client-subscribe-to-change-example.c

Subscribe and receive notification to a change of a single resource.

/************************************************************************************************************************
 Copyright (c) 2016, Imagination Technologies Limited and/or its affiliated group companies.
 All rights reserved.

 Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
 following conditions are met:
     1. Redistributions of source code must retain the above copyright notice, this list of conditions and the
        following disclaimer.
     2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
        following disclaimer in the documentation and/or other materials provided with the distribution.
     3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote
        products derived from this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
************************************************************************************************************************/

/*
 * This example demonstrates how to subscribe to the client for notifications of
 * changes to the value of a resource, using a SUBSCRIBE to CHANGE operation.
 *
 * This example is a little contrived in that it creates a subscription and then
 * triggers the notification itself. In most cases, the notification will be
 * triggered by a WRITE operation initiated by the server.
 */

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

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

#define IPC_PORT (12345)
#define IPC_ADDRESS "127.0.0.1"
#define OPERATION_PERFORM_TIMEOUT 1000

/*
 * This function will be called by the API when the client sends
 * a notification of change. When invoked, changeSet provides information
 * about the value(s) that triggered the notification, and context
 * is the supplied pointer to any application data.
 */
static void changeCallback(const AwaChangeSet * changeSet, void * context)
{
    const char * userData = (const char *)context;
    printf("Callback received. Context = %s\n", userData);

    const char * value;
    AwaChangeSet_GetValueAsCStringPointer(changeSet, "/3/0/0", &value);
    printf("Value of resource /3/0/0 changed to: %s\n", value);
}

int main(void)
{
    /* Create and initialise client session */
    AwaClientSession * session = AwaClientSession_New();

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

    /* Application-specific data */
    const char * userData = "My custom data";

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

    /*
     * Create a new change subscription to resource /3/0/0.
     * Data can be provided to the callback function via the context pointer.
     */
    AwaClientChangeSubscription * subscription = AwaClientChangeSubscription_New("/3/0/0", changeCallback,
                                                                                 (void *)userData);

    /* Start listening to notifications */
    AwaClientSubscribeOperation * subscribeOperation = AwaClientSubscribeOperation_New(session);
    AwaClientSubscribeOperation_AddChangeSubscription(subscribeOperation, subscription);
    AwaClientSubscribeOperation_Perform(subscribeOperation, OPERATION_PERFORM_TIMEOUT);
    AwaClientSubscribeOperation_Free(&subscribeOperation);

    /* Change the value of resource /3/0/0 so that a notification will be sent to our subscription */
    AwaClientSetOperation * setOperation = AwaClientSetOperation_New(session);
    AwaClientSetOperation_AddValueAsCString(setOperation, "/3/0/0", "HotAir Systems Inc");
    AwaClientSetOperation_Perform(setOperation, OPERATION_PERFORM_TIMEOUT);
    AwaClientSetOperation_Free(&setOperation);

    /* Receive notifications */
    AwaClientSession_Process(session, OPERATION_PERFORM_TIMEOUT);
    AwaClientSession_DispatchCallbacks(session);

    /* Unsubscribe from resource /3/0/0 */
    AwaClientSubscribeOperation * cancelSubscribeOperation = AwaClientSubscribeOperation_New(session);
    AwaClientSubscribeOperation_AddCancelChangeSubscription(cancelSubscribeOperation, subscription);
    AwaClientSubscribeOperation_Perform(cancelSubscribeOperation, OPERATION_PERFORM_TIMEOUT);
    AwaClientSubscribeOperation_Free(&cancelSubscribeOperation);

    /* Free the change subscription */
    AwaClientChangeSubscription_Free(&subscription);

    AwaClientSession_Disconnect(session);
    AwaClientSession_Free(&session);
    return 0;
}