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

["Derek MacDonald" <derek@xxxxxxxx>]

I have changed DnsResult in my async-xten branch to fix a race condition;
I'll try to merge that back in today or tonight.

--Derek

> -----Original Message-----
> From: resiprocate-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:resiprocate-
> devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Scott Godin
> Sent: Monday, December 06, 2004 6:24 AM
> To: 'kaiduan xie'; Scott Godin; resiprocate-devel@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [reSIProcate] Repost: DNS assert in
> TransactionState::handle() while unplugging the network cable
> 
> I see.  However, I'm not convinced that the change you recommended is the
> best solution.  In the trap scenario you mentioned, handle() gets calls
> synchronously because of the socket failure.  But... what if processHost
> is
> called asynchronously with some error status code and there are valid DNS
> results to return from the other queries - in this case setting to
> Finished
> may not be the best approach.
> 
> The proper solution will likely involve either making sure handle() is
> never
> called synchronously (from DnsResult::lookup()) or making sure mDnsResult
> is
> set in Transaction state before lookup() is called.
> 
> Can someone who is more familiar with this DnsResult code - please look
> into
> what the appropriate fix would be?
> 
> Thanks,
> 
> Scott
> 
> -----Original Message-----
> From: kaiduan xie [mailto:kaiduanx@xxxxxxxx]
> Sent: Friday, December 03, 2004 3:24 PM
> To: Scott Godin; resiprocate-devel@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [reSIProcate] Repost: DNS assert in TransactionState::handle(
> )
> while unplugging the network cable
> 
> Scott,
> 
> The case is after unplugging the network cable, the
> call stack looks like as follow,
> 
> mDnsResult =
> mController.mTransportSelector.dnsResolve(sip, this);
>  -> TransportSelector::dnsResolve()
>     ...
>     -> ares_gethostbyname()
>        ...
>        ->ares__send_query(), and in this function
>          open_udp_socket() failed immediately due to
> no network connection !!!!
>          ....
>           -> ares::end_query()
>              ->DnsResult::aresHostCallback()
>                 ->DnsResult::processHost(), the status
> of ares query is 4 (ARES_ENOTFOUND).
> without the change, it will go to
> TransactionState::handle(), since the mDnsResult() was
> not yet assigned, the assert(mDnsResult) failed. In
> simple words,
> 
> mDnsResult =
> mController.mTransportSelector.dnsResolve(sip, this);
>    ---> TransactionState::handle(),
> TransactionState::handle() function was called BEFORE
> mDnsResult was assigned!!!
> 
> Hope this time it is clear.
> 
> kaiduan
> 
> 
> 
>  --- Scott Godin <slgodin@xxxxxxxxxxxx> wrote:
> > Kaidun,
> >
> > If status != ARES_SUCCESS, then should mSrvCount ==
> > 0 and mResults should be
> > empty.  If that is the case then the state is set to
> > Finished and it just
> > returns.  Did you see a case where status !=
> > ARES_SUCCESS and mSrvCount !=
> > 0?
> >
> > I commited a change for the init_by_defaults issue.
> >
> > Thanks,
> >
> > Scott
> >
> > -----Original Message-----
> > From: kaiduan xie [mailto:kaiduanx@xxxxxxxx]
> > Sent: Thursday, November 25, 2004 11:51 PM
> > To: resiprocate-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: [reSIProcate] Repost: DNS assert in
> > TransactionState::handle()
> > while unplugging the network cable
> >
> > 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
> >
> >
> >
> >
> ______________________________________________________________________
> >
> > Post your free ad now! http://personals.yahoo.ca
> > _______________________________________________
> > resiprocate-devel mailing list
> > resiprocate-devel@xxxxxxxxxxxxxxxxxxx
> >
> https://list.sipfoundry.org/mailman/listinfo/resiprocate-devel
> >
> 
> ______________________________________________________________________
> Post your free ad now! http://personals.yahoo.ca
> _______________________________________________
> resiprocate-devel mailing list
> resiprocate-devel@xxxxxxxxxxxxxxxxxxx
> https://list.sipfoundry.org/mailman/listinfo/resiprocate-devel