zkjs

A js node client for ZooKeeper

Example

 
var ZK = require('zkjs')
 
var zk = new ZK({
    hosts: ['localhost:2181', 'localhost:2182', 'localhost:2183'],
    root: '/myapp/root'
})
 
zk.start(function (err) {
 
    zk.create(
        '/foo',
        'some ephemeral data',
        ZK.create.EPHEMERAL,
        function (err, path) {
            if (!err) {
                console.log(path, 'was created')
            }
        }
    )
 
    zk.getChildren(
        '/',
        function (err, children, zstat) {
            if (!err) {
                console.log('/', 'has', children.length, 'children')
            }
        }
    )
 
    zk.get(
        '/some/known/node',
        function (watch) {
            console.log(watch.path, 'was', watch.type)
        },
        function (err, value, zstat) {
            console.log('the current value is ', value.toString())
 
            zk.set(
                '/some/known/node',
                'some new data',
                zstat.version,
                function (err, zstat) {
                    if (!err) {
                        console.log('the new version number is', zstat.version)
                    }
                }
            )
        }
    )
})

---

API

ZK

new

var ZK = require('zkjs')
 
var zk = new ZK({
    hosts: ['localhost:2181'],        // array of zookeeper instances
    root: '/',                        // the root path for the session
    readOnly: false,                  // allow read-only connections
    timeout: 120000,                  // requested timeout for the session
    requestTimeout: 30000,            // milliseconds before timing out a zk request
    maxReconnectAttempts: 15,         // number of attempts to re-establish a connection
    retryPolicy: ZK.retry.no()        // default retry policy
    retryOn: ZK.errors.RETRY_DEFAULTS,// array of error codes to automatically retry
    autoResetWatches: true,           // maintain watches if the zookeeper instance changes
    credentials: []                   // array of credentials to auth the session with
    logger: null                      // an object that implements the 'global.console' interface (for debugging)
})

zk.start([callback])

Start a ZooKeeper session.

Arguments

• callback(err) - An optional callback. If err is defined the connection failed.

zk.close()

Close the ZooKeeper session and it's connection

zk.create(path, data, [flags], [acls], callback)

Create a new node

Arguments

• path - path of the new node
• data - the value to set
• flags - optional ZK.create flags
• acls - optional array of ACL objects
• callback(errno, path) - returns an errno or the path that was created

Flags

ZK.create.NONE
ZK.create.EPHEMERAL
ZK.create.SEQUENCE
ZK.create.EPHEMERAL_SEQUENCE

zk.del(path, version, callback)

Delete a node

Arguments

• path - path of the node
• version - the version of the node

zk.exists(path, [watch], callback)

Checks whether a node exists

Arguments

• path - path of the node
• watch(info) - optional register a function that will be called if this path changes
• callback(errno, exists, zstat) - returns an errno or boolean and stat info

zk.get(path, [watch], callback)

Get the value of a node

Arguments

• path - path of the node
• watch(info) - optional register a function that will be called if this path changes
• callback(errno, data, zstat) - returns an errno or data and stat info

zk.getACL(path, callback)

Get ACL information of a node

Arguments

• path - path of the node
• callback(errno, acls, zstat) - returns an errno or an array of ACLs and stat info

zk.getChildren(path, [watch], callback)

Get the children of a node

Arguments

• path - path of the node
• watch(info) - optional register a function that will be called if this path's children
• callback(errno, children, zstat) - returns an errno or an array of child names and stat info

zk.mkdirp(path, callback)

Create a path of nodes

Arguments

• path - the path to create
• callback(err) - returns an errno if the path wasn't created

zk.set(path, data, version, callback)

Set the value of a node

Arguments

• path - path of the node
• data - data to set
• version - most recent version number of the node
• callback(errno, zstat) - returns an errno or stat info

zk.setACL(path, acls, version, callback)

Sets the ACL of a node

Arguments

• path - path of the node
• acls - array of ACLs to set
• version - the latest ACL version number of the node
• callback(errno, zstat) - returns an errno or stat info

zk.sync(path, callback)

Sync the node with the leader

Arguments

• path - path of the node
• callback(errno, path) - returns an errno or the path

zk.toString()

A string value of the session. For debugging.

zk.transaction()

Begin a ZooKeeper transaction. See Transactions

Events

started

The session is ready to use... or not.

zk.on('started', function (err) {
    if (err) {
        // well, now what?
    }
})

connected

The session connected to a new ZooKeeper server. This may be emitted more than once per session.

disconnected

The session disconnected from a ZooKeeper server. This may be emitted more than once per session. It is recommended to stop issuing ZooKeeper requests until the connected event fires.

expired

The session has expired. Any ephemeral nodes create are gone. You must start() again before making any other calls or they will throw an Error.

zk.on('expired', function () {
    // clean up and reconnect
    console.log('crap, my ephemeral nodes are gone')
    zk.start()
})

maxReconnectAttempts

This fires when the connection to ZooKeeper could not be restored after options.maxReconnectAttempts tries.

Watch Events

You can listen to watch events globally from the session with these events. The event includes the path that triggered the watch.

• created
• deleted
• changed
• child

zk.on('changed', function (path) {
    console.log('the node at', path, 'changed')
})

---

ZK.retry

A set of policies for retrying requests.

ZK.retry.no()

Don't retry.

ZK.retry.once(wait)

Retry once, wait milliseconds between requests.

ZK.retry.nTimes(times, wait)

Retry n times, wait milliseconds between requests.

ZK.retry.elapsed(timespan, wait)

Retry for timespan milliseconds, wait milliseconds between requests.

ZK.retry.exponential(times, wait, [maxWait])

Retry n times, increasing delay between tries exponentially starting at wait milliseconds, optionally bounded by maxWait milliseconds.

---

Transactions

zk.transaction()
  .check('/foo', 4)
  .create('/foo/bar', 'bubbles')
  .set('/baz', 'buzz', 0)
  .del('/cuz', 0)
  .commit(
    function (errno, results) {
      if (!err) {
        results.forEach(console.log.bind(this, 'op result'))
      }
    }
  )

Transactions execute all or none of the member operations atomically. Create a Transaction with zk.transaction() and execute the transaction with commit.

Operations are added to the transaction with the following functions and may be chained.

tx.create(path, data, [flags], [acls])

Create a node

tx.del(path, version)

Delete a node

tx.set(path, data, version)

Set the value of a node

tx.check(path, version)

Assert that the given version is the latest for path

tx.commit(callback)

Execute the transaction.

• callback(errno, results) - returns an errno or an array of results

---

ZK.ACL

ZK.ACL.Permissions

• READ
• WRITE
• CREATE
• DELETE
• ADMIN
• ALL

Default ACLs

• ZK.ACL.OPEN
  • All permissions for anyone
• ZK.ACL.READ
  • Read permissions for anyone
• ZK.ACL.CREATOR
  • All permissions for the creator

ZK.ACL.digestAcl(name, password, permissions)

Create a digest ACL with name, password and permissions

---

License

MIT