diff options
| -rw-r--r-- | include/asterisk/srv.h | 7 | ||||
| -rw-r--r-- | main/srv.c | 186 |
2 files changed, 150 insertions, 43 deletions
diff --git a/include/asterisk/srv.h b/include/asterisk/srv.h index 2a98c69f6..b15ebdc5f 100644 --- a/include/asterisk/srv.h +++ b/include/asterisk/srv.h @@ -26,9 +26,10 @@ /*! \file srv.h \brief Support for DNS SRV records, used in to locate SIP services. - \note Note: The Asterisk DNS SRV record support is broken, it only - supports the first DNS SRV record and will give no load - balancing or failover support. + \note Note: This SRV record support is very minimal; it will only + return the first (lowest priority) answer that is received, and + has no provisions for the 'weight' elements of the records or + retrying if the first returned result fails. */ /*! Lookup entry in SRV records Returns 1 if found, 0 if not found, -1 on hangup diff --git a/main/srv.c b/main/srv.c index 4fe85a070..898195dc1 100644 --- a/main/srv.c +++ b/main/srv.c @@ -52,90 +52,196 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$") #include "asterisk/dns.h" #include "asterisk/options.h" #include "asterisk/utils.h" +#include "asterisk/linkedlists.h" #ifdef __APPLE__ #undef T_SRV #define T_SRV 33 #endif -struct srv { +struct srv_entry { unsigned short priority; unsigned short weight; - unsigned short portnum; -} __attribute__ ((__packed__)); + unsigned short port; + unsigned int weight_sum; + AST_LIST_ENTRY(srv_entry) list; + char host[1]; +}; -static int parse_srv(char *host, int hostlen, int *portno, unsigned char *answer, int len, unsigned char *msg) +struct srv_context { + unsigned int have_weights:1; + 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; - struct srv *srv = (struct srv *)answer; char repl[256] = ""; + struct srv_entry *entry; - if (len < sizeof(struct srv)) { - printf("Length too short\n"); + if (len < sizeof(*srv)) return -1; - } - answer += sizeof(struct srv); - len -= sizeof(struct srv); - if ((res = dn_expand(msg, answer + len, answer, repl, sizeof(repl) - 1)) < 0) { + 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; } - if (res && strcmp(repl, ".")) { - ast_verb(3, "parse_srv: SRV mapped to host %s, port %d\n", repl, ntohs(srv->portnum)); - if (host) { - ast_copy_string(host, repl, hostlen); - host[hostlen-1] = '\0'; - } - if (portno) - *portno = ntohs(srv->portnum); - return 0; - } - return -1; -} -struct srv_context { - char *host; - int hostlen; - int *port; -}; + /* 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_context *c = (struct srv_context *) context; + struct srv_entry *entry = NULL; + struct srv_entry *current; - if (parse_srv(c->host, c->hostlen, c->port, answer, len, fullanswer)) { - ast_log(LOG_WARNING, "Failed to parse srv\n"); + 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(&c->entries, entry, list); + entry = NULL; + break; } + AST_LIST_TRAVERSE_SAFE_END; - if (!ast_strlen_zero(c->host)) - return 1; + /* 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_REMOVE_CURRENT(&context->entries, list); + AST_LIST_INSERT_TAIL(&temp_list, current, 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_REMOVE_CURRENT(&temp_list, list); + AST_LIST_INSERT_TAIL(&newlist, current, list); + } + 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_get_srv(struct ast_channel *chan, char *host, int hostlen, int *port, const char *service) { - struct srv_context context; + struct srv_context context = { .entries = AST_LIST_HEAD_NOLOCK_INIT_VALUE }; + struct srv_entry *current; int ret; - context.host = host; - context.hostlen = hostlen; - context.port = port; - 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); - if (ret <= 0) { + /* 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); + if (option_verbose > 3) { + ast_verbose(VERBOSE_PREFIX_3 "ast_get_srv: SRV lookup for '%s' mapped to host %s, port %d\n", + service, host, *port); + } + } else { host[0] = '\0'; *port = -1; - return ret; } + + while ((current = AST_LIST_REMOVE_HEAD(&context.entries, list))) + ast_free(current); + return ret; } |