Websocket and Javascript
Since machbase-neo v8.0.28, it supports MQTT over websocket.
We will be utilizing the MQTT.js library for our JavaScript client, which can be found at https://github.com/mqttjs/MQTT.js.
To include mqtt.js in our project, we can simply embed it from the CDN using the following script tag: <script src="https://unpkg.com/mqtt/dist/mqtt.min.js"></script>.
By default, the web socket address for MQTT is set to ws://127.0.0.1:5654/web/api/mqtt, and it is served by the machbase-neo HTTP server.
<html>
<head>
<script src="https://unpkg.com/mqtt/dist/mqtt.min.js"></script>
</head>
<body>
<script type="text/javascript">
const url = 'ws://localhost:5654/web/api/mqtt'
// Create an MQTT client instance
const options = {
// Clean session
clean: true,
connectTimeout: 4000,
// Authentication
clientId: 'mqtt_test',
username: 'mqtt_test',
password: 'mqtt_test',
}
const client = mqtt.connect(url, options)
client.on('connect', function () {
console.log('Connected')
// Subscribe to a 'db/reply' topic to receive the result of our query
client.subscribe('db/reply', function (err) {
if (!err) {
// Publish a query to a topic 'db/query'
const req = '{"q": "SELECT * FROM example limit 10", "format":"box", "precision": 2}'
client.publish('db/query', req)
}
})
})
// Receive messages
client.on('message', function (topic, message) {
// display the message we received
document.getElementById("rspQuery").innerHTML = '<pre>'+message.toString()+'</pre>'
client.end()
})
</script>
<div id="rspQuery"></div>
</body>
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