Fixes 16

[baranyaib90]

Hi Aaron,
here we go again. I have a few changes:

1. @stangri faced a few divide by 0 crashes because of my new code in DNS truncation logic. Hopefully that got fixed in this pack.
2. I have fixed a few warnings I met while compiling in Alpine container.
3. cmake version requirement raised becaused of deprecation warning.
4. I made some clang tidy changes, because I had enough of NOLINT comments in code. I hope it is OK for you.

Take your time.
Best regards,
Balázs

[baranyaib90]

Hy @aarond10, any update?

[aarond10]

Oh, sorry! I reviewed but didn't merge.

[aarond10]

Do you think we should simplify this whole function to something like this (nb: untested)?

while (*buflen > 0) {
    ares_status_t status = ares_dns_parse((const unsigned char *)buf, *buflen, 0, &dnsrec);
    if (status != ARES_SUCCESS) {
      WLOG("Failed to parse DNS response: %s", ares_strerror((int)status));
      return;
    }
    int32_t packet_len = *buflen;
    while (packet_len > size_limit) {
        size_t current_count = ares_dns_record_rr_cnt(dnsrec, ARES_DNS_SECTION_ANSWER);
        if (current_count <= 1) { // Stop if we are about to delete the last record
            ELOG("Cannot trim any more records. Still too large.");
            break;
        }

        // Get the last record
        const ares_dns_rr_t *last_record = ares_dns_record_rr_get_const(dns_record, ARES_DNS_SECTION_ANSWER, current_count - 1);
        if (last_record == NULL) {
            printf("Error finding last record.\n");
            break;
        }

        // Estimate the size of the record we are about to delete
        size_t size_to_remove = 10 + strlen(lat_record->name) + 1 + last_record->rdata_len;

        status = ares_dns_record_rr_del(dns_record, ARES_DNS_SECTION_ANSWER, current_count - 1);
        if (status != ARES_SUCCESS) {
            ELOG("Error deleting record: %s", ares_strerror(status));
            break;
        }
        
        // Subtract the estimated size from our total
        // Note: This is an approximation. The actual size reduction
        // might differ slightly due to name compression effects.
        packet_len -= size_to_remove;
    }
    status = ares_dns_record_write_packet(dnsrec, buf, buflen);
}
...

[aarond10]

I still think this might be a good idea...

[baranyaib90]

Hi, I will check later more deeply, but this code looks to be AI generated with lots of mistakes:

• Underlying structure of ares_dns_rr_t is not reachable via public API and
• ares_dns_rr_t does not even have rdata_len.

This was my bigges issue with truncation: you can't know trough public API how large the record is that you intend to remove.
That is why I suppose that records are even sized (not true for TXT records obviously) and I'm using ratio-based estimation how much should be removed. If the DNS response would be still over the limit, I'm starting to aggressively reduce the size by dropping half of the records all the time until limit is reached or 1 remains (because even for TXT record, the maximum string limit is 255 char, so should fit in minimum 512).
I try not to waste CPU time by calling ares_dns_write() way too many times, but with current public API of c-ares there is no better option.
I agree, that current function is large and complicated, but at lest it seems to work and I would better not touch it until there is an issue with it.
Br, Balázs