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"

Include dependency graph for srv.c:

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)
	Lookup entry in SRV records Returns 1 if found, 0 if not found, -1 on hangup.

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 marks.nosp@m.ter@.nosp@m.digiu.nosp@m.m.co.nosp@m.m

See also AstENUM

Note: Funding provided by nic.at

Definition in file srv.c.

Function Documentation

◆ ast_get_srv()

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 260 of file srv.c.

{
    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;
}

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

Referenced by ast_get_ip_or_srv_with_preference().

◆ ast_srv_cleanup()

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 248 of file srv.c.

{
    const char *host;
    unsigned short port;
 
    if (*context) {
        /* We have a context to clean up. */
        while (!(ast_srv_lookup(context, NULL, &host, &port))) {
        }
    }
}

References ast_srv_lookup(), srv_entry::host, NULL, and srv_entry::port.

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

◆ ast_srv_get_nth_record()

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 309 of file srv.c.

{
    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;
}

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

Referenced by srv_result_read().

◆ ast_srv_get_record_count()

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 304 of file srv.c.

{
    return context->num_records;
}

Referenced by srv_result_read().

◆ ast_srv_lookup()

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.

{
    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;
    }
}

References ast_calloc, ast_free, AST_LIST_EMPTY, AST_LIST_FIRST, AST_LIST_HEAD_INIT_NOLOCK, AST_LIST_NEXT, AST_LIST_REMOVE_HEAD, AST_LIST_TRAVERSE, ast_search_dns(), srv_entry::host, srv_entry::list, NULL, srv_entry::port, process_weights(), service, and srv_callback().

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

◆ parse_srv()

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.

{
    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;
}

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

Referenced by srv_callback().

◆ process_weights()

static void process_weights ( struct srv_context * context )

static

Definition at line 150 of file srv.c.

{
    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);
}

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(), current, and srv_entry::priority.

Referenced by ast_get_srv(), and ast_srv_lookup().

◆ srv_callback()

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

static

Definition at line 113 of file srv.c.

{
    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;
}

References answer(), AST_LIST_INSERT_BEFORE_CURRENT, AST_LIST_INSERT_TAIL, AST_LIST_TRAVERSE_SAFE_BEGIN, AST_LIST_TRAVERSE_SAFE_END, c, current, len(), srv_entry::list, NULL, parse_srv(), srv_entry::priority, and srv_entry::weight.

Referenced by ast_get_srv(), and ast_srv_lookup().

Data Structures

Functions

Detailed Description

Function Documentation

◆ ast_get_srv()

◆ ast_srv_cleanup()

◆ ast_srv_get_nth_record()

◆ ast_srv_get_record_count()

◆ ast_srv_lookup()

◆ parse_srv()

◆ process_weights()

◆ srv_callback()