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

include/asterisk/autoconfig.h.in

@@ -578,6 +578,10 @@
 /* Define if your system has the PJPROJECT libraries. */
 #undef HAVE_PJPROJECT
 
+/* Define to 1 if PJPROJECT has the PJSIP External Resolver Support feature.
+   */
+#undef HAVE_PJSIP_EXTERNAL_RESOLVER
+
 /* Define to 1 if PJPROJECT has the pjsip_get_dest_info support feature. */
 #undef HAVE_PJSIP_GET_DEST_INFO
 

include/asterisk/dns_core.h

@@ -204,6 +204,15 @@ int ast_dns_record_get_ttl(const struct ast_dns_record *record);
  */
 const char *ast_dns_record_get_data(const struct ast_dns_record *record);
 
+/*!
+ * \brief Retrieve the size of the raw DNS record
+ *
+ * \param record The DNS record
+ *
+ * \return the size of the raw DNS record
+ */
+size_t ast_dns_record_get_data_size(const struct ast_dns_record *record);
+
 /*!
  * \brief Get the next DNS record
  *

include/asterisk/dns_internal.h

@@ -23,6 +23,12 @@
  * \author Joshua Colp <jcolp@digium.com>
  */
 
+/*! \brief For AST_VECTOR */
+#include "asterisk/vector.h"
+
+/*! \brief For ast_dns_query_set_callback */
+#include "asterisk/dns_query_set.h"
+
 /*! \brief Generic DNS record information */
 struct ast_dns_record {
 	/*! \brief Resource record type */
@@ -151,6 +157,30 @@ struct ast_dns_query_recurring {
 	char name[0];
 };
 
+/*! \brief A DNS query set query, which includes its state */
+struct dns_query_set_query {
+	/*! \brief Whether the query started successfully or not */
+	unsigned int started;
+	/*! \brief THe query itself */
+	struct ast_dns_query *query;
+};
+
+/*! \brief A set of DNS queries */
+struct ast_dns_query_set {
+	/*! \brief DNS queries */
+	AST_VECTOR(, struct dns_query_set_query) queries;
+	/* \brief Whether the query set is in progress or not */
+	int in_progress;
+	/*! \brief The total number of completed queries */
+	int queries_completed;
+	/*! \brief The total number of cancelled queries */
+	int queries_cancelled;
+	/*! \brief Callback to invoke upon completion */
+	ast_dns_query_set_callback callback;
+	/*! \brief User-specific data */
+	void *user_data;
+};
+
 /*! \brief An active DNS query */
 struct ast_dns_query_active {
 	/*! \brief The underlying DNS query */
@@ -241,3 +271,25 @@ int dns_parse_short(unsigned char *cur, uint16_t *val);
  * \return The number of bytes consumed while parsing
  */
 int dns_parse_string(char *cur, uint8_t *size, char **val);
+
+/*!
+ * \brief Allocate a DNS query (but do not start resolution)
+ *
+ * \param name The name of what to resolve
+ * \param rr_type Resource record type
+ * \param rr_class Resource record class
+ * \param callback The callback to invoke upon completion
+ * \param data User data to make available on the query
+ *
+ * \retval non-NULL success
+ * \retval NULL failure
+ *
+ * \note The result passed to the callback does not need to be freed
+ *
+ * \note The user data MUST be an ao2 object
+ *
+ * \note This function increments the reference count of the user data, it does NOT steal
+ *
+ * \note The query must be released upon completion or cancellation using ao2_ref
+ */
+struct ast_dns_query *dns_query_alloc(const char *name, int rr_type, int rr_class, ast_dns_resolve_callback callback, void *data);

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