axon-function-js

The axon-function-js is a consumer / producer agent. It can receive any type of message. It executes a script written in JavaScript. This script is exeuted every time a message arrives from the subject the agent is subscribed for. The script gets the incoming message injected into a variable, named message. The script also can get parameters, using the scriptparams agrument of the command. This is a string, that the script can get as a variable, named parameters and the script implementation decides how to evaluate it.

Inside the script the standard JavaScript built-in functions, variables and constants are usable, including console.log(). The value of the last expression of the script will be the message that the agent will forward into the target subject.

The examples/th-sensor-simu/ folder shows an example for the usage of this agent.

This axon-function-js agent, that loads the examples/th-sensor-simu/axon-sensor-th-simu.js script below, that expects a message, that contains a timestamp value in the body of the incoming message.

The JSON example below demonstrates such a message:

    {
        "meta": {
            "timePrecision":"ns"
        },
        body: {
            "time": 1578655455000164640
        }
    }

This is the script, that will process the incoming message:

    // The inbound message is placed into the 'message' variable as a string
    // Parse the JSON format string of the input message
    input = JSON.parse(message)

    // Create random values like if it were measured
    temperature = 20. + Math.random() * 2
    humidity = 55. + Math.random() * 3

    // Creates the output message object
    output = {
        device: "143a0c9d-291a-4077-8fcc-d2aa259b8de2",
        time: input.body.time,
        meta: input.meta,
        body: {
            humidity: humidity,
            temperature: temperature
        }
    }

    // Serialize the JSON object to string
    result = JSON.stringify(output)

    // The last expression will be the outbound message as a string
    result

Then the following example below shows how the result, that will be send to the target, looks like:

    {
        "body": {
            "device": "143a0c9d-291a-4077-8fcc-d2aa259b8de2",
            "humidity": 56.683517562784935,
            "temperature": 20.6242920550331,
            "time":1578654765000150272
        },
        "meta": {
            "timePrecision": "ns"
        }
    }

Execute the agent with the -h switch to get help:

$ go install && axon-function-js -h
Usage: axon-function-js [-u server] [-creds file] [-s] <source-subject> [-t] <target-subject> -scriptfile <script-filename> -scriptparams <script-parameters>
  -creds string
    	User Credentials File
  -h	Show help message
  -s string
    	The subject to subscribe for inbound messages (default "axon.func.in")
  -scriptfile string
    	The name of the JavaScript file that holds the function implementation. (default "function.js")
  -scriptparams string
    	THe parameters of the script.
  -t string
    	The subject to send the outbound messages into (default "axon.func.out")
  -u string
    	The nats server URLs (separated by comma) (default "nats://127.0.0.1:4222")