source: azure_iot_hub/trunk/musl-1.1.18/src/network/res_mkquery.c@ 388

#include <resolv.h>
#include <string.h>
#include <time.h>
#include "libc.h"

int __res_mkquery(int op, const char *dname, int class, int type,
        const unsigned char *data, int datalen,
        const unsigned char *newrr, unsigned char *buf, int buflen)
{
        int id, i, j;
        unsigned char q[280];
        struct timespec ts;
        size_t l = strnlen(dname, 255);
        int n;

        if (l && dname[l-1]=='.') l--;
        n = 17+l+!!l;
        if (l>253 || buflen<n || op>15u || class>255u || type>255u)
                return -1;

        /* Construct query template - ID will be filled later */
        memset(q, 0, n);
        q[2] = op*8 + 1;
        q[5] = 1;
        memcpy((char *)q+13, dname, l);
        for (i=13; q[i]; i=j+1) {
                for (j=i; q[j] && q[j] != '.'; j++);
                if (j-i-1u > 62u) return -1;
                q[i-1] = j-i;
        }
        q[i+1] = type;
        q[i+3] = class;

        /* Make a reasonably unpredictable id */
        clock_gettime(CLOCK_REALTIME, &ts);
        id = ts.tv_nsec + ts.tv_nsec/65536UL & 0xffff;
        q[0] = id/256;
        q[1] = id;

        memcpy(buf, q, n);
        return n;
}

weak_alias(__res_mkquery, res_mkquery);