Objective-C: DNS TXT Record

Question

I've been searching for a while without any success, how am I supposed to get a DNS TXT record for a domain in Objective-C?

My goal is to get the same output as: dig -t txt google.com +short

PS: No NSTask/pipping please! (I'm currently doing that but it's bad). The code can be written in C, I'll just write a wrapper later. I don't care about AppStore rules.

Thank you!

Answer 1

Use DNSServiceQueryRecord in dns_sd.h:

#import <dns_sd.h>

// ...

DNSServiceRef serviceRef;

DNSServiceQueryRecord(&serviceRef, 0, 0, "hmspl.de", kDNSServiceType_TXT,
                      kDNSServiceClass_IN, queryCallback, NULL);

DNSServiceProcessResult(serviceRef);
DNSServiceRefDeallocate(serviceRef);

// ...

static void queryCallback(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) {

    if (errorCode == kDNSServiceErr_NoError && rdlen > 1) {
        NSMutableData *txtData = [NSMutableData dataWithCapacity:rdlen];

        for (uint16_t i = 1; i < rdlen; i += 256) {
            [txtData appendBytes:rdata + i length:MIN(rdlen - i, 255)];
        }

        NSString *theTXT = [[NSString alloc] initWithBytes:txtData.bytes length:txtData.length encoding:NSASCIIStringEncoding];
        NSLog(@"%@", theTXT);
    }
}

See https://developer.apple.com/library/mac/#documentation/Networking/Reference/DNSServiceDiscovery_CRef/Reference/reference.html#//apple_ref/doc/c_ref/DNSServiceQueryRecord

Answer 2

can use like this code remove \x02 \x03, I removed \0x12 \0x17 use $man ascii check char result[256]={0}; dn_expand(rdata, rdata + rdlen, rdata, result, 256);

        NSMutableData *txtData = [NSMutableData dataWithCapacity:rdlen];

        char *p=(char*)rdata;

        for (uint16_t i = 0; i < rdlen; i++) {

            DLog(@"%c\n",*p);
            if (*p > 0x20) {
                [txtData appendBytes:p length:1];


            }
            p++;
        }