20210511:

https://github.com/eclipse/paho.mqtt.m2mqtt
https://m2mqtt.wordpress.com/
https://m2mqtt.wordpress.com/using-mqttclient/

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20210511

https://github.com/eclipse/paho.mqtt.m2mqtt

MQTT Client Library for .Net and WinRT

Project Description

M2Mqtt is a MQTT client available for all .Net platforms (.Net Framework, .Net Compact Framework and .Net Micro Framework) and WinRT platforms (Windows 8.1, Windows Phone 8.1 and Windows 10) 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.
訊息佇列遙測傳輸 Message Queue Telemetry Transport 簡稱為 MQTT.
適用於輕量級的設備在受限網路中通訊用途.

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.
MQTT 通訊協定是建立在發佈/訂閱的概念上, Client端可以訂閱(來自其他Client端發佈的)主題後接收訊息. 

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 :
可用在以下執行環境:
.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.)

There is also the support for WinRT platforms :
Windows 8.1
Windows Phone 8.1
Windows 10
It can be used on Windows O.S, Windows Embedded Compact 7 / 2013 and Linux O.S. (thanks to Mono Project).

提供原始碼:
The project has an official website here : https://m2mqtt.wordpress.com/
The binaries for all platforms are also available as package from Nuget web site https://www.nuget.org/packages/M2Mqtt/
For all information about MQTT protocol, please visit official web site http://mqtt.org/.
Follow the project on Twitter @m2mqtt and Facebook.

Building the source code
The library is available for the following solution and project files :
M2Mqtt.sln : solution for Visual Studio that contains projects file for .Net Framework, .Net Compact Framework 3.9, .Net Micro Framework 4.2, .Net Micro Framework 4.3 and WinRT (a portable class library) for Windows 8.1, Window Phone 8.1 and Windows 10 applications
M2MqttVS2008.sln : solution for Visual Studio 2008 that contains project file for .Net Compact Framework 3.5;
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

SSL/TLS support
For SSL/TLS feature, the definition of the symbol "SSL" is needed before compile the project. On the repository, this symbol is already defined and all assemblies (needed for SSL/TLS) are referenced (for Debug and Release configuration). If you want to disable SSL/TLS feature, so that you can reduce memory occupation, you can delete "SSL" symbol and remove all assemblies referenced for SSL/TLS. However, you can leave the default project configuration and set "secure" parameter to false and "cacert" to null for MqttClient constructor (these are already default if you don't specify any values).
ATTENTION : .Net Micro Framework supports up to TLSV1

Example

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));  // 預設 port=1883
 
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, false); 
 
...

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MQTT 限制
  Broker
  Publisher
  Subscriber
  Topic: UTF-8
  


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Using MqttClient
Using MQTT client from library is very simple. First you have to create an instance of MqttClient class which provides only one mandatory parameter (the IP address or the host name of the broker you want to connect to) and some optional parameters with default values (MQTT broker port, secure connection and X.509 certificate). In the simpler case, you can use the default port (1883) and you don’t have the support for secure connection based on SSL/TLS using default values for optional parameters and specifying only broker address (or host name).
只要提供 Hostname/IP, 就可以使用 MqttClient, 以(預設 port=1883, 無 X.509 安全憑證)的方式連線到遠端位址.

MqttClient client = new MqttClient(IPAddress.Parse("192.168.10.53")); // 預設 port=1883

Before connect to the broker, you can register to the event MqttMsgPublishReceived raised when a message is published on a topic the client is subscribed to. In this case, you have to provide an event handler to handle the incoming message using the instance of MqttMsgPublishEventArgs that exposes the data bytes through the Message property.
經由 MqttMsgPublishReceived 事件通知, 可以接收來自Client 發佈的主題訊息.

client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;
...
void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
{
// access data bytes throug e.Message
}


You can also be interested to know if a subscription and/or unsubscription to a topic is completed and registered to the broker. In this case, you can define two event handlers for the events MqttMsgSubscribed and MqttMsgUnsubscribed.
經由 MqttMsgSubscribed, MqttMsgUnsubscribed 事件通知, 可以接收(註冊主題成功, 或停止註冊主題)的事件.

