Connect MQTT in Delphi?

Delphi does not have a standard MQTT library included with the IDE, and the availability of third-party libraries can vary. As of my last knowledge update in January 2022, there might be changes or new libraries developed after that time.

If you are having difficulty finding an MQTT library for Delphi, consider using the Synapse library, which is a general-purpose TCP/IP library that includes support for MQTT.

Here’s a basic example using Synapse for MQTT communication:

1. Download Synapse: Download the Synapse library from its official repository on GitHub: https://github.com/synopse/mORMot.
2. Add Synapse to Your Project:
   • Extract the Synapse archive.
   • Add the necessary Synapse units to your Delphi project.
3. Use Synapse for MQTT: Below is a simple example of using Synapse to connect to an MQTT broker and subscribe to a topic:
   
   Delphi/Pascal

   unit MainUnit; interface uses System.SysUtils, System.Classes, Vcl.Forms, blcksock, synsock; type TForm1 = class(TForm) procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); private MQTTClient: TTCPBlockSocket; procedure ConnectToMQTTBroker; procedure SubscribeToTopic(const Topic: string); public { Public declarations } end; var Form1: TForm1; implementation {$R *.dfm} procedure TForm1.FormCreate(Sender: TObject); begin MQTTClient := TTCPBlockSocket.Create; ConnectToMQTTBroker; end; procedure TForm1.FormDestroy(Sender: TObject); begin MQTTClient.Free; end; procedure TForm1.ConnectToMQTTBroker; begin try MQTTClient.Connect(‘mqtt.eclipse.org’, ‘1883’); // Handle successful connection SubscribeToTopic(‘test/topic’); except // Handle connection error end; end; procedure TForm1.SubscribeToTopic(const Topic: string); var SubscribePacket: string; begin // Construct MQTT SUBSCRIBE packet SubscribePacket := Char($82) + // MQTT SUBSCRIBE packet header Char(8) + // Remaining Length (8 bytes) Char(0) + // MSB of Message ID (0 for QoS 0) Char(1) + // LSB of Message ID (1 for QoS 0) Char(0) + // Length of Topic Name MSB Char(4) + // Length of Topic Name LSB ‘test’ + // Topic Name Char(0); // Requested QoS level (0 for QoS 0) // Send the SUBSCRIBE packet MQTTClient.SendString(SubscribePacket); end; end.

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   unit MainUnit;   interface   uses   System.SysUtils, System.Classes, Vcl.Forms, blcksock, synsock;   type   TForm1 = class(TForm)     procedure FormCreate(Sender: TObject);     procedure FormDestroy(Sender: TObject);   private     MQTTClient: TTCPBlockSocket;     procedure ConnectToMQTTBroker;     procedure SubscribeToTopic(const Topic: string);   public     { Public declarations }   end;   var   Form1: TForm1;   implementation   {$R *.dfm}   procedure TForm1.FormCreate(Sender: TObject); begin   MQTTClient := TTCPBlockSocket.Create;   ConnectToMQTTBroker; end;   procedure TForm1.FormDestroy(Sender: TObject); begin   MQTTClient.Free; end;   procedure TForm1.ConnectToMQTTBroker; begin   try     MQTTClient.Connect(‘mqtt.eclipse.org’, ‘1883’);     // Handle successful connection     SubscribeToTopic(‘test/topic’);   except     // Handle connection error   end; end;   procedure TForm1.SubscribeToTopic(const Topic: string); var   SubscribePacket: string; begin   // Construct MQTT SUBSCRIBE packet   SubscribePacket :=     Char($82) +   // MQTT SUBSCRIBE packet header     Char(8) +      // Remaining Length (8 bytes)     Char(0) +      // MSB of Message ID (0 for QoS 0)     Char(1) +      // LSB of Message ID (1 for QoS 0)     Char(0) +      // Length of Topic Name MSB     Char(4) +      // Length of Topic Name LSB     ‘test’ +       // Topic Name     Char(0);       // Requested QoS level (0 for QoS 0)     // Send the SUBSCRIBE packet   MQTTClient.SendString(SubscribePacket); end;   end.

   
   Please note that this example is a basic illustration using Synapse for MQTT communication. For a more complete and production-ready solution, you may want to consider