Introduction
M2Mqtt is a MQTT client available for all .Net platform (.Net Framework, .Net Compact Framework and .Net Micro Framework) 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 sample is a library contains an MQTT client that you can use to connect to any MQTT broker. It is developed in C# language and works on all the following .Net platforms :
- .Net Framework (up to 4.5)
- .Net Compact Framework 3.5 & 3.9 (for Windows Embedded Compact 7 / 2013)
- .Net Micro Framework 4.2 & 4.3
- Mono (for Linux O.S.)
It can be used on Windows O.S, Windows Embedded Compact 7 / 2013 and Linux O.S. (thanks to Mono Project).
Official web site on CodePlex : https://m2mqtt.codeplex.com/
Building the Sample
The library is available for the following solution and project files :
- M2MqttVS2012.sln : solution for Visual Studio 2012 that contains projects file for .Net Framework, .Net Compact Framework 3.9, .Net Micro Framework 4.2 and .Net Micro Framework 4.3;
- M2MqttVS2010.sln : solution for Visual Studio 2010 that contains projects file for .Net Framework and .Net Micro Framework 4.2;
- M2MqttVS2008.sln : solution for Visual Studio 2008 that contains project file for .Net Compact Framework 3.5;
- M2MqttMono.sln : solution for MonoDevelop for building project under Linux O.S. with Mono Project;
In this sample there is only the Visual Studio 2012 solution but on the CodePlex web site https://m2mqtt.codeplex.com/ all other versions are available.
To build sample based on .Net Micro Framework (4.2 and 4.3) you need to download .Net Micro Framework SDK from the official CodePlex web site : https://netmf.codeplex.com/
To build sample based on .Net Compact Framework 3.9 you need to download Application Builder for Windows Embedded Compact 2013 from here : http://www.microsoft.com/en-us/download/details.aspx?id=38819
Description
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();
client.Connect(clientId);
// subscribe to the topic "/home/temperature" with QoS 2
client.Subscribe(new string[] { "/home/temperature" }, new byte[] { MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE });
...
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();
client.Connect(clientId);
string strValue = Convert.ToString(value);
// publish a message on "/home/temperature" topic with QoS 2
client.Publish("/home/temperature", Encoding.UTF8.GetBytes(strValue), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE);