Binder Overview =============== The ***binder*** provides the way to connect applications to the services that it needs. It provides a fast way to securely offer APIs to applications written in any language and running almost anywhere. The ***binder*** is developed for AGL. The ***binder*** is the usual name. The binary is named **afb-daemon**. The name **afb-daemon** stands for ***Application Framework Binder Daemon***. The word *daemon*, here, denote the fact that the ***binder*** makes witchcraft to connect applications to their expected services (note that usually the term of daemon denotes background process but not here). Each ***binder*** **afb-daemon** is in charge to bind one instance of an application or service to the rest of the system, applications and services. Within AGL, the connection between services and/or applications is tuned by the AGL framework and the AGL system. The basis of the binder ======================= The following figure shows main concepts linked to the ***binder***. ![Figure: binder basis](pictures/basis.svg) The shown elements are: * The SECURITY CONTEXT The primary intend of any ***binder*** is to provide a secured environment for any application. On AGL, the **security context** is ensured by [Smack][Smack] a security context, the security context of the application or service. * The BINDER This is the central element. It makes possible to run HTML5 applications and provides the unified access to APIs provided by the ***bindings***. Running a pure HTML5 application doesn't require any ***binding***. in that case , the ***binder*** acts as a simple HTTP server for the web runtime. * The BINDINGs A ***binding*** adds one **API** to the ***binder***. An **API** is a set of **verbs** that can be called using either REST over HTTP or a kind of JSON RPC. ***bindings*** are either: - dynamically loaded libraries in the ***binder*** process - remote service running on the same host - remote service running on other hosts When acting as an HTTP server, the binder treats the language settings of the HTTP requests to provide internationalized content as specified by [widget specifications](https://www.w3.org/TR/widgets/#internationalization-and-localization). * The APPLICATION An ***application*** connects to the binder to get access to the **API** that it provides or to get its HTTP services to access resources. Interconnection of binders ========================== The AGL framework interprets the **widget/application** manifests to setup the ***bindings*** configuration of the ***binders***. The figure below shows that ***binders*** are interconnected. ![Figure: binder interconnection](pictures/interconnection.svg) The figure shows 4 several **application/service**: **A**, **B**, **C** and **D**. The application **A** might use an **API** that is shown as a local ***binding*** but that in reality runs within the context of **D**. The framework AGL takes care of making the plumbing working.