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round robin DNS without Ares only takes first IP

From: A Nonymous <anon_at_ymous.none>
Date: Mon, 25 Apr 2005 12:28:37 +0200

Daniel Stenberg wrote:

>> How frequently does libCurl ask the DNS server? In other words: How
>> frequently is there a chance to get a different order?
> Ah, very good point. I didn't think of the DNS cache.
> It caches the entries in there for 60 seconds by default (and as long
> as the entry is "in use") and during that period it will use the same
> address order... Of course, as long as it re-uses the same connection
> it will also remain using that same address (as then it won't even
> check its IP address again).
> I guess this calls for a shuffle function to use when using cached
> results.
> Anyone up for making a patch?

The following is an excerpt of hostip.c
Would you find it appropriate to check an option set in the session data
and randomize the entryies before assigning them in
dns->addr = addr; /* this is the address(es) */

struct Curl_dns_entry *
Curl_cache_addr(struct SessionHandle *data,
                Curl_addrinfo *addr,
                char *hostname,
                int port)
  char *entry_id;
  size_t entry_len;
  struct Curl_dns_entry *dns;
  struct Curl_dns_entry *dns2;
  time_t now;

  /* Create an entry id, based upon the hostname and port */
  entry_id = create_hostcache_id(hostname, port);
  /* If we can't create the entry id, fail */
  if (!entry_id)
    return NULL;
  entry_len = strlen(entry_id);

  /* Create a new cache entry */
  dns = (struct Curl_dns_entry *) malloc(sizeof(struct Curl_dns_entry));
  if (!dns) {
    return NULL;

  dns->inuse = 0; /* init to not used */
  dns->addr = addr; /* this is the address(es) */

  /* Store the resolved data in our DNS cache. This function may return a
     pointer to an existing struct already present in the hash, and it may
     return the same argument we pass in. Make no assumptions. */
  dns2 = Curl_hash_add(data->hostcache, entry_id, entry_len+1, (void *)dns);
  if(!dns2) {
    /* Major badness, run away. */
    return NULL;
  dns = dns2;

  dns->timestamp = now; /* used now */
  dns->inuse++; /* mark entry as in-use */

  /* free the allocated entry_id again */

  return dns;
Received on 2005-04-25