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<h2><a href="https://wiki.asterisk.org/wiki/display/AST/Event+Subscription+and+Publication+Design">Event Subscription and Publication Design</a></h2>
<h4>Page <b>added</b> by <a href="https://wiki.asterisk.org/wiki/display/~mmichelson">Mark Michelson</a>
</h4>
<br/>
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<p>Asterisk's SIP implementation has a need for supporting RFC 3265's event subscription system since the original <tt>chan_sip</tt> had support for it.</p>
<h1><a name="EventSubscriptionandPublicationDesign-Requirements"></a>Requirements</h1>
<p>Asterisk needs to fully support RFC 3265. Support should be approached in a modular fashion. It should be easy to write a module that handles a specific Event and Accept type. So for instance, a module should exist for the "presence" event and the "application/pidf" type. A separate module should exist for the "presence" event and the "application/xpidf" type.</p>
<h1><a name="EventSubscriptionandPublicationDesign-Pubsubcore"></a>Pubsub core</h1>
<p>The core of the pubsub feature comes in Asterisk's ability to register different event types as being handled. A module can register itself as a subscription handler for a specific event type. By doing so, Asterisk will know to call into that module when SUBSCRIBE or NOTIFY requests or responses are received for that event type.</p>
<p>At the base of it all is PJSIP's evsub framework. It takes care of a large portion of our job for us, like maintaining timers, maintaining the state of the subscription, and maintaining the state of the underlying dialog and transactions. Asterisk's pubsub core will sit on top of this and help further take care of automatic duties. The pubsub core will also help to associate PJSIP's event subscriptions with our own representation. Asterisk's pubsub core will also provide some abstractions for common dealings in PJSIP.</p>
<p>PJSIP's evsub API is quite extensive, and there is no good reason to try to completely hide it from subscription handlers. Thus Asterisk will not attempt to wrap every single thing that the evsub API provides. However, certain operations will be wrapped if there are additional duties that will be performed by the core or if it makes things easier to handle.</p>
<h1><a name="EventSubscriptionandPublicationDesign-API"></a>API</h1>
<div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent">
<pre class="theme: Confluence; brush: c; gutter: false">/*!
* \brief Opaque structure representing an RFC 3265 SIP subscription
*/
struct ast_sip_subscription;
/*!
* \brief Data for responses to SUBSCRIBEs and NOTIFIEs
*
* Some of PJSIP's evsub callbacks expect us to provide them
* with data so that they can craft a response rather than have
* us create our own response.
*
* The entire structure is itself optional, since the framework
* will automatically respond with a 200 OK response if we do
* not provide it with any data.
*/
struct ast_sip_subscription_response_data {
/*! Status code of the response */
int status_code;
/*! Optional status text */
const char *status_text;
/*! Optional additional headers to add to the response */
struct ast_variable *headers;
/*! Optional body to add to the response */
struct ast_sip_body *body;
};
struct ast_sip_subscription_handler {
/*! The name of the event this handler deals with */
const char *event_name;
/*! The types of body this handler accepts */
const char *accept[];
/*!
* \brief Called when a subscription is to be destroyed
*
* This is a subscriber and notifier callback.
*
* The handler is not expected to send any sort of requests or responses
* during this callback. This callback is useful for performing any
* necessary cleanup
*/
void (*subscription_shutdown)(struct ast_sip_subscription *subscription);
/*!
* \brief Called when a SUBSCRIBE arrives in order to create a new subscription
*
* This is a notifier callback.
*
* If the notifier wishes to accept the subscription, then it can create
* a new ast_sip_subscription to do so.
*
* If the notifier chooses to create a new subscription, then it must accept
* the incoming subscription using pjsip_evsub_accept() and it must also
* send an initial NOTIFY with the current subscription state.
*
* \param endpoint The endpoint from which we received the SUBSCRIBE
* \param rdata The SUBSCRIBE request
* \retval NULL The SUBSCRIBE has not been accepted
* \retval non-NULL The newly-created subscription
*/
struct ast_sip_subscription *(*new_subscribe)(struct ast_sip_endpoint *endpoint,
pjsip_rx_data *rdata);
/*!
* \brief Called when an endpoint renews a subscription.
*
* This is a notifier callback.
*
* Because of the way that the PJSIP evsub framework works, it will automatically
* send a response to the SUBSCRIBE.
*
* \param sub The subscription that is being renewed
* \param rdata The SUBSCRIBE request in question
* \retval NULL Allow the default 200 OK response to be sent
* \retval non-NULL Send a response with the specified data present
*/
struct ast_sip_subscription_response_data *(*resubscribe)(struct ast_sip_subscription *sub,
pjsip_rx_data *rdata);
/*!
* \brief Called when a subscription times out.
*
* This is a notifier callback
*
* This indicates that the subscription has timed out. The subscription handler is
* expected to send a NOTIFY that terminates the subscription.
*
* \param sub The subscription that has timed out
*/
void (*subscription_timeout)(struct ast_sip_subscription *sub);
/*!
* \brief Called when a subscription is terminated via a SUBSCRIBE request
*
* This is a notifier callback.
*
* The PJSIP subscription framework will automatically send the response to the
* SUBSCRIBE. The subscription handler is expected to send a final NOTIFY to
* terminate the subscription.
*
* \param sub The subscription being terminated
* \param rdata The SUBSCRIBE request that terminated the subscription
*/
void (*subscription_terminated)(struct ast_sip_subscription *sub, pjsip_rx_data *rdata);
/*!
* \brief Called when a subscription handler's outbound NOTIFY receives a response
*
* This is a notifier callback.
