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Published: Jun 30, 2020 License: BSD-3-Clause Imports: 22 Imported by: 2


Native Go Zookeeper Client Library

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3-clause BSD. See LICENSE file.



Package zk is a native Go client library for the ZooKeeper orchestration service.



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const (
	FlagEphemeral = 1
	FlagSequence  = 2
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const (
	PermRead = 1 << iota
	PermAll = 0x1f

Constants for ACL permissions

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const (
	DefaultPort = 2181


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var (
	ErrConnectionClosed        = errors.New("zk: connection closed")
	ErrUnknown                 = errors.New("zk: unknown error")
	ErrAPIError                = errors.New("zk: api error")
	ErrNoNode                  = errors.New("zk: node does not exist")
	ErrNoAuth                  = errors.New("zk: not authenticated")
	ErrBadVersion              = errors.New("zk: version conflict")
	ErrNoChildrenForEphemerals = errors.New("zk: ephemeral nodes may not have children")
	ErrNodeExists              = errors.New("zk: node already exists")
	ErrNotEmpty                = errors.New("zk: node has children")
	ErrSessionExpired          = errors.New("zk: session has been expired by the server")
	ErrInvalidACL              = errors.New("zk: invalid ACL specified")
	ErrAuthFailed              = errors.New("zk: client authentication failed")
	ErrClosing                 = errors.New("zk: zookeeper is closing")
	ErrNothing                 = errors.New("zk: no server responsees to process")
	ErrSessionMoved            = errors.New("zk: session moved to another server, so operation is ignored")
	ErrReconfigDisabled        = errors.New("attempts to perform a reconfiguration operation when reconfiguration feature is disabled")
	ErrBadArguments            = errors.New("invalid arguments")
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var (
	// ErrDeadlock is returned by Lock when trying to lock twice without unlocking first
	ErrDeadlock = errors.New("zk: trying to acquire a lock twice")
	// ErrNotLocked is returned by Unlock when trying to release a lock that has not first be acquired.
	ErrNotLocked = errors.New("zk: not locked")
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var (
	ErrUnhandledFieldType = errors.New("zk: unhandled field type")
	ErrPtrExpected        = errors.New("zk: encode/decode expect a non-nil pointer to struct")
	ErrShortBuffer        = errors.New("zk: buffer too small")
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var ErrInvalidPath = errors.New("zk: invalid path")

ErrInvalidPath indicates that an operation was being attempted on an invalid path. (e.g. empty path)

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var ErrNoServer = errors.New("zk: could not connect to a server")

ErrNoServer indicates that an operation cannot be completed because attempts to connect to all servers in the list failed.


func FLWRuok

func FLWRuok(servers []string, timeout time.Duration) []bool

FLWRuok is a FourLetterWord helper function. In particular, this function pulls the ruok output from each server.

func FormatServers

func FormatServers(servers []string) []string

FormatServers takes a slice of addresses, and makes sure they are in a format that resembles <addr>:<port>. If the server has no port provided, the DefaultPort constant is added to the end.

func WithDialer

func WithDialer(dialer Dialer) connOption

WithDialer returns a connection option specifying a non-default Dialer.

func WithEventCallback

func WithEventCallback(cb EventCallback) connOption

WithEventCallback returns a connection option that specifies an event callback. The callback must not block - doing so would delay the ZK go routines.

func WithHostProvider

func WithHostProvider(hostProvider HostProvider) connOption

WithHostProvider returns a connection option specifying a non-default HostProvider.

func WithLogInfo

func WithLogInfo(logInfo bool) connOption

WithLogInfo returns a connection option specifying whether or not information messages shoud be logged.

func WithLogger

func WithLogger(logger Logger) connOption

WithLogger returns a connection option specifying a non-default Logger

func WithMaxBufferSize

func WithMaxBufferSize(maxBufferSize int) connOption

WithMaxBufferSize sets the maximum buffer size used to read and decode packets received from the Zookeeper server. The standard Zookeeper client for Java defaults to a limit of 1mb. For backwards compatibility, this Go client defaults to unbounded unless overridden via this option. A value that is zero or negative indicates that no limit is enforced.

This is meant to prevent resource exhaustion in the face of potentially malicious data in ZK. It should generally match the server setting (which also defaults ot 1mb) so that clients and servers agree on the limits for things like the size of data in an individual znode and the total size of a transaction.

For production systems, this should be set to a reasonable value (ideally that matches the server configuration). For ops tooling, it is handy to use a much larger limit, in order to do things like clean-up problematic state in the ZK tree. For example, if a single znode has a huge number of children, it is possible for the response to a "list children" operation to exceed this buffer size and cause errors in clients. The only way to subsequently clean up the tree (by removing superfluous children) is to use a client configured with a larger buffer size that can successfully query for all of the child names and then remove them. (Note there are other tools that can list all of the child names without an increased buffer size in the client, but they work by inspecting the servers' transaction logs to enumerate children instead of sending an online request to a server.

func WithMaxConnBufferSize

func WithMaxConnBufferSize(maxBufferSize int) connOption

WithMaxConnBufferSize sets maximum buffer size used to send and encode packets to Zookeeper server. The standard Zookeepeer client for java defaults to a limit of 1mb. This option should be used for non-standard server setup where znode is bigger than default 1mb.


type ACL

type ACL struct {
	Perms  int32
	Scheme string
	ID     string

func AuthACL

func AuthACL(perms int32) []ACL

AuthACL produces an ACL list containing a single ACL which uses the provided permissions, with the scheme "auth", and ID "", which is used by ZooKeeper to represent any authenticated user.

func DigestACL

func DigestACL(perms int32, user, password string) []ACL

func WorldACL

func WorldACL(perms int32) []ACL

WorldACL produces an ACL list containing a single ACL which uses the provided permissions, with the scheme "world", and ID "anyone", which is used by ZooKeeper to represent any user at all.

type CheckVersionRequest

type CheckVersionRequest PathVersionRequest

type Conn

type Conn struct {
	// contains filtered or unexported fields

func Connect

func Connect(servers []string, sessionTimeout time.Duration, options ...connOption) (*Conn, <-chan Event, error)

Connect establishes a new connection to a pool of zookeeper servers. The provided session timeout sets the amount of time for which a session is considered valid after losing connection to a server. Within the session timeout it's possible to reestablish a connection to a different server and keep the same session. This is means any ephemeral nodes and watches are maintained.

func ConnectWithDialer

func ConnectWithDialer(servers []string, sessionTimeout time.Duration, dialer Dialer) (*Conn, <-chan Event, error)

ConnectWithDialer establishes a new connection to a pool of zookeeper servers using a custom Dialer. See Connect for further information about session timeout. This method is deprecated and provided for compatibility: use the WithDialer option instead.

func (*Conn) AddAuth

func (c *Conn) AddAuth(scheme string, auth []byte) error

func (*Conn) Children

func (c *Conn) Children(path string) ([]string, *Stat, error)

func (*Conn) ChildrenW

func (c *Conn) ChildrenW(path string) ([]string, *Stat, <-chan Event, error)

func (*Conn) Close

func (c *Conn) Close()

func (*Conn) Create

func (c *Conn) Create(path string, data []byte, flags int32, acl []ACL) (string, error)

func (*Conn) CreateProtectedEphemeralSequential

func (c *Conn) CreateProtectedEphemeralSequential(path string, data []byte, acl []ACL) (string, error)

CreateProtectedEphemeralSequential fixes a race condition if the server crashes after it creates the node. On reconnect the session may still be valid so the ephemeral node still exists. Therefore, on reconnect we need to check if a node with a GUID generated on create exists.

func (*Conn) Delete

func (c *Conn) Delete(path string, version int32) error

func (*Conn) Exists

func (c *Conn) Exists(path string) (bool, *Stat, error)

func (*Conn) ExistsW

func (c *Conn) ExistsW(path string) (bool, *Stat, <-chan Event, error)

func (*Conn) Get

func (c *Conn) Get(path string) ([]byte, *Stat, error)

func (*Conn) GetACL

func (c *Conn) GetACL(path string) ([]ACL, *Stat, error)

func (*Conn) GetW

func (c *Conn) GetW(path string) ([]byte, *Stat, <-chan Event, error)

GetW returns the contents of a znode and sets a watch

func (*Conn) IncrementalReconfig

func (c *Conn) IncrementalReconfig(joining, leaving []string, version int64) (*Stat, error)

IncrementalReconfig is the zookeeper reconfiguration api that allows adding and removing servers by lists of members. Return the new configuration stats.

