Presence Module

The modules handles PUBLISH and SUBSCRIBE messages and generates NOTIFY messages in a general, event independent way. It allows registering events to it from other OpenSIPS modules. Events that can currently be added to it are: presence, presence.winfo, dialog;sla from presence_xml module and message-summary from presence_mwi module.

The modules uses database storage. It has later been improved with memory caching operations to improve performance. The Subscribe dialog information are stored in memory and are periodically updated in database, while for Publish only the presence or absence of stored info for a certain resource is maintained in memory to avoid unnecessary, costly db operations. It is possible to configure a fallback to database mode(by setting module parameter "fallback2db"). In this mode, in case a searched record is not found in cache, the search is continued in database. This is useful for an architecture in which processing and memory load might be divided on more machines using the same database.

The module can also work only with the functionality of a library, with no message processing and generation, but used only for the exported functions. This mode of operation is enabled if the db_url parameter is not set to any value.

The server follows the specifications in: RFC3265, RFC3856, RFC3857, RFC3858.

The module requires 3 table in OpenSIPS database: presentity, active_watchers and watchers tables. The SQL syntax to create them can be found in presence-create.sql script in the database directories in the opensips/scripts folder. You can also find the complete database documentation on the project webpage, http://www.opensips.org/html/docs/db/db-schema-1.4.x.html.

This function binds the presence modules and fills the structure with one exported function -> add_event, which when called adds a new event to be handled by presence.

...
typedef struct presence_api {
	add_event_t add_event;
	contains_event_t contains_event;
	search_event_t search_event;
	get_event_list_t get_event_list;
	
	update_watchers_t update_watchers_status;
	
	/* subs hash table handling functions */
	new_shtable_t new_shtable;
	destroy_shtable_t destroy_shtable;
	insert_shtable_t insert_shtable;
	search_shtable_t search_shtable;
	delete_shtable_t delete_shtable;
	update_shtable_t update_shtable;
	/* function to duplicate a subs structure*/
	mem_copy_subs_t  mem_copy_subs;
	/* function used for update in database*/
	update_db_subs_t update_db_subs;
	/* function to extract dialog information from a
	SUBSCRIBE message */
	extract_sdialog_info_t extract_sdialog_info;
	/* function to request sphere defition for a presentity */
	pres_get_sphere_t get_sphere;

}presence_api_t;
...

Field type:

...
typedef int (*add_event_t)(pres_ev_t* event);
...

This function receives as a parameter a structure with event specific information and adds it to presence event list.

The structure received as a parameter:

...
typedef struct pres_ev
{
	str name;
	event_t* evp;
	str content_type;
	int default_expires;
	int type;
	int etag_not_new;
	/*
	 *  0 - the standard mechanism (allocating new etag
			for each Publish)
	 *  1 - allocating an etag only
			for an initial Publish 
	*/
	int req_auth;
	get_rules_doc_t* get_rules_doc;
	apply_auth_t*  apply_auth_nbody;
	is_allowed_t*  get_auth_status;
	
	/* an agg_body_t function should be registered
	 * if the event permits having multiple published
	 * states and requires an aggregation of the information
	 * otherwise, this field should be NULL and the last
	 * published state is taken when constructing Notify msg
	 */
	agg_nbody_t* agg_nbody;
	publ_handling_t  * evs_publ_handl;
	subs_handling_t  * evs_subs_handl;
	free_body_t* free_body;
	struct pres_ev* wipeer;			
	struct pres_ev* next;
	
}pres_ev_t;
...

Filed type:

...
typedef int (get_rules_doc_t)(str* user, str* domain, str** rules_doc);
...
			

This function returns the authorization rules document that will be used in obtaining the status of the subscription and processing the notified body. A reference to the document should be put in the auth_rules_doc of the subs_t structure given as a parameter to the functions described bellow.

This filed is a function to be called for a subscription request to return the state for that subscription according to authorization rules. In the auth_rules_doc field of the subs_t structure received as a parameter should contain the rules document of the presentity in case, if it exists.

It is called only if the req_auth field is not 0.

Filed type:

...
typedef int (is_allowed_t)(struct subscription* subs);
...
			

This parameter should be a function to be called for an event that requires authorization, when constructing final body. The authorization document is taken from the auth_rules_doc field of the subs_t structure given as a parameter. It is called only if the req_auth field is not 0.

Filed type:

...
typedef int (apply_auth_t)(str* , struct subscription*, str** );
...
			

If present, this field marks that the events requires aggregation of states. This function receives a body array and should return the final body. If not present, it is considered that the event does not require aggregation and the most recent published information is used when constructing Notifies.

Filed type:

...
typedef str* (agg_nbody_t)(str* pres_user, str* pres_domain, 
str** body_array, int n, int off_index);
..
			

This field must be field in if subsequent processing is performed on the info from database before being inserted in Notify message body(if agg_nbody or apply_auth_nbody fields are filled in). It should match the allocation function used when processing the body.

Filed type:

...
typedef void(free_body_t)(char* body);
..
			

This function is called when handling Publish requests. Most contain body correctness check.

...
typedef int (publ_handling_t)(struct sip_msg*);
..
			

It is not compulsory. Should contain event specific handling for Subscription requests.

Filed type:

...
typedef int (subs_handling_t)(struct sip_msg*);
..

Field type:

..
typedef pres_ev_t* (*contains_event_t)(str* name,
event_t* parsed_event);
...

The function parses the event name received as a parameter and searches the result in the list. It returns the found event or NULL, if not found. If the second argument is an allocated event_t* structure it fills it with the result of the parsing.

Field type:

...
typedef int (*get_event_list_t) (str** ev_list);
...

This function returns a string representation of the events registered in presence module.( used for Allowed-Events header).

Field type:

...
typedef int (*update_watchers_t)(str pres_uri, pres_ev_t* ev,
str* rules_doc);
...

This function is an external command that can be used to announce a change in authorization rules for a presentity. It updates the stored status and sends a Notify to the watchers whose status has changes. (used by presence_xml module when notified through an MI command of a change in an xcap document).

Field type:

...
typedef char* (*pres_get_sphere_t)(str* pres_uri);
...

This function searches for a sphere definition in the published information if this has type RPID. If not found returns NULL. (the return value is allocated in private memory and should be freed)