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About API Guide - C++

The About Feature was integrated with the core library with the AllJoyn™ 14.12 release. The reference code found in this document refers to the About Feature code developed before the the About Feature integration.

As a developer you are encouraged to discontinue use of these APIs and move to the newer About Feature API.

Current About API C++ Guide

Reference code

Classes used to send AboutData

Server class Description
AboutService Class that implements the org.alljoynAbout interface.
AboutIconService Class that implements the org.alljoynIcon interface.
PropertyStore Interface that supplies the list of properties required for Announce signal payload and GetAboutData().

Classes used to receive AboutData

Client class Description
AboutClient Helper class for discovering AboutServer that provides access to the Announcements and to the AboutService. It listens for Announcements sent using the org.alljoyn.About interface.
AboutIconClient Helper class that provides access to the AboutIconService.

Reference C++ application code

Application class Description
AboutServerMain Command line application that announces the About and DeviceIcon AllJoyn™ interfaces and handles remote access to these interfaces by registering an instance of AboutService and AboutIconService the AllJoyn bus.
AboutClientMain Command line application that uses AboutClient to discover About servers and exercise their interfaces.

Build an application that uses AboutService

The following steps provide the high-level process to build an application that will broadcast AboutData.

  1. Implement PropertyStore to produce an AboutStore. (See Create a PropertyStore implementation.)
  2. Instantiate an AboutStore.
  3. Create and register the AboutService, providing it with the AboutStore.

Build an application that uses AboutClient

The following steps provide the high-level process to build an application that will receive AboutData.

  1. Create the base for the AllJoyn application.
  2. Create a new AboutClient.
  3. Register the AnnounceListener.
  4. Register the AboutClient.

Setting Up the AllJoyn Framework

Create instance of BusAttachment

To use the About feature, an AllJoyn object call the BusAttachment is needed that is used internally by the service to leverage the AllJoyn API calls.

BusAttachment* msgBus = new BusAttachment("AboutService", true);

Create password for the bundled router

NOTE: Thin libraries at AllSeen Alliance version 14.06 or higher do not require this step.

To allow thin libraries to connect to the bundled router, the router requires a password.

PasswordManager::SetCredentials("ALLJOYN_PIN_KEYX", PassCode);
}

Start and connect the BusAttachment

Once created, the BusAttachment must be connected to the AllJoyn framework.

QStatus status = msgBus->Start();
if( status == ER_OK ) {
   status = msgBus->Connect(NULL);
}

Implementing an Application that Uses AboutService

Implementing an AboutServer requires creating and registering an instance of the AboutService class.

NOTE: Verify the BusAttachment has been created, started and connected before implementing the AboutService. See Setting Up the AllJoyn Framework for the code snippets. Code in this section references a variable msgBus (the BusAttachment variable name).

Declare listener class

Declare a listener class to receive the SessionPortListener callback.

Typically, an AcceptSessionJoiner callback in SessionPortListener has a check to allow or disallow access. Since the AboutService requires access to any application using AboutClient, return true when this callback is triggered. Use the SessionJoined handler to set the session timeout to 20 seconds.

class MyListener : public SessionPortListener {
   private:
      BusAttachment *mMsgBus;

   public:
      MyListener( BusAttachment *msgBus ) {
         mMsgBus = msgBus;
   }

      bool AcceptSessionJoiner( SessionPort sessionPort, const
         char* joiner, const SessionOpts& opts ) {

         printf("Accepting join session request from %s (opts.proximity=%x,
            opts.traffic=%x, opts.transports=%x)\n",
               joiner, opts.proximity, opts.traffic, opts.transports);

         return true;
      }

      void SessionJoined( SessionPort sessionPort, SessionId id, const char*
joiner ) {
         printf("SessionJoined with %s (id=%d)\n", joiner, id);
         mMsgBus->EnableConcurrentCallbacks();
         uint32_t timeout = 20;
         QStatus status = mMsgBus->SetLinkTimeout(id, timeout);
         if( status == ER_OK ) {
            printf("Link timeout has been set to %ds\n", timeout);

         } else {
            printf("SetLinkTimeout(%d) failed\n", timeout);
         }
      }
};

Bind session port

To allow incoming connections, the formation of a session is needed. The AllJoyn framework must be told that connections are allowed.

SessionOpts opts(SessionOpts::TRAFFIC_MESSAGES, false,
    SessionOpts::PROXIMITY_ANY, TRANSPORT_ANY);
SessionPort sPort = SERVICES_PORT;
if( status == ER_OK )
    status = msgBus->BindSessionPort(sPort, opts, *busListener);

Create a PropertyStore implementation

The PropertyStore interface is required by the AboutService to store the provisioned values for the About interface data fields. See the About Interface Definition for more information.

