AMPS JavaScript Client
powerful. fast. easy.
The AMPS JavaScript Client lets you write cross-platform messaging applications for both web apps working in a browser,
as well as server-side applications that use Node.js. It uses the power of WebSocket technology combined with
the asynchronous nature of JavaScript.
Installation
The client can be installed using NPM or manually downloaded from the releases page.
npm install --save amps
Quick Start
Once the client is downloaded, it can be used in your JavaScript/TypeScript projects:
Node.js:
const { Client } = require('amps');
console.log(Client.version());
TypeScript
import * as amps from 'amps';
console.log(amps.Client.version());
import { Client, Command } from 'amps';
console.log(Client.version());
import * as amps from './amps';
import { Client, Command } from './amps';
Application that uses AMD modules:
define(['dist/amps'], amps => {
console.log(amps.Client.version());
});
Global import in Browser:
<script src="es6-promise.min.js"></script>
<script src="amps.js"></script>
You are now ready to use AMPS in your project!
Here are a few JavaScript examples to get you started:
EXAMPLE 1: CONNECT AND SUBSCRIBE
import { Client } from 'amps';
(async () => {
const client = new Client('my-application');
try {
await client.connect('ws://localhost:9100/amps/json');
const subscriptionId = await client.subscribe(
message => console.log(message.data),
'orders'
);
console.log(subscriptionId);
client.publish('orders', {order: 'Tesla 3', qty: 10});
}
catch (err) {
console.log(err);
}
})();
In this example, we connect to an AMPS server running locally and initiate a subscription to the "orders" topic.
As new orders are posted, the message handler is invoked with each message, and prints the data of each order to
the console:
const onMessage = message => console.log('message: ', message);
try {
await client.subscribe(onMessage, 'orders');
await client.subscribe(onMessage, 'reservations');
await client.subscribe(onMessage, 'notifications');
}
catch (err) {
console.error('subscription error:', err);
}
Since every command (except publish()) is asynchronous and returns a Promise object, it is very easy
to chain commands and handle errors.
EXAMPLE 2: PUBLISH A MESSAGE
try {
const client = new Client('publish-example');
await client.connect('ws://localhost:9100/amps/xml');
client.publish('messages', '<hi>Hello, world!</hi>');
}
catch (err) {
console.log(err);
}
With AMPS, publishing is simple, as shown in this example. We connect to an AMPS server running locally, and publish a
single message to the messages
topic. To simply publish a message, there is no need to predeclare the topic or
configure complex routing. Any subscription that has asked for XML messages on the messages
topic will receive
the message.
EXAMPLE 3: DISCONNECT HANDLING
import { Client } from 'amps';
const sleep = interval => new Promise(resolve => setTimeout(resolve, interval));
const client = new Client('my-app').errorHandler(async err => {
client.disconnect();
console.error(err, 'Reconnecting after 5 seconds...');
await sleep(5000);
reconnect();
});
async function reconnect() {
try {
await client.connect('wss://localhost:9100/amps/json');
try {
await client.subscribe(message => console.log('message: ', message), 'orders');
}
catch (err) {
console.error('Subscription error: ', err);
}
}
catch (err) {
console.error('Connection error: ', err);
await sleep(5000);
reconnect();
}
}
reconnect();
In this example, we need to be subscribed to the "orders" topic, even if connectivity to our AMPS server is temporarily
interrupted. We use a reconnect function to enable recovery from a connection error.
When AMPS detects a connection error, the reconnect function is called from errorHandler to re-establish connection,
and our onConnect method subscribes to the topic again once a successful connection is made. Notice that the
errorHandler is only called after a successful connection has been established, otherwise a connection error is
caught by the catch
callback of the connect Promise.
EXAMPLE 4: QUERY THE CONTENTS OF A "SOW" TOPIC
State-of-the-World ("SOW") topics in AMPS combine the power of a database table with the performance of a
publish-subscribe system. Use the AMPS JavaScript client to query the contents of a SOW topic.
try {
const client = new Client('my-application');
await client.connect('ws://localhost:9100/amps/json');
await client.sow(
message => {
if (message.header.command() == 'sow') {
console.log(message.data);
}
},
'orders',
"/symbol='ROL'",
{
batchSize: 100,
timeout: 5000
}
);
}
catch (err) {
console.error('Error: ', err);
}
This example queries for all orders for the symbol ROL
, and simply prints the messages to the console.
EXAMPLE 5: COMMAND INTERFACE
Even though AMPS clients provide the above named convenience methods for core AMPS functionality,
you can use the Command object to customize the messages that AMPS sends. This is useful for more advanced
scenarios where you need precise control over the message, or in cases where you need to use an earlier version of
the client to communicate with a more recent version of AMPS, or in cases where a named method is not available.
try {
const client = new Client('my-application');
await client.connect('ws://localhost:9100/amps/json')
const subCmd = new Command('subscribe').topic('messages').filter('/id > 20');
await client.execute(subCmd, message => console.log('message: ', message.data));
}
catch (err) {
console.error('Error: ', err);
}
This example provides the subscription to a 'messages' topic with a filter applied.
AMPS Server Configuration for Websockets
To configure AMPS for Websocket support, you need to specify the following Transport:
<Transports>
<Transport>
<Name>json-websocket</Name>
<Type>tcp</Type>
<Protocol>websocket</Protocol>
<InetAddr>9100</InetAddr>
<MessageType>json</MessageType>
</Transport>
</Transports>
With the above configuration, AMPS will listen for incoming Websocket connections on port 9100 and will support
the json
message type. To use TLS/SSL, you'd specify a Certificate
and PrivateKey
(and optionally the Ciphers):
<Transport>
<Name>json-websocket-secure</Name>
<Type>tcp</Type>
<Protocol>websocket</Protocol>
<InetAddr>9443</InetAddr>
<MessageType>json</MessageType>
<Certificate>./cert.pem</Certificate>
<PrivateKey>./key.pem</PrivateKey>
<Ciphers>HIGH:!aNULL:!MD5:@STRENGTH</Ciphers>
</Transport>
You can read more about it in the AMPS User Guide.
Authentication
Starting from 5.2.0.0, AMPS provides a new option for websocket protocol: WWWAuthenticate. This option provides
a flexible way of setting up authentication for the JavaScript client.
The option can have the following values:
- Negotiate (Kerberos)
- NTLM
- Basic realm="Secure Area" (Basic Auth)
When using Negotiate or NTLM, you don't have to do anything from the JavaScript client, it's automatically
handled by browser/environment. In case of using Basic Auth (we recommend using wss in this scenario), you'll
need to set a URI of the form wss://user:password@ip:port/amps/json
.
By default, no authentication is performed until the 'logon' command is performed after connection.
In order to enable authentication for AMPS JavaScript client, you need to specify the following settings:
- Add a protocol in the
Protocols
section of the config:
<Protocol>
<Name>websocket-portal</Name>
<Module>websocket</Module>
<WWWAuthenticate>Basic realm="Secure Area"</WWWAuthenticate>
<WWWAuthenticate>Negotiate</WWWAuthenticate>
<WWWAuthenticate>NTLM</WWWAuthenticate>
</Protocol>
- Specify a transport in the
Transports
section of the config that will be used for the JavaScript client:
<Transport>
<Name>websocket-auth</Name>
<Type>tcp</Type>
<Protocol>websocket-portal</Protocol>
<InetAddr>9002</InetAddr>
</Transport>
EVERYTHING YOU NEED
If you need more help getting started, the 60East Technologies support and services team is ready to provide the
support you need to help you CRANK UP THE AMPS.