Decoder

Input:

In the preceding code snippet, the uplink payload is retrieved using getUplinkMessage(). The use of the getRequest() function can be seen in the following Output section, where the request correlator ID is obtained.

Output:

The decode function must return the decoded payload details by calling an util function as shown in the following code snippet:

var utils = Java.type('com.nokia.transformation.script.model.TransformUtil');
function CodecName() {
    this.decode = function (decodeCtx) {
        return utils.createJsonResponse(JSON.stringify(resp));
    }
     
    // ...

In the preceding code, the decode function returns the decoded payload details in JSON string format.

The identity of the device needs to be retrieved and this can be done using the client.getEndpoint() built-in function.

function CodecName() {
    this.decode = function (decodeCtx) {
        var clientName = client.getEndpoint();

Unsolicited Uplink

The majority of traffic for uplinks is unsolicited, meaning that the device sends this spontaneously without request from the Server. To set this up an OBSERVE operation needs to be received from the server with the resources that are to be observed.

The JSON structure for notification from the device into IMPACT IoT is as follows:

{
    "details": {
        "device/0/endPointClientName": "<output of client.getEndpoint()>",

        //Below are name-value pairs as decoded from uplink payload
        "resource1": "value1", 
        "resource2": "value2"
    }
}

Under details, the “device/0/endPointClientName” is a mandatory field whose value must correspond to the device identity. The built-in function client.getEndpoint() can be used to retrieve the device id. Other details include name-value pairs of device resources that are found after decoding the uplink payload.

Solicited Uplink

For commands such as READ, DELETE, WRITE, and EXECUTE a correlator can be used to link together the request and response such that the status of the request can be recorded in IMPACT IoT.

The JSON structure for response is common for all solicited uplink messages is as follows:

{
    "responseCode": 0,  zero means success
    "requestStatus": 0,
    "response": [
        {
            "device/0/endPointClientName": "<output of client.getEndpoint()>",
            "resource1": "value1",  name-value pairs as decoded from uplink payload
            "resource2": "value2"
        }
    ],
    "correlatorId": "<output of decodeCtx.getRequest().getCorrelatorId()>"
}

In the preceding JSON structure, the correlatorId is mandatory which refers to the correlator ID of the IMPACT IoT downlink request associated with the current uplink response. The value of the correlatorId is stored in IMPACT IoT. There can be only one outstanding downlink request for a particular device. The value of correlatorId can be obtained from the input argument as follows:

function CodecName() {
    this.decode = function (decodeCtx) {
        var corrId = decodeCtx.getRequest().getCorrelatorId();

Also, the “device/0/endPointClientName” field is mandatory, whose value can be obtained by using the built-in function client.getEndpoint().

Processing:

The process of decoding the input payload is specific to the protocol specification of the device. Refer to Sample scripts section.

If there is any error while decoding the uplink payload then the script can throw an exception as shown in the following code snippet:

function CodecName() {
    this.decode = function (decodeCtx) {
        if (decoding_failure) {
            throw new Error(`boot message with invalid reset reason`);
        }

        // ...