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.NET nanoFramework M2Mqtt

Welcome to the MQTT Client Library for .NET nanoFramework. The current version supports v3.1, v3.1.1 and v5.0.

This is an initial port of the MQTT Client Library M2Mqtt. The original project has an official website here.

Since that time, the MQTT Client had quite some changes and has been adapted to .NET nanoFramework.

Build status

Component Build Status NuGet Package
nanoFramework.M2Mqtt Build Status NuGet
nanoFramework.M2Mqtt (preview) Build Status NuGet

Project Description

M2Mqtt is a MQTT client for Internet of Things and M2M communication.

MQTT, short for Message Queue Telemetry Transport, is a light weight messaging protocol that enables embedded devices with limited resources to perform asynchronous communication on a constrained network.

MQTT protocol is based on publish/subscribe pattern so that a client can subscribe to one or more topics and receive messages that other clients publish on these topics.

This library contains an sample MQTT client that you can use to connect to any MQTT broker.

The binaries are available as a NuGet package.

For all information about MQTT protocol, please visit MQTT official web site. It is recommended to have a good understanding of how MQTT protocol is working to properly use it. The mechanism of Quality of Service is an important one to understand.


The usage is globally the same whatever version is used. There are some specificities between v3.1.1 and v5.0. The version 5.0 brings more control and additional properties. For convenience, they are all commented with v5.0 only in the properties comments. If you're using a v5.0 property with the v3.1 or v3.1.1 protocol, they'll just be ignored.

Here is a basic example of creating a v3.1.1 server and connecting to it:

MqttClient mqtt = new MqttClient("", 8883, true, new X509Certificate(CertMosquitto), null, MqttSslProtocols.TLSv1_2);
var ret = mqtt.Connect("nanoTestDevice", true);
if (ret != MqttReasonCode.Success)
    Debug.WriteLine($"ERROR connecting: {ret}");

For the v5.0, you just need to specify the version before the connection:

MqttClient mqtt = new MqttClient("", 8883, true, new X509Certificate(CertMosquitto), null, MqttSslProtocols.TLSv1_2);
mqtt.ProtocolVersion = MqttProtocolVersion.Version_5;
var ret = mqtt.Connect("nanoTestDevice", true);
if (ret != MqttReasonCode.Success)
    Debug.WriteLine($"ERROR connecting: {ret}");

Note: in both example, a specific certificate is needed to connect to the Mosquitto server. You will find it in the sample.

v5.0 specific Authentication flow

The MQTT version 5.0 supports specific Authentication flow. After a Connect, the Authentication mechanism can be used like a challenge request. In this case, you'll have to:

  • Make sure you setup v5 as a protocol
  • Place the property IsAuthenticationFlow to true
  • Register to the Authentication event
  • Manage the answers accordingly by sending another Authentication message or anything that is needed regarding your case.

Note: the protocol is using the AuthenticationMethod and AuthenticationData as properties for this specific mechanism.

Here are examples given by the specifications:

Non-normative example showing a SCRAM challenge

  • Client to Server: CONNECT Authentication Method="SCRAM-SHA-1" Authentication Data=client-first-data
  • Server to Client: AUTH rc=0x18 Authentication Method="SCRAM-SHA-1" Authentication Data=server-first-data
  • Client to Server AUTH rc=0x18 Authentication Method="SCRAM-SHA-1" Authentication Data=client-final-data
  • Server to Client CONNACK rc=0 Authentication Method="SCRAM-SHA-1" Authentication Data=server-final-data

Non-normative example showing a Kerberos challenge

  • Client to Server CONNECT Authentication Method="GS2-KRB5"
  • Server to Client AUTH rc=0x18 Authentication Method="GS2-KRB5"
  • Client to Server AUTH rc=0x18 Authentication Method="GS2-KRB5" Authentication Data=initial context token
  • Server to Client AUTH rc=0x18 Authentication Method="GS2-KRB5" Authentication Data=reply context token
  • Client to Server AUTH rc=0x18 Authentication Method="GS2-KRB5"
  • Server to Client CONNACK rc=0 Authentication Method="GS2-KRB5" Authentication Data=outcome of authentication

In those mechanism, the IsConnected property will be setup only once a Connack with a success code will be received. As those authentication mechanism are specific and user setup, this specific MqttClient offers the ability to use this mechanism.

Subscribing to events

The MqttClient offers events. You can subscribe to them. As an example, you can get additional information on when the connection is opened with the v5.0 protocol. The below example show what is required to connect to Azure IoT Hub with the MQTT v5.0 protocol enabled:

// Create the client
MqttClient mqtt = new MqttClient(IoTHub, 8883, true, new X509Certificate(CertAzure), null, MqttSslProtocols.TLSv1_2);
// Setup the version
mqtt.ProtocolVersion = MqttProtocolVersion.Version_5;
// Register to events
mqtt.ConnectionOpened += MqttConnectionOpened;
// You can add additional properties
var at = DateTime.UtcNow;
var atString = (at.ToUnixTimeSeconds() * 1000).ToString();
var expiry = at.AddMinutes(40);
var expiryString = (expiry.ToUnixTimeSeconds() * 1000).ToString();
string toSign = $"{IoTHub}\n{DeviceID}\n\n{atString}\n{expiryString}\n";
var hmac = new HMACSHA256(Convert.FromBase64String(Sas));
var sas = hmac.ComputeHash(Encoding.UTF8.GetBytes(toSign));
mqtt.AuthenticationMethod = "SAS";
mqtt.AuthenticationData = sas;
mqtt.UserProperties.Add(new UserProperty("sas-at", atString));
mqtt.UserProperties.Add(new UserProperty("sas-expiry", expiryString));
mqtt.UserProperties.Add(new UserProperty("api-version", "2020-10-01-preview"));
mqtt.UserProperties.Add(new UserProperty("host", IoTHub));
var ret = mqtt.Connect(DeviceID, null, null, false, MqttQoSLevel.AtLeastOnce, false, null, null, true, 60);
// You will have more code here

