npm package: @marudor/node-zookeeper-client
Description: A pure Javascript ZooKeeper client for Node.js.
Author: Alex Guan
Latest version: 0.4.0

# node-zookeeper-client

A pure Javascript [ZooKeeper](http://zookeeper.apache.org) client module for
[Node.js](http://nodejs.org).

[![NPM](https://nodei.co/npm/node-zookeeper-client.png?downloads=true&downloadRank=true&stars=true)](https://nodei.co/npm/node-zookeeper-client/)

[![Build Status](https://travis-ci.org/alexguan/node-zookeeper-client.png?branch=master)](https://travis-ci.org/alexguan/node-zookeeper-client)

This module is designed to resemble the ZooKeeper Java client API but with
tweaks to follow the convention of Node.js modules. Developers that are familiar
with the ZooKeeper Java client would be able to pick it up quickly.

This module has been tested to work with ZooKeeper version 3.4.*.

---

+ [Installation](#installation)
+ [Example](#example)
+ [Documentation](#documentation)
    + [createClient](#client-createclientconnectionstring-options)
    + [Client](#client)
        + [connect](#void-connect)
        + [close](#void-close)
        + [create](#void-createpath-data-acls-mode-callback)
        + [remove](#void-removepath-version-callback)
        + [exists](#void-existspath-watcher-callback)
        + [getChildren](#void-getchildrenpath-watcher-callback)
        + [getData](#void-getdatapath-watcher-callback)
        + [setData](#void-setdatapath-data-version-callback)
        + [getACL](#void-getaclpath-callback)
        + [setACL](#void-setaclpath-acls-version-callback)
        + [transaction](#transaction-transaction)
        + [mkdirp](#void-mkdirppath-data-acls-mode-callback)
        + [addAuthInfo](#void-addauthinfoscheme-auth)
        + [getState](#state-getstate)
        + [getSessionId](#buffer-getsessionid)
        + [getSessionPassword](#buffer-getsessionpassword)
        + [getSessionTimeout](#number-getsessiontimeout)
    + [State](#state)
    + [Event](#event)
    + [Transaction](#transaction)
        + [create](#transaction-createpath-data-acls-mode)
        + [setData](#transaction-setdatapath-data-version)
        + [check](#transaction-checkpath-version)
        + [remove](#transaction-removepath-data-version)
        + [commit](#void-commitcallback)
    + [Exception](#exception)
        + [getCode](#number-getcode)
        + [getPath](#string-getpath)
        + [getName](#string-getname)
        + [toString](#string-tostring)
    + [Exception](#exception)
+ [Dependency](#dependency)
+ [License](#license)

## Installation

You can install it using npm:

```bash
$ npm install node-zookeeper-client
```

## Example

1\. Create a node using given path:

```javascript
var zookeeper = require('node-zookeeper-client');

var client = zookeeper.createClient('localhost:2181');
var path = process.argv[2];

client.once('connected', function () {
    console.log('Connected to the server.');

    client.create(path, function (error) {
        if (error) {
            console.log('Failed to create node: %s due to: %s.', path, error);
        } else {
            console.log('Node: %s is successfully created.', path);
        }

        client.close();
    });
});

client.connect();
```

2\. List and watch the children of given node:

```javascript
var zookeeper = require('node-zookeeper-client');

var client = zookeeper.createClient('localhost:2181');
var path = process.argv[2];

function listChildren(client, path) {
    client.getChildren(
        path,
        function (event) {
            console.log('Got watcher event: %s', event);
            listChildren(client, path);
        },
        function (error, children, stat) {
            if (error) {
                console.log(
                    'Failed to list children of %s due to: %s.',
                    path,
                    error
                );
                return;
            }

            console.log('Children of %s are: %j.', path, children);
        }
    );
}

client.once('connected', function () {
    console.log('Connected to ZooKeeper.');
    listChildren(client, path);
});

client.connect();
```

More examples can be found [here](examples).


## Documentation

#### Client createClient(connectionString, [options])

Factory method to create a new zookeeper [client](#client) instance.

