Incomplete packet error

[ShiSHcat]

Next Amp\Dns\DnsException: All query attempts failed for mozilla.cloudflare-dns.com: Unexpected error during resolution: Decode error: Incomplete packet (tried to read 12 bytes from index 0, Unexpected error during resolution: Decode error: Incomplete packet (tried to read 12 bytes from index 0 in /home/shishcat1/redacted/vendor/amphp/dns/lib/Rfc1035StubResolver.php:193 Stack trace:

0 [internal function]: Amp\Dns\Rfc1035StubResolver->Amp\Dns{closure}()

PHP 7.4.2 debian

[kelunik]

@ShiSHcat Can you reproduce this issue? Which DNS server are you using?

[ShiSHcat]

I'm not having this problem anymore.

[kelunik]

Thanks for reporting back!

[karelvasicek]

I had exactly the same problem (for different domain, of course). The problem was caused by:

• "not accessible" nameserver defined (as first server) in /etc/resolv.conf. There was some problems with DNS cache (the actual server was accessible, but somewhat refused connections) what resulted in following output (the output was shown immediately, so there was no timeout)

  host www.google.com nonworking.dns.server.ip
  ;; communications error to nonworking.dns.server.ip#53: connection refused
  ;; communications error to nonworking.dns.server.ip#53: connection refused
  ;; no servers could be reached

• under "standard" circumstances, connection to the nameserver times out ((the output was shown incrementally with considerable delay between each attempt)

  host www.google.com nonworking.dns.server.ip
  ;; communications error to nonworking.dns.server.ip#53: timed out
  ;; communications error to nonworking.dns.server.ip#53: timed out
  ;; no servers could be reached

• so the connection seems to be considered established and it does not timeout at https://github.com/amphp/dns/blob/c2bddbd80b3b80030cd7d3af591414e0dbc7a272/lib/Internal/Socket.php#L171
• https://github.com/amphp/dns/blob/c2bddbd80b3b80030cd7d3af591414e0dbc7a272/lib/Rfc1035StubResolver.php#L331 throws UnexpectedValueException ('Decode error: Incomplete packet (tried to read 12 bytes from index 0') that is received from vendor/daverandom/libdns/src/Decoder/Decoder.php:121 and is converted to DnsException by https://github.com/amphp/dns/blob/c2bddbd80b3b80030cd7d3af591414e0dbc7a272/lib/Internal/Socket.php#L89

• it seems to start working by replacing $response = yield $socket->ask($question, $this->config->getTimeout()); with following code, but I'm totally unsure if it's correct or not especially considering my poor library and async-logic knowledge - f.ex. if another unintended DnsException isn't newly caught, how the socket should be closed etc. In addition, potential infinite loop (when all servers are not accessible) must be secured. Thus I'm not creating PR, it's just a concept how the issue could be fixed.

                  try {
                      /** @var Message $response */
                      $response = yield $socket->ask($question, $this->config->getTimeout());
                  } catch (DnsException $e) {
                      if ($protocol === "udp") {
                          Loop::defer(function () use ($socket, $uri) {
                              unset($this->sockets[$uri]);
                              $socket->close();
                          });
  
                          $uri = $protocol . "://" . $nameservers[++$attempt % $nameserversCount];
                          $socket = yield $this->getSocket($uri);
  
                          continue;
                      }
                  }