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Using the AMQ JavaScript Client

Red Hat AMQ 7.2

For Use with AMQ Clients 2.2

Abstract

This guide describes how to install and configure the client, run hands-on examples, and use your client with other AMQ components.

Chapter 1. Overview

AMQ JavaScript is a library for developing messaging applications. It enables you to write JavaScript applications that send and receive AMQP messages.

AMQ JavaScript is part of AMQ Clients, a suite of messaging libraries supporting multiple languages and platforms. For an overview of the clients, see AMQ Clients Overview. For information about this release, see AMQ Clients 2.2 Release Notes.

AMQ JavaScript is based on the Rhea messaging library.

1.1. Key features

  • An event-driven API that simplifies integration with existing applications
  • SSL/TLS for secure communication
  • Flexible SASL authentication
  • Automatic reconnect and failover
  • Seamless conversion between AMQP and language-native data types
  • Access to all the features and capabilities of AMQP 1.0

1.2. Supported standards and protocols

AMQ JavaScript supports the following industry-recognized standards and network protocols:

1.3. Supported configurations

AMQ JavaScript supports the following OS and language versions:

  • Red Hat Enterprise Linux 6 with Node.js 4, 6, and 8 from Software Collections
  • Red Hat Enterprise Linux 7 with Node.js 4, 6, and 8 from Software Collections
  • Microsoft Windows Server 2012 R2 with Node.js 4, 6, and 8

For more information, see Red Hat AMQ 7 Supported Configurations.

1.4. Terms and concepts

This section introduces the core API entities and describes how they operate together.

Table 1.1. API terms

EntityDescription

Container

A top-level container of connections

Connection

A channel for communication between two peers on a network

Session

A context for sending and receiving messages

Sender

A channel for sending messages to a target

Receiver

A channel for receiving messages from a source

Source

A named point of origin for messages

Target

A named destination for messages

Message

A mutable holder of application data

Delivery

A message transfer

AMQ JavaScript sends and receives messages. Messages are transferred between connected peers over senders and receivers. Senders and receivers are established over sessions. Sessions are established over connections. Connections are established between two uniquely identified containers. Though a connection can have multiple sessions, often this is not needed. The API allows you to ignore sessions unless you require them.

A sending peer creates a sender to send messages. The sender has a target that identifies a queue or topic at the remote peer. A receiving peer creates a receiver to receive messages. The receiver has a source that identifies a queue or topic at the remote peer.

The sending of a message is called a delivery. The message is the content sent, including all metadata such as headers and annotations. The delivery is the protocol exchange associated with the transfer of that content.

To indicate that a delivery is complete, either the sender or the receiver settles it. When the other side learns that it has been settled, it will no longer communicate about that delivery. The receiver can also indicate whether it accepts or rejects the message.

1.5. Document conventions

In this document, sudo is used for any command that requires root privileges. You should always exercise caution when using sudo, as any changes can affect the entire system.

For more information about using sudo, see The sudo Command.

Chapter 2. Installation

This chapter guides you through the steps to install AMQ JavaScript in your environment.

2.1. Prerequisites

To begin installation, use your subscription to access AMQ distribution files and repositories.

To use AMQ JavaScript, you must also install and configure Node.js for your environment. See the Node.js website for more information.

AMQ JavaScript depends on the Node.js debug module. See the npm page for installation instructions.

2.2. Installing on Red Hat Enterprise Linux

AMQ JavaScript is distributed as a zip archive. Follow these steps to install it in your environment.

  1. Open a browser and log in to the Red Hat Customer Portal Product Downloads page at access.redhat.com/downloads.
  2. Locate the Red Hat AMQ Clients entry in the JBOSS INTEGRATION AND AUTOMATION category.
  3. Click Red Hat AMQ Clients. The Software Downloads page opens.
  4. Download the AMQ JavaScript Client zip file.
  5. Use the unzip command to extract the file contents into a directory of your choosing. This creates a new subdirectory named nodejs-rhea-<version>.

    $ unzip nodejs-rhea-<version>.zip
    Archive:  nodejs-rhea-<version>.zip
       creating: nodejs-rhea-<version>/
       creating: nodejs-rhea-<version>/node_modules/
       creating: nodejs-rhea-<version>/node_modules/rhea/
    [...]
  6. Configure your environment to use the installed library. Add the node_modules directory to the NODE_PATH environment variable.

    $ cd nodejs-rhea-<version>
    $ export NODE_PATH=$PWD/node_modules:$NODE_PATH

    To make this configuration take effect for all new console sessions, set NODE_PATH in your $HOME/.bashrc file.

  7. Test your installation. The following command returns zero if it can successfully import the installed library.

    $ node -e 'require("rhea")'; echo $?
    0

2.3. Installing on Microsoft Windows

  1. Open a browser and log in to the Red Hat Customer Portal Product Downloads page at access.redhat.com/downloads.
  2. Locate the Red Hat AMQ Clients entry in the JBOSS INTEGRATION AND AUTOMATION category.
  3. Click Red Hat AMQ Clients. The Software Downloads page opens.
  4. Download the AMQ JavaScript Client zip file.
  5. Extract the file contents into a directory of your choosing by right-clicking on the zip file and selecting Extract All. This creates a new subdirectory named nodejs-rhea-<version>.
  6. Configure your environment to use the installed library. Add the node_modules directory to the NODE_PATH environment variable.

    $ cd nodejs-rhea-<version>
    $ set NODE_PATH=%cd%\node_modules;%NODE_PATH%

2.4. Preparing the library for use in browsers

AMQ JavaScript can run inside a web browser. To create a browser-compatible version of the library, use the npm run browserify command.

$ cd nodejs-rhea-<version>/node_modules/rhea
$ npm install
$ npm run browserify

This produces a file named rhea.js that can be used in browser-based applications.

Chapter 3. Getting started

This chapter guides you through a simple exercise to help you get started using AMQ JavaScript.

3.1. Preparing the broker

The example programs require a running broker with a queue named examples. Follow these steps to define the queue and start the broker:

Procedure

  1. Install the broker.
  2. Create a broker instance. Enable anonymous access.
  3. Start the broker instance and check the console for any critical errors logged during startup.

    $ <broker-instance-dir>/bin/artemis run
    ...
    14:43:20,158 INFO  [org.apache.activemq.artemis.integration.bootstrap] AMQ101000: Starting ActiveMQ Artemis Server
    ...
    15:01:39,686 INFO  [org.apache.activemq.artemis.core.server] AMQ221020: Started Acceptor at 0.0.0.0:5672 for protocols [AMQP]
    ...
    15:01:39,691 INFO  [org.apache.activemq.artemis.core.server] AMQ221007: Server is now live
  4. Use the artemis queue command to create a queue called examples.

    <broker-instance-dir>/bin/artemis queue create --name examples --auto-create-address --anycast

    You are prompted to answer a series of questions. For yes or no questions, type N. Otherwise, press Enter to accept the default value.

3.2. Running Hello World

The Hello World example sends a message to the examples queue on the broker and then fetches it back. On success it prints Hello World! to the console.

Using your configured installation environment, run the helloworld.js example.

$ cd nodejs-rhea-<version>/node_modules/rhea/examples
$ node helloworld.js
Hello World!

Chapter 4. Examples

This chapter demonstrates the use of AMQ JavaScript through example programs.

See the Rhea examples for more sample programs. Note that some of the sample programs there require the minimist package in order to parse command-line options.

4.1. Sending messages

This client program connects to a server using <connection-url>, creates a sender for target <address>, sends a message containing <message-body>, closes the connection, and exits.

Example: Sending messages

"use strict";

var rhea = require("rhea");
var url = require("url");

if (process.argv.length !== 5) {
    console.error("Usage: send.js <connection-url> <address> <message-body>");
    process.exit(1);
}

var conn_url = url.parse(process.argv[2]);
var address = process.argv[3];
var message_body = process.argv[4];

var container = rhea.create_container();

container.on("sender_open", function (event) {
    console.log("SEND: Opened sender for target address '" +
                event.sender.target.address + "'");
});

container.on("sendable", function (event) {
    var message = {
        "body": message_body
    };

    event.sender.send(message);

    console.log("SEND: Sent message '" + message.body + "'");

    event.sender.close();
    event.connection.close();
});

var opts = {
    host: conn_url.hostname,
    port: conn_url.port || 5672
};

var conn = container.connect(opts);
conn.open_sender(address);

Running the example

To run the example program, copy it to a local file and invoke it using the node command.

$ node send.js amqp://localhost queue1 hello

4.2. Receiving messages

This client program connects to a server using <connection-url>, creates a receiver for source <address>, and receives messages until it is terminated or it reaches <count> messages.