**Arguments**

* connectionString `String` - Comma separated `host:port` pairs, each
  represents a ZooKeeper server. You can optionally append a chroot path, then
  the client would be rooted at the given path. e.g.

  ```javascript
  'localhost:3000,locahost:3001,localhost:3002'
  'localhost:2181,localhost:2182/test'
  ```

* options `Object` - An object to set the client options. Currently available
  options are:

    * `sessionTimeout` Session timeout in milliseconds, defaults to 30 seconds.
    * `spinDelay` The delay (in milliseconds) between each connection attempts.
    * `retries` The number of retry attempts for connection loss exception.

  Defaults options:

    ```javascript
    {
        sessionTimeout: 30000,
        spinDelay : 1000,
        retries : 0
    }
    ```

**Example**

```javascript
var client = zookeeper.createClient(
    'localhost:2181/test',
    { sessionTimeout: 10000 }
);
```

---

### Client

This is the main class of ZooKeeper client module. An application must
use [`createClient`](#createclientconnectionstring-options) method to
instantiate the client.

Once a connection from the client to the server is established, a session id is
assigned to the client. The client will starts sending heart beats to the server
periodically to keep the session valid.

If the client fails to send heart beats to the server for a prolonged period of
time (exceeding the sessionTimeout value), the server will expire the session.
The client object will no longer be usable.

If the ZooKeeper server the client currently connects to fails or otherwise
does not respond, the client will automatically try to connect to another server
before its session times out. If successful, the application can continue to
use the client.

This class inherits from [events.EventEmitter](http://nodejs.org/api/events.html)
class, see [Event](#event) for details.

#### void connect()

Initiate the connection to the provided server list (ensemble). The client will
pick an arbitrary server from the list and attempt to connect to it. If the
establishment of the connection fails, another server will be tried (picked
randomly) until a connection is established or [close](#close) method is
invoked.

---

#### void close()

Close this client. Once the client is closed, its session becomes invalid.
All the ephemeral nodes in the ZooKeeper server associated with the session
will be removed. The watchers left on those nodes (and on their parents) will
be triggered.

---

#### void create(path, [data], [acls], [mode], callback)

Create a node with given path, data, acls and mode.

**Arguments**

* path `String` - Path of the node.
* data `Buffer` - The data buffer, optional, defaults to null.
* acls `Array` - An array of [ACL](#acl) objects, optional, defaults to
  `ACL.OPEN_ACL_UNSAFE` 
* mode `CreateMode` -  The creation mode, optional, defaults to
  `CreateMode.PERSISTENT`
* callback(error, path) `Function` - The callback function.

**Example**

```javascript
zookeeper.create(
    '/test/demo',
    new Buffer('data'),
    CreateMode.EPHEMERAL,
    function (error, path) {
        if (error) {
            console.log(error.stack);
            return;
        }

        console.log('Node: %s is created.', path);
    }
);
```

---

#### void remove(path, [version], callback)

Delete a node with the given path and version. If version is provided and not
equal to -1, the request will fail when the provided version does not match the
server version.

**Arguments**

* path `String` - Path of the node.
* version `Number` - The version of the node, optional, defaults to -1.
* callback(error) `Function` - The callback function.

**Example**

```javascript
zookeeper.remove('/test/demo', -1, function (error) {
    if (error) {
        console.log(error.stack);
        return;
    }

    console.log('Node is deleted.');
});
```

---

#### void exists(path, [watcher], callback)

Check the existence of a node. The callback will be invoked with the
stat of the given path, or `null` if no such node exists.

If the watcher function is provided and the operation is successful (no error),
a watcher will be placed on the node with the given path. The watcher will be
triggered by a successful operation that creates the node, deletes the node or
sets the data on the node.

**Arguments**

* path `String` - Path of the node.
* watcher(event) `Function` - The watcher function, optional. The `event` is an
  instance of [`Event`](#event)
* callback(error, stat) `Function` - The callback function. The `stat` is an
  instance of [`Stat`](#stat).

**Example**

```javascript
zookeeper.exists('/test/demo', function (error, stat) {
    if (error) {
        console.log(error.stack);
        return;
    }

    if (stat) {
        console.log('Node exists.');
    } else {
        console.log('Node does not exist.');
    }
});
```

---

#### void getChildren(path, [watcher], callback)

For the given node path, retrieve the children list and the stat. The children
will be an unordered list of strings.

