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

main/dns_query_set.c

@@ -33,39 +33,117 @@ ASTERISK_REGISTER_FILE()
 
 #include "asterisk/vector.h"
 #include "asterisk/astobj2.h"
+#include "asterisk/utils.h"
+#include "asterisk/linkedlists.h"
 #include "asterisk/dns_core.h"
 #include "asterisk/dns_query_set.h"
+#include "asterisk/dns_internal.h"
+#include "asterisk/dns_resolver.h"
 
-/*! \brief A set of DNS queries */
-struct ast_dns_query_set {
-	/*! \brief DNS queries */
-	AST_VECTOR(, struct ast_dns_query *) queries;
-	/*! \brief The total number of completed queries */
-	unsigned int queries_completed;
-	/*! \brief Callback to invoke upon completion */
-	ast_dns_query_set_callback callback;
-	/*! \brief User-specific data */
-	void *user_data;
-};
+/*! \brief The default number of expected queries to be added to the query set */
+#define DNS_QUERY_SET_EXPECTED_QUERY_COUNT 5
+
+/*! \brief Release all queries held in a query set */
+static void dns_query_set_release(struct ast_dns_query_set *query_set)
+{
+	int idx;
+
+	for (idx = 0; idx < AST_VECTOR_SIZE(&query_set->queries); ++idx) {
+		struct dns_query_set_query *query = AST_VECTOR_GET_ADDR(&query_set->queries, idx);
+
+		ao2_ref(query->query, -1);
+	}
+
+	AST_VECTOR_FREE(&query_set->queries);
+}
+
+/*! \brief Destructor for DNS query set */
+static void dns_query_set_destroy(void *data)
+{
+	struct ast_dns_query_set *query_set = data;
+
+	dns_query_set_release(query_set);
+	ao2_cleanup(query_set->user_data);
+}
 
 struct ast_dns_query_set *ast_dns_query_set_create(void)
 {
-	return NULL;
+	struct ast_dns_query_set *query_set;
+
+	query_set = ao2_alloc_options(sizeof(*query_set), dns_query_set_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
+	if (!query_set) {
+		return NULL;
+	}
+
+	if (AST_VECTOR_INIT(&query_set->queries, DNS_QUERY_SET_EXPECTED_QUERY_COUNT)) {
+		ao2_ref(query_set, -1);
+		return NULL;
+	}
+
+	return query_set;
+}
+
+/*! \brief Callback invoked upon completion of a DNS query */
+static void dns_query_set_callback(const struct ast_dns_query *query)
+{
+	struct ast_dns_query_set *query_set = ast_dns_query_get_data(query);
+
+	if (ast_atomic_fetchadd_int(&query_set->queries_completed, +1) != (AST_VECTOR_SIZE(&query_set->queries) - 1)) {
+		return;
+	}
+
+	/* All queries have been completed, invoke final callback */
+	if (query_set->queries_cancelled != AST_VECTOR_SIZE(&query_set->queries)) {
+		query_set->callback(query_set);
+	}
+
+	ao2_cleanup(query_set->user_data);
+	query_set->user_data = NULL;
+
+	dns_query_set_release(query_set);
 }
 
 int ast_dns_query_set_add(struct ast_dns_query_set *query_set, const char *name, int rr_type, int rr_class)
 {
-	return -1;
+	struct dns_query_set_query query = {
+		.started = 0,
+	};
+
+	ast_assert(!query_set->in_progress);
+	if (query_set->in_progress) {
+		ast_log(LOG_ERROR, "Attempted to add additional query to query set '%p' after resolution has started\n",
+			query_set);
+		return -1;
+	}
+
+	query.query = dns_query_alloc(name, rr_type, rr_class, dns_query_set_callback, query_set);
+	if (!query.query) {
+		return -1;
+	}
+
+	AST_VECTOR_APPEND(&query_set->queries, query);
+
+	return 0;
 }
 
 size_t ast_dns_query_set_num_queries(const struct ast_dns_query_set *query_set)
 {
-	return 0;
+	return AST_VECTOR_SIZE(&query_set->queries);
 }
 
 struct ast_dns_query *ast_dns_query_set_get(const struct ast_dns_query_set *query_set, unsigned int index)
 {
-	return NULL;
+	/* Only once all queries have been completed can results be retrieved */
+	if (query_set->queries_completed != AST_VECTOR_SIZE(&query_set->queries)) {
+		return NULL;
+	}
+
+	/* If the index exceeds the number of queries... no query for you */
+	if (index >= AST_VECTOR_SIZE(&query_set->queries)) {
+		return NULL;
+	}
+
+	return AST_VECTOR_GET_ADDR(&query_set->queries, index)->query;
 }
 
 void *ast_dns_query_set_get_data(const struct ast_dns_query_set *query_set)
@@ -75,19 +153,104 @@ void *ast_dns_query_set_get_data(const struct ast_dns_query_set *query_set)
 
 void ast_dns_query_set_resolve_async(struct ast_dns_query_set *query_set, ast_dns_query_set_callback callback, void *data)
 {
+	int idx;
+
+	ast_assert(!query_set->in_progress);
+	if (query_set->in_progress) {
+		ast_log(LOG_ERROR, "Attempted to start asynchronous resolution of query set '%p' when it has already started\n",
+			query_set);
+		return;
+	}
+
+	query_set->in_progress = 1;
 	query_set->callback = callback;
 	query_set->user_data = ao2_bump(data);
+
+	for (idx = 0; idx < AST_VECTOR_SIZE(&query_set->queries); ++idx) {
+		struct dns_query_set_query *query = AST_VECTOR_GET_ADDR(&query_set->queries, idx);
+
+		if (!query->query->resolver->resolve(query->query)) {
+			query->started = 1;
+			continue;
+		}
+
+		dns_query_set_callback(query->query);
+	}
 }
 
-void ast_query_set_resolve(struct ast_dns_query_set *query_set)
+/*! \brief Structure used for signaling back for synchronous resolution completion */
+struct dns_synchronous_resolve {
+	/*! \brief Lock used for signaling */
+	ast_mutex_t lock;
+	/*! \brief Condition used for signaling */
+	ast_cond_t cond;
+	/*! \brief Whether the query has completed */
+	unsigned int completed;
+};
+
+/*! \brief Destructor for synchronous resolution structure */
+static void dns_synchronous_resolve_destroy(void *data)
 {
+	struct dns_synchronous_resolve *synchronous = data;
+
+	ast_mutex_destroy(&synchronous->lock);
+	ast_cond_destroy(&synchronous->cond);
+}
+
+/*! \brief Callback used to implement synchronous resolution */
+static void dns_synchronous_resolve_callback(const struct ast_dns_query_set *query_set)
+{
+	struct dns_synchronous_resolve *synchronous = ast_dns_query_set_get_data(query_set);
+
+	ast_mutex_lock(&synchronous->lock);
+	synchronous->completed = 1;
+	ast_cond_signal(&synchronous->cond);
+	ast_mutex_unlock(&synchronous->lock);
+}
+
+int ast_query_set_resolve(struct ast_dns_query_set *query_set)
+{
+	struct dns_synchronous_resolve *synchronous;
+
+	synchronous = ao2_alloc_options(sizeof(*synchronous), dns_synchronous_resolve_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
+	if (!synchronous) {
+		return -1;
+	}
+
+	ast_mutex_init(&synchronous->lock);
+	ast_cond_init(&synchronous->cond, NULL);
+
+	ast_dns_query_set_resolve_async(query_set, dns_synchronous_resolve_callback, synchronous);
+
+	/* Wait for resolution to complete */
+	ast_mutex_lock(&synchronous->lock);
+	while (!synchronous->completed) {
+		ast_cond_wait(&synchronous->cond, &synchronous->lock);
+	}
+	ast_mutex_unlock(&synchronous->lock);
+
+	ao2_ref(synchronous, -1);
+
+	return 0;
 }
 
 int ast_dns_query_set_resolve_cancel(struct ast_dns_query_set *query_set)
 {
-	return -1;
-}
+	int idx;
+	size_t query_count = AST_VECTOR_SIZE(&query_set->queries);
 
-void ast_dns_query_set_free(struct ast_dns_query_set *query_set)
-{
-}
+	for (idx = 0; idx < AST_VECTOR_SIZE(&query_set->queries); ++idx) {
+		struct dns_query_set_query *query = AST_VECTOR_GET_ADDR(&query_set->queries, idx);
+
+		if (query->started) {
+			if (!query->query->resolver->cancel(query->query)) {
+				query_set->queries_cancelled++;
+				dns_query_set_callback(query->query);
+			}
+		} else {
+			query_set->queries_cancelled++;
+		}
+	}
+
+	return (query_set->queries_cancelled == query_count) ? 0 : -1;
+}