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+Binding Reference
+=================
+
+Structure for declaring binding
+-------------------------------
+
+### struct afb_binding_v2
+
+The main structure, of type **afb_binding_v2**, for describing the binding
+must be exported under the name **afbBindingV2**.
+
+This structure is defined as below.
+
+```C
+/*
+ * Description of the bindings of type version 2
+ */
+struct afb_binding_v2
+{
+        const char *api;			/* api name for the binding */
+        const char *specification;		/* textual openAPIv3 specification of the binding */
+        const struct afb_verb_v2 *verbs;	/* array of descriptions of verbs terminated by a NULL name */
+        int (*preinit)();                       /* callback at load of the binding */
+        int (*init)();                          /* callback for starting the service */
+        void (*onevent)(const char *event, struct json_object *object); /* callback for handling events */
+        unsigned noconcurrency: 1;		/* avoids concurrent requests to verbs */
+};
+```
+
+### struct afb_verb_v2
+
+Each verb is described with a structure of type **afb_verb_v2**
+defined below:
+
+```C
+/*
+ * Description of one verb of the API provided by the binding
+ * This enumeration is valid for bindings of type version 2
+ */
+struct afb_verb_v2
+{
+        const char *verb;                       /* name of the verb */
+        void (*callback)(struct afb_req req);   /* callback function implementing the verb */
+        const struct afb_auth *auth;		/* required authorisation */
+        uint32_t session;                       /* authorisation and session requirements of the verb */
+};
+```
+
+The session flags is an or of the constant defined below:
+
+  - AFB_SESSION_NONE : no flag, synonym to 0
+  - AFB_SESSION_LOA_0 : Requires the LOA to be 0 or more, synonym to 0 or AFB_SESSION_NONE
+  - AFB_SESSION_LOA_1 : Requires the LOA to be 1 or more
+  - AFB_SESSION_LOA_2 : Requires the LOA to be 2 or more
+  - AFB_SESSION_LOA_3 : Requires the LOA to be 3 or more
+  - AFB_SESSION_CHECK : Requires the token to be set and valid
+  - AFB_SESSION_REFRESH : Implies a token refresh
+  - AFB_SESSION_CLOSE : Implies cloing the session
+
+The LOA is set binding by binding using the function **afb_req_session_set_LOA**.
+
+### struct afb_auth and enum afb_auth_type
+
+The structure **afb_auth** is used within verb description to
+set security requirements. The interpretation of the structure
+depends on the value of the field **type**.
+
+```C
+struct afb_auth
+{
+        const enum afb_auth_type type;
+        union {
+                const char *text;
+                const unsigned loa;
+                const struct afb_auth *first;
+        };
+        const struct afb_auth *next;
+};
+```
+The possible values for **type** is defined here:
+
+```C
+/*
+ * Enum for Session/Token/Assurance middleware.
+ */
+enum afb_auth_type
+{
+        afb_auth_No = 0,	/** never authorized, no data */
+        afb_auth_Token,		/** authorized if token valid, no data */
+        afb_auth_LOA,		/** authorized if LOA greater than data 'loa' */
+        afb_auth_Permission,	/** authorized if permission 'text' is granted */
+        afb_auth_Or,		/** authorized if 'first' or 'next' is authorized */
+        afb_auth_And,		/** authorized if 'first' and 'next' are authorized */
+        afb_auth_Not,		/** authorized if 'first' is not authorized */
+        afb_auth_Yes		/** always authorized, no data */
+};
+```
+
+Example:
+
+```C
+static const struct afb_auth _afb_auths_v2_monitor[] = {
+	{ .type = afb_auth_Permission, .text = "urn:AGL:permission:monitor:public:set" },
+	{ .type = afb_auth_Permission, .text = "urn:AGL:permission:monitor:public:get" },
+	{ .type = afb_auth_Or, .first = &_afb_auths_v2_monitor[1], .next = &_afb_auths_v2_monitor[0] }
+};
+```
+
+Functions of class afb_daemon...
+-------------------------
+
+The 3 following functions are linked to libsystemd.
+They allow use of **sd_event** features and access
+to **sd_bus** features.
+
+```C
+/*
+ * Retrieves the common systemd's event loop of AFB
+ */
+struct sd_event *afb_daemon_get_event_loop();
+
+/*
+ * Retrieves the common systemd's user/session d-bus of AFB
+ */
+struct sd_bus *afb_daemon_get_user_bus();
+
+/*
+ * Retrieves the common systemd's system d-bus of AFB
+ */
+struct sd_bus *afb_daemon_get_system_bus();
+```
+
+The 2 following functions are linked to event management.
