Wed Jan 27 20:02:50 2016

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_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 
)

Lookup entry in SRV records Returns 1 if found, 0 if not found, -1 on hangup Only do SRV record lookup if you get a domain without a port. If you get a port #, it's a DNS host name.

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 263 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, srv_context::entries, srv_context::have_weights, srv_entry::host, srv_entry::port, process_weights(), and srv_callback().

Referenced by ast_get_ip_or_srv(), and create_addr().

00264 {
00265    struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE };
00266    struct srv_entry *current;
00267    int ret;
00268 
00269    if (chan && ast_autoservice_start(chan) < 0) {
00270       return -1;
00271    }
00272 
00273    ret = ast_search_dns(&context, service, C_IN, T_SRV, srv_callback);
00274 
00275    if (context.have_weights) {
00276       process_weights(&context);
00277    }
00278 
00279    if (chan) {
00280       ret |= ast_autoservice_stop(chan);
00281    }
00282 
00283    /* TODO: there could be a "." entry in the returned list of
00284       answers... if so, this requires special handling */
00285 
00286    /* the list of entries will be sorted in the proper selection order
00287       already, so we just need the first one (if any) */
00288 
00289    if ((ret > 0) && (current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
00290       ast_copy_string(host, current->host, hostlen);
00291       *port = current->port;
00292       ast_free(current);
00293       ast_verb(4, "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n",
00294                 service, host, *port);
00295    } else {
00296       host[0] = '\0';
00297       *port = -1;
00298    }
00299 
00300    while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list))) {
00301       ast_free(current);
00302    }
00303 
00304    return ret;
00305 }

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 251 of file srv.c.

References ast_srv_lookup(), and srv_entry::port.

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

00252 {
00253    const char *host;
00254    unsigned short port;
00255 
00256    if (*context) {
00257       /* We have a context to clean up. */
00258       while (!(ast_srv_lookup(context, NULL, &host, &port))) {
00259       }
00260    }
00261 }

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 312 of file srv.c.

References AST_LIST_TRAVERSE, srv_context::entries, srv_entry::host, srv_context::num_records, srv_entry::port, srv_entry::priority, and srv_entry::weight.

Referenced by srv_result_read().

00314 {
00315    int i = 1;
00316    int res = -1;
00317    struct srv_entry *entry;
00318 
00319    if (record_num < 1 || record_num > context->num_records) {
00320       return res;
00321    }
00322 
00323    AST_LIST_TRAVERSE(&context->entries, entry, list) {
00324       if (i == record_num) {
00325          *host = entry->host;
00326          *port = entry->port;
00327          *priority = entry->priority;
00328          *weight = entry->weight;
00329          res = 0;
00330          break;
00331       }
00332       ++i;
00333    }
00334 
00335    return res;
00336 }

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 307 of file srv.c.

References srv_context::num_records.

Referenced by srv_result_read().

00308 {
00309    return context->num_records;
00310 }

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 206 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(), process_weights(), and srv_callback().

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

00207 {
00208    struct srv_entry *cur;
00209 
00210    if (*context == NULL) {
00211       if (!(*context = ast_calloc(1, sizeof(struct srv_context)))) {
00212          return -1;
00213       }
00214       AST_LIST_HEAD_INIT_NOLOCK(&(*context)->entries);
00215 
00216       if ((ast_search_dns(*context, service, C_IN, T_SRV, srv_callback)) < 0) {
00217          ast_free(*context);
00218          *context = NULL;
00219          return -1;
00220       }
00221 
00222       if ((*context)->have_weights) {
00223          process_weights(*context);
00224       }
00225 
00226       (*context)->prev = AST_LIST_FIRST(&(*context)->entries);
00227       *host = (*context)->prev->host;
00228       *port = (*context)->prev->port;
00229       AST_LIST_TRAVERSE(&(*context)->entries, cur, list) {
00230          ++((*context)->num_records);
00231       }
00232       return 0;
00233    }
00234 
00235    if (((*context)->prev = AST_LIST_NEXT((*context)->prev, list))) {
00236       /* Retrieve next item in result */
00237       *host = (*context)->prev->host;
00238       *port = (*context)->prev->port;
00239       return 0;
00240    } else {
00241       /* No more results */
00242       while ((cur = AST_LIST_REMOVE_HEAD(&(*context)->entries, list))) {
00243          ast_free(cur);
00244       }
00245       ast_free(*context);
00246       *context = NULL;
00247       return 1;
00248    }
00249 }

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

Definition at line 76 of file srv.c.

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

Referenced by srv_callback().

00077 {
00078    struct srv {
00079       unsigned short priority;
00080       unsigned short weight;
00081       unsigned short port;
00082    } __attribute__((__packed__)) *srv = (struct srv *) answer;
00083 
00084    int res = 0;
00085    char repl[256] = "";
00086    struct srv_entry *entry;
00087 
00088    if (len < sizeof(*srv))
00089       return -1;
00090 
00091    answer += sizeof(*srv);
00092    len -= sizeof(*srv);
00093 
00094    if ((res = dn_expand(msg, answer + len, answer, repl, sizeof(repl) - 1)) <= 0) {
00095       ast_log(LOG_WARNING, "Failed to expand hostname\n");
00096       return -1;
00097    }
00098 
00099    /* the magic value "." for the target domain means that this service
00100       is *NOT* available at the domain we searched */
00101    if (!strcmp(repl, "."))
00102       return -1;
00103 
00104    if (!(entry = ast_calloc(1, sizeof(*entry) + strlen(repl))))
00105       return -1;
00106    
00107    entry->priority = ntohs(srv->priority);
00108    entry->weight = ntohs(srv->weight);
00109    entry->port = ntohs(srv->port);
00110    strcpy(entry->host, repl);
00111 
00112    *result = entry;
00113    
00114    return 0;
00115 }

static void process_weights ( struct srv_context context  )  [static]

Definition at line 154 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(), srv_context::entries, srv_entry::priority, srv_entry::weight, and srv_entry::weight_sum.

Referenced by ast_get_srv(), and ast_srv_lookup().

00155 {
00156    struct srv_entry *current;
00157    struct srv_entries newlist = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
00158 
00159    while (AST_LIST_FIRST(&context->entries)) {
00160       unsigned int random_weight;
00161       unsigned int weight_sum;
00162       unsigned short cur_priority = AST_LIST_FIRST(&context->entries)->priority;
00163       struct srv_entries temp_list = AST_LIST_HEAD_NOLOCK_INIT_VALUE;
00164       weight_sum = 0;
00165 
00166       AST_LIST_TRAVERSE_SAFE_BEGIN(&context->entries, current, list) {
00167          if (current->priority != cur_priority)
00168             break;
00169 
00170          AST_LIST_MOVE_CURRENT(&temp_list, list);
00171       }
00172       AST_LIST_TRAVERSE_SAFE_END;
00173 
00174       while (AST_LIST_FIRST(&temp_list)) {
00175          weight_sum = 0;
00176          AST_LIST_TRAVERSE(&temp_list, current, list)
00177             current->weight_sum = weight_sum += current->weight;
00178 
00179          /* if all the remaining entries have weight == 0,
00180             then just append them to the result list and quit */
00181          if (weight_sum == 0) {
00182             AST_LIST_APPEND_LIST(&newlist, &temp_list, list);
00183             break;
00184          }
00185 
00186          random_weight = 1 + (unsigned int) ((float) weight_sum * (ast_random() / ((float) RAND_MAX + 1.0)));
00187 
00188          AST_LIST_TRAVERSE_SAFE_BEGIN(&temp_list, current, list) {
00189             if (current->weight < random_weight)
00190                continue;
00191 
00192             AST_LIST_MOVE_CURRENT(&newlist, list);
00193             break;
00194          }
00195          AST_LIST_TRAVERSE_SAFE_END;
00196       }
00197 
00198    }
00199 
00200    /* now that the new list has been ordered,
00201       put it in place */
00202 
00203    AST_LIST_APPEND_LIST(&context->entries, &newlist, list);
00204 }

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

Definition at line 117 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, parse_srv(), srv_entry::priority, and srv_entry::weight.

Referenced by ast_get_srv(), and ast_srv_lookup().

00118 {
00119    struct srv_context *c = (struct srv_context *) context;
00120    struct srv_entry *entry = NULL;
00121    struct srv_entry *current;
00122 
00123    if (parse_srv(answer, len, fullanswer, &entry))
00124       return -1;
00125 
00126    if (entry->weight)
00127       c->have_weights = 1;
00128 
00129    AST_LIST_TRAVERSE_SAFE_BEGIN(&c->entries, current, list) {
00130       /* insert this entry just before the first existing
00131          entry with a higher priority */
00132       if (current->priority <= entry->priority)
00133          continue;
00134 
00135       AST_LIST_INSERT_BEFORE_CURRENT(entry, list);
00136       entry = NULL;
00137       break;
00138    }
00139    AST_LIST_TRAVERSE_SAFE_END;
00140 
00141    /* if we didn't find a place to insert the entry before an existing
00142       entry, then just add it to the end */
00143    if (entry)
00144       AST_LIST_INSERT_TAIL(&c->entries, entry, list);
00145 
00146    return 0;
00147 }


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