*
* \param sub The subscription
* \param rdata The NOTIFY response
*/
void (*notify_response)(struct ast_sip_subscription *sub, pjsip_rx_data *rdata);
/*!
* \brief Called when a subscription handler receives an inbound NOTIFY
*
* This is a subscriber callback.
*
* Because of the way that the PJSIP evsub framework works, it will automatically
* send a response to the NOTIFY. By default this will be a 200 OK response, but
* this callback can change details of the response by returning response data
* to use.
*
* \param sub The subscription
* \param rdata The NOTIFY request
* \retval NULL Have the framework send the default 200 OK response
* \retval non-NULL Send a response with the specified data
*/
struct ast_sip_subscription_response_data *(*notify_request)(struct ast_sip_subscription *sub,
pjsip_rx_data *rdata);
/*!
* \brief Called when it is time for a subscriber to resubscribe
*
* This is a subscriber callback.
*
* The subscriber can reresh the subscription using the pjsip_evsub_initiate()
* function.
*
* \param sub The subscription to refresh
* \retval 0 Success
* \retval non-zero Failure
*/
int (*refresh_subscription)(struct ast_sip_subscription *sub);
};
/*!
* \brief Register a subscription handler
*
* \retval 0 Handler was registered successfully
* \retval non-zero Handler was not registered successfully
*/
int ast_sip_register_subscription_handler(const struct ast_sip_subscription_handler *handler);
/*!
* \brief Unregister a subscription handler
*/
void ast_sip_unregister_subscription_handler(const struct ast_sip_subscription_handler *handler);
enum ast_sip_subscription_role {
AST_SIP_SUBSCRIBER,
AST_SIP_NOTIFIER,
};
/*!
* \brief Create a new ast_sip_subscription structure
*/
struct ast_sip_subscription *ast_sip_create_subscription(const struct ast_sip_subscription_handler *handler,
enum ast_sip_subscription_role role, struct ast_sip_endpoint *endpoint);
/*!
* \brief Get the endpoint that is associated with this subscription
*
* \retval NULL Could not get endpoint
* \retval non-NULL The endpoint
*/
struct ast_sip_endpoint *ast_sip_subscription_get_endpoint(struct ast_sip_subscription *sub);
/*!
* \brief Get the serializer for the subscription
*
* Tasks that originate outside of a SIP servant thread should get the serializer
* and push the task to the serializer.
*
* \param sub The subscription
* \retval NULL Failure
* \retval non-NULL The subscription's serializer
*/
struct ast_sip_serializer *ast_sip_subscription_get_serializer(struct ast_sip_subscription *sub);
/*!
* \brief Get the underlying PJSIP evsub structure
*
* This is useful when wishing to call PJSIP's API calls in order to
* create SUBSCRIBEs, NOTIFIES, etc. as well as get subscription state
*
* This function, as well as all methods called on the pjsip_evsub should
* be done in a SIP servant thread.
*
* \param sub The subscription
* \retval NULL Failure
* \retval non-NULL The underlying pjsip_evsub
*/
pjsip_evsub *ast_sip_subscription_get_evsub(struct ast_sip_subscription *sub);
/*!
* \brief Send a request created via a PJSIP evsub method
*
* Callers of this function should take care to do so within a SIP servant
* thread.
*
* \param sub The subscription on which to send the request
* \param tdata The request to send
* \retval 0 Success
* \retval non-zero Failure
*/
int ast_sip_subscription_send_request(struct ast_sip_subscription *sub, pjsip_tx_data *tdata);
/*!
* \brief Alternative for ast_datastore_alloc()
*
* There are two major differences between this and ast_datastore_alloc()
* 1) This allocates a refcounted object
* 2) This will fill in a uid if one is not provided
*
* DO NOT call ast_datastore_free() on a datastore allocated in this
* way since that function will attempt to free the datastore rather
* than play nicely with its refcount.
*
* \param info Callbacks for datastore
* \param uid Identifier for datastore
* \retval NULL Failed to allocate datastore
* \retval non-NULL Newly allocated datastore
*/
struct ast_datastore *ast_sip_subscription_alloc_datastore(const struct ast_datastore_info *info, const char *uid);
/*!
* \brief Add a datastore to a SIP subscription
*
* Note that SIP uses reference counted datastores. The datastore passed into this function
* must have been allocated using ao2_alloc() or there will be serious problems.
*
* \param subscription The ssubscription to add the datastore to
* \param datastore The datastore to be added to the subscription
* \retval 0 Success
* \retval -1 Failure
*/
int ast_sip_subscription_add_datastore(struct ast_sip_subscription *subscription, struct ast_datastore *datastore);
/*!
* \brief Retrieve a subscription datastore
*
* The datastore retrieved will have its reference count incremented. When the caller is done
* with the datastore, the reference counted needs to be decremented using ao2_ref().
*
* \param subscription The subscription from which to retrieve the datastore
* \param name The name of the datastore to retrieve
* \retval NULL Failed to find the specified datastore
* \retval non-NULL The specified datastore
*/
struct ast_datastore *ast_sip_subscription_get_datastore(struct ast_sip_subscription *subscription, const char *name);
/*!
* \brief Remove a subscription datastore from the subscription
*
* This operation may cause the datastore's free() callback to be called if the reference
* count reaches zero.
*
* \param subscription The subscription to remove the datastore from
* \param name The name of the datastore to remove
*/
void ast_sip_subscription_remove_datastore(struct ast_sip_subscription *subscription, const char *name);</pre>
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