions) (pair *store.KVPair, err error) {
resp, meta, err := s.get(key)
if err != nil {
return nil, err
}
pair = &store.KVPair{
Key: key,
Value: resp,
LastIndex: uint64(meta.Version),
}
return pair, nil
}
// createFullPath creates the entire path for a directory
// that does not exist and sets the value of the last
// znode to data
func (s *Zookeeper) createFullPath(path []string, data []byte, ephemeral bool) error {
for i := 1; i <= len(path); i++ {
newpath := "/" + strings.Join(path[:i], "/")
if i == len(path) {
flag := 0
if ephemeral {
flag = zk.FlagEphemeral
}
_, err := s.client.Create(newpath, data, int32(flag), zk.WorldACL(zk.PermAll))
return err
}
_, err := s.client.Create(newpath, []byte{}, 0, zk.WorldACL(zk.PermAll))
if err != nil {
// Skip if node already exists
if err != zk.ErrNodeExists {
return err
}
}
}
return nil
}
// Put a value at "key"
func (s *Zookeeper) Put(key string, value []byte, opts *store.WriteOptions) error {
fkey := s.normalize(key)
exists, err := s.Exists(key, nil)
if err != nil {
return err
}
if !exists {
if opts != nil && opts.TTL > 0 {
_ = s.createFullPath(store.SplitKey(strings.TrimSuffix(key, "/")), value, true)
} else {
_ = s.createFullPath(store.SplitKey(strings.TrimSuffix(key, "/")), value, false)
}
} else {
_, err = s.client.Set(fkey, value, -1)
}
return err
}
// Delete a value at "key"
func (s *Zookeeper) Delete(key string) error {
err := s.client.Delete(s.normalize(key), -1)
if err == zk.ErrNoNode {
return store.ErrKeyNotFound
}
return err
}
// Exists checks if the key exists inside the store
func (s *Zookeeper) Exists(key string, opts *store.ReadOptions) (bool, error) {
exists, _, err := s.client.Exists(s.normalize(key))
if err != nil {
return false, err
}
return exists, nil
}
// Watch for changes on a "key"
// It returns a channel that will receive changes or pass
// on errors. Upon creation, the current value will first
// be sent to the channel. Providing a non-nil stopCh can
// be used to stop watching.
func (s *Zookeeper) Watch(key string, stopCh <-chan struct{}, opts *store.ReadOptions) (<-chan *store.KVPair, error) {
// Catch zk notifications and fire changes into the channel.
watchCh := make(chan *store.KVPair)
go func() {
defer close(watchCh)
var fireEvt = true
for {
resp, meta, eventCh, err := s.getW(key)
if err != nil {
return
}
if fireEvt {
watchCh <- &store.KVPair{
Key: key,
Value: resp,
LastIndex: uint64(meta.Version),
}
}
select {
case e := <-eventCh:
// Only fire an event if the data in the node changed.
// Simply reset the watch if this is any other event
// (e.g. a session event).
fireEvt = e.Type == zk.EventNodeDataChanged
case <-stopCh:
// There is no way to stop GetW so just quit
return
}
}
}()
return watchCh, nil
}
// WatchTree watches for changes on a "directory"
// It returns a channel that will receive changes or pass
// on errors. Upon creating a watch, the current childs values
// will be sent to the channel .Providing a non-nil stopCh can
// be used to stop watching.
func (s *Zookeeper) WatchTree(directory string, stopCh <-chan struct{}, opts *store.ReadOptions) (<-chan []*store.KVPair, error) {
// Catch zk notifications and fire changes into the channel.
watchCh := make(chan []*store.KVPair)
go func() {
defer close(watchCh)
var fireEvt = true
for {
WATCH:
keys, _, eventCh, err := s.client.ChildrenW(s.normalize(directory))
if err != nil {
return
}
if fireEvt {
kvs, err := s.getListWithPath(directory, keys, opts)
if err != nil {
// Failed to get values for one or more of the keys,
// the list may be out of date so try again.
goto WATCH
}
watchCh <- kvs
}
select {
case e := <-eventCh:
// Only fire an event if the children have changed.
