About API Guide - C (Thin Core)

Obtain the About feature

The source code for this feature can be found on the AllSeen Alliance gerrit page as a git project. In addition, the ajtcl project is needed to compile this feature.

If the target platform already supports the AllJoyn® Thin Library framework, refer to the target platform documentation for detailed setup and download instructions.

If the target platform does not support the AllJoyn Thin Library framework, porting work is required to support this target. See the Introduction to AllJoyn Thin Library for more information about the AllJoyn Thin Library framework.

Reference code

The reference code consists of a module implementing the About Server layer that allows for Announcements to be composed and sent, and provides remote access to AboutData. It also has an AboutService-specific sample code for integrating with the ServerSample application code.

About feature modules

Module Description
AboutIcon AboutIcon code
AboutSample This module is responsible for the general flow of the About sample application including initialization and shutdown of the AboutService and AboutIcon modules, and performing any AboutService and AboutIcon-related business logic when the application's message loop is idling.
AboutService About feature code
ApplicationProvisioning Application provisioning code for all services. This module is part of the ServerSample.
PropertyStore PropertyStore implementation code. This supports all core services. This module is part of the AppsCommon.

Build an About Server

The following steps provide the high-level process to build an About Server. See the Build an Application using the Thin Library section for instructions.

  1. Create the base for the AllJoyn application.
  2. Implement the PropertyStore and provision its values.

Implementing an About Server

Create the base for the AllJoyn application

See the Build an Application using the Thin Library section for instructions.

Provision the PropertyStore for the About feature

A PropertyStore structure is required by the AboutService to store the provisioned values for the data fields listed in AboutData fields. See the About Interface Definition for more information.

AboutData fields

Field name Required Announced Type
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

PropertyStore implementation

The code in PropertyStore.c file is an example PropertyStore implementation that supports the requirements of the AboutService and is included as part of the ServerSample code. The PropertyStore uses the provisioning structures that are defined in the PropertyStoreOEMProvisioning.h file in the AppsCommon. A provisioning example is provided in the ServerSample code and explained in the Build an Application using the Thin Library section.

Adding custom field definition and values

Complete the following steps to add your own custom fields to extend AboutData.

  1. Decide to which subset the field belongs (persisted keys or all keys) and add it to the enumeration AJSVC_PropertyStoreFieldIndices accordingly.
  2. Add a new field entry at the respective index to the propertyStoreProperties.
  3. Decide whether the field is publicly accessible from remote clients. If the field is public then set the mode7Public bit to 1.
  4. Decide whether the field is to be included in the Announcement. If the field is announced then set the mode1Announce bit to 1. NOTE: It is recommended to limit the inclusion of a field in the Announcement according to its immediate relevance to the appropriate service framework's discovery.Only the value associated with the current DefaultLanguage will be sent in the Announcement.
  5. Decide whether the field is multi-language and add the relevant values for the provisioned languages. If the field is multi-language then set the mode2MultiLng bit to 1.
  6. Decide whether the field is to be provisioned dynamically in code and persisted during first-time (or post-factory reset) device startup. If the field is to be initialized once, then set the mode3Init bit to 1 and add the relevant code to initialize it. Refer to PropertyStore_Init() and InitMandatoryPropertiesInRAM() in PropertyStore.c file for an example setup for the DeviceId and AppId fields. NOTE: If you set this bit, the field's index must be included in the Persisted keys subset.
  7. Add an entry in the corresponding index of propertyStoreDefaultValues to provision default value(s).
  8. Add an entry in the corresponding index of propertyStoreRuntimeValues to provision for runtime value(s) buffer(s).


  • This is required if the field was defined as runtime initialized, i.e., the mode3Init bit to 1 in the corresponding entry in propertyStoreProperties.
  • The example implementation of PropertyStore supports properties with value of type String ('s') only. If your property must be of a different type, you must provision the default value as a String and perform the relevant de/serialization on the client side.

About icon

In addition to AboutData, the About feature supports the publication of an icon. The icon is published directly as a byte array or a reference URL. The provisioinbg is done by the application and passed to AJ_AboutIcon_Start() in AboutSample.c.

An example provisioning is provided in the ServerSample's ServerSample.c:

* Mime type of the About Device icon
const char* aboutIconMimetype = { "image/png" };
* Content of the About Device icon
const uint8_t aboutIconContent[] =
{ 0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, ... , 0x60, 0x82, 0x82 };
* Size of the About Device icon
const size_t aboutIconContentSize = sizeof(aboutIconContent);
* url of the icon About Device icon
const char* aboutIconUrl = { " https://www.allseemalliance.org/sites/all/themes/at_alljoyn/images/img-alljoyn-logo.png "

Start the About Server

For the About Server to be initiated properly, the application requires to pass it the relevant settings and callbacks. The application achieves this by calling AJ_About_Start() and optionally AJ_AboutIcon_Start().

An example is in About_Init() of AboutSample.c.

AJ_Status About_Init(AJ_Object* announceObjects, const char* aboutIconMimetype,
   const uint8_t* aboutIconContent, const size_t aboutIconContentSize,
   const char* aboutIconUrl) {
AJ_Status status = AJ_About_Start(AJ_ABOUT_SERVICE_PORT, announceObjects);
if (status == AJ_OK) {
status = AJ_AboutIcon_Start(aboutIconMimetype, aboutIconContent,
   aboutIconContentSize, aboutIconUrl);
return status;

Compile the code

The process to compile varies depending on the host and target platform. Each host and platform needs may require a specific directory and file layout, build toolchains, procedures, and supported AllJoyn service frameworks. Refer to the target platform documentation that contains instructions on how to organize and set up the build process to incorporate the necessary files to compile your Thin Library application.

For more details on how to combine this AllJoyn feature with other AllJoyn service framework software, see the Build an Application Using Thin Library section.