Mon Mar 19 11:30:55 2012

Asterisk developer's documentation


srv.c File Reference

DNS SRV Record Lookup Support for Asterisk. More...

#include "asterisk.h"
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include "asterisk/channel.h"
#include "asterisk/srv.h"
#include "asterisk/dns.h"
#include "asterisk/utils.h"
#include "asterisk/linkedlists.h"

Go to the source code of this file.

Data Structures

struct  srv_context
struct  srv_context::srv_entries
struct  srv_entry

Functions

int ast_get_srv (struct ast_channel *chan, char *host, int hostlen, int *port, const char *service)
void ast_srv_cleanup (struct srv_context **context)
 Cleanup resources associated with ast_srv_lookup.
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)
 Retrieve details from a specific SRV record.
unsigned int ast_srv_get_record_count (struct srv_context *context)
 Get the number of records for a given SRV context.
int ast_srv_lookup (struct srv_context **context, const char *service, const char **host, unsigned short *port)
 Retrieve set of SRV lookups, in order.
static int parse_srv (unsigned char *answer, int len, unsigned char *msg, struct srv_entry **result)
static void process_weights (struct srv_context *context)
static int srv_callback (void *context, unsigned char *answer, int len, unsigned char *fullanswer)


Detailed Description

DNS SRV Record Lookup Support for Asterisk.

Author:
Mark Spencer <markster@digium.com>
Note:
Funding provided by nic.at

Definition in file srv.c.


Function Documentation

int ast_get_srv ( struct ast_channel chan,
char *  host,
int  hostlen,
int *  port,
const char *  service 
)

Parameters:
chan Ast channel
host host name (return value)
hostlen Length of string "host"
port Port number (return value)
service Service tag for SRV lookup (like "_sip._udp" or "_stun._udp"

Definition at line 259 of file srv.c.

References ast_autoservice_start(), ast_autoservice_stop(), ast_copy_string(), ast_free, AST_LIST_HEAD_NOLOCK_INIT_VALUE, AST_LIST_REMOVE_HEAD, ast_search_dns(), ast_verb, context, srv_entry::host, srv_entry::list, srv_entry::port, process_weights(), and srv_callback().

Referenced by ast_get_ip_or_srv(), and create_addr().

00260 {
00261    struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE };
00262    struct srv_entry *current;
00263    int ret;
00264 
00265    if (chan && ast_autoservice_start(chan) < 0) {
00266       return -1;
00267    }
00268 
00269    ret = ast_search_dns(&context, service, C_IN, T_SRV, srv_callback);
00270 
00271    if (context.have_weights) {
00272       process_weights(&context);
00273    }
00274 
00275    if (chan) {
00276       ret |= ast_autoservice_stop(chan);
00277    }
00278 
00279    /* TODO: there could be a "." entry in the returned list of
00280       answers... if so, this requires special handling */
00281 
00282    /* the list of entries will be sorted in the proper selection order
00283       already, so we just need the first one (if any) */
00284 
00285    if ((ret > 0) && (current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
00286       ast_copy_string(host, current->host, hostlen);
00287       *port = current->port;
00288       ast_free(current);
00289       ast_verb(4, "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n",
00290                 service, host, *port);
00291    } else {
00292       host[0] = '\0';
00293       *port = -1;
00294    }
00295 
00296    while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
00297       ast_free(current);
00298    }
00299 
00300    return ret;
00301 }

void ast_srv_cleanup ( struct srv_context **  context  ) 

Cleanup resources associated with ast_srv_lookup.

Parameters:
context Pointer passed into ast_srv_lookup

Definition at line 247 of file srv.c.

References ast_srv_lookup(), context, and srv_entry::port.

Referenced by launch_ha_netscript(), srds_destroy_cb(), and srv_datastore_setup().

00248 {
00249    const char *host;
00250    unsigned short port;
00251 
00252    if (*context) {
00253       /* We have a context to clean up. */
00254       while (!(ast_srv_lookup(context, NULL, &host, &port))) {
00255       }
00256    }
00257 }

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 
)

Retrieve details from a specific SRV record.

After calling ast_srv_lookup, the srv_context will contain the data from several records. You can retrieve the data of a specific one by asking for a specific record number. The records are sorted based on priority and secondarily based on weight. See RFC 2782 for the exact sorting rules.

Parameters:
context The context returned by ast_srv_lookup
record_num The 1-indexed record number to retrieve
[out] host The host portion of the record
[out] port The port portion of the record
[out] priority The priority portion of the record
[out] weight The weight portion of the record
Return values:
-1 Failed to retrieve information. Likely due to an out of range record_num
0 Success

Definition at line 308 of file srv.c.

