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 authorization */
        uint32_t session;                       /* authorization 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 re-executed 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 initialization.

```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. 'status' a status being 0 on success or negative 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 status, 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 0 in case of success or a negative value 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 recommended 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 asynchronous 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'.
 * 'status' is 0 on success or negative when on 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 status, 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 success or a negative value on error answer.
 * 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.