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

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.

  • 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

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.