Re: DNSServiceQueryRecord callback won't do

• Subject: Re: DNSServiceQueryRecord callback won't do
• From: Marc Krochmal <email@hidden>
• Date: Tue, 2 Nov 2004 12:51:36 -0800
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Olger,

So I feel that the next code should do the same:

    const char* fullname = "machost._afpovertcp._tcp.local.";
    //const char* fullname = "_afpovertcp._tcp.local";
    printf("looking for %s\n", fullname);
    DNSServiceErrorType err;
    DNSServiceRef client = NULL;

err = DNSServiceQueryRecord(&client,0,0,fullname,ns_t_ptr,ns_c_in,query_rep ly,NULL);
if (err != kDNSServiceErr_NoError) {
printf("register returned failure:%d\n", err);
}

    DNSServiceProcessResult(client);
    DNSServiceRefDeallocate(client);

The DNSServiceQueryRecord gives a result for a query :_afpovertcp._tcp.local. (as found in the comment)
(it actually returns an rrtype = 12 not a rrtype = 1)

But it doesn't work for a single service name. (e.g: machost.....) it seems.

The documentation states to use QueryRecord if you have shared services. I am working on a service that could be available multiple times and the rendezvous based client can select on of them (you can make some algorithms which to pick)

It's not clear what you're trying to do. Have you tried using DNSServiceBrowse()? Are you using DNSServiceRegister() to advertise your services?

I use DNSServiceRegister to advertise my services and I need a mechanism to find them back (but there might be more than one of them with the same name

(id) Looking at the documentation on DNSServiceBrowse, I would say that it gives me all services (as a char* serviceName) that match to the patterns of a servicetype (like _http._tcp or things alike) in a certain domain.
I already know the servicename I am looking for, so a query is more like MyService._http._tcp.local. and do not need to Browse as far as I can see. So Resolv or Query seem to do the job, but according to the documentation you need Query if you expect to find more than 1 MyService._http._tcp.local.

Is it possible to have shared services like that ? and how to use QueryRecord to get these ?
Does the DDNS close the connection after the answer or can more answers be expected based on the query at a later time ?

In your example code, you're calling DNSServiceRefDeallocate() immediately after getting the first answer, which closes the connection. You should use select() and put the socket FD in your select() loop so you can receive notifications asynchronously. You should only call DNSServiceRefDeallocate() when you no longer wish to receive notifications.

Yes, I know, it is just a codesnippet put together to show that the same input for Resolve or for Query give different answers (Resolve gives a host + port back of the MyService._http._tcp.local. and Query stays waiting for the answer as it seems not to get the right answer back (or it does not give the right query)

Best Regards,

-Marc

On Nov 1, 2004, at 8:56 PM, Olger Warnier wrote:

Hi List,

I found quite an extensive discussion on the use of DNSServiceQueryRecord
and the callback found in:

Subject: DNSServiceQueryRecord (was Re: FreeBSD and Solaris)
From: Eric Wing <email@hidden>
Date: Thu, 15 Jul 2004 20:50:15 -0700 (PDT)

it is: http://lists.apple.com/archives/rendezvous-dev/2004/Jul/ msg00095.html

But it ends with the remark that the callback doesn't seem to work.
On a linux system, I have a situation like that:

When I use DNSServiceResolve(...) and call the DNSServiceProcessResult
(direct or with a select() loop), the service gets resolved and a hostname
+ port number is available.

But I'd like to use the DNSServiceQueryRecord instead with a seperate
select() loop to make it possible keep shared services.
Using DNSServiceQueryRecord with and call the DNSServiceProcessResult
(again direct of with a select() loop), nothing happens.

I use exact the same servicename,type and domain for both and for the
rrtype and rrclass = 1;

In order to use the DNSServiceQueryRecord, do I need to do some
initialization or something ? Or to make my question a bit more generic.
Someone has any suggestions what could solve this ?

Kind Regards,

Olger

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