References AST_LIST_TRAVERSE, context, srv_entry::host, srv_entry::list, srv_entry::port, srv_entry::priority, and srv_entry::weight.

Referenced by srv_result_read().

00310 {
00311    int i = 1;
00312    int res = -1;
00313    struct srv_entry *entry;
00314 
00315    if (record_num < 1 || record_num > context->num_records) {
00316       return res;
00317    }
00318 
00319    AST_LIST_TRAVERSE(&context->entries, entry, list) {
00320       if (i == record_num) {
00321          *host = entry->host;
00322          *port = entry->port;
00323          *priority = entry->priority;
00324          *weight = entry->weight;
00325          res = 0;
00326          break;
00327       }
00328       ++i;
00329    }
00330 
00331    return res;
00332 }

unsigned int ast_srv_get_record_count ( struct srv_context context  ) 

Get the number of records for a given SRV context.

This is meant to be used after calling ast_srv_lookup, so that one may retrieve the number of records returned during a specific SRV lookup.

Parameters:
context The context returned by ast_srv_lookup
Returns:
Number of records in context

Definition at line 303 of file srv.c.

References context.

Referenced by srv_result_read().

00304 {
00305    return context->num_records;
00306 }

int ast_srv_lookup ( struct srv_context **  context,
const char *  service,
const char **  host,
unsigned short *  port 
)

Retrieve set of SRV lookups, in order.

Parameters:
[in] context A pointer in which to hold the result
[in] service The service name to look up
[out] host Result host
[out] port Associated TCP portnum
Return values:
-1 Query failed
0 Result exists in host and port
1 No more results

Definition at line 202 of file srv.c.

References ast_calloc, ast_free, AST_LIST_FIRST, AST_LIST_HEAD_INIT_NOLOCK, AST_LIST_NEXT, AST_LIST_REMOVE_HEAD, AST_LIST_TRAVERSE, ast_search_dns(), context, srv_entry::list, process_weights(), and srv_callback().

Referenced by ast_srv_cleanup(), launch_ha_netscript(), and srv_datastore_setup().

00203 {
00204    struct srv_entry *cur;
00205 
00206    if (*context == NULL) {
00207       if (!(*context = ast_calloc(1, sizeof(struct srv_context)))) {
00208          return -1;
00209       }
00210       AST_LIST_HEAD_INIT_NOLOCK(&(*context)->entries);
00211 
00212       if ((ast_search_dns(*context, service, C_IN, T_SRV, srv_callback)) < 0) {
00213          ast_free(*context);
00214          *context = NULL;
00215          return -1;
00216       }
00217 
00218       if ((*context)->have_weights) {
00219          process_weights(*context);
00220       }
00221 
00222       (*context)->prev = AST_LIST_FIRST(&(*context)->entries);
00223       *host = (*context)->prev->host;
00224       *port = (*context)->prev->port;
00225       AST_LIST_TRAVERSE(&(*context)->entries, cur, list) {
00226          ++((*context)->num_records);
00227       }
00228       return 0;
00229    }
00230 
00231    if (((*context)->prev = AST_LIST_NEXT((*context)->prev, list))) {
00232       /* Retrieve next item in result */
00233       *host = (*context)->prev->host;
00234       *port = (*context)->prev->port;
00235       return 0;
00236    } else {
00237       /* No more results */
00238       while ((cur = AST_LIST_REMOVE_HEAD(&(*context)->entries, list))) {
00239          ast_free(cur);
00240       }
00241       ast_free(*context);
00242       *context = NULL;
00243       return 1;
00244    }
00245 }

static int parse_srv ( unsigned char *  answer,
int  len,
unsigned char *  msg,
struct srv_entry **  result 
) [static]

Definition at line 72 of file srv.c.

References ast_calloc, ast_log(), LOG_WARNING, srv_entry::port, srv_entry::priority, and srv_entry::weight.

Referenced by srv_callback().

00073 {
00074    struct srv {
00075       unsigned short priority;
00076       unsigned short weight;
00077       unsigned short port;
00078    } __attribute__((__packed__)) *srv = (struct srv *) answer;
00079 
00080    int res = 0;
00081    char repl[256] = "";
00082    struct srv_entry *entry;
00083 
00084    if (len < sizeof(*srv))
00085       return -1;
00086 
00087    answer += sizeof(*srv);
00088    len -= sizeof(*srv);
00089 
00090    if ((res = dn_expand(msg, answer + len, answer, repl, sizeof(repl) - 1)) <= 0) {
00091       ast_log(LOG_WARNING, "Failed to expand hostname\n");
00092       return -1;
00093    }
00094 
00095    /* the magic value "." for the target domain means that this service
00096       is *NOT* available at the domain we searched */
00097    if (!strcmp(repl, "."))
00098       return -1;
00099 
00100    if (!(entry = ast_calloc(1, sizeof(*entry) + strlen(repl))))
00101       return -1;
00102    
00103    entry->priority = ntohs(srv->priority);
00104    entry->weight = ntohs(srv->weight);
00105    entry->port = ntohs(srv->port);
00106    strcpy(entry->host, repl);
00107 
00108    *result = entry;
00109    
00110    return 0;
00111 }

static void process_weights ( struct srv_context context  )  [static]

Definition at line 150 of file srv.c.

