Fix connection timeout issue when try combine MX + A records for specfic DNS when A record not exists

[alexander-schranz]

Copied from #408

---

I have a IONOS and google cloud server and some A records fail to resolve the DNS_A + DNS_MX part:

php -r 'require_once("vendor/autoload.php"); $dnsCheckValidation = new \Egulias\EmailValidator\Validation\DNSCheckValidation(); var_dump($dnsCheckValidation->isValid("[email protected]", new \Egulias\EmailValidator\EmailLexer())); var_dump($dnsCheckValidation->getError());'

Locally all works like expected.

PS: Tried today a Hetzner Cloud server which has the same issue. I also tried directly the PHP:

php -r 'var_dump(dns_get_record("adif.es", DNS_A + DNS_MX));'

And it fails. Did found out the used DNS and tried dig command which ends in:

dig @185.12.64.2 +short A adif.es

Goes into ;; connection timed out; no servers could be reache

while over google it not errors just return nothing what is expected as only a MX record exists:

dig @8.8.8.8 +short A adif.es

[alexander-schranz]

unsure when we should return UnableToGetDNSRecord if one DNS lookup failed or when all failed?

[alexander-schranz]

is this expected as soon as one record doesn't pass validateMXRecord it marks the domain as failed? Didn't found any issue with it but thought about if we should do instead of 3 lookup check after every lookup if we already found a valid dns record and early return true. But that would mean this line would not work as expected that it early return false.

[alexander-schranz]

personally I would expect something like this:

        // For each DNS record
        foreach ($dnsRecords as $dnsRecord) {
            if ($this->validateMXRecord($dnsRecord)) {
                return true; // do not check all domains
            }
            
            //if (empty($this->mxRecords)) {
            //    $this->warnings[NoDNSMXRecord::CODE] = new NoDNSMXRecord();
            // }
        }

        return false;

and then do something like todo A and AAAA check only when MX failed:

        $mxRecordsResult = $this->dnsGetRecord->getRecords($host, DNS_MX);

        if (! $mxRecordsResult->withError()
+           && $this->validateMxRecords($mxRecordsResult->getRecords())) {
-            $dnsRecords = $mxRecordsResult->getRecords();
+            return true;
        }

        // Combined check for A+MX can fail with connection timed out, even in the presence of valid MX record
        $aRecordsResult = $this->dnsGetRecord->getRecords($host, DNS_A);

        if (! $aRecordsResult->withError()
+           && $this->validateMxRecords($aRecordsResult->getRecords())) {
-            $dnsRecords = array_merge($dnsRecords, $aRecordsResult->getRecords());
+            return true;
        }

        // Combined check for A+MX+AAAA can fail with SERVFAIL, even in the presence of valid A/MX records
        $aaaaRecordsResult = $this->dnsGetRecord->getRecords($host, DNS_AAAA);

        if (! $aaaaRecordsResult->withError()
+           && $this->validateMxRecords($aaaaRecordsResult->getRecords())) {
-            $dnsRecords = array_merge($dnsRecords, $aaaaRecordsResult->getRecords());
+            return true;
        }
        
+        if ($mxRecordsResult->withError()
+            && $aRecordsResult->withError()
+            && $aaaaRecordsResult->withError()
+        ) {
+            $this->error = new InvalidEmail(new UnableToGetDNSRecord(), '');
+            return false;
+        }
+        if ([] === $mxRecordsResult->getRecords()
+            && [] === $aRecordsResult->getRecords()
+            && [] === $aaaaRecordsResult->getRecords()
+        ) {
+            $this->error = new InvalidEmail(new ReasonNoDNSRecord(), '');
+            return false;
+        }

+        $this->warnings[NoDNSMXRecord::CODE] = new NoDNSMXRecord();
        
        return false;

but I'm not deep into this Lib or DNS records and maybe the early return false make sense here to avoid something unexpectly happening.

[egulias]

The general strategy of the lib is fail fast . Now for this case, given that there are network roundtrips was to "confirm fase" if that make sense. Hence not checking all records, with one we do have a valid MX. Happy to change if you believe will improve accuracy.

With a more in depth validation like your proposal, I agree to the general idea you are suggesting on this comment: we go from more accurate to less accurate and we short-circuit when we find a match.

Implementation wise, I'd go for something like

        if (! $mxRecordsResult->withError()
            && $this->validateMxRecords($mxRecordsResult->getRecords())) {
             $dnsRecords = $mxRecordsResult->getRecords();
              return true;
        }
       // We know there are no MX records already
       $this->warnings[NoDNSMXRecord::CODE] = new NoDNSMXRecord();
      //If you feel like so, you can create new warnings for each missing DNS record
      //...

     //do the logic for error setting here
     $this->setError($mxRecordsResult, $aRecordsResult, $aaaaRecordsResult)

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[egulias]

Thanks for the PR @alexander-schranz , did a comment on your thoughts. I agree with them, just added some notes.

[egulias]

The general strategy of the lib is fail fast . Now for this case, given that there are network roundtrips was to "confirm fase" if that make sense. Hence not checking all records, with one we do have a valid MX. Happy to change if you believe will improve accuracy.

With a more in depth validation like your proposal, I agree to the general idea you are suggesting on this comment: we go from more accurate to less accurate and we short-circuit when we find a match.

Implementation wise, I'd go for something like

        if (! $mxRecordsResult->withError()
            && $this->validateMxRecords($mxRecordsResult->getRecords())) {
             $dnsRecords = $mxRecordsResult->getRecords();
              return true;
        }
       // We know there are no MX records already
       $this->warnings[NoDNSMXRecord::CODE] = new NoDNSMXRecord();
      //If you feel like so, you can create new warnings for each missing DNS record
      //...

     //do the logic for error setting here
     $this->setError($mxRecordsResult, $aRecordsResult, $aaaaRecordsResult)

[egulias]

Please check Pslam, its complaining :)