Getting Started

Let's say that we want to publish weather data such as (1) precipitation (2) temperature, and (3) humidity using CBOR. However, now that we are only interested in the temperature and humidity (filtering).

Note: You MUST complete the installation and building steps as described in the GitHub NetCoap before proceeding to the next steps.

string g_NetCoapCONFIG_FILE = "..." ;

Client* g_client = nullptr;

UdpClientDtlsIo g_dtls;

JsonPropTree g_cfg;

g_cfg.fromJsonFile(g_NetCoapCONFIG_FILE);

g_client = new Client(g_cfg, g_dtls);

bool connected = g_client->connect();

if (!connected) {

        exit(1);

}

string g_dataUriPath = "/www/topic/ps/weather";

string g_topicName = "Weather";

string g_topicUriPath = "/www/topic/ps";

// Create topic and register the below callback

g_client->createTopic(

        g_topicName, g_topicUriPath, g_dataUriPath,

        "weather", Message::CONTENT_FORMAT::APP_CBOR,

        createTopicCb);

void createTopicCb(

        Client::STATUS status,

        const shared_ptr<Message> respMsg) {

        // Output helpful info return from creating topic

        Helper::syncOut() << "***** Create Topic Helpful Info *****\n";

        JsonPropTree jsonTree;

        jsonTree.fromCborStr(*respMsg->getPayload());

        jsonTree.print();

}

// Subscribe to Weather topic and register the below callback

// We are only interested in temperature and humidity

g_client->subscribe(g_dataUriPath, subscribeCb, "temperature&humidity");

void subscribeCb(

        Client::STATUS status,

        const shared_ptr<Message> respMsg) {

        shared_ptr<string> payLoad = respMsg->getPayload();

        JsonPropTree jsonPropTree;

        jsonPropTree.fromCborStr(*payLoad);

        float temperature = jsonPropTree.get<float>("temperature");

        Helper::syncOut() << "Temperature: " << fixed << setprecision(2)

                << temperature << "\n";

        float humidity = jsonPropTree.get<int>("humidity");

        Helper::syncOut() << "Humidity: " << humidity << "\n";

}

// ===== Publish Temperature and Humidity =====

float temperature = 70.5; // Assume Fahrenheit

int humidity = 100; //  Assume percent. Air is saturated 

string jsonTempHumidity =

        string("{") +

        "\"" + "humidity" + "\"" + ':' + to_string(humidity) + "," +

        "\"" + "temperature" + "\"" + ':' + to_string(temperature) +

        string("}");

shared_ptr<string> tempHumidityDat(new string());

jsonPropTree.fromJsonStr(jsonTempHumidity);

jsonPropTree.toCborStr(*tempHumidityDat);

// Publish data using CBOR and reliable transmit

// The humidity&temperature param allows the subscriber

// to query for keywords

g_client->publish(

        g_dataUriPath, tempHumidityDat,

        Message::CONTENT_FORMAT::APP_CBOR,

        true, "humidity&temperature");

// ===== Publish Precipitation =====

// ===== May be subscribe later but not using it now.

// ===== The data will be delivered to the CoapBroker and

// ===== discarded because there is no subscriber

// ===== to query for keyword precipitation

float precipitation = .25; // Rain .25 inch

string jsonPrecipitation =

        string("{") +

        "\"" + "precipitation" + "\"" + ':' + to_string(precipitation) +

        string("}");

shared_ptr<string> precipitationDat(new string());

jsonPropTree.fromJsonStr(jsonPrecipitation);

jsonPropTree.toCborStr(*precipitationDat);

// Publish data using CBOR and reliable transmit

g_client->publish(

        g_dataUriPath, precipitationDat,

        Message::CONTENT_FORMAT::APP_CBOR,

        true, "precipitation");