asterisk/main/srv.c

334 lines
7.9 KiB
C

/*
* Asterisk -- An open source telephony toolkit.
*
* Copyright (C) 1999 - 2005, Digium, Inc.
*
* Mark Spencer <markster@digium.com>
*
* Funding provided by nic.at
*
* 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 SRV Record Lookup Support for Asterisk
*
* \author Mark Spencer <markster@digium.com>
*
* \arg See also \ref ast_extension_states "AstENUM"
*
* \note Funding provided by nic.at
*/
/*** MODULEINFO
<support_level>core</support_level>
***/
#include "asterisk.h"
#include <netinet/in.h>
#include <arpa/nameser.h>
#ifdef __APPLE__
#include <arpa/nameser_compat.h>
#endif
#include <resolv.h>
#include "asterisk/channel.h"
#include "asterisk/srv.h"
#include "asterisk/dns.h"
#include "asterisk/utils.h"
#include "asterisk/linkedlists.h"
#ifdef __APPLE__
#undef T_SRV
#define T_SRV 33
#endif
struct srv_entry {
unsigned short priority;
unsigned short weight;
unsigned short port;
unsigned int weight_sum;
AST_LIST_ENTRY(srv_entry) list;
char host[1];
};
struct srv_context {
unsigned int have_weights:1;
struct srv_entry *prev;
unsigned int num_records;
AST_LIST_HEAD_NOLOCK(srv_entries, srv_entry) entries;
};
static int parse_srv(unsigned char *answer, int len, unsigned char *msg, struct srv_entry **result)
{
struct srv {
unsigned short priority;
unsigned short weight;
unsigned short port;
} __attribute__((__packed__)) *srv = (struct srv *) answer;
int res = 0;
char repl[256] = "";
struct srv_entry *entry;
if (len < sizeof(*srv))
return -1;
answer += sizeof(*srv);
len -= sizeof(*srv);
if ((res = dn_expand(msg, answer + len, answer, repl, sizeof(repl) - 1)) <= 0) {
ast_log(LOG_WARNING, "Failed to expand hostname\n");
return -1;
}
/* the magic value "." for the target domain means that this service
is *NOT* available at the domain we searched */
if (!strcmp(repl, "."))
return -1;
if (!(entry = ast_calloc(1, sizeof(*entry) + strlen(repl))))
return -1;
entry->priority = ntohs(srv->priority);
entry->weight = ntohs(srv->weight);
entry->port = ntohs(srv->port);
strcpy(entry->host, repl);
*result = entry;
return 0;
}
static int srv_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
{
struct srv_context *c = (struct srv_context *) context;
struct srv_entry *entry = NULL;
struct srv_entry *current;
if (parse_srv(answer, len, fullanswer, &entry))
return -1;
if (entry->weight)
c->have_weights = 1;
AST_LIST_TRAVERSE_SAFE_BEGIN(&c->entries, current, list) {
/* insert this entry just before the first existing
entry with a higher priority */
if (current->priority <= entry->priority)
continue;
AST_LIST_INSERT_BEFORE_CURRENT(entry, list);
entry = NULL;
break;
}
AST_LIST_TRAVERSE_SAFE_END;
/* if we didn't find a place to insert the entry before an existing
entry, then just add it to the end */
if (entry)
AST_LIST_INSERT_TAIL(&c->entries, entry, list);
return 0;
}
/* Do the bizarre SRV record weight-handling algorithm
involving sorting and random number generation...