Example: Receiving messages

"use strict";

var rhea = require("rhea");
var url = require("url");

if (process.argv.length !== 4 && process.argv.length !== 5) {
    console.error("Usage: receive.js <connection-url> <address> [<message-count>]");
    process.exit(1);
}

var conn_url = url.parse(process.argv[2]);
var address = process.argv[3];
var desired = 0;
var received = 0;

if (process.argv.length === 5) {
    desired = parseInt(process.argv[4]);
}

var container = rhea.create_container();

container.on("receiver_open", function (event) {
    console.log("RECEIVE: Opened receiver for source address '" +
                event.receiver.source.address + "'");
});

container.on("message", function (event) {
    var message = event.message;

    console.log("RECEIVE: Received message '" + message.body + "'");

    received++;

    if (received == desired) {
        event.receiver.close();
        event.connection.close();
    }
});

var opts = {
    host: conn_url.hostname,
    port: conn_url.port || 5672
};

var conn = container.connect(opts);
conn.open_receiver(address);

Running the example

To run the example program, copy it to a local file and invoke it using the python command.

$ node receive.js amqp://localhost queue1

Chapter 5. Using the API

This chapter explains how to use the AMQ JavaScript API to perform common messaging tasks.

5.1. Basic operation

5.1.1. Handling messaging events

AMQ JavaScript is an asynchronous event-driven API. To define how the application handles events, the user registers event-handling functions on the container object. These functions are then called as network activity or timers trigger new events.

Example: Handling messaging events

var rhea = require("rhea");
var container = rhea.create_container();

container.on("sendable", function (event) {
    console.log("A message can be sent");
});

container.on("message", function (event) {
    console.log("A message is received");
});

These are only a few common-case events. The full set is documented in the API reference.

5.1.2. Creating a container

The container is the top-level API object. It is the entry point for creating connections, and it is responsible for running the main event loop. It is often constructed with a global event handler.

Example: Creating a container

var rhea = require("rhea");
var container = rhea.create_container();

Setting the container identity

Each container instance has a unique identity called the container ID. When AMQ JavaScript makes a network connection, it sends the container ID to the remote peer. To set the container ID, pass the id option to the create_container method.

Example: Setting the container identity

var container = rhea.create_container({"id": "job-processor-3"});

If the user does not set the ID, the library will generate a UUID when the container is constucted.

5.2. Network connections

5.2.1. Creating outgoing connections

To connect to a remote server, pass connection options containing the host and port to the container.connect() method.

Example: Creating outgoing connections

container.on("connection_open", function (event) {
    console.log("Connection " + event.connection + " is open");
});

var opts = {
    "host": "example.com",
    "port": 5672
};

container.connect(opts);

The default host is localhost. The default port is 5672.

See the Section 5.3, “Security” section for information about creating secure connections.

5.2.2. Configuring reconnect

Reconnect allows a client to recover from lost connections. It is used to ensure that the components in a distributed system reestablish communication after temporary network or component failures.

AMQ JavaScript enables reconnect by default. If a connection attempt fails, the client will try again after a brief delay. The delay increases exponentially for each new attempt, up to a default maximum of 60 seconds.

To disable reconnect, set the reconnect connection option to false.

Example: Disabling reconnect

var opts = {
    "host": "example.com",
    "reconnect": false
};

container.connect(opts);

To control the delays between connection attempts, set the initial_reconnect_delay and max_reconnect_delay connection options. Delay options are specified in milliseconds.

To limit the number of reconnect attempts, set the reconnect_limit option.

Example: Configuring reconnect

var opts = {
    "host": "example.com",
    "initial_reconnect_delay": 100,
    "max_reconnect_delay": 60 * 1000,
    "reconnect_limit": 10
};

container.connect(opts);

5.2.3. Configuring failover

AMQ JavaScript allows you to configure alternate connection endpoints programatically.

To specify multiple connection endpoints, define a function that returns new connection options and pass the function in the connection_details option. The function is called once for each connection attempt.

Example: Configuring failover

var hosts = ["alpha.example.com", "beta.example.com"];
var index = -1;

function failover_fn() {
    index += 1;

    if (index == hosts.length) index = 0;

    return {"host": hosts[index].hostname};
};

var opts = {
    "host": "example.com",
    "connection_details": failover_fn
}

container.connect(opts);

This example implements repeating round-robin failover for a list of hosts. You can use this interface to implement your own failover behavior.

