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LightDB Observe Request

Use the Golioth Firmware SDK for all Zephyr projects

The Golioth Zephyr SDK is deprecated. Please use the Golioth Firmware SDK. (Migration Guide)

The LightDB Observe sample application demonstrates how to use the Golioth Zephyr SDK to register a LightDB State endpoint and receive an update whenever data changes on the cloud. The observe request works in a similar way to the get request and much of the setup is the same. Data is received asynchronously and sent to a handler function registered when the observe request is first made.

Includes​

#include <net/golioth/system_client.h>

Including the Golioth System Client header file makes the LightDB Observe API functions available to your program.

Asynchronous Observe​

Registering a callback​

static void golioth_on_connect(struct golioth_client *client)
{
	int err;

	err = golioth_lightdb_observe_cb(client, "counter",
					 GOLIOTH_CONTENT_FORMAT_APP_JSON,
					 counter_handler, NULL);

	if (err) {
		LOG_WRN("failed to observe lightdb path: %d", err);
	}
}

Use the golioth_lightdb_observe_cb() to register a non-blocking callback that will execute asynchronously when receiving data updates from the Golioth Cloud. Parameters include a desired endpoint and the name of the callback function. The final parameter can be used to pass additional user-defined arguments to the callback. The Golioth servers will send an update when the callback is first registered and each time data changes on the cloud. When the response is received from Golioth, the registered callback will run, allowing you to validate and react to the data.

Register Observe requests whenever connected

We recommend that this callback be registered in the client->on_connect callback that runs each time the device connects to Golioth. This way, the device will receive endpoint data at every reconnect as well as whenever data changes on the cloud.

Callback function​

static int counter_handler(struct golioth_req_rsp *rsp)
{
	if (rsp->err) {
		LOG_ERR("Failed to receive counter value: %d", rsp->err);
		return rsp->err;
	}

	LOG_HEXDUMP_INF(rsp->data, rsp->len, "Counter (async)");

	return 0;
}

The response is passed to the callback function as a golioth_req_rsp struct that includes err, data, and len. It is recommended that callbacks test for an error code to ensure the expected data was received.

User-defined arguments are passed to the callback as rsp.user_data.

Summary​

The best example of an Observe request is found in the LightDB Observe sample code.

Further documentation of the device SDK is available in the Golioth Zephyr SDK Reference (Doxygen).