See RFC 2782 if you want know why this code does this
*/
static void process_weights(struct srv_context *context)
{
struct srv_entry *current;
struct srv_entries newlist = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
while (AST_LIST_FIRST(&context->entries)) {
unsigned int random_weight;
unsigned int weight_sum;
unsigned short cur_priority = AST_LIST_FIRST(&context->entries)->priority;
struct srv_entries temp_list = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
weight_sum = 0;
AST_LIST_TRAVERSE_SAFE_BEGIN(&context->entries, current, list) {
if (current->priority != cur_priority)
break;
AST_LIST_MOVE_CURRENT(&temp_list, list);
}
AST_LIST_TRAVERSE_SAFE_END;
while (AST_LIST_FIRST(&temp_list)) {
weight_sum = 0;
AST_LIST_TRAVERSE(&temp_list, current, list)
current->weight_sum = weight_sum += current->weight;
/* if all the remaining entries have weight == 0,
then just append them to the result list and quit */
if (weight_sum == 0) {
AST_LIST_APPEND_LIST(&newlist, &temp_list, list);
break;
}
random_weight = 1 + (unsigned int) ((float) weight_sum * (ast_random() / ((float) RAND_MAX + 1.0)));
AST_LIST_TRAVERSE_SAFE_BEGIN(&temp_list, current, list) {
if (current->weight < random_weight)
continue;
AST_LIST_MOVE_CURRENT(&newlist, list);
break;
}
AST_LIST_TRAVERSE_SAFE_END;
}
}
/* now that the new list has been ordered,
put it in place */
AST_LIST_APPEND_LIST(&context->entries, &newlist, list);
}
int ast_srv_lookup(struct srv_context **context, const char *service, const char **host, unsigned short *port)
{
struct srv_entry *cur;
if (*context == NULL) {
if (!(*context = ast_calloc(1, sizeof(struct srv_context)))) {
return -1;
}
AST_LIST_HEAD_INIT_NOLOCK(&(*context)->entries);
if (((ast_search_dns(*context, service, C_IN, T_SRV, srv_callback)) < 1) ||
AST_LIST_EMPTY(&(*context)->entries)) {
ast_free(*context);
*context = NULL;
return -1;
}
if ((*context)->have_weights) {
process_weights(*context);
}
(*context)->prev = AST_LIST_FIRST(&(*context)->entries);
*host = (*context)->prev->host;
*port = (*context)->prev->port;
AST_LIST_TRAVERSE(&(*context)->entries, cur, list) {
++((*context)->num_records);
}
return 0;
}
if (((*context)->prev = AST_LIST_NEXT((*context)->prev, list))) {
/* Retrieve next item in result */
*host = (*context)->prev->host;
*port = (*context)->prev->port;
return 0;
} else {
/* No more results */
while ((cur = AST_LIST_REMOVE_HEAD(&(*context)->entries, list))) {
ast_free(cur);
}
ast_free(*context);
*context = NULL;
return 1;
}
}
void ast_srv_cleanup(struct srv_context **context)
{
const char *host;
unsigned short port;
if (*context) {
/* We have a context to clean up. */
while (!(ast_srv_lookup(context, NULL, &host, &port))) {
}
}
}
int ast_get_srv(struct ast_channel *chan, char *host, int hostlen, int *port, const char *service)
{
struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE };
struct srv_entry *current;
int ret;
if (chan && ast_autoservice_start(chan) < 0) {
return -1;
}
ret = ast_search_dns(&context, service, C_IN, T_SRV, srv_callback);
if (context.have_weights) {
process_weights(&context);
}
if (chan) {
ret |= ast_autoservice_stop(chan);
}
/* TODO: there could be a "." entry in the returned list of
answers... if so, this requires special handling */
/* the list of entries will be sorted in the proper selection order
already, so we just need the first one (if any) */
if ((ret > 0) && (current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
ast_copy_string(host, current->host, hostlen);
*port = current->port;
ast_free(current);
ast_debug(4, "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n",
service, host, *port);
} else {
host[0] = '\0';
*port = -1;
}
while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
ast_free(current);
}
return ret;
}
unsigned int ast_srv_get_record_count(struct srv_context *context)
{
return context->num_records;
}
int ast_srv_get_nth_record(struct srv_context *context, int record_num, const char **host,
unsigned short *port, unsigned short *priority, unsigned short *weight)
{
int i = 1;
int res = -1;
struct srv_entry *entry;
if (record_num < 1 || record_num > context->num_records) {
return res;
}
AST_LIST_TRAVERSE(&context->entries, entry, list) {
if (i == record_num) {
*host = entry->host;
*port = entry->port;
*priority = entry->priority;
*weight = entry->weight;
res = 0;
break;
}
++i;
}
return res;
}