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;
}