// Simply reset the watch if this is any other event
// (e.g. a session event).
fireEvt = e.Type == zk.EventNodeChildrenChanged
case <-stopCh:
// There is no way to stop ChildrenW so just quit
return
}
}
}()
return watchCh, nil
}
// listChildren lists the direct children of a directory
func (s *Zookeeper) listChildren(directory string) ([]string, error) {
children, _, err := s.client.Children(s.normalize(directory))
if err != nil {
if err == zk.ErrNoNode {
return nil, store.ErrKeyNotFound
}
return nil, err
}
return children, nil
}
// listChildrenRecursive lists the children of a directory as well as
// all the descending childs from sub-folders in a recursive fashion.
func (s *Zookeeper) listChildrenRecursive(list *[]string, directory string) error {
children, err := s.listChildren(directory)
if err != nil {
return err
}
// We reached a leaf.
if len(children) == 0 {
return nil
}
for _, c := range children {
c = strings.TrimSuffix(directory, "/") + "/" + c
err := s.listChildrenRecursive(list, c)
if err != nil && err != zk.ErrNoChildrenForEphemerals {
return err
}
*list = append(*list, c)
}
return nil
}
// List child nodes of a given directory
func (s *Zookeeper) List(directory string, opts *store.ReadOptions) ([]*store.KVPair, error) {
children := make([]string, 0)
err := s.listChildrenRecursive(&children, directory)
if err != nil {
return nil, err
}
kvs, err := s.getList(children, opts)
if err != nil {
// If node is not found: List is out of date, retry
if err == store.ErrKeyNotFound {
return s.List(directory, opts)
}
return nil, err
}
return kvs, nil
}
// DeleteTree deletes a range of keys under a given directory
func (s *Zookeeper) DeleteTree(directory string) error {
children, err := s.listChildren(directory)
if err != nil {
return err
}
var reqs []interface{}
for _, c := range children {
reqs = append(reqs, &zk.DeleteRequest{
Path: s.normalize(directory + "/" + c),
Version: -1,
})
}
_, err = s.client.Multi(reqs...)
return err
}
// AtomicPut put a value at "key" if the key has not been
// modified in the meantime, throws an error if this is the case
func (s *Zookeeper) AtomicPut(key string, value []byte, previous *store.KVPair, _ *store.WriteOptions) (bool, *store.KVPair, error) {
var lastIndex uint64
if previous != nil {
meta, err := s.client.Set(s.normalize(key), value, int32(previous.LastIndex))
if err != nil {
// Compare Failed
if err == zk.ErrBadVersion {
return false, nil, store.ErrKeyModified
}
return false, nil, err
}
lastIndex = uint64(meta.Version)
} else {
// Interpret previous == nil as create operation.
_, err := s.client.Create(s.normalize(key), value, 0, zk.WorldACL(zk.PermAll))
if err != nil {
// Directory does not exist
if err == zk.ErrNoNode {
// Create the directory
parts := store.SplitKey(strings.TrimSuffix(key, "/"))
parts = parts[:len(parts)-1]
if err = s.createFullPath(parts, []byte{}, false); err != nil {
// Failed to create the directory.
return false, nil, err
}
// Create the node
if _, err := s.client.Create(s.normalize(key), value, 0, zk.WorldACL(zk.PermAll)); err != nil {
// Node exist error (when previous nil)
if err == zk.ErrNodeExists {
return false, nil, store.ErrKeyExists
}
return false, nil, err
}
} else {
// Node Exists error (when previous nil)
if err == zk.ErrNodeExists {
return false, nil, store.ErrKeyExists
}
// Unhandled error
return false, nil, err
}
}
lastIndex = 0 // Newly created nodes have version 0.
}
pair := &store.KVPair{
Key: key,
Value: value,
LastIndex: lastIndex,
}
return true, pair, nil
}
// AtomicDelete deletes a value at "key" if the key
// has not been modified in the meantime, throws an
// error if this is the case
func (s *Zookeeper) AtomicDelete(key string, previous *store.KVPair) (bool, error) {
if previous == nil {
return false, store.ErrPreviousNotSpecified
}
err := s.client.Delete(s.normalize(key), int32(previous.LastIndex))
if err != nil {
// Key not found
if err == zk.ErrNoNode {
return false, store.ErrKeyNotFound
}
// Compare failed
if err == zk.ErrBadVersion {
return false, store.ErrKeyModified
}
// General store error
return false, err
}
return true, nil
}
// NewLock returns a handle to a lock struct which can
// be used to provide mutual exclusion on a key
func (s *Zookeeper) NewLock(key string, options *store.LockOptions) (lock store.Locker, err error) {
value := []byte("")
// Apply options
if options != nil {
if options.Value != nil {
value = options.Value
}
}
lock = &zookeeperLock{
client: s.client,
key: s.normalize(key),
value: value,
lock: zk.NewLock(s.client, s.normalize(key), zk.WorldACL(zk.PermAll)),
}
return lock, err
}
// Lock attempts to acquire the lock and blocks while
// doing so. It returns a channel that is closed if our
// lock is lost or if an error occurs
func (l *zookeeperLock) Lock(stopChan chan struct{}) (<-chan struct{}, error) {
err := l.lock.Lock()
lostCh := make(chan struct{})
if err == nil {
// We hold the lock, we can set our value
_, err = l.client.Set(l.key, l.value, -1)
if err == nil {
go l.monitorLock(stopChan, lostCh)
}
}
return lostCh, err
}
// Unlock the "key". Calling unlock while
// not holding the lock will throw an error
func (l *zookeeperLock) Unlock() error {
return l.lock.Unlock()
}
// Close closes the client connection
func (s *Zookeeper) Close() {
s.client.Close()
}
// Normalize the key for usage in Zookeeper
func (s *Zookeeper) normalize(key string) string {
key = store.Normalize(key)
return strings.TrimSuffix(key, "/")
}
func (l *zookeeperLock) monitorLock(stopCh <-chan struct{}, lostCh chan struct{}) {
defer close(lostCh)
for {
_, _, eventCh, err := l.client.GetW(l.key)
if err != nil {
// We failed to set watch, relinquish the lock
return
}
select {
case e := <-eventCh:
if e.Type == zk.EventNotWatching ||
(e.Type == zk.EventSession && e.State == zk.StateExpired) {
// Either the session has been closed and our watch has been
// invalidated or the session has expired.
return
} else if e.Type == zk.EventNodeDataChanged {
// Somemone else has written to the lock node and believes
// that they have the lock.
return
}
case <-stopCh:
// The caller has requested that we relinquish our lock
return
}
}
}
func (s *Zookeeper) get(key string) ([]byte, *zk.Stat, error) {
var resp []byte
var meta *zk.Stat
var err error
// To guard against older versions of valkeyrie
// creating and writing to znodes non-atomically,
// We try to resync few times if we read SOH or
// an empty string
for i := 0; i <= syncRetryLimit; i++ {
resp, meta, err = s.client.Get(s.normalize(key))
if err != nil {
if err == zk.ErrNoNode {
return nil, nil, store.ErrKeyNotFound
}
return nil, nil, err
}
if string(resp) != SOH && string(resp) != "" {
return resp, meta, nil
}
if i < syncRetryLimit {
if _, err = s.client.Sync(s.normalize(key)); err != nil {
return nil, nil, err
}
}
}
return resp, meta, nil
}
func (s *Zookeeper) getW(key string) ([]byte, *zk.Stat, <-chan zk.Event, error) {
var resp []byte
var meta *zk.Stat
var ech <-chan zk.Event
var err error
// To guard against older versions of valkeyrie
// creating and writing to znodes non-atomically,
// We try to resync few times if we read SOH or
// an empty string
for i := 0; i <= syncRetryLimit; i++ {
resp, meta, ech, err = s.client.GetW(s.normalize(key))
if err != nil {
if err == zk.ErrNoNode {
return nil, nil, nil, store.ErrKeyNotFound
}
return nil, nil, nil, err
}
if string(resp) != SOH && string(resp) != "" {
return resp, meta, ech, nil
}
if i < syncRetryLimit {
if _, err = s.client.Sync(s.normalize(key)); err != nil {
return nil, nil, nil, err
}
}
}
return resp, meta, ech, nil
}
// getListWithPath gets the key/value pairs for a list of keys under
// a given path.
//
// This is generally used when we get a list of child keys which
// are stripped out of their path (for example when using ChildrenW).
func (s *Zookeeper) getListWithPath(path string, keys []string, opts *store.ReadOptions) ([]*store.KVPair, error) {
kvs := []*store.KVPair{}
for _, key := range keys {
pair, err := s.Get(strings.TrimSuffix(path, "/")+s.normalize(key), opts)
if err != nil {
return nil, err
}
kvs = append(kvs, &store.KVPair{
Key: key,
Value: pair.Value,
LastIndex: pair.LastIndex,
})
}
return kvs, nil
}
// getList returns key/value pairs from a list of keys.
//
// This is generally used when we have a full list of keys with
// their full path included.
func (s *Zookeeper) getList(keys []string, opts *store.ReadOptions) ([]*store.KVPair, error) {
kvs := []*store.KVPair{}
for _, key := range keys {
pair, err := s.Get(strings.TrimSuffix(key, "/"), nil)
if err != nil {
return nil, err
}
kvs = append(kvs, &store.KVPair{
Key: key,
Value: pair.Value,
LastIndex: pair.LastIndex,
})
}
return kvs, nil
}