If the watcher callback is provided and the operation is successfully, a watcher
will be placed the given node. The watcher will be triggered
when an operation successfully deletes the given node or creates/deletes
the child under it.

**Arguments**

* path `String` - Path of the node.
* watcher(event) `Function` - The watcher function, optional. The `event` is an
  instance of [`Event`](#event)
* callback(error, children, stat) `Function` - The callback function. The
  children is an array of strings and the `stat` is an instance of
  [`Stat`](#stat).

**Example**

```javascript
zookeeper.getChildren('/test/demo', function (error, children, stats) {
    if (error) {
        console.log(error.stack);
        return;
    }

    console.log('Children are: %j.', children);
});
```

#### void getData(path, [watcher], callback)

Retrieve the data and the stat of the node of the given path. If the watcher
function is provided and the operation is successful (no error), a watcher
will be placed on the node with the given path. The watch will be triggered by
a successful operation which sets data on the node, or deletes the node.

**Arguments**

* path `String` - Path of the node.
* watcher(event) `Function` - The watcher function, optional. The `event` is an
  instance of [`Event`](#event)
* callback(error, data, stat) `Function` - The callback function. The `data` is
  an instance of [`Buffer`](http://nodejs.org/api/buffer.html) and stat is an
  instance of [`Stat`](#stat).

**Example**

```javascript
zookeeper.getData(
    '/test/demo',
    function (event) {
        console.log('Got event: %s.', event);
    },
    function (error, data, stat) {
        if (error) {
            console.log(error.stack);
            return;
        }

        console.log('Got data: %s', data.toString('utf8'));
    }
);
```

---

#### void setData(path, data, [version], callback)

Set the data for the node of the given path if such a node exists and the
optional given version matches the version of the node (if the given
version is -1, it matches any node's versions). The [stat](#stat) of the node
will be returned through the callback function.

**Arguments**

* path `String` - Path of the node.
* data `Buffer` - The data buffer.
* version `Number` - The version of the node, optional, defaults to -1.
* callback(error, stat) `Function` - The callback function. The `stat` is an
  instance of [`Stat`](#stat).

**Example**

```javascript
zookeeper.setData('/test/demo', null, 2, function (error, stat) {
    if (error) {
        console.log(error.stack);
        return;
    }

    console.log('Data is set.');
});
```

---

#### void getACL(path, callback)

Retrieve the list of [ACL](#acl) and stat of the node of the given path.

**Arguments**

* path `String` - Path of the node.
* callback(error, acls, stat) `Function` - The callback function. `acls` is an
  array of [`ACL`](#acl) instances. The `stat` is an instance of
  [`Stat`](#stat).

**Example**

```javascript
zookeeper.getACL('/test/demo', function (error, acls, stat) {
    if (error) {
        console.log(error.stack);
        return;
    }

    console.log('ACL(s) are: %j', acls);
});
```

---

#### void setACL(path, acls, [version], callback)

Set the [ACL](#acl) for the node of the given path if such a node exists and the
given version (optional) matches the version of the node on the server. (if the
given version is -1, it matches any versions).

**Arguments**

* path `String` - Path of the node.
* acls `Array` - An array of [`ACL`](#acl) instances.
* version `Number` - The version of the node, optional, defaults to -1.
* callback(error, stat) `Function` - The callback function. The `stat` is an
  instance of [`Stat`](#stat).

**Example**

```javascript
zookeeper.setACL(
    '/test/demo',
    [
        new zookeeper.ACL(
            zookeeeper.Permission.ADMIN,
            new zookeeper.Id('ip', '127.0.0.1')
        )
    ],
    function (error, acls, stat) {
        if (error) {
            console.log(error.stack);
            return;
        }

        console.log('New ACL is set.');
    }
);
```

---

#### Transaction transaction()

Create and return a new Transaction instance which provides a builder object
that can be used to construct and commit a set of operations atomically.

See [Transaction](#transaction) for details.


**Example**

```javascript
var transaction = zookeeper.transaction();
```

---

#### void mkdirp(path, [data], [acls], [mode], callback)

Create given path in a way similar to `mkdir -p`.

