dns_query_set.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2015, Digium, Inc.
 *
 * Joshua Colp <[email protected]>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief DNS Query Set API
 *
 * \author Joshua Colp <[email protected]>
 */

/*** MODULEINFO
 <support_level>core</support_level>
 ***/

#include "asterisk.h"

#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 The default number of expected queries to be added to the query set */
#define DNS_QUERY_SET_EXPECTED_QUERY_COUNT 5

/*! \brief Destructor for DNS query set */
static void dns_query_set_destroy(void *data)
{
 struct ast_dns_query_set *query_set = data;
 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);

 ao2_cleanup(query_set->user_data);
}

struct ast_dns_query_set *ast_dns_query_set_create(void)
{
 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);

 /* The reference count of the query set is bumped here in case this query holds the last reference */
 ao2_ref(query_set, +1);

 /* Drop the query set from the query so the query set can be destroyed if this is the last one */
 ao2_cleanup(((struct ast_dns_query *)query)->user_data);
 ((struct ast_dns_query *)query)->user_data = NULL;

 if (ast_atomic_fetchadd_int(&query_set->queries_completed, +1) != (AST_VECTOR_SIZE(&query_set->queries) - 1)) {
 ao2_ref(query_set, -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;

 ao2_ref(query_set, -1);
}

int ast_dns_query_set_add(struct ast_dns_query_set *query_set, const char *name, int rr_type, int rr_class)
{
 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;
 }

 /*
 * We are intentionally passing NULL for the user data even
 * though dns_query_set_callback() is not NULL tolerant. Doing
 * this avoids a circular reference chain until the queries are
 * started. ast_dns_query_set_resolve_async() will set the
 * query user_data for us later when we actually kick off the
 * queries.
 */
 query.query = dns_query_alloc(name, rr_type, rr_class, dns_query_set_callback, NULL);
 if (!query.query) {
 return -1;
 }

 if (AST_VECTOR_APPEND(&query_set->queries, query)) {
 ao2_ref(query.query, -1);
 return -1;
 }

 return 0;
}

size_t ast_dns_query_set_num_queries(const struct ast_dns_query_set *query_set)
{
 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)
{
 /* 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)
{
 return query_set->user_data;
}

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);

 /*
 * Bump the query_set ref in case all queries complete
 * before we are done kicking them off.
 */
 ao2_ref(query_set, +1);
 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);

 query->query->user_data = ao2_bump(query_set);

 if (!query->query->resolver->resolve(query->query)) {
 query->started = 1;
 continue;
 }

 dns_query_set_callback(query->query);
 }
 if (!idx) {
 /*
 * There were no queries in the set;
 * therefore all queries are "completed".
 * Invoke the final callback.
 */
 query_set->callback(query_set);
 ao2_cleanup(query_set->user_data);
 query_set->user_data = NULL;
 }
 ao2_ref(query_set, -1);
}

/*! \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)
{
 int idx;
 size_t query_count = AST_VECTOR_SIZE(&query_set->queries);

 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;
}