About interface data fields

Field name Required Announced Signature
AppId yes yes ay
DefaultLanguage yes yes s
DeviceName yes yes s
DeviceId yes yes s
AppName yes yes s
Manufacturer yes yes s
ModelNumber yes yes s
SupportedLanguages yes no as
Description yes no s
DateofManufacture no no s
SoftwareVersion yes no s
AJSoftwareVersion yes no s
HardwareVersion no no s
SupportUrl no no s

An example PropertyStore implementation (AboutPropertyStoreImp) is provided. All fields above can easily be set by calling the appropriate setter function.

aboutStore = new AboutPropertyStoreImpl();
aboutStore ->setDeviceId("1231232145667745675477");
aboutStore ->setDeviceName("MyDeviceName", "en");
aboutStore ->setDeviceName("NombreDeMiDispositivo", "es");
aboutStore ->setDeviceName("NomDispositif", "fr");
aboutStore ->setAppId("000102030405060708090A0B0C0D0E0C");
aboutStore ->setDefaultLang("en");

aboutStore ->setAppName("AboutConfig", "en");
aboutStore ->setAppName("AboutConfig", "es");
aboutStore ->setAppName("AboutConfig", "fr");
aboutStore ->setModelNumber("Wxfy388i");
aboutStore ->setDateOfManufacture("10/1/2199");
aboutStore ->setSoftwareVersion("12.20.44 build 44454");
aboutStore ->setAjSoftwareVersion(ajn::GetVersion());
aboutStore ->setHardwareVersion("355.499. b");

std::vector<qcc::String> languages(3);
languages[0] = "en";
languages[1] = "es";
languages[2] = "fr";
aboutStore ->setSupportedLangs(languages);

aboutStore ->setDescription("This is an AllJoyn application", "en");
aboutStore ->setDescription("Esta es una AllJoyn aplicacion", "es");
aboutStore ->setDescription("C'est une AllJoyn application", "fr");

aboutStore ->setManufacturer("Company", "en");
aboutStore ->setManufacturer("Empresa", "es");
aboutStore ->setManufacturer("Entreprise", "fr");

aboutStore ->setSupportUrl("http://www.allseenalliance.org");

Create the AboutService object

For an application to send AboutData, it requires an instance of the AboutService class. AboutService is an implementation wrapper around AllJoyn native calls that handle the interactions between AboutServer and AboutClient.

AboutService* aboutService = NULL;
aboutService = aboutService = new AboutService(msgBus,aboutStore);
aboutService->Register(SERVICES_PORT);
msgBus->RegisterBusObject(*aboutService);

Add interfaces to Announcement

std::vector<qcc::String> interfaces;
interfaces.push_back("org.alljoyn.About");
aboutService->AddObjectDescription("/About", interfaces);

Register AboutService object with BusAttachment

Register the AboutService with the obtained session port.

aboutService->Register(sPort);
msgBus->RegisterBusObject(*aboutService);

Add an AboutIconService (optional)

An applicaton that sends AboutData can be extended to broadcast a device icon using an instance of the AboutIconService class. AboutIconService is an implementation wrapper around AllJoyn native calls that handle the interactions between applications that use the AboutIconClient class.

Provision for the Icon content and URL

An Icon is published directly as a byte array or a reference URL, and must be provisioned as follows:

uint8_t aboutIconContent[] = { 0x89, 0x50, 0x4E, 0x47, 0x0D /* Add relevant data here */ };
qcc::String mimeType("image/png"); /* This should correspond to the content */
qcc::String url("http://myurl"); /* An alternate access to the Icon */

AddDeviceIcon object and interfaces to Announcement

std::vector<qcc::String> interfaces;
interfaces.push_back("org.alljoyn.Icon");
aboutService->AddObjectDescription("/About/DeviceIcon", interfaces);

Create and register DeviceIcon object

AboutIconService* aboutIconService = NULL;
aboutIconService = new AboutIconService(msgBus, mimeType, url,
   aboutIconContent, sizeof(aboutIconContent) / sizeof (*aboutIconContent));
aboutIconService->Register();
msgBus->RegisterBusObject(*aboutIconService);
if( status == ER_OK )
   status = msgBus->AdvertiseName(msgBus->GetUniqueName().c_str(),
      opts.transports);

Announce name

if( status == ER_OK )
status = aboutService->Announce();

Unregister and delete AboutService, AboutStore, and AboutIconService

When your process is done with the AboutService and no longer wishes to send announcements, unregister the process from the AllJoyn bus and then delete variables used.

if( aboutService != NULL ) {
   msgBus->UnregisterBusObject(*aboutService);
   delete aboutService;
}
if( aboutStore != NULL ) {
   delete aboutStore;
}
if( aboutIconService != NULL ) {
   msgBus->UnregisterBusObject(*aboutIconService);
   delete aboutIconService;
}

Implementing an Application that Uses AboutClient

To implement an application to receive AboutData, use the AboutClient class. By using the AboutClient class, your application is notified when AboutServer instances send announcements.