5.3. Security

5.3.1. Securing connections with SSL/TLS

AMQ JavaScript uses SSL/TLS to encrypt communication between clients and servers.

To connect to a remote server with SSL/TLS, set the transport connection option to tls.

Example: Enabling SSL/TLS

var opts = {
    "host": "example.com",
    "port": 5671,
    "transport": "tls"
};

container.connect(opts);

Note

By default, the client will reject connections to servers with untrusted certificates. This is sometimes the case in test environments. To bypass certificate authorization, set the rejectUnauthorized connection option to false. Be aware that this compromises the security of your connection.

5.3.2. Connecting with a user and password

AMQ JavaScript can authenticate connections with a user and password.

To specify the credentials used for authentication, set the username and password connection options.

Example: Connecting with a user and password

var opts = {
    "host": "example.com",
    "username": "alice",
    "password": "secret"
};

container.connect(opts);

5.3.3. Configuring SASL authentication

AMQ JavaScript uses the SASL protocol to perform authentication. SASL can use a number of different authentication mechanisms. When two network peers connect, they exchange their allowed mechanisms, and the strongest mechanism allowed by both is selected.

AMQ JavaScript enables SASL mechanisms based on the presence of user and password information. If the user and password are both specified, PLAIN is used. If only a user is specified, ANONYMOUS is used. If neither is specified, SASL is disabled.

5.4. More information

For more information, see the API reference.

Chapter 6. Interoperability

This chapter discusses how to use AMQ JavaScript in combination with other AMQ components. For an overview of the compatibility of AMQ components, see the product introduction.

6.1. Interoperating with other AMQP clients

AMQP messages are composed using the AMQP type system. This common format is one of the reasons AMQP clients in different languages are able to interoperate with each other.

When sending messages, AMQ JavaScript automatically converts language-native types to AMQP-encoded data. When receiving messages, the reverse conversion takes place.

Note

More information about AMQP types is available at the interactive type reference maintained by the Apache Qpid project.

Table 6.1. AMQP types

AMQP typeDescription

null

An empty value

boolean

A true or false value

char

A single Unicode character

string

A sequence of Unicode characters

binary

A sequence of bytes

byte

A signed 8-bit integer

short

A signed 16-bit integer

int

A signed 32-bit integer

long

A signed 64-bit integer

ubyte

An unsigned 8-bit integer

ushort

An unsigned 16-bit integer

uint

An unsigned 32-bit integer

ulong

An unsigned 64-bit integer

float

A 32-bit floating point number

double

A 64-bit floating point number

array

A sequence of values of a single type

list

A sequence of values of variable type

map

A mapping from distinct keys to values

uuid

A universally unique identifier

symbol

A 7-bit ASCII string from a constrained domain

timestamp

An absolute point in time

JavaScript has fewer native types than AMQP can encode. To send messages containing specific AMQP types, use the wrap_ functions from the rhea/types.js module.

Table 6.2. AMQ JavaScript types before encoding and after decoding

AMQP typeAMQ JavaScript type before encodingAMQ JavaScript type after decoding

null

null

null

boolean

boolean

boolean

char

wrap_char(number)

number

string

string

string

binary

wrap_binary(string)

string

byte

wrap_byte(number)

number

short

wrap_short(number)

number

int

wrap_int(number)

number

long

wrap_long(number)

number

ubyte

wrap_ubyte(number)

number

ushort

wrap_ushort(number)

number

uint

wrap_uint(number)

number

ulong

wrap_ulong(number)

number

float

wrap_float(number)

number

double

wrap_double(number)

number

array

wrap_array(Array, code)

Array

list

wrap_list(Array)

Array

map

wrap_map(object)

object

uuid

wrap_uuid(number)

number

symbol

wrap_symbol(string)

string

timestamp

wrap_timestamp(number)

number

Table 6.3. AMQ JavaScript and other AMQ client types (1 of 2)

AMQ JavaScript type before encodingAMQ C++ typeAMQ .NET type

null

nullptr

null

boolean

bool

System.Boolean

wrap_char(number)

wchar_t

System.Char

string

std::string

System.String

wrap_binary(string)

proton::binary

System.Byte[]

wrap_byte(number)

int8_t

System.SByte

wrap_short(number)

int16_t

System.Int16

wrap_int(number)

int32_t

System.Int32

wrap_long(number)

int64_t

System.Int64

wrap_ubyte(number)

uint8_t

System.Byte

wrap_ushort(number)

uint16_t

System.UInt16

wrap_uint(number)

uint32_t

System.UInt32

wrap_ulong(number)

uint64_t

System.UInt64

wrap_float(number)

float

System.Single

wrap_double(number)

double

System.Double

wrap_array(Array, code)

-

-

wrap_list(Array)

std::vector

Amqp.List

wrap_map(object)

std::map

Amqp.Map

wrap_uuid(number)

proton::uuid

System.Guid

wrap_symbol(string)

proton::symbol

Amqp.Symbol

wrap_timestamp(number)

proton::timestamp

System.DateTime

Table 6.4. AMQ JavaScript and other AMQ client types (2 of 2)

AMQ JavaScript type before encodingAMQ Python typeAMQ Ruby type

null

None

nil

boolean

bool

true, false

wrap_char(number)

unicode

String

string

unicode

String

wrap_binary(string)

bytes

String

wrap_byte(number)

int

Integer

wrap_short(number)

int

Integer

wrap_int(number)

long

Integer

wrap_long(number)

long

Integer

wrap_ubyte(number)

long

Integer

wrap_ushort(number)

long

Integer

wrap_uint(number)

long

Integer

wrap_ulong(number)

long

Integer

wrap_float(number)

float

Float

wrap_double(number)

float

Float

wrap_array(Array, code)

proton.Array

Array

wrap_list(Array)

list

Array

wrap_map(object)

dict

Hash

wrap_uuid(number)

-

-

wrap_symbol(string)

str

Symbol

wrap_timestamp(number)

long

Time

6.2. Interoperating with AMQ JMS

AMQP defines a standard mapping to the JMS messaging model. This section discusses the various aspects of that mapping. For more information, see the AMQ JMS Interoperability chapter.

JMS message types

AMQ JavaScript provides a single message type whose body type can vary. By contrast, the JMS API uses different message types to represent different kinds of data. The table below indicates how particular body types map to JMS message types.

For more explicit control of the resulting JMS message type, you can set the x-opt-jms-msg-type message annotation. See the AMQ JMS Interoperability chapter for more information.

Table 6.5. AMQ JavaScript and JMS message types

AMQ JavaScript body typeJMS message type

string

TextMessage

null

TextMessage

wrap_binary(string)

BytesMessage

Any other type

ObjectMessage

6.3. Connecting to AMQ Broker

AMQ Broker is designed to interoperate with AMQP 1.0 clients. Check the following to ensure the broker is configured for AMQP messaging.

  • Port 5672 in the network firewall is open.
  • The AMQ Broker AMQP acceptor is enabled. See Configuring Network Access.
  • The necessary addresses are configured on the broker. See Addresses, Queues, and Topics.
  • The broker is configured to permit access from your client, and the client is configured to send the required credentials. See Broker Security.

6.4. Connecting to AMQ Interconnect

AMQ Interconnect works with any AMQP 1.0 client. Check the following to ensure the components are configured correctly.

  • Port 5672 in the network firewall is open.
  • The router is configured to permit access from your client, and the client is configured to send the required credentials. See Interconnect Security.

Appendix A. Using your subscription

AMQ is provided through a software subscription. To manage your subscriptions, access your account at the Red Hat Customer Portal.

Accessing your account

  1. Go to access.redhat.com.
  2. If you do not already have an account, create one.
  3. Log in to your account.

Activating a subscription

  1. Go to access.redhat.com.
  2. Navigate to My Subscriptions.
  3. Navigate to Activate a subscription and enter your 16-digit activation number.

Downloading zip and tar files

To access zip or tar files, use the customer portal to find the relevant files for download. If you are using RPM packages, this step is not required.

  1. Open a browser and log in to the Red Hat Customer Portal Product Downloads page at access.redhat.com/downloads.
  2. Locate the Red Hat AMQ entries in the JBOSS INTEGRATION AND AUTOMATION category.
  3. Select the desired AMQ product. The Software Downloads page opens.
  4. Click the Download link for your component.

Registering your system for packages

To install RPM packages on Red Hat Enterprise Linux, your system must be registered. If you are using zip or tar files, this step is not required.

  1. Go to access.redhat.com.
  2. Navigate to Registration Assistant.
  3. Select your OS version and continue to the next page.
  4. Use the listed command in your system terminal to complete the registration.

To learn more see How to Register and Subscribe a System to the Red Hat Customer Portal.

Revised on 2018-11-15 13:02:05 UTC

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