Azure IOT Hub + Table Storage function App

gardenSensorDataProcessor.js

'use strict';

const https = require("https");
const uuid = require("uuid/v4");
const IotClient = require("azure-iothub").Client;
const IotMessage = require("azure-iot-common").Message;

// main function 
module.exports = function (context, eventHubMessage) {
    // log this for debugging
    context.log("JavaScript event hub trigger function processed work item:", JSON.stringify(eventHubMessage));

    // put the initial table storage metadata together
    const tableMetadata = {
        "PartitionKey": "sensorReading",
        "RowKey": uuid()
    };

    // get precipitation data to commit to table row
    getWeatherData(function(error, precipData) {
        // if we got weather data, proceed
        if (!error) {
            const deviceOrigin = eventHubMessage.IoTHub.ConnectionDeviceId;

            sendPrecipDataToDevice(precipData, deviceOrigin, function(error) {
                // we can just log this, as we can safely ignore any failed attempts at cloud to device messaging
                if (error) context.log(error);

                // merge table storage metadata, sensor data, and precipitation data
                const outData = Object.assign(tableMetadata, eventHubMessage, precipData);

                // finally return all data for output into table storage
                context.done(null, outData);
            });
        } else { // if we couldn't get the weather data, we should at least store the sensor data
        
            // merge table storage metadata and sensor data
            const outData = Object.assign(tableMetadata, eventHubMessage);

            // return all data for output into table storage
            context.done(null, outData);
        }
    });
};

// weather api function
const getWeatherData = function(callback) {

    const options = {
        host: "api.darksky.net",
        path: `/forecast/${process.env.DARK_SKY_KEY}/40.679225,-74.012153`,
        method: "GET",
        headers: {
            "Content-Type": "application/json"
        }
    };

    // set up the weather api request
    const req = https.request(options, function (res) {
        let responseString = "";

        // on each data event, append the data to the entire response string
        res.on("data", function (data) {
            responseString += data;
        });

        // on response end, parse the response string, pull out the precipitation data and return it to the callback
        res.on("end", function () {
            const weatherInfo = JSON.parse(responseString);

            const precipData = {
                precipIntensity: weatherInfo.currently.precipIntensity,
                precipProbability: weatherInfo.currently.precipProbability
            };

            // return data to callback when response ends
            return callback(null, precipData);
        });
    });

    // if there's an error in making the API request
    req.on("error", function(error) {
        return callback(error);
    });
    
    // end the request to send it out immediately without a body
    req.end();
}

// iot hub function to dispatch weather data back to device
const sendPrecipDataToDevice = function(data, deviceid, callback) {
    const iotClient = IotClient.fromConnectionString(process.env.IOT_CONN_STRING);

    // open a client to iot hub, and send precipitation data back to the device
    iotClient.open(function (error) {
        if (error) return callback(error);
        const dataString = JSON.stringify(data);
        const message = new IotMessage(dataString);
        iotClient.send(deviceid, message, callback);
    });
}