client.MqttMsgSubscribed += client_MqttMsgSubscribed;
client.MqttMsgUnsubscribed += client_MqttMsgUnsubscribed;
...
void client_MqttMsgUnsubscribed(object sender, MqttMsgUnsubscribedEventArgs e)
{
// write your code
}
 
void client_MqttMsgSubscribed(object sender, MqttMsgSubscribedEventArgs e)
{
// write your code
}


If you are using QoS Level 1 or 2 to publish a message on a specified topic, you can also register to MqttMsgPublished event that will be raised when the message will be delivered (exactly once) to all subscribers on the topic.
經由 MqttMsgPublished 事件通知, 可以在發佈主題訊息到指定的主題時接收到通知.

client.MqttMsgPublished += client_MqttMsgPublished;
...
void client_MqttMsgPublished(object sender, MqttMsgPublishedEventArgs e)
{
// write your code
}


After you have registered to all events you are interested in, you can use the Connect() method of MqttClient class to connect to the broker. The only mandatory parameter is the client ID that must be unique; the other parameters have some default values and they are related to :
 1. Username and password for client authentication (default values are null, no authentication);
 2. Will message feature (default values provides NO Will message);
 3. Clean session for removing subscriptions on disconnection (default value is true);
 4. Keep Alive period for keeping alive connection with ping message (default value is 60 seconds);
註冊完以上需要的事件通知後, 就可以以 Connect()方法, 連線到 Broker.
Connect()方法必要的參數為 ClientID (必須唯一), 其餘的參數都非必要, 並且有預設值.
 1. Client 的使用者名稱及密碼. 預設為 null, 無須驗證.
 2. Will Message 功能預設為無.
 3. 斷線後清除 Session. 預設為 true.
 4. 保持連線. 預設60秒發出 ping 訊息.

Without using all the MQTT advanced features (authentication and “will” message), you can specify only the client ID (for example a generated GUID) and leave the default keep alive period with clean session flag set.
若不需要驗證, 也不需要 Will Message 功能, 則只要如下, 提供唯一的 ClientID(例如 Guid), 執行 Connect() 方法.
client.Connect(Guid.NewGuid().ToString());

To subscribe and unsubscribe to a topic, the MqttClient class provides Subscribe() and Unsubscribe() methods. The former needs the list of topics and relative QoS levels to subscribe and the latter needs only the list of topic to unsubscribe.
經由 Subscribe() and Unsubscribe() 方法, 可以訂閱或停止訂閱一個主題.

Subscript() 訂閱須提供 topic 及 qosLevels 參數如下:

string[] topic = { "sensor/temp", "sensor/humidity" };
 
byte[] qosLevels = { MqttMsgBase.QOS_LEVEL_AT_MOST_ONCE, MqttMsgBase.QOS_LEVEL_AT_MOST_ONCE };
client.Subscribe(topic, qosLevels);  


Subscribe() method returns the message id for subscription.
Subscribe() 訂閱回傳 message id 作為訂閱代號.

Unsubscribe() 停止訂閱如下例:
string[] topic = { "sensor/temp", "sensor/humidity" };
client.Unsubscribe(topics);


The last method is Publish() by which you can publish a message to a topic, specifying topic itself and the data bytes for the message. You can also set the QoS level parameter (that has a default value level 0) and the retain flag for delivery message also to the clients that aren’t already connected when the message is published. In this case, the broker saves the message and send it to a new client as soon as it connects and subscribe to the topic.
最後是 Publish() 發佈訊息方法, 可發佈 BytesArray 訊息到主題.
Publish()方法還可以選擇,  Qos level (預設為0級), 以及保留訊息給尚未連線的 Client.

client.Publish("sensor/temp", Encoding.UTF8.GetBytes(temp)

The M2Mqtt client library supports an internal “inflight queue” to execute all publish requests asynchronously (also subscribe and unsubscribe actions). The methods related to the above features (Publish(), Subscribe() and Unsubscribe()) return the message id assigned to the MQTT message sent to the broker. When the asynchronous operation is executed, the corresponding event is raised and the event args contains info on message id so that the user can match it.
M2Mqtt client library 內部會以佇列, 依序執行非同步的訂閱及停止訂閱的動作.
當收到broker轉來的訊息時, Publish(), Subscribe(), Unsubscribe() 方法都會收到來源的 Message id 可以比對.