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| -rw-r--r-- | doc/afb-plugin-writing.md | 109 |
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diff --git a/doc/afb-plugin-writing.md b/doc/afb-plugin-writing.md index 486b141d..32cd202d 100644 --- a/doc/afb-plugin-writing.md +++ b/doc/afb-plugin-writing.md @@ -9,95 +9,84 @@ TABLE-OF-CONTENT-HERE Summary ------- -The binder afb-daemon serves files through -the HTTP protocol and offers access to API's through +The binder afb-daemon serves files through HTTP protocol +and offers to developers the capability to expose application APIs through HTTP or WebSocket protocol. -The plugins are used to add API's to afb-daemon. +Binder plugins are used to add API to afb-daemon. This part describes how to write a plugin for afb-daemon. Excepting this summary, this part is intended to be read -by developpers. +by developers. -Before going into details, through a tiny example, -a short overview plugins basis is needed. +Before moving further through an example, here after +a short overview of binder plugins fundamentals. ### Nature of a plugin -A plugin is a separate piece of code made of a shared library. -The plugin is loaded and activated by afb-daemon when afb-daemon -starts. +A plugin is an independent piece of software, self contain and expose as a dynamically loadable library. +A plugin is loaded by afb-daemon that exposes contained API dynamically at runtime. -Technically, a plugin is not linked to any library of afb-daemon. +Technically, a binder plugins does not reference and is not linked with any library from afb-daemon. -### Kinds of plugins +### Class of plugins -There is two kinds of plugins: application plugins and service -plugins. +Application binder supports two kinds of plugins: application plugins and service +plugins. Technically both class of plugin are equivalent and coding API is shared. Only sharing mode and security context diverge. -#### Application plugins +#### Application-plugins -Application plugins are intended to be instanciated for each -application: when an application using that plugin is started, -its binder starts a new instance of the plugin. +Application-plugins implements the glue in between application's UI and services. Every AGL application +has a corresponding binder that typically activates one or many plugins to interface the application logic with lower platform services. +When an application is started by AGL application framework, a dedicate binder is started that loads/activates application plugin(s). +The API expose by application-plugin are executed within corresponding application security context. -It means that the application plugins mainly have only one -context to manage for one client. +Application plugins generally handle a unique context for a unique client. As the application framework start +a dedicated instance of afb_daemon for each AGL application, if a given plugin is used within multiple application each of those +application get a new and private instance of this "shared" plugin. -#### Service plugins +#### Service-plugins -Service plugins are intended to be instanciated only one time -only and connected to many clients. +Service-plugins enable API activation within corresponding service security context and not within calling application context. +Service-plugins are intended to run as a unique instance that is shared in between multiple clients. -So either it does not manage context at all or otherwise, -if it manages context, it should be able to manage one context -per client. +Service-plugins can either be stateless or manage client context. When managing context each client get a private context. -In details, it may be useful to have service plugins at a user -level. +Sharing may either be global to the platform (ie: GPS service) or dedicated to a given user (ie: preference management) -### Live cycle of a plugin within afb-daemon +### Live cycle of plugins within afb-daemon -The plugins are loaded and activated when afb-daemon starts. +Application and service plugins are loaded and activated each time a new afb-daemon is started. -At start, the plugin initialise itself. -If it fails to initialise then afb-daemon stops. +At launch time, every loaded plugin initialise itself. +If a single plugin initialisation fail corresponding instance of afb-daemon self aborts. -Conversely, if it success to initialize, it must declare -a name, that must be unique, and a list of API's verbs. +Conversely, when plugin initialisation succeeds, it should register +its unique name and the list of API verbs it exposes. -When initialized, the functions implementing the API's verbs -of the plugin are activated on call. +When initialised, on request from clients plugin's function corresponding to expose API verbs +are activated by the afb-daemon instance attached to the application or service. -At the end, nothing special is done by afb-daemon. -Consequently, developpers of plugins should use 'atexit' -or 'on_exit' during initialisation if they need to -perform specific actions when stopping. +At exit time, no special action is enforced by afb-daemon. When a specific actions is required at afb-daemon stop, +developers should use 'atexit/on_exit' during plugin initialisation sequence to register a custom exit function. -### Content of a plugin +### Plugin Contend -For afb-daemon, a plugin contains 2 different -things: names and functions. +Afb-daemon's plugin register two classes of objects: names and functions. -There is two kind of names: - - the name of the plugin, - - the names of the verbs. +Plugins declare categories of names: + - A unique plugin name, + - Multiple API verb's names. -There is two kind of functions: - - the initialisation function - - functions implementing verbs +Plugins declare two categories of functions: + - initialisation function + - API functions implementing verbs -Afb-daemon translates the name of the method that is -invoked to a pair of API and verb names. For example, -the method named **foo/bar** translated to the API -name **foo** and the verb name **bar**. -To serve it, afb-daemon search the plugin that record -the name **foo** and if it also recorded the verb **bar**, -it calls the implementation function declared for this verb. +Afb-daemon parses URI requests to extract plugin name and API verb. +As an example, URI **foo/bar** translates to API verb named **bar** within plugin named **foo**. +To serve such a request, afb-daemon looks for an active plugin named **foo** and then within this plugin for an API verb named **bar**. +When find afb-daemon calls corresponding function with attached parameter if any. -Afb-daemon make no distinction between lower case -and upper case when searching for a method. -Thus, The names **TicTacToe/Board** and **tictactoe/borad** -are equals. +Afb-daemon ignores letter case when parsing URI. Thus **TicTacToe/Board** and **tictactoe/borad** are equivalent. #### The name of the plugin @@ -271,7 +260,7 @@ and upper case when searching for an API by its name. The names of the verbs are not checked. However, the validity rules for verb's names are the -same as for API's names except that the dot (.) character +same as for API names except that the dot (.) character is forbidden. Afb-daemon make no distinction between lower case |