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I'm trying to implement a simple DNS SRV query by using res_query. My code for the res_query part is following:

char* target;
short* port;

union {
    HEADER hdr;
    u_char buf[1024];
} response;

ns_msg handle;
ns_rr rr;
u_char buf[256], *p;
int t, len, priority, weight;

if ((len = res_query(query, C_IN, ns_t_srv, (u_char *)&response, sizeof(response))) <0 ) {
    cout << "res_query returned -1, no answer" << endl;
    return 0;

This is just a part of the code, but I guess there's all the required things to do the res_query. Every time I execute the SRV query, the res_query returns '-1', meaning it fails. Is the problem in my res_query or am I doing something else wrong?

I've tried to do the SRV query to www.example.com.

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1 Answer

up vote 0 down vote accepted

res_query will return -1 if no matching record is found.

Apart from that your code works fine for me, although OSX requires ns_c_in instead of C_IN.

Try testing with _nicname._tcp.us. instead of www.example.com.

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I've tried to do the SRV query to several domains now and it seems that it's just random when some sites return the SRV record. The suggested _nicname._tcp.us first returned nothing, but after sometime it gave me an answer. The same happened when I tried to do the SRV query with dig and nslookupcommands. I thought that every domain returns at least something when they get the SRV query. Also I found some other suggested sites like _sip._udp_columbia.edu and it behaves exactly the same way: Sometimes it returns the record and sometimes it doesn't. –  zaplec Mar 2 '12 at 7:36
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