server-observe-example.c

Create, process and free a basic Observe request on a single resource and receive notifications containing the initial and changed value.

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/*
 * This example demonstrates how to observe a client's resource via the server.
 * If the resource changes and a notification is generated, an application callback
 * is invoked.
 *
 * This example is a little contrived in that it creates an observation and then
 * triggers the notification itself with a WRITE. In many cases, the notification
 * will be triggered by an update to the resource value by another entity such as
 * the client itself.
 */

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

#include <awa/common.h>
#include <awa/server.h>

#define IPC_PORT (54321)
#define IPC_ADDRESS "127.0.0.2"
#define OPERATION_PERFORM_TIMEOUT 1000
#define CLIENT_ID "TestClient1"

/*
 * This function will be called by the API when the server receives
 * a notification of change from the client. When invoked, changeSet
 * provides information about the value(s) that triggered the notification,
 * and context is the supplied pointer to any application data.
 *
 * This callback is called once when the observation is set up.
 */
static void observeCallback(const AwaChangeSet * changeSet, void * context)
{
    int * notificationCount = (int *)context;
    printf("Callback received, notification count = %d\n", *notificationCount);

    const char * value;
    AwaChangeSet_GetValueAsCStringPointer(changeSet, "/3/0/15", &value);
    if (*notificationCount == 0)
        printf("Initial value of resource /3/0/15 is: %s\n", value);
    else
        printf("Value of resource /3/0/15 changed to: %s\n", value);
    (*notificationCount)++;
}

int main(void)
{
    /* Create and initialise server session */
    AwaServerSession * session = AwaServerSession_New();

    /* Use default IPC configuration */
    AwaServerSession_Connect(session);

    int notificationCount = 0;

    /*
     * This example uses resource /3/0/15 which is the Timezone
     * resource in the standard Device object. It is a string.
     */

    /* Create a new observation to resource /3/0/15 */
    AwaServerObservation * observation = AwaServerObservation_New(CLIENT_ID, "/3/0/15", observeCallback,
                                                                  (void *)&notificationCount);

    /* Start listening to notifications */
    AwaServerObserveOperation * observeOperation = AwaServerObserveOperation_New(session);
    AwaServerObserveOperation_AddObservation(observeOperation, observation);
    AwaServerObserveOperation_Perform(observeOperation, OPERATION_PERFORM_TIMEOUT);
    AwaServerObserveOperation_Free(&observeOperation);

    /* Change the value of resource /3/0/15 so that a notification will be sent to our observation */
    AwaServerWriteOperation * writeOperation = AwaServerWriteOperation_New(session, AwaWriteMode_Update);
    AwaServerWriteOperation_AddValueAsCString(writeOperation, "/3/0/15", "Pacific/Auckland");
    AwaServerWriteOperation_Perform(writeOperation, CLIENT_ID, OPERATION_PERFORM_TIMEOUT);
    AwaServerWriteOperation_Free(&writeOperation);

    /* Sleep for a period to ensure we don't process before the notification is received */
    sleep(1);

    /* Receive notifications */
    AwaServerSession_Process(session, OPERATION_PERFORM_TIMEOUT);
    AwaServerSession_DispatchCallbacks(session);

    /* Cancel observation from resource /3/0/15 */
    AwaServerObserveOperation * cancelObserveOperation = AwaServerObserveOperation_New(session);
    AwaServerObserveOperation_AddCancelObservation(cancelObserveOperation, observation);
    AwaServerObserveOperation_Perform(cancelObserveOperation, OPERATION_PERFORM_TIMEOUT);
    AwaServerObserveOperation_Free(&cancelObserveOperation);

    /* Operations must be freed after use */
    AwaServerObservation_Free(&observation);

    AwaServerSession_Disconnect(session);
    AwaServerSession_Free(&session);
    return 0;
}