res_pjsip_exten_state: Check if body generator is available.

When starting the extension state publishers, check if the requested
message body generator is available.  If not available give error message
and skip starting that publisher.

* res_pjsip_pubsub.c: Create new API if type/subtype generator
registered.

* res_pjsip_exten_state.c: Use new body generator API for validation.

ASTERISK-25922

Change-Id: I4ad69200666e3cc909d4619e3c81042d7f9db25c

include/asterisk/res_pjsip_pubsub.h

@@ -648,6 +648,19 @@ struct ast_sip_pubsub_body_supplement {
 int ast_sip_pubsub_generate_body_content(const char *content_type,
 		const char *content_subtype, struct ast_sip_body_data *data, struct ast_str **str);
 
+/*!
+ * \brief Is a body generator registered for the given type/subtype.
+ * \since 14.0.0
+ *
+ * \param type The content type of the body
+ * \param subtype The content subtype of the body
+ *
+ * \note In "plain/text", "plain" is the type and "text" is the subtype.
+ *
+ * \retval non-zero if a generator is registered.
+ */
+int ast_sip_pubsub_is_body_generator_registered(const char *type, const char *subtype);
+
 /*!
  * \since 13.0.0
  * \brief Register a body generator with the pubsub core.

res/res_pjsip_exten_state.c

@@ -680,6 +680,12 @@ static int publisher_start(struct ast_sip_outbound_publish *configuration, struc
 		return -1;
 	}
 
+	if (!ast_sip_pubsub_is_body_generator_registered(body_type, body_subtype)) {
+		ast_log(LOG_ERROR, "Outbound extension state publisher '%s': '%s' body generator not registered\n",
+			name, body_full);
+		return -1;
+	}
+
 	name_size = strlen(name) + 1;
 	body_type_size = strlen(body_type) + 1;
 	body_subtype_size = strlen(body_subtype) + 1;

res/res_pjsip_pubsub.c

@@ -3086,6 +3086,11 @@ const char *ast_sip_publication_get_event_configuration(const struct ast_sip_pub
 	return pub->event_configuration_name;
 }
 
+int ast_sip_pubsub_is_body_generator_registered(const char *type, const char *subtype)
+{
+	return !!find_body_generator_type_subtype(type, subtype);
+}
+
 int ast_sip_pubsub_register_body_generator(struct ast_sip_pubsub_body_generator *generator)
 {
 	struct ast_sip_pubsub_body_generator *existing;