Unable to connect to MQTT broker: MqttCommunicationException

[MattHoneycutt]

I'm getting a generic "Exception of type 'uPLibrary.Networking.M2Mqtt.Exceptions.MqttCommunicationException' was thrown." while trying to connect to an MQTT broker. I can connect to the broker just fine using MQTT.fx, and I can connect to another MQTT broker just fine using the M2MQTT libraries, so I'm thinking that the client isn't compatible with this particular broker for some reason.

Is there some way to get additional logging details or a deeper view into what's going wrong?

[xingzhougmu]

@MattHoneycutt I have similar issue. my broker is talking over ssl. On server side (broker side) I used self-signed cert signed by self-signed CA. On client side, I install the CA cert in the trusted authority. However, I always get the generic uPLibrary.Networking.M2Mqtt.Exceptions.MqttCommunicationException.

{uPLibrary.Networking.M2Mqtt.Exceptions.MqttCommunicationException: Exception of type 'uPLibrary.Networking.M2Mqtt.Exceptions.MqttCommunicationException' was thrown.
at uPLibrary.Networking.M2Mqtt.MqttClient.SendReceive(Byte[] msgBytes, Int32 timeout)
at uPLibrary.Networking.M2Mqtt.MqttClient.Connect(String clientId, String username, String password, Boolean willRetain, Byte willQosLevel, Boolean willFlag, String willTopic, String willMessage, Boolean cleanSession, UInt16 keepAlivePeriod)
at uPLibrary.Networking.M2Mqtt.MqttClient.Connect(String clientId, String username, String password)

The code to create the client is as below:

X509Certificate2 caCert = new X509Certificate2(Directory.GetCurrentDirectory() + "/Certs/Development/RootCA.crt");
                MqttClient client = new MqttClient(brokerHostName, 443, true, caCert, null, MqttSslProtocols.TLSv1_2);
string clientId = Guid.NewGuid().ToString();
client.Connect(clientId, userName, password);

By checking the network trace, it seems the SSL channel has been established. However, after some time (few seconds) the connection is failed with communication error.

[amguilmet]

I'm having this exact same issue, as well. I'm using Mosquitto 0.15, M2Mqtt 4.3.0 and MQTT.fx 1.5. When connecing with MQTT.fx, I can connect to mosquitto but only with v3.1. If I use v3.1.1 instead, it immediately looses the connection. When connecting to mosquitto via m2mqtt, I get the same error message in the logs as when I try MQTT.fx with v3.1.1.

`1527514650: New connection from 127.0.0.1.

1527514650: Invalid protocol "MQTT" in CONNECT from 127.0.0.1.
1527514650: Socket read error on client (null), disconnecting.`

Before the m2mqtt client throws the MqttCommunicationException exception, it pegs the CPU out at 100%

What I did to 'fix' this issue was force m2mqtt to use v3.1 with

client.ProtocolVersion = MqttProtocolVersion.Version_3_1

That seemed to make it work.

[ghost]

Hello, I'm also having this issue and the fix proposed by amguilmet didn't work. Does anyone have additional suggestions?

[benjamincoven]

Hello everyone, I am working on Unity for Hololens, and I am facing the same problem whatever the server is active or not. The problem only happens on Hololens and not in my desktop Unity Editor. Thank you.

[dillipdala]

Hello everyone
i am working with uPLibrary.Networking.M2Mqtt library to connect aws iot device but facing problem when try to connect IotMqttClient.Connect("teleConnect") .

var CaCert = X509Certificate.CreateFromCertFile(@"D:\Aws\root-CA.crt");
X509Certificate2 clientCert = new X509Certificate2(@"D:\Aws\04d500d157.pfx","password");

        MqttClient IotMqttClient = new MqttClient(AwsEndPoint, 8883, true, CaCert, clientCert, MqttSslProtocols.TLSv1_2);
           IotMqttClient.MqttMsgPublishReceived += Client_MqttMsgPublishReceived;
           IotMqttClient.MqttMsgSubscribed += Client_MqttMsgSubscribed;
        IotMqttClient.Connect("teleConnect");

Error:
An unhandled exception of type 'uPLibrary.Networking.M2Mqtt.Exceptions.MqttConnectionException' occurred in M2Mqtt.Net.dll

please help me
thank you

[rusty-boffin]

I'm also getting this exception - I'm trying to connect to www.mosquitto.org (without SSL) and get the exception 35 secs after the call to .Connect(). As well as this exception, when I try to close my WPF app, the window disappears by the process remains, and I have to kill it. The debugger shows me that there's a worker thread stuck in Socket.Receive().
The interesting thing is that this doesn't always happen - sometimes the client connects OK and everything works fine. I suspect that the problem comes when I terminate my app without disconnecting the client (typically during a debugging session). Is it possible that the broker has a problem with dropped connections?

[inforaudio]

Hello
somebody have some solution??
We test with mqttClient.ProtocolVersion = MqttProtocolVersion.Version_3_1; and nothing

The server detect a new conection but the client cant connect
VisualStudio show
uPLibrary.Networking.M2Mqtt.Exceptions.MqttConnectionException: Exception connecting to the broker

[rauleteee]

@inforaudio did you find the solution? I am having the same issue

[tejswiniK]

Hello Everyone,
Facing same exception. Did anyone found solution?

[rakesh5283]

seems no one have the solution yet ?