**Arguments**

* path `String` - Path of the node.
* data `Buffer` - The data buffer, optional, defaults to `null`.
* acls `Array` - An array of [ACL](#acl) objects, optional, defaults to
  `ACL.OPEN_ACL_UNSAFE` 
* mode `CreateMode` -  The creation mode, optional, defaults to
  `CreateMode.PERSISTENT`
* callback(error, path) `Function` - The callback function.

**Example**

```javascript
zookeeper.mkdirp('/test/demo/1/2/3', function (error, path) {
    if (error) {
        console.log(error.stack);
        return;
    }

    console.log('Node: %s is created.', path);
});
```

---

#### void addAuthInfo(scheme, auth)

Add the specified scheme:auth information to this client.

**Arguments**

* scheme `String` - The authentication scheme.
* auth `Buffer` - The authentication data buffer.

**Example**

```javascript
zookeeper.addAuthInfo('ip', new Buffer('127.0.0.1'));
```

---

#### State getState()

Return the current client [state](#state).

**Example**

```javascript
var client = zookeeper.createClient({...});
var state = client.getState();
console.log('Current state is: %s', state);
```

---

#### Buffer getSessionId()

Returns the session id of this client instance. The value returned is not valid
until the client connects to a server and may change after a re-connect.

The id returned is a long integer stored into a 8 bytes
[`Buffer`](http://nodejs.org/api/buffer.html) since Javascript does not support
long integer natively.

**Example**

```javascript
var client = zookeeper.createClient({...});
var id = client.getSessionId();
console.log('Session id is: %s', id.toString('hex'));
```

---

#### Buffer getSessionPassword()

Returns the session password of this client instance. The value returned is not
valid until the client connects to a server and may change after a re-connect.

The value returned is an instance of
[`Buffer`](http://nodejs.org/api/buffer.html).

**Example**

```javascript
var client = zookeeper.createClient({...});
var pwd = client.getSessionPassword();
```

---

#### Number getSessionTimeout()
 
Returns the *negotiated* session timeout (in milliseconds) for this client
instance. The value returned is not valid until the client connects to a server
and may change after a re-connect.

**Example**

```javascript
var client = zookeeper.createClient({...});
var sessionTimeout = client.getSessionTimeout();
```

---

### State

After the `connect()` method is invoked, the ZooKeeper client starts its
life cycle and transitions its state as described in the following diagram.

![state transition](http://zookeeper.apache.org/doc/r3.4.5/images/state_dia.jpg)

There are two ways to watch the client state changes:

1\. **Node.js convention:** Register event listener on the specific event
which interests you. The following is the list of events that can be watched:

* `connected` - Client is connected and ready.
* `connectedReadOnly` - Client is connected to a readonly server.
* `disconnected` - The connection between client and server is dropped.
* `expired` - The client session is expired.
* `authenticationFailed` - Failed to authenticate with the server.

Note: some events (e.g. `connected` or `disconnected`) maybe be emitted more
than once during the client life cycle.

**Example**

```javascript
client.on('connected', function () {
    console.log('Client state is changed to connected.');
});
```

2\. **Java client convention:** Register one event listener on the `state` event
to watch all state transitions. The listener callback will be called with an
instance of the `State` class. The following is the list of exported state
instances:

* `State.CONNECTED` - Client is connected and ready.
* `State.CONNECTED_READ_ONLY` - Client is connected to a readonly server.
* `State.DISCONNECTED` - The connection between client and server is dropped.
* `State.EXPIRED` - The client session is expired.
* `State.AUTH_FAILED` - Failed to authenticate with the server.

```javascript
client.on('state', function (state) {
    if (state === zookeeper.State.SYNC_CONNECTED) {
        console.log('Client state is changed to connected.');
    }
});
```

---

### Event

Optionally, you can register watcher functions when calling
[`exists`](#void-existspath-watcher-callback),
[`getChildren`](#void-getchildrenpath-watcher-callback) and
[`getData`](#void-getdatapath-watcher-callback) methods. The watcher function
will be called with an instance of `Event`. 

**Properties**

There are four type of events are exposed as `Event` class properties.

* `NODE_CREATED` - Watched node is created.
* `NODE_DELETED` - watched node is deleted.
* `NODE_DATA_CHANGED` - Data of watched node is changed.
* `NODE_CHILDREN_CHANGED` - Children of watched node is changed.

