Scripting

This page describes available functionalities and features for running scripts.

akenza provides the possibility to run scripts as part of a data flow in order to decode data sent by devices and turn it into an actionable and human readable format (uplink decoder), encode data that is used to send commands to devices (downlink encoder), or run a script (custom logic block) as part of the rule engine to evaluate logic used to trigger actions (e.g. SMS notification or downlink).

The scripts support JavaScript using the ECMAScript 2020 (ES 11) standard in strict mode. The scripts are plain JavaScript and every JavaScript and ES 11 functionality can be used. However, there are certain restrictions which are listed below. Importantly, loading of node.js modules and other files is disabled.

When creating a Custom Device Type or Custom Logic Block, the script can be executed and debugged allowing for easy development of a script. The script can also be executed by calling the API directly (more information below).

Script Structure

An uplink decoder, downlink encoder or custom logic block script has to implement the function consume(object) which takes an event object as argument. An error will be returned if the script doesn't implement a consume(event) function.

function consume(event) {
    emit('<emitType>', { data: {}, topic: 'default' });
}

The consume(event) function is the entry point for the script and will be invoked upon execution. Each execution loads the script again, resetting any variable values which were set in previous runs.

Emit Function

The emit('string', object) function is used to publish data back to the system, e.g. the generated sample which should be stored in the database or forwarded to a 3rd party system using an output connector. If the emit function is never called in a script, the script just runs through without any effects and no error is thrown.

Any of the following emit types can be used multiple times throughout script.

• sample (only for uplink decoders of a device type)

• log

• downlink (only for downlink encoders of a device type)

• state (for uplink decoders and custom logic blocks)

A maximum of 50 emit function invocations is allowed per script run.

sample

If the emit function is invoked with sample as first argument, the second argument will be forwarded to the output connector

The object needs to contain the following structure:

{
    "data": {
        // the generated sample during the script run
    },
    "meta": {
        // optional, can contain meta info about value calculation or similar
    },
    "timestamp": new Date(), // optional, can contain a date object which overwrites the emited time 
    "topic": "string" // the topic of the sample
}

If the object does not follow the above structure, an error will occur during forwarding the sample to the output connector.

downlink

If the emit function is invoked with downlink as first argument, the second argument will be sent back to the device. The resulting object needs to follow a strict convention and is explained in more detail in the Downlink page.

log

If the emit function is invoked with log as first argument, the second argument will be emitted as a log object. Log objects are only displayed when developing the script in the Akenza UI. They are otherwise omitted and won't be processed any further.

state

In order to pass state to the next execution of the script (see Stateful Operations), the new state has to be emitted using the state emit type.

Module Imports

Certain ES6 Modules can be imported during script runtime using the following syntax (more info on imports can be found here).

The imported functions, objects, constants, etc... can be used throughout the script.

Timestamp manipulation example with luxon:

import { DateTime } from 'luxon'; 

function consume(event) {
	let data = {};
	// ...
	let timestamp = DateTime.fromJSDate(new Date(), {zone: 'America/Denver'})
		.minus({minutes: 10});
	// ...
	emit('sample', {data: data, timestamp: timestamp.toISO()});
}

Available Modules

Currently, the following modules are provided:

• luxon ^2.4.0 -> date and time manipulation, see their docs for more details

  • NOTE: it is required to invoke .toISO() or .toJSDate() when emitting the timestamp, otherwise the whole luxon date object will be emitted which can't be converted to a valid timestamp by akenza.

For additional modules to be made available, contact our customer support team.

Disabled Functionality

There are certain restrictions when it comes to Scripting and not every JavaScript functionality is available during script running:

• invoking any of the console or print functions, use emit('log', object) instead

• javascript syntax extensions

• any file loading functionality

Uplink Metrics are extracted automatically based on type, as described in the respective page.

One Time Script Running

Run Script

POST https://api.akenza.io/v3/run-script

Scripts can be executed once without any further processing by calling an endpoint of the akenza API. Invocations of the emit('string', object) function have no further impact and are instead returned in the response body.

Headers

Name	Type	Description
x-api-key	string	api key required for authentication

Request Body

Name	Type	Description
script	string	the script to be processed
event	string	the event to process

200

[
    {
        "type": "SAMPLE",
        "event": {
            "data": {
                "tmp": 24.5
            }
        }
    },
    {
        "type": "ERROR",
        "event": {
            "message": "invalid emit type foo"
        }
    },
    {
        "type": "LOG",
        "event": {
            "data": {
                "tmp": 24.5
            }
        }
    }
]

In the above request the following script is used

function consume(event) { 
    emit('sample', {data: {tmp: event.data.temperature}});
    emit('foo', {data: event.foo});
    emit('log', {tmp: event.data.temperature});
}

And the following event

{
    "data": {
	"temperature": 24.5
    },
    "timestamp": "2020-09-07T18:20:05.199Z"
}

Which produces the output as seen in the response of the example. The type reflects the emit type used to invoke the emit('string', object) function. The resulting event contains whatever was passed as second argument. In case of errors during runtime of the script, the event contains a message property detailing the error.