[reSIProcate] Repost: DNS assert in TransactionState::handle() while unplugging the network cable

[kaiduan xie <kaiduanx@xxxxxxxx>]

hi, all,

If the network connection is unplugged while running,
DNS assert failed at TransactionState.cxx #1282

TransactionState::handle(DnsResult* result)
{
   // got a DNS response, so send the current message
   StackLog (<< *this << " got DNS result: " <<
*result);

   if (mTarget.getType() == UNKNOWN_TRANSPORT) 
   {
    assert(mDnsResult);// failed here, xkd 
    ......
   }

Cullen also posted the same problem on 27 Aug, please
refer
http://list.sipfoundry.org/archive/resiprocate-devel/msg01316.html

After digging into the ares library and Dns related
class, I though I have found the reason, :).

In DnsResult::processHost()

void
DnsResult::processHost(int status, struct hostent*
result)
{
   StackLog (<< "DnsResult::processHost() " <<
status);
   
   // This function assumes that the A query that
caused this callback
   // is the _only_ outstanding DNS query that might
result in a
   // callback into this function
   if ( mType == Destroyed )
   {
      destroy();
      return;
   }

   if (status == ARES_SUCCESS)
   {
    .....
   }
   else
   {
      char* errmem=0;
      StackLog (<< "Failed async A query: " <<
ares_strerror(status, &errmem));
      ares_free_errmem(errmem);
      mType = Finished;//xkd-2004-11-25-begin
      // Just set the status as Finished, donot delete
or destroy it
     // It will be deleted in TransactionState's
destructor after receiving 408 (timeout)        
      return; //xkd-2004-11-25-end
   }

Also I found a mis-consideration in ares_init().
In init_by_defaults()

{
....
        num = 0;
        pIPAddr = &FixedInfo->DnsServerList;     
        while ( pIPAddr &&
strlen(pIPAddr->IpAddress.String) > 0)
        {
          num++;
          pIPAddr = pIPAddr ->Next;
        }
        channel->servers = malloc( (num) *
sizeof(struct server_state));
...
}

It is better to check the value of num, if num is
zero, i.e., no network connection, no DNS server, in
this case it should return error.

kaiduan



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