---

#### Number getType()

Return the type of the event.

---

#### String getName()

Return the name of the event.

---

#### Number getPath()

Return the path of the event.

---

#### String toString()

Return a string representation of the event.

---

### Transaction

Transaction provides a builder interface to construct and commit a set of
operations atomically.

**Example**

```javascript
var client = zookeeper.createClient(process.argv[2] || 'localhost:2181');

client.once('connected', function () {
    client.transaction().
        create('/txn').
        create('/txn/1', new Buffer('transaction')).
        setData('/txn/1', new Buffer('test'), -1).
        check('/txn/1').
        remove('/txn/1', -1).
        remove('/txn').
        commit(function (error, results) {
            if (error) {
                console.log(
                    'Failed to execute the transaction: %s, results: %j',
                    error,
                    results
                );

                return;
            }

            console.log('Transaction completed.');
            client.close();
        });
});

client.connect();
```

#### Transaction create(path, [data], [acls], [mode])

Add a create operation with given path, data, acls and mode.

**Arguments**

* path `String` - Path of the node.
* data `Buffer` - The data buffer, optional, defaults to null.
* acls `Array` - An array of [ACL](#acl) objects, optional, defaults to
  `ACL.OPEN_ACL_UNSAFE` 
* mode `CreateMode` -  The creation mode, optional, defaults to
  `CreateMode.PERSISTENT`

---

#### Transaction setData(path, data, [version])

Add a set-data operation with the given path, data and optional version.

**Arguments**

* path `String` - Path of the node.
* data `Buffer` - The data buffer, or null.
* version `Number` - The version of the node, optional, defaults to -1.

---

#### Transaction check(path, [version])

Add a check (existence) operation with given path and optional version.

**Arguments**

* path `String` - Path of the node.
* version `Number` - The version of the node, optional, defaults to -1.

---

#### Transaction remove(path, data, version)
 
Add a delete operation with the given path and optional version.

**Arguments**

* path `String` - Path of the node.
* version `Number` - The version of the node, optional, defaults to -1.

---

#### void commit(callback)

Execute the transaction atomically.

**Arguments**

* callback(error, results) `Function` - The callback function.

---

### Exception

If the requested operation fails due to reason related to ZooKeeper, the error
which is passed into callback function will be an instance of `Exception` class.

The exception can be identified through its error code, the following is the
list of error codes that are exported through `Exception` class.

* `Exception.OK`
* `Exception.SYSTEM_ERROR`
* `Exception.RUNTIME_INCONSISTENCY`
* `Exception.DATA_INCONSISTENCY`
* `Exception.CONNECTION_LOSS`
* `Exception.MARSHALLING_ERROR`
* `Exception.UNIMPLEMENTED`
* `Exception.OPERATION_TIMEOUT`
* `Exception.BAD_ARGUMENTS`
* `Exception.API_ERROR`
* `Exception.NO_NODE`
* `Exception.NO_AUTH`
* `Exception.BAD_VERSION`
* `Exception.NO_CHILDREN_FOR_EPHEMERALS`
* `Exception.NODE_EXISTS`
* `Exception.NOT_EMPTY`
* `Exception.SESSION_EXPIRED`
* `Exception.INVALID_CALLBACK`
* `Exception.INVALID_ACL`
* `Exception.AUTH_FAILED`

**Example**

```javascript
zookeeper.create('/test/demo', function (error, path) {
    if (error) {
        if (error.getCode() == zookeeper.Exception.NODE_EXISTS) {
            console.log('Node exists.');
        } else {
            console.log(error.stack);
        }
        return;
    }

    console.log('Node: %s is created.', path);
});
```

#### Number getCode()

Return the error code of the exception. 

---

#### String getPath()

Return the associated node path of the exception. The path can be `undefined`
if the exception is not related to node.

--

#### String getName()

Return the exception name as defined in aforementioned list.

---

### String toString()

Return the exception in a readable string.

---


## Dependency

This module depends on the following third-party libraries:

* [async](https://github.com/caolan/async)
* [underscore](http://underscorejs.org)

## License

This module is licensed under [MIT License](raw/master/LICENSE)