NOTE: Verify the BusAttachment has been created, started and connected before using an AboutClient. See Setting Up the AllJoyn Framework for the code snippets. Code in this section references a variable msgBus (the BusAttachment variable name).

Setup to receive the Announce signal

In order to receive the Announce signal, implement a class that inherits from the AnnounceHandler base class.

Create class to implement AnnounceHandler

This declaration of a class will allow for the signals to be received. It needs to implement pure virtual function Announce.

class AnnounceHandlerImpl : public ajn::services::AnnounceHandler (){
   void Announce(unsigned short version, unsigned short port,
      const char* busName, const ObjectDescriptions& objectDescs,
         const AboutData& aboutData);
}

Implement the Announce method that handles the Announce signal

With everything linked up using the AllJoyn framework, the method registered with the AllJoyn framework will be executed upon receipt of an Announce signal.

Because every application is different, as a developer you will need to process the AboutData and determine the following:

  • How in the UI it should be rendered
  • When to request the data that is not contained in the Announce signal
  • Any logic that is needed

Register the announceHandler using the AnnouncementRegistrar class

When registering an announcement listener, specify which interfaces the application is interested in. The code below shows a listener registered to receive Announce signals that include an object implementing the INTERFACE_NAME interface.

AnnounceHandlerImpl* announceHandlerImpl = new AnnounceHandlerImpl();
const char* interfaces[] = { INTERFACE_NAME };
AnnouncementRegistrar::RegisterAnnounceHandler(*busAttachment,
   *announceHandlerImpl, interfaces, 1);

Using Ping to determine presence

The BusAttachment Ping member function can be used to determine if a device is responsive. Contents of an Announce signal can be stale so it is recommended to ping the device to see if it is still present and responsive before attempting to form a connection.

NOTE: The BusAttachment.Ping method makes a bus call. If Ping is called inside an AllJoyn callback, BusAttachment.EnableConcurrentCallbacks must be called first.

// when pinging a remote bus wait a max of 5 seconds
#define PING_WAIT_TIME    5000
msgBus->EnableConcurrentCallbacks();
   QStatus status = msgBus->Ping(busName.c_str(), PING_WAIT_TIME);
   if( ER_OK == status) {
   ...
}

Request non-announced data

If there is a need to request information that is not contained in the announcement, perform the following steps.

  1. Join the session

    Create a session with the application by using the BusAttachment JoinSession API.

    NOTE: The variables name and port are set from the AboutData from the Announce method.

    SessionId sessionId;
       SessionOpts opts(SessionOpts::TRAFFIC_MESSAGES, false,
          SessionOpts::PROXIMITY_ANY, TRANSPORT_ANY);
       QStatus status = msgBus->JoinSession(name, port, NULL, sessionId, opts);
       if (status == ER_OK) {
          QCC_DbgTrace(("JoinSession SUCCESS (Session id=%d)", sessionId));
       } else {
          QCC_LogError(status, ("JoinSession failed"));
       }
    
  2. Create AboutClient

    Generate an AboutProxyBusObject from the org.alljoyn.About Introspection XML and create an instance passing ButAttachment and sessionId.

    AboutProxyBusObject * aboutClient = new AboutProxyBusObject
       (msgBus, sender_name,"\About", sessionId);
    aboutClient->GetAboutData("");
    
  3. Create AboutIconClient

    Generate an IconProxyBusObject from the org.alljoyn.Icon Introspection XML and create an instance passing ButAttachment, port, and sessionId.

    IconProxyBusObject * aboutIconClient = new IconProxyBusObject
       (msgBus, sender_name, "About\DeviceIcon", sessionId);
    aboutIconClient->GetUrl();
    

Shutdown

Once you are done using the About feature and the AllJoyn framework, free the variables used in the application.

NOTE: The AboutClient object must be deleted before the BusAttachment object.

delete aboutClient;
delete aboutIconClient;
delete msgBus;
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