+Broadcasting an event send it to any possible listener.
+
+```C
+/*
+ * Broadcasts widely the event of 'name' with the data 'object'.
+ * 'object' can be NULL.
+ *
+ * For convenience, the function calls 'json_object_put' for 'object'.
+ * Thus, in the case where 'object' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ *
+ * Returns the count of clients that received the event.
+ */
+int afb_daemon_broadcast_event(const char *name, struct json_object *object);
+
+/*
+ * Creates an event of 'name' and returns it.
+ *
+ * See afb_event_is_valid to check if there is an error.
+ */
+struct afb_event afb_daemon_make_event(const char *name);
+```
+
+The following function is used by logging macros and should normally
+not be used. Instead, you should use the macros 
+**AFB\_ERROR**, **AFB\_WARNING**, **AFB\_NOTICE**,
+**AFB\_INFO**, **AFB\_DEBUG**
+
+```C
+/*
+ * Send a message described by 'fmt' and following parameters
+ * to the journal for the verbosity 'level'.
+ *
+ * 'file', 'line' and 'func' are indicators of position of the code in source files
+ * (see macros __FILE__, __LINE__ and __func__).
+ *
+ * 'level' is defined by syslog standard:
+ *      EMERGENCY         0        System is unusable
+ *      ALERT             1        Action must be taken immediately
+ *      CRITICAL          2        Critical conditions
+ *      ERROR             3        Error conditions
+ *      WARNING           4        Warning conditions
+ *      NOTICE            5        Normal but significant condition
+ *      INFO              6        Informational
+ *      DEBUG             7        Debug-level messages
+ */
+void afb_daemon_verbose(int level, const char *file, int line, const char * func, const char *fmt, ...);
+```
+
+The 2 following functions MUST be used to access data of the bindings.
+
+```C
+/*
+ * Get the root directory file descriptor. This file descriptor can
+ * be used with functions 'openat', 'fstatat', ...
+ */
+int afb_daemon_rootdir_get_fd();
+
+/*
+ * Opens 'filename' within the root directory with 'flags' (see function openat)
+ * using the 'locale' definition (example: "jp,en-US") that can be NULL.
+ * Returns the file descriptor or -1 in case of error.
+ */
+int afb_daemon_rootdir_open_locale(const char *filename, int flags, const char *locale);
+```
+
+The following function is used to queue jobs.
+
+```C
+/*
+ * Queue the job defined by 'callback' and 'argument' for being executed asynchronously
+ * in this thread (later) or in an other thread.
+ * If 'group' is not NUL, the jobs queued with a same value (as the pointer value 'group')
+ * are executed in sequence in the order of there submission.
+ * If 'timeout' is not 0, it represent the maximum execution time for the job in seconds.
+ * At first, the job is called with 0 as signum and the given argument.
+ * The job is executed with the monitoring of its time and some signals like SIGSEGV and
+ * SIGFPE. When a such signal is catched, the job is terminated and reexecuted but with
+ * signum being the signal number (SIGALRM when timeout expired).
+ *
+ * Returns 0 in case of success or -1 in case of error.
+ */
+int afb_daemon_queue_job(void (*callback)(int signum, void *arg), void *argument, void *group, int timeout)
+```
+
+The following function must be used when a binding depends on other
+bindings at its initialisation.
+
+```C
+/*
+ * Tells that it requires the API of "name" to exist
+ * and if 'initialized' is not null to be initialized.
+ * Returns 0 in case of success or -1 in case of error.
+ */
+int afb_daemon_require_api(const char *name, int initialized)
+```
+
+Functions of class afb_service...
+-------------------------
+
+The following functions allow services to call verbs of other
+bindings for themselves.
+
+```C
+/**
+ * Calls the 'verb' of the 'api' with the arguments 'args' and 'verb' in the name of the binding.
+ * The result of the call is delivered to the 'callback' function with the 'callback_closure'.
+ *
+ * For convenience, the function calls 'json_object_put' for 'args'.
+ * Thus, in the case where 'args' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ *
+ * The 'callback' receives 3 arguments:
+ *  1. 'closure' the user defined closure pointer 'callback_closure',
+ *  2. 'iserror' a boolean status being true (not null) when an error occured,
+ *  2. 'result' the resulting data as a JSON object.
