7.4. Send method for LwM2M Gateway EIDs
7.4.1. Overview
The LwM2M Gateway specification supports the LwM2M Send method, allowing efficient data transmission from End IoT Devices (EIDs). Anjay fully supports this feature, and it works similarly to the API used for standard LwM2M devices.
7.4.1.1. Why use the LwM2M Send method?
Batch Data Transmission – You can send multiple resource values at once without needing Observations.
Multi-Device Support – A single Send message can include data from multiple EIDs, reducing communication overhead.
Gateway & EID Data Combination – You can send data from both the LwM2M Gateway (Client) and its connected EIDs in one message.
Note
If you’re new to the LwM2M Send method and how it works in Anjay for standard LwM2M clients, read the Send method tutorial first.
7.4.1.2. LwM2M Send for EIDs vs. standard Devices
The main difference when using the Send method for EIDs is that the family of
anjay_send_batch_[data_]add_* functions require an extra parameter—the
EID. This EID parameter is an integer ID assigned when calling
anjay_lwm2m_gateway_register_device(),
as shown here.
7.4.1.3. Send method API comparison
Below is a side-by-side comparison of the original Send API and its counterpart for LwM2M Gateway EIDs:
Standard Send API |
Send API for LwM2M Gateway EIDs |
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These APIs are meant to be used with other standard APIs for Send method, such as:
anjay_send_batch_builder_new()– To build batch messages.anjay_send()– To transmit data efficiently.
7.4.2. Example
Note
Complete code of this example can be found in
examples/tutorial/LwM2M-Gateway subdirectory of the main
Anjay project repository.
For specifics on how this example works, refer to the LwM2M Gateway API article.
7.4.2.1. How it works
This example periodically sends the temperature measured by all EIDs.
The function temperature_object_send() (defined in temperature_object.c):
Creates a new batch for collecting data.
Iterates through the list of EIDs, fetching their temperature values.
Compiles the batch and schedules it for transmission.
void temperature_object_send(anjay_t *anjay,
AVS_LIST(end_device_t) end_devices) {
if (!anjay) {
return;
}
const anjay_ssid_t server_ssid = 1;
if (!end_devices) {
avs_log(temperature_object, TRACE,
"No end devices found, skipping sending data");
return;
}
// Allocate new batch builder.
anjay_send_batch_builder_t *builder = anjay_send_batch_builder_new();
if (!builder) {
avs_log(temperature_object, ERROR, "Failed to allocate batch builder");
return;
}
AVS_LIST(end_device_t) it;
AVS_LIST_FOREACH(it, end_devices) {
// Add current values of resource from Temperature Object.
temperature_object_t *obj = get_obj(it->temperature_object);
temperature_instance_t *inst = &obj->instances[0];
if (anjay_lwm2m_gateway_send_batch_data_add_current(
builder, anjay, obj->end_device_iid, obj->def->oid,
inst->iid, RID_SENSOR_VALUE)) {
anjay_send_batch_builder_cleanup(&builder);
avs_log(temperature_object, ERROR, "Failed to add batch data");
return;
}
}
// After adding all values, compile our batch for sending.
anjay_send_batch_t *batch = anjay_send_batch_builder_compile(&builder);
if (!batch) {
anjay_send_batch_builder_cleanup(&builder);
avs_log(temperature_object, ERROR, "Batch compile failed");
return;
}
// Schedule our send to be run on next `anjay_sched_run()` call.
int res =
anjay_send(anjay, server_ssid, batch, send_finished_handler, NULL);
if (res) {
avs_log(temperature_object, ERROR, "Failed to send, result: %d", res);
}
// After scheduling, we can release our batch.
anjay_send_batch_release(&batch);
}
7.4.2.2. Differences from standard LwM2M Send
Compared to the standard LwM2M Send method described in the Send method tutorial, this implementation includes:
Support for Multiple EIDs – Instead of sending data from a single device, this function accepts a list of EIDs and retrieves temperature readings from each one.
New API Function with Extra Parameter: – The function
anjay_lwm2m_gateway_send_batch_data_add_current()is used to support EIDs. The function takes an additional parameter,obj->end_device_iid, which:Specifies the data source (the correct EID).
Encodes a proper URI prefix retrieved internally from Gateway module.
7.4.2.3. Scheduling periodic data transmission
To ensure temperature readings are sent at regular intervals, this function is called periodically by the scheduler as shown below:
// Periodically issues a Send message with measured values of the temperature
static void send_job(avs_sched_t *sched, const void *args_ptr) {
gateway_srv_t *gateway_srv = *(gateway_srv_t *const *) args_ptr;
temperature_object_send(gateway_srv->anjay, gateway_srv->end_devices);
// Schedule run of the same function after 10 seconds
AVS_SCHED_DELAYED(sched, NULL,
avs_time_duration_from_scalar(10, AVS_TIME_S), send_job,
&gateway_srv, sizeof(gateway_srv));
}
This periodic behavior is set up in main(), just before
anjay_event_loop_run() is called:
int main(int argc, char *argv[]) {
// ...
if (!result) {
// Run send_job the first time;
// this will schedule periodic calls to themselves via the scheduler
send_job(anjay_get_scheduler(anjay), &gateway_srv_ptr);
result = anjay_event_loop_run(
anjay, avs_time_duration_from_scalar(1, AVS_TIME_S));
}
// ...
}