References AST_LIST_APPEND_LIST, AST_LIST_FIRST, AST_LIST_HEAD_NOLOCK_INIT_VALUE, AST_LIST_MOVE_CURRENT, AST_LIST_TRAVERSE, AST_LIST_TRAVERSE_SAFE_BEGIN, AST_LIST_TRAVERSE_SAFE_END, ast_random(), context, srv_entry::list, srv_entry::priority, srv_entry::weight, and srv_entry::weight_sum.

Referenced by ast_get_srv(), and ast_srv_lookup().

00151 {
00152    struct srv_entry *current;
00153    struct srv_entries newlist = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
00154 
00155    while (AST_LIST_FIRST(&context->entries)) {
00156       unsigned int random_weight;
00157       unsigned int weight_sum;
00158       unsigned short cur_priority = AST_LIST_FIRST(&context->entries)->priority;
00159       struct srv_entries temp_list = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
00160       weight_sum = 0;
00161 
00162       AST_LIST_TRAVERSE_SAFE_BEGIN(&context->entries, current, list) {
00163          if (current->priority != cur_priority)
00164             break;
00165 
00166          AST_LIST_MOVE_CURRENT(&temp_list, list);
00167       }
00168       AST_LIST_TRAVERSE_SAFE_END;
00169 
00170       while (AST_LIST_FIRST(&temp_list)) {
00171          weight_sum = 0;
00172          AST_LIST_TRAVERSE(&temp_list, current, list)
00173             current->weight_sum = weight_sum += current->weight;
00174 
00175          /* if all the remaining entries have weight == 0,
00176             then just append them to the result list and quit */
00177          if (weight_sum == 0) {
00178             AST_LIST_APPEND_LIST(&newlist, &temp_list, list);
00179             break;
00180          }
00181 
00182          random_weight = 1 + (unsigned int) ((float) weight_sum * (ast_random() / ((float) RAND_MAX + 1.0)));
00183 
00184          AST_LIST_TRAVERSE_SAFE_BEGIN(&temp_list, current, list) {
00185             if (current->weight < random_weight)
00186                continue;
00187 
00188             AST_LIST_MOVE_CURRENT(&newlist, list);
00189             break;
00190          }
00191          AST_LIST_TRAVERSE_SAFE_END;
00192       }
00193 
00194    }
00195 
00196    /* now that the new list has been ordered,
00197       put it in place */
00198 
00199    AST_LIST_APPEND_LIST(&context->entries, &newlist, list);
00200 }

static int srv_callback ( void *  context,
unsigned char *  answer,
int  len,
unsigned char *  fullanswer 
) [static]

Definition at line 113 of file srv.c.

References AST_LIST_INSERT_BEFORE_CURRENT, AST_LIST_INSERT_TAIL, AST_LIST_TRAVERSE_SAFE_BEGIN, AST_LIST_TRAVERSE_SAFE_END, srv_context::entries, srv_context::have_weights, srv_entry::list, parse_srv(), srv_entry::priority, and srv_entry::weight.

Referenced by ast_get_srv(), and ast_srv_lookup().

00114 {
00115    struct srv_context *c = (struct srv_context *) context;
00116    struct srv_entry *entry = NULL;
00117    struct srv_entry *current;
00118 
00119    if (parse_srv(answer, len, fullanswer, &entry))
00120       return -1;
00121 
00122    if (entry->weight)
00123       c->have_weights = 1;
00124 
00125    AST_LIST_TRAVERSE_SAFE_BEGIN(&c->entries, current, list) {
00126       /* insert this entry just before the first existing
00127          entry with a higher priority */
00128       if (current->priority <= entry->priority)
00129          continue;
00130 
00131       AST_LIST_INSERT_BEFORE_CURRENT(entry, list);
00132       entry = NULL;
00133       break;
00134    }
00135    AST_LIST_TRAVERSE_SAFE_END;
00136 
00137    /* if we didn't find a place to insert the entry before an existing
00138       entry, then just add it to the end */
00139    if (entry)
00140       AST_LIST_INSERT_TAIL(&c->entries, entry, list);
00141 
00142    return 0;
00143 }


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