+ *
+ * @param api      The api name of the method to call
+ * @param verb     The verb name of the method to call
+ * @param args     The arguments to pass to the method
+ * @param callback The to call on completion
+ * @param callback_closure The closure to pass to the callback
+ *
+ * @see also 'afb_req_subcall'
+ */
+void afb_service_call(
+	const char *api,
+	const char *verb,
+	struct json_object *args,
+	void (*callback)(void*closure, int iserror, struct json_object *result),
+	void *callback_closure);
+
+/**
+ * Calls the 'verb' of the 'api' with the arguments 'args' and 'verb' in the name of the binding.
+ * 'result' will receive the response.
+ *
+ * For convenience, the function calls 'json_object_put' for 'args'.
+ * Thus, in the case where 'args' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ *
+ * @param api      The api name of the method to call
+ * @param verb     The verb name of the method to call
+ * @param args     The arguments to pass to the method
+ * @param result   Where to store the result - should call json_object_put on it -
+ *
+ * @returns 1 in case of success or 0 in case of error.
+ *
+ * @see also 'afb_req_subcall'
+ */
+int afb_service_call_sync(
+	const char *api,
+	const char *verb,
+	struct json_object *args,
+	struct json_object **result);
+```
+
+Functions of class afb_event...
+-------------------------
+
+This function checks whether the event is valid. It must be used
+when creating events.
+
+```C
+/*
+ * Checks wether the 'event' is valid or not.
+ *
+ * Returns 0 if not valid or 1 if valid.
+ */
+int afb_event_is_valid(struct afb_event event);
+```
+
+The two following functions are used to broadcast or push
+event with its data.
+
+```C
+/*
+ * Broadcasts widely the 'event' with the data 'object'.
+ * 'object' can be NULL.
+ *
+ * For convenience, the function calls 'json_object_put' for 'object'.
+ * Thus, in the case where 'object' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ *
+ * Returns the count of clients that received the event.
+ */
+int afb_event_broadcast(struct afb_event event, struct json_object *object);
+
+/*
+ * Pushes the 'event' with the data 'object' to its observers.
+ * 'object' can be NULL.
+ *
+ * For convenience, the function calls 'json_object_put' for 'object'.
+ * Thus, in the case where 'object' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ *
+ * Returns the count of clients that received the event.
+ */
+int afb_event_push(struct afb_event event, struct json_object *object);
+```
+
+The following function destiys the event.
+
+```C
+/*
+ * Drops the data associated to the 'event'
+ * After calling this function, the event
+ * MUST NOT BE USED ANYMORE.
+ */
+void afb_event_drop(struct afb_event event);
+```
+
+This function allows to retrieve the exact name of the event.
+
+```C
+/*
+ * Gets the name associated to the 'event'.
+ */
+const char *afb_event_name(struct afb_event event);
+```
+
+Functions of class afb_req...
+-------------------------
+
+This function checks the validity of the **req**.
+
+```C
+/*
+ * Checks wether the request 'req' is valid or not.
+ *
+ * Returns 0 if not valid or 1 if valid.
+ */
+int afb_req_is_valid(struct afb_req req);
+```
+
+The following functions retrieves parameters of the request.
+
+```C
+/*
+ * Gets from the request 'req' the argument of 'name'.
+ * Returns a PLAIN structure of type 'struct afb_arg'.
+ * When the argument of 'name' is not found, all fields of result are set to NULL.
+ * When the argument of 'name' is found, the fields are filled,
+ * in particular, the field 'result.name' is set to 'name'.
+ *
+ * There is a special name value: the empty string.
+ * The argument of name "" is defined only if the request was made using
+ * an HTTP POST of Content-Type "application/json". In that case, the
+ * argument of name "" receives the value of the body of the HTTP request.
+ */
+struct afb_arg afb_req_get(struct afb_req req, const char *name);
+
+/*
+ * Gets from the request 'req' the string value of the argument of 'name'.
+ * Returns NULL if when there is no argument of 'name'.
+ * Returns the value of the argument of 'name' otherwise.
+ *
+ * Shortcut for: afb_req_get(req, name).value
+ */
+const char *afb_req_value(struct afb_req req, const char *name);
+
+/*
+ * Gets from the request 'req' the path for file attached to the argument of 'name'.
+ * Returns NULL if when there is no argument of 'name' or when there is no file.
+ * Returns the path of the argument of 'name' otherwise.
+ *
+ * Shortcut for: afb_req_get(req, name).path
+ */
+const char *afb_req_path(struct afb_req req, const char *name);
+
+/*
+ * Gets from the request 'req' the json object hashing the arguments.
+ * The returned object must not be released using 'json_object_put'.