private static void MqttConnectionOpened(object sender, ConnectionOpenedEventArgs e)
    Debug.WriteLine($"Connection open");
    Debug.WriteLine($"  ClientID: {((MqttClient)sender).ClientId}");
    Debug.WriteLine($"  Assigned client id: {e.Message.AssignedClientIdentifier}");
    if (e.Message.AuthenticationData != null) Debug.WriteLine($"  Auth data length: {e.Message.AuthenticationData.Length}");
    Debug.WriteLine($"  Auth method: {e.Message.AuthenticationMethod}");
    Debug.WriteLine($"  Dup flag: {e.Message.DupFlag}");
    Debug.WriteLine($"  Max packet size: {e.Message.MaximumPacketSize}");
    Debug.WriteLine($"  Max QoS: {e.Message.MaximumQoS}");
    Debug.WriteLine($"  Msg ID: {e.Message.MessageId}");
    Debug.WriteLine($"  Qos level: {e.Message.QosLevel}");
    Debug.WriteLine($"  Reason: {e.Message.Reason}");
    Debug.WriteLine($"  Receive max: {e.Message.ReceiveMaximum}");
    Debug.WriteLine($"  Rep info: {e.Message.ResponseInformation}");
    Debug.WriteLine($"  Retain: {e.Message.Retain}");
    Debug.WriteLine($"  Retain available: {e.Message.RetainAvailable}");
    Debug.WriteLine($"  Return code: {e.Message.ReturnCode}");
    Debug.WriteLine($"  Server keep alive: {e.Message.ServerKeepAlive}");
    Debug.WriteLine($"  Server ref: {e.Message.ServerReference}");
    Debug.WriteLine($"  Session exp inter: {e.Message.SessionExpiryInterval}");
    Debug.WriteLine($"  Session present: {e.Message.SessionPresent}");
    Debug.WriteLine($"  Shared subs available: {e.Message.SharedSubscriptionAvailable}");
    Debug.WriteLine($"  Shared identifier available: {e.Message.SubscriptionIdentifiersAvailable}");
    Debug.WriteLine($"  Topic alias max: {e.Message.TopicAliasMaximum}");
    Debug.WriteLine($"  Num user props: {e.Message.UserProperties.Count}");
    foreach (UserProperty prop in e.Message.UserProperties)
        Debug.WriteLine($"    Key  : {prop.Name}");
        Debug.WriteLine($"    Value: {prop.Value}");

    Debug.WriteLine($"  Wildcard available: {e.Message.WildcardSubscriptionAvailable}");


The M2Mqtt library provides a main class MqttClient that represents the MQTT client to connect to a broker. You can connect to the broker providing its IP address or host name and optionally some parameters related to MQTT protocol.

After connecting to the broker you can use Publish() method to publish a message to a topic and Subscribe() method to subscribe to a topic and receive message published on it. The MqttClient class is events based so that you receive an event when a message is published to a topic you subscribed to. You can receive event when a message publishing is complete, you have subscribed or unsubscribed to a topic.

Following an example of client subscriber to a topic :

// create client instance
MqttClient client = new MqttClient(IPAddress.Parse(MQTT_BROKER_ADDRESS));

// register to message received
client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;

string clientId = Guid.NewGuid().ToString();

// subscribe to the topic "/home/temperature" with QoS 2
client.Subscribe(new string[] { "/home/temperature" }, new MqttQoSLevel[] { MqttMsgBase.ExactlyOnce });

// You can add some code here

static void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
// handle message received 

Following an example of client publisher to a topic :

// create client instance
MqttClient client = new MqttClient(IPAddress.Parse(MQTT_BROKER_ADDRESS));

string clientId = Guid.NewGuid().ToString();

string strValue = Convert.ToString(value);

// publish a message on "/home/temperature" topic with QoS 2
client.Publish("/home/temperature", Encoding.UTF8.GetBytes(strValue), MqttQoSLevel.ExactlyOnce, false);

// More code goes here

Feedback and documentation

For documentation, providing feedback, issues and finding out how to contribute please refer to the Home repo.

Join our Discord community here.


The list of contributors to this project can be found at CONTRIBUTORS. This library was created and maintained by Paolo Patierno and it's part of the Eclipse Project.


The nanoFramework Class Libraries are licensed under the MIT license.

Code of Conduct

This project has adopted the code of conduct defined by the Contributor Covenant to clarify expected behaviour in our community. For more information see the .NET Foundation Code of Conduct.

.NET Foundation

This project is supported by the .NET Foundation.

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NuGet packages (3)

Showing the top 3 NuGet packages that depend on nanoFramework.M2Mqtt:

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nanoFramework.Azure.Devices.Client The ID prefix of this package has been reserved for one of the owners of this package by

This package includes the .NET nanoFramework.Azure.Devices.Client assembly for .NET nanoFramework C# projects. This is an SDK for Azure IoT Hub using MQTT broker.

nanoFramework.Aws.IoTCore.Devices The ID prefix of this package has been reserved for one of the owners of this package by

This package includes the .NET nanoFramework.Aws.IoTCore.Devices assembly for nanoFramework C# projects. This is an SDK for Aws IoTCore.


Homie implementation for nanoFramework.

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