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/*
* Asterisk -- An open source telephony toolkit.
*
* Copyright (C) 2015, Digium, Inc.
*
* Ashley Sanders <asanders@digium.com>
*
* 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 The default DNS resolver for Asterisk.
*
* \arg See also \ref res_resolver_unbound
*
* \author Ashley Sanders <asanders@digium.com>
*/
#include "asterisk.h"
#include "asterisk/_private.h"
#include "asterisk/astobj2.h"
#include "asterisk/dns.h"
#include "asterisk/dns_core.h"
#include "asterisk/dns_resolver.h"
#include "asterisk/linkedlists.h"
#include "asterisk/taskprocessor.h"
#include "asterisk/utils.h"
/*! \brief The consideration priority for this resolver implementation. */
#define DNS_SYSTEM_RESOLVER_PRIORITY INT_MAX
/*! \brief Resolver return code upon success. */
#define DNS_SYSTEM_RESOLVER_SUCCESS 0
/*! \brief Resolver return code upon failure. */
#define DNS_SYSTEM_RESOLVER_FAILURE -1
static int dns_system_resolver_add_record(void *context, unsigned char *record, int record_len, int ttl);
static int dns_system_resolver_cancel(struct ast_dns_query *query);
static void dns_system_resolver_destroy(void);
static int dns_system_resolver_process_query(void *data);
static int dns_system_resolver_resolve(struct ast_dns_query *query);
static int dns_system_resolver_set_response(void *context, unsigned char *dns_response, int dns_response_len, int rcode);
/*! \brief The task processor to use for making DNS searches asynchronous. */
static struct ast_taskprocessor *dns_system_resolver_tp;
/*! \brief The base definition for the dns_system_resolver */
struct ast_dns_resolver dns_system_resolver_base = {
.name = "system",
.priority = DNS_SYSTEM_RESOLVER_PRIORITY,
.resolve = dns_system_resolver_resolve,
.cancel = dns_system_resolver_cancel,
};
/*!
* \brief Callback to handle processing resource records.
*
* \details Adds an individual resource record discovered with ast_search_dns_ex to the
* ast_dns_query currently being resolved.
*
* \internal
*
* \param context A void pointer to the ast_dns_query being processed.
* \param record An individual resource record discovered during the DNS search.
* \param record_len The length of the resource record.
* \param ttl The resource record's expiration time limit (time to live).
*
* \retval 0 on success
* \retval -1 on failure
*/
static int dns_system_resolver_add_record(void *context, unsigned char *record, int record_len, int ttl)
{
struct ast_dns_query *query = context;
/* Add the record to the query.*/
return ast_dns_resolver_add_record(query,
ast_dns_query_get_rr_type(query),
ast_dns_query_get_rr_class(query),
ttl,
(const char*) record,
record_len);
}
/*!
* \brief Cancels processing resolution for a given query.
*
* \note The system API calls block so there is no way to cancel them. Therefore, this function always
* returns failure when invoked.
*
* \internal
*
* \param query The ast_dns_query to cancel.
*
* \retval 0 on success
* \retval -1 on failure
*/
static int dns_system_resolver_cancel(struct ast_dns_query *query)
{
return DNS_SYSTEM_RESOLVER_FAILURE;
}
/*!
* \brief Destructor.
*
* \internal
*/
static void dns_system_resolver_destroy(void)
{
/* Unreference the task processor */
dns_system_resolver_tp = ast_taskprocessor_unreference(dns_system_resolver_tp);
/* Unregister the base resolver */
ast_dns_resolver_unregister(&dns_system_resolver_base);
}
/*!
* \brief Callback to handle processing the query from the ast_taskprocessor instance.
*
* \internal
*
* \param data A void pointer to the ast_dns_query being processed.
*
* \retval -1 on search failure
* \retval 0 on no records found
* \retval 1 on success
*/
static int dns_system_resolver_process_query(void *data)
{
struct ast_dns_query *query = data;
/* Perform the DNS search */
enum ast_dns_search_result res = ast_search_dns_ex(query,
ast_dns_query_get_name(query),
ast_dns_query_get_rr_class(query),
ast_dns_query_get_rr_type(query),
dns_system_resolver_set_response,
dns_system_resolver_add_record);
/* Handle the possible return values from the DNS search */
if (res == AST_DNS_SEARCH_FAILURE) {
ast_debug(1, "DNS search failed for query: '%s'\n",
ast_dns_query_get_name(query));
} else if (res == AST_DNS_SEARCH_NO_RECORDS) {
ast_debug(1, "DNS search failed to yield any results for query: '%s'\n",
ast_dns_query_get_name(query));
}
/* Mark the query as complete */
ast_dns_resolver_completed(query);
/* Reduce the reference count on the query object */
ao2_ref(query, -1);
return res;
}
/*!
* \brief Resolves a DNS query.
*
* \internal
*
* \param query The ast_dns_query to resolve.
*
* \retval 0 on successful load of query handler to the ast_taskprocessor instance
* \retval -1 on failure to load the query handler to the ast_taskprocessor instance
*/
static int dns_system_resolver_resolve(struct ast_dns_query *query)
{
/* Add query processing handler to the task processor */
int res = ast_taskprocessor_push(dns_system_resolver_tp,
dns_system_resolver_process_query,
ao2_bump(query));
/* The query processing handler was not added to the task processor */
if (res < 0) {
ast_log(LOG_ERROR, "Failed to perform async DNS resolution of '%s'\n",
ast_dns_query_get_name(query));
ao2_ref(query, -1);
}
/* Return the result of adding the query processing handler to the task processor */
return res;
}
/*!
* \brief Callback to handle initializing the results field.
*
* \internal
*
* \param dns_response The full DNS response.
* \param dns_response The length of the full DNS response.
* \param rcode The DNS response code.
*
* \retval 0 on success
* \retval -1 on failure
*/
static int dns_system_resolver_set_response(void *context, unsigned char *dns_response, int dns_response_len, int rcode)
{
struct ast_dns_query *query = context;
int res;
/* Instantiate the query's result field (if necessary). */
if (!ast_dns_query_get_result(query)) {
res = ast_dns_resolver_set_result(query,
0,
0,
rcode,
ast_dns_query_get_name(query),
(const char*) dns_response,
dns_response_len);
if (res) {
/* There was a problem instantiating the results field. */
ast_log(LOG_ERROR, "Could not instantiate the results field for query: '%s'\n",
ast_dns_query_get_name(query));
}
} else {
res = DNS_SYSTEM_RESOLVER_SUCCESS;
}
return res;
}
/*!
* \brief Initializes the resolver.
*
* \retval 0 on success
* \retval -1 on failure
*/
int ast_dns_system_resolver_init(void)
{
/* Register the base resolver */
int res = ast_dns_resolver_register(&dns_system_resolver_base);
if (res) {
return DNS_SYSTEM_RESOLVER_FAILURE;
}
/* Instantiate the task processor */
dns_system_resolver_tp = ast_taskprocessor_get("dns_system_resolver_tp",
TPS_REF_DEFAULT);
/* Return error if the task processor failed to instantiate */
if (!dns_system_resolver_tp) {
dns_system_resolver_destroy();
return DNS_SYSTEM_RESOLVER_FAILURE;
}
/* Register the cleanup function */
ast_register_cleanup(dns_system_resolver_destroy);
return DNS_SYSTEM_RESOLVER_SUCCESS;
}