iOS Resolve SRV Record without Domain - ios

Question

I am trying to resolve a SRV Record with my iOS App.
I have come so far that I indeed can resolve the DNS record.
This works only if the SRV Record Contains a valid Domain Ending.
Each Customer has its on domain so I can't hard Code the Domain.
Furthermore I don't want the User to specify a Domain Name. This would make the SRV record useless.
I hope Somebody can explain to me how the resolve an DNS Record without the Domain. Or Resolve the Domain first an the do the SRV query. Thanks a lot.
This Works: _sip._tls.mydomain.com
This Should be the Goal: _sip._tls
And please do not give me a suggestion for how to resolve _sip._tls
this is only a placeholder. My real SRV record is a custom record like "_myApplication._tcp" THX
- (void)updateDnsRecords
{
NSLog(#"DNS update");
DNSServiceRef sdRef;
DNSServiceErrorType err;
NSTimeInterval remainingTime = 3.0;
NSDate* startTime = [NSDate date];
err = DNSServiceQueryRecord(&sdRef, 0, 0,
"_sip._tls.mydomain.com",
kDNSServiceType_SRV,
kDNSServiceClass_IN,
processDnsReply,
&remainingTime);
// This is necessary so we don't hang forever if there are no results
int dns_sd_fd = DNSServiceRefSockFD(sdRef);
int nfds = dns_sd_fd + 1;
fd_set readfds;
int result;
while (remainingTime > 0)
{
FD_ZERO(&readfds);
FD_SET(dns_sd_fd, &readfds);
struct timeval tv;
tv.tv_sec = (time_t)remainingTime;
tv.tv_usec = (remainingTime - tv.tv_sec) * 1000000;
result = select(nfds, &readfds, (fd_set*)NULL, (fd_set*)NULL, &tv);
if (result == 1)
{
if (FD_ISSET(dns_sd_fd, &readfds))
{
err = DNSServiceProcessResult(sdRef);
if (err != kDNSServiceErr_NoError)
{
NSLog(#"There was an error reading the DNS SRV records.");
break;
}
}
}
else if (result == 0)
{
NSLog(#"DNS SRV select() timed out");
break;
}
else
{
if (errno == EINTR)
{
NSLog(#"DNS SRV select() interrupted, retry.");
}
else
{
NSLog(#"DNS SRV select() returned %d errno %d %s.", result, errno, strerror(errno));
break;
}
}
NSTimeInterval elapsed = [[NSDate date] timeIntervalSinceDate:startTime];
remainingTime -= elapsed;
}
DNSServiceRefDeallocate(sdRef);
}
static void processDnsReply(DNSServiceRef sdRef,
DNSServiceFlags flags,
uint32_t interfaceIndex,
DNSServiceErrorType errorCode,
const char* fullname,
uint16_t rrtype,
uint16_t rrclass,
uint16_t rdlen,
const void* rdata,
uint32_t ttl,
void* context
)
{
NSTimeInterval* remainingTime = (NSTimeInterval*)context;
// If a timeout occurs the value of the errorCode argument will be
// kDNSServiceErr_Timeout.
if (errorCode != kDNSServiceErr_NoError)
{
return;
}
// The flags argument will have the kDNSServiceFlagsAdd bit set if the
// callback is being invoked when a record is received in response to
// the query.
//
// If kDNSServiceFlagsAdd bit is clear then callback is being invoked
// because the record has expired, in which case the ttl argument will
// be 0.
if ((flags & kDNSServiceFlagsMoreComing) == 0)
{
*remainingTime = 0;
}
// Record parsing code below was copied from Apple SRVResolver sample.
NSMutableData * rrData = [NSMutableData data];
dns_resource_record_t * rr;
uint8_t u8;
uint16_t u16;
uint32_t u32;
u8 = 0;
[rrData appendBytes:&u8 length:sizeof(u8)];
u16 = htons(kDNSServiceType_SRV);
[rrData appendBytes:&u16 length:sizeof(u16)];
u16 = htons(kDNSServiceClass_IN);
[rrData appendBytes:&u16 length:sizeof(u16)];
u32 = htonl(666);
[rrData appendBytes:&u32 length:sizeof(u32)];
u16 = htons(rdlen);
[rrData appendBytes:&u16 length:sizeof(u16)];
[rrData appendBytes:rdata length:rdlen];
rr = dns_parse_resource_record([rrData bytes], (uint32_t) [rrData length]);
// If the parse is successful, add the results.
if (rr != NULL)
{
NSString *target;
target = [NSString stringWithCString:rr->data.SRV->target encoding:NSASCIIStringEncoding];
if (target != nil)
{
uint16_t priority = rr->data.SRV->priority;
uint16_t weight = rr->data.SRV->weight;
uint16_t port = rr->data.SRV->port;
char *adresse = rr->data.SRV->target;
NSLog(#"Prio:%hu",priority);
NSLog(#"weight:%hu",weight);
NSLog(#"port:%hu",port);
NSLog(#"adresse:%s",adresse);
NSLog(#"fullname:%s",fullname);
//[[FailoverWebInterface sharedInterface] addDnsServer:target priority:priority weight:weight port:port ttl:ttl]; // You'll have to do this in with your own method.
}
}
dns_free_resource_record(rr);
}