#include <string.h>

int __dns_parse(const unsigned char* r, int rlen,
                int (*callback)(void*, int, const void*, int, const void*), void* ctx) {
    int qdcount, ancount;
    const unsigned char* p;
    int len;

    if (rlen < 12)
        return -1;
    if ((r[3] & 15))
        return 0;
    p = r + 12;
    qdcount = r[4] * 256 + r[5];
    ancount = r[6] * 256 + r[7];
    if (qdcount + ancount > 64)
        return -1;
    while (qdcount--) {
        while (p - r < rlen && *p - 1U < 127)
            p++;
        if (*p > 193 || (*p == 193 && p[1] > 254) || p > r + rlen - 6)
            return -1;
        p += 5 + !!*p;
    }
    while (ancount--) {
        while (p - r < rlen && *p - 1U < 127)
            p++;
        if (*p > 193 || (*p == 193 && p[1] > 254) || p > r + rlen - 6)
            return -1;
        p += 1 + !!*p;
        len = p[8] * 256 + p[9];
        if (p + len > r + rlen)
            return -1;
        if (callback(ctx, p[1], p + 10, len, r) < 0)
            return -1;
        p += 10 + len;
    }
    return 0;
}