res_pjsip: Add external PJSIP resolver implementation using core DNS API.

This change adds the following:

1. A query set implementation. This is an API that allows queries to be executed in parallel and once all have completed a callback is invoked.
2. Unit tests for the query set implementation.
3. An external PJSIP resolver which uses the DNS core API to do NAPTR, SRV, AAAA, and A lookups.

For the resolver it will do NAPTR, SRV, and AAAA/A lookups in parallel. If NAPTR or SRV
are available it will then do more queries. And so on. Preference is NAPTR > SRV > AAAA/A,
with IPv6 preferred over IPv4. For transport it will prefer TLS > TCP > UDP if no explicit
transport has been provided. Configured transports on the system are taken into account to
eliminate resolved addresses which have no hope of completing.

ASTERISK-24947 #close
Reported by: Joshua Colp

Change-Id: I56cb03ce4f9d3d600776f36928e0b3e379b5d71e

1 files changed, 10 insertions, 10 deletions

diff --git a/include/asterisk/dns_query_set.h b/include/asterisk/dns_query_set.h
index c89fdfde7..fac732ae0 100644
--- a/include/asterisk/dns_query_set.h
+++ b/include/asterisk/dns_query_set.h
@@ -43,6 +43,8 @@ typedef void (*ast_dns_query_set_callback)(const struct ast_dns_query_set *query
  *
  * \retval non-NULL success
  * \retval NULL failure
+ *
+ * \note The query set must be released upon cancellation or completion using ao2_ref
  */
 struct ast_dns_query_set *ast_dns_query_set_create(void);
 
@@ -76,6 +78,8 @@ size_t ast_dns_query_set_num_queries(const struct ast_dns_query_set *query_set);
  *
  * \retval non-NULL success
  * \retval NULL failure
+ *
+ * \note The returned query is only valid for the lifetime of the query set itself
  */
 struct ast_dns_query *ast_dns_query_set_get(const struct ast_dns_query_set *query_set, unsigned int index);
 
@@ -106,29 +110,25 @@ void ast_dns_query_set_resolve_async(struct ast_dns_query_set *query_set, ast_dn
  *
  * \param query_set The query set
  *
+ * \retval 0 success
+ * \retval -1 failure
+ *
  * \note This function will return when all queries have been completed
  */
-void ast_query_set_resolve(struct ast_dns_query_set *query_set);
+int ast_query_set_resolve(struct ast_dns_query_set *query_set);
 
 /*!
  * \brief Cancel an asynchronous DNS query set resolution
  *
  * \param query_set The DNS query set
  *
- * \retval 0 success
- * \retval -1 failure
+ * \retval 0 success (all queries have been cancelled)
+ * \retval -1 failure (some queries could not be cancelled)
  *
  * \note If successfully cancelled the callback will not be invoked
  */
 int ast_dns_query_set_resolve_cancel(struct ast_dns_query_set *query_set);
 
-/*!
- * \brief Free a query set
- *
- * \param query_set A DNS query set
- */
-void ast_dns_query_set_free(struct ast_dns_query_set *query_set);
-
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif