Error while authenticating. Unexpected Maximum QoS value: 2

[jaimestuardo]

Hello.

I have these options to connect to my own broker:

_options = new MqttClientOptionsBuilder()
                    .WithClientId(ClientID)
                    .WithTcpServer(Globals.BROKER_ADDRESS, Globals.BROKER_PORT)
                    .WithCredentials(Globals.BROKER_USER, Globals.BROKER_PASSWORD) 
                    .WithProtocolVersion(MQTTnet.Formatter.MqttProtocolVersion.V500) // Use MQTT version 5.0
                    .WithTlsOptions(o =>
                    {
                        o.UseTls(true);
                        o.WithAllowUntrustedCertificates(false);
                        o.WithIgnoreCertificateChainErrors(false);
                        o.WithIgnoreCertificateRevocationErrors(false);

                        o.WithCertificateValidationHandler(_ => true);

                        Assembly assembly = Assembly.GetExecutingAssembly();

                        byte[]? certPubicKeyData = null;
                        using (MemoryStream mem = new())
                        {
                            assembly.GetManifestResourceStream("MqttClient.Certs.client.key")?.CopyTo(mem);

                            certPubicKeyData = mem.ToArray();
                        }

                        byte[]? certClientData = null;
                        using (MemoryStream mem = new())
                        {
                            assembly.GetManifestResourceStream("MqttClient.Certs.client.crt")?.CopyTo(mem);

                            certClientData = mem.ToArray();
                        }

                        byte[]? certRootData = null;
                        using (MemoryStream mem = new())
                        {
                            assembly.GetManifestResourceStream("MqttClient.Certs.root.crt")?.CopyTo(mem);

                            certRootData = mem.ToArray();
                        }

                        var rootCert = new X509Certificate2(certRootData);
                        var clientCert = new X509Certificate2(certClientData);
                        //var clientKey= new X509Certificate2(certPubicKeyData);
                        o.WithClientCertificates([rootCert, clientCert]);
                        o.WithSslProtocols(System.Security.Authentication.SslProtocols.Tls12);
                    })
                    .WithKeepAlivePeriod(TimeSpan.FromSeconds(60))
                    .WithWillQualityOfServiceLevel(MqttQualityOfServiceLevel.ExactlyOnce)
                    .WithCleanStart(true)
                    .WithSessionExpiryInterval(Globals.BROKER_SESSION_INTERVAL)
                    .Build();

When I try to connect the Disconnected handler is called with this exception:

**

Error while authenticating. Unexpected Maximum QoS value: 2

**

I tried even with MqttQualityOfServiceLevel.AtLeastOnce but no avail. Always the same error with the same number.

Is there a way to solve this without editing MQTTnet source code??

Digging inside the source code, I have found:

public MqttQualityOfServiceLevel ReadMaximumQoS()
{
	var value = _body.ReadByte();
	if (value > 1)
	{
		throw new MqttProtocolViolationException($"Unexpected Maximum QoS value: {value}");
	}

	return (MqttQualityOfServiceLevel)value;
}

I think this if (value > 1) is wrong. It should be if (value > 2)

Thanks
Jaime

[MattBrittan]

Responded to OP on stackoverflow (this issue is a copy/paste from there). Server in use is CrystalMQ and this server appears to breach the MQTTV5 spec requirement that Maximum QoS valid values are 0 or 1 only (it sends 2 - verified via wireshark). I believe that MQTTNet is behaving correctly when it rejects this.

Also appears to be a duplicate of #1056.

Update from OP on stackoverflow: "I have contacted CrystalMQ provider, and in fact, they are fixing the issue now."

Further update: the authors of crystalmq have acknowledged the issue and are realising a fix (very quick response!).