func (*Conn) Multi

func (c *Conn) Multi(ops ...interface{}) ([]MultiResponse, error)

Multi executes multiple ZooKeeper operations or none of them. The provided ops must be one of *CreateRequest, *DeleteRequest, *SetDataRequest, or *CheckVersionRequest.

func (*Conn) Reconfig

func (c *Conn) Reconfig(members []string, version int64) (*Stat, error)

Reconfig is the non-incremental update functionality for Zookeeper where the list preovided is the entire new member list. the optional version allows for conditional reconfigurations, -1 ignores the condition.

func (*Conn) Server

func (c *Conn) Server() string

Server returns the current or last-connected server name.

func (*Conn) SessionID

func (c *Conn) SessionID() int64

SessionID returns the current session id of the connection.

func (*Conn) Set

func (c *Conn) Set(path string, data []byte, version int32) (*Stat, error)

func (*Conn) SetACL

func (c *Conn) SetACL(path string, acl []ACL, version int32) (*Stat, error)

func (*Conn) SetLogger

func (c *Conn) SetLogger(l Logger)

SetLogger sets the logger to be used for printing errors. Logger is an interface provided by this package.

func (*Conn) State

func (c *Conn) State() State

State returns the current state of the connection.

func (*Conn) Sync

func (c *Conn) Sync(path string) (string, error)

type CreateRequest

type CreateRequest struct {
	Path  string
	Data  []byte
	Acl   []ACL
	Flags int32

type DNSHostProvider

type DNSHostProvider struct {
	// contains filtered or unexported fields

DNSHostProvider is the default HostProvider. It currently matches the Java StaticHostProvider, resolving hosts from DNS once during the call to Init. It could be easily extended to re-query DNS periodically or if there is trouble connecting.

func (*DNSHostProvider) Connected

func (hp *DNSHostProvider) Connected()

Connected notifies the HostProvider of a successful connection.

func (*DNSHostProvider) Init

func (hp *DNSHostProvider) Init(servers []string) error

Init is called first, with the servers specified in the connection string. It uses DNS to look up addresses for each server, then shuffles them all together.

func (*DNSHostProvider) Len

func (hp *DNSHostProvider) Len() int

Len returns the number of servers available

func (*DNSHostProvider) Next

func (hp *DNSHostProvider) Next() (server string, retryStart bool)

Next returns the next server to connect to. retryStart will be true if we've looped through all known servers without Connected() being called.

type DeleteRequest

type DeleteRequest PathVersionRequest

type Dialer

type Dialer func(network, address string, timeout time.Duration) (net.Conn, error)

type ErrCode

type ErrCode int32

type Event

type Event struct {
	Type   EventType
	State  State
	Path   string // For non-session events, the path of the watched node.
	Err    error
	Server string // For connection events

type EventCallback

type EventCallback func(Event)

EventCallback is a function that is called when an Event occurs.

type EventType

type EventType int32
const (
	EventNodeCreated         EventType = 1
	EventNodeDeleted         EventType = 2
	EventNodeDataChanged     EventType = 3
	EventNodeChildrenChanged EventType = 4

	EventSession     EventType = -1
	EventNotWatching EventType = -2

func (EventType) String

func (t EventType) String() string

type HostProvider

type HostProvider interface {
	// Init is called first, with the servers specified in the connection string.
	Init(servers []string) error
	// Len returns the number of servers.
	Len() int
	// Next returns the next server to connect to. retryStart will be true if we've looped through
	// all known servers without Connected() being called.
	Next() (server string, retryStart bool)
	// Notify the HostProvider of a successful connection.

HostProvider is used to represent a set of hosts a ZooKeeper client should connect to. It is an analog of the Java equivalent: http://svn.apache.org/viewvc/zookeeper/trunk/src/java/main/org/apache/zookeeper/client/HostProvider.java?view=markup

type Lock

type Lock struct {
	// contains filtered or unexported fields

Lock is a mutual exclusion lock.

func NewLock

func NewLock(c *Conn, path string, acl []ACL) *Lock

NewLock creates a new lock instance using the provided connection, path, and acl. The path must be a node that is only used by this lock. A lock instances starts unlocked until Lock() is called.

func (*Lock) Lock

func (l *Lock) Lock() error

Lock attempts to acquire the lock. It will wait to return until the lock is acquired or an error occurs. If this instance already has the lock then ErrDeadlock is returned.

func (*Lock) Unlock

func (l *Lock) Unlock() error

Unlock releases an acquired lock. If the lock is not currently acquired by this Lock instance than ErrNotLocked is returned.

type Logger

type Logger interface {
	Printf(string, ...interface{})

Logger is an interface that can be implemented to provide custom log output.

var DefaultLogger Logger = defaultLogger{}

DefaultLogger uses the stdlib log package for logging.

type Mode

type Mode uint8

Mode is used to build custom server modes (leader|follower|standalone).

const (
	ModeUnknown    Mode = iota
	ModeLeader     Mode = iota
	ModeFollower   Mode = iota
	ModeStandalone Mode = iota

func (Mode) String

func (m Mode) String() string

type MultiResponse

type MultiResponse struct {
	Stat   *Stat
	String string
	Error  error

type PathVersionRequest

type PathVersionRequest struct {
	Path    string
	Version int32

type ServerClient

type ServerClient struct {
	Queued        int64
	Received      int64
	Sent          int64
	SessionID     int64
	Lcxid         int64
	Lzxid         int64
	Timeout       int32
	LastLatency   int32
	MinLatency    int32
	AvgLatency    int32
	MaxLatency    int32
	Established   time.Time
	LastResponse  time.Time
	Addr          string
	LastOperation string // maybe?
	Error         error

ServerClient is the information for a single Zookeeper client and its session. This is used to parse/extract the output fo the `cons` command.

type ServerClients

type ServerClients struct {
	Clients []*ServerClient
	Error   error

ServerClients is a struct for the FLWCons() function. It's used to provide the list of Clients.

This is needed because FLWCons() takes multiple servers.

func FLWCons

func FLWCons(servers []string, timeout time.Duration) ([]*ServerClients, bool)

FLWCons is a FourLetterWord helper function. In particular, this function pulls the ruok output from each server.

As with FLWSrvr, the boolean value indicates whether one of the requests had an issue. The Clients struct has an Error value that can be checked.

type ServerStats

type ServerStats struct {
	Sent        int64
	Received    int64
	NodeCount   int64
	MinLatency  int64
	AvgLatency  int64
	MaxLatency  int64
	Connections int64
	Outstanding int64
	Epoch       int32
	Counter     int32
	BuildTime   time.Time
	Mode        Mode
	Version     string
	Error       error

ServerStats is the information pulled from the Zookeeper `stat` command.

func FLWSrvr

func FLWSrvr(servers []string, timeout time.Duration) ([]*ServerStats, bool)

FLWSrvr is a FourLetterWord helper function. In particular, this function pulls the srvr output from the zookeeper instances and parses the output. A slice of *ServerStats structs are returned as well as a boolean value to indicate whether this function processed successfully.

If the boolean value is false there was a problem. If the *ServerStats slice is empty or nil, then the error happened before we started to obtain 'srvr' values. Otherwise, one of the servers had an issue and the "Error" value in the struct should be inspected to determine which server had the issue.

type SetDataRequest

type SetDataRequest struct {
	Path    string
	Data    []byte
	Version int32

type Stat

type Stat struct {
	Czxid          int64 // The zxid of the change that caused this znode to be created.
	Mzxid          int64 // The zxid of the change that last modified this znode.
	Ctime          int64 // The time in milliseconds from epoch when this znode was created.
	Mtime          int64 // The time in milliseconds from epoch when this znode was last modified.
	Version        int32 // The number of changes to the data of this znode.
	Cversion       int32 // The number of changes to the children of this znode.
	Aversion       int32 // The number of changes to the ACL of this znode.
	EphemeralOwner int64 // The session id of the owner of this znode if the znode is an ephemeral node. If it is not an ephemeral node, it will be zero.
	DataLength     int32 // The length of the data field of this znode.
	NumChildren    int32 // The number of children of this znode.
	Pzxid          int64 // last modified children

type State

type State int32
const (
	StateUnknown           State = -1
	StateDisconnected      State = 0
	StateConnecting        State = 1
	StateAuthFailed        State = 4
	StateConnectedReadOnly State = 5
	StateSaslAuthenticated State = 6
	StateExpired           State = -112

	StateConnected  = State(100)
	StateHasSession = State(101)

func (State) String

func (s State) String() string


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