+ */
+struct json_object *afb_req_json(struct afb_req req);
+```
+
+The following functions emit the reply to the request.
+
+```C
+/*
+ * Sends a reply of kind success to the request 'req'.
+ * The status of the reply is automatically set to "success".
+ * Its send the object 'obj' (can be NULL) with an
+ * informationnal comment 'info (can also be NULL).
+ *
+ * For convenience, the function calls 'json_object_put' for 'obj'.
+ * Thus, in the case where 'obj' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_success(struct afb_req req, struct json_object *obj, const char *info);
+
+/*
+ * Same as 'afb_req_success' but the 'info' is a formatting
+ * string followed by arguments.
+ *
+ * For convenience, the function calls 'json_object_put' for 'obj'.
+ * Thus, in the case where 'obj' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_success_f(struct afb_req req, struct json_object *obj, const char *info, ...);
+
+/*
+ * Same as 'afb_req_success_f' but the arguments to the format 'info'
+ * are given as a variable argument list instance.
+ *
+ * For convenience, the function calls 'json_object_put' for 'obj'.
+ * Thus, in the case where 'obj' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_success_v(struct afb_req req, struct json_object *obj, const char *info, va_list args);
+
+/*
+ * Sends a reply of kind failure to the request 'req'.
+ * The status of the reply is set to 'status' and an
+ * informationnal comment 'info' (can also be NULL) can be added.
+ *
+ * Note that calling afb_req_fail("success", info) is equivalent
+ * to call afb_req_success(NULL, info). Thus even if possible it
+ * is strongly recommanded to NEVER use "success" for status.
+ */
+void afb_req_fail(struct afb_req req, const char *status, const char *info);
+
+/*
+ * Same as 'afb_req_fail' but the 'info' is a formatting
+ * string followed by arguments.
+ */
+void afb_req_fail_f(struct afb_req req, const char *status, const char *info, ...);
+
+/*
+ * Same as 'afb_req_fail_f' but the arguments to the format 'info'
+ * are given as a variable argument list instance.
+ */
+void afb_req_fail_v(struct afb_req req, const char *status, const char *info, va_list args);
+```
+
+The following functions handle the session data.
+
+```C
+/*
+ * Gets the pointer stored by the binding for the session of 'req'.
+ * When the binding has not yet recorded a pointer, NULL is returned.
+ */
+void *afb_req_context_get(struct afb_req req);
+
+/*
+ * Stores for the binding the pointer 'context' to the session of 'req'.
+ * The function 'free_context' will be called when the session is closed
+ * or if binding stores an other pointer.
+ */
+void afb_req_context_set(struct afb_req req, void *context, void (*free_context)(void*));
+
+/*
+ * Gets the pointer stored by the binding for the session of 'req'.
+ * If the stored pointer is NULL, indicating that no pointer was
+ * already stored, afb_req_context creates a new context by calling
+ * the function 'create_context' and stores it with the freeing function
+ * 'free_context'.
+ */
+void *afb_req_context(struct afb_req req, void *(*create_context)(), void (*free_context)(void*));
+
+/*
+ * Frees the pointer stored by the binding for the session of 'req'
+ * and sets it to NULL.
+ *
+ * Shortcut for: afb_req_context_set(req, NULL, NULL)
+ */
+void afb_req_context_clear(struct afb_req req);
+
+/*
+ * Closes the session associated with 'req'
+ * and delete all associated contexts.
+ */
+void afb_req_session_close(struct afb_req req);
+
+/*
+ * Sets the level of assurance of the session of 'req'
+ * to 'level'. The effect of this function is subject of
+ * security policies.
+ * Returns 1 on success or 0 if failed.
+ */
+int afb_req_session_set_LOA(struct afb_req req, unsigned level);
+```
+
+
+The 4 following functions must be used for asynchronous handling requests.
+
+```C
+/*
+ * Adds one to the count of references of 'req'.
+ * This function MUST be called by asynchronous implementations
+ * of verbs if no reply was sent before returning.
+ */
+void afb_req_addref(struct afb_req req);
+
+/*
+ * Substracts one to the count of references of 'req'.
+ * This function MUST be called by asynchronous implementations
+ * of verbs after sending the asynchronous reply.
+ */
+void afb_req_unref(struct afb_req req);
+
+/*
+ * Stores 'req' on heap for asynchrnous use.
+ * Returns a handler to the stored 'req' or NULL on memory depletion.
+ * The count of reference to 'req' is incremented on success
+ * (see afb_req_addref).
+ */
+struct afb_stored_req *afb_req_store(struct afb_req req);
+
+/*
+ * Retrieves the afb_req stored at 'sreq'.
+ * Returns the stored request.
+ * The count of reference is UNCHANGED, thus, the
+ * function 'afb_req_unref' should be called on the result
+ * after that the asynchronous reply if sent.
+ */
+struct afb_req afb_req_unstore(struct afb_stored_req *sreq);
+```
+
+The two following functions are used to associate client with events
+(subscription).
+
+```C
+/*
+ * Establishes for the client link identified by 'req' a subscription
+ * to the 'event'.
+ * Returns 0 in case of successful subscription or -1 in case of error.
+ */
+int afb_req_subscribe(struct afb_req req, struct afb_event event);
+
+/*
+ * Revokes the subscription established to the 'event' for the client
+ * link identified by 'req'.
+ * Returns 0 in case of successful subscription or -1 in case of error.
+ */
+int afb_req_unsubscribe(struct afb_req req, struct afb_event event);
+```
+
+The following functions must be used to make request in the name of the
+client (with its permissions).
+
+```C
+/*
+ * Makes a call to the method of name 'api' / 'verb' with the object 'args'.
+ * This call is made in the context of the request 'req'.
+ * On completion, the function 'callback' is invoked with the
+ * 'closure' given at call and two other parameters: 'iserror' and 'result'.
+ * 'iserror' is a boolean that indicates if the reply is an error reply.
+ * 'result' is the json object of the reply, you must not call json_object_put
+ * on the result.
+ *
+ * For convenience, the function calls 'json_object_put' for 'args'.
+ * Thus, in the case where 'args' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_subcall(
+                struct afb_req req,
+                const char *api,
+                const char *verb,
+                struct json_object *args,
+                void (*callback)(void *closure, int iserror, struct json_object *result),
+                void *closure);
+
+/*
+ * Makes a call to the method of name 'api' / 'verb' with the object 'args'.
+ * This call is made in the context of the request 'req'.
+ * This call is synchronous, it waits untill completion of the request.
+ * It returns 0 on an error answer and returns 1 when no error was detected.
+ * The object pointed by 'result' is filled and must be released by the caller
+ * after its use by calling 'json_object_put'.
+ *
+ * For convenience, the function calls 'json_object_put' for 'args'.
+ * Thus, in the case where 'args' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+int afb_req_subcall_sync(
+                struct afb_req req,
+                const char *api,
+                const char *verb,
+                struct json_object *args,
+                struct json_object **result);
+```
+
+The following function is used by logging macros and should normally
+not be used. Instead, you should use the macros 
+**AFB_REQ_ERROR**, **AFB_REQ_WARNING**, **AFB_REQ_NOTICE**,
+**AFB_REQ_INFO**, **AFB_REQ_DEBUG**
+
+```C
+/*
+ * Send associated to 'req' a message described by 'fmt' and following parameters
+ * to the journal for the verbosity 'level'.
+ *
+ * 'file', 'line' and 'func' are indicators of position of the code in source files
+ * (see macros __FILE__, __LINE__ and __func__).
+ *
+ * 'level' is defined by syslog standard:
+ *      EMERGENCY         0        System is unusable
+ *      ALERT             1        Action must be taken immediately
+ *      CRITICAL          2        Critical conditions
+ *      ERROR             3        Error conditions
+ *      WARNING           4        Warning conditions
+ *      NOTICE            5        Normal but significant condition
+ *      INFO              6        Informational
+ *      DEBUG             7        Debug-level messages
+ */
+void afb_req_verbose(struct afb_req req, int level, const char *file, int line, const char * func, const char *fmt, ...);
+```
+
+Logging macros
+--------------
+
+The following macros must be used for logging:
+
+```C
+AFB_ERROR(fmt,...)
+AFB_WARNING(fmt,...)
+AFB_NOTICE(fmt,...)
+AFB_INFO(fmt,...)
+AFB_DEBUG(fmt,...)
+```
+
+The following macros can be used for logging in the context
+of a request **req** of type **afb_req**:
+
+```C
+AFB_REQ_ERROR(req,fmt,...)
+AFB_REQ_WARNING(req,fmt,...)
+AFB_REQ_NOTICE(req,fmt,...)
+AFB_REQ_INFO(req,fmt,...)
+AFB_REQ_DEBUG(req,fmt,...)
+```
+
+By default, the logging macros add file, line and function
+indication.
+
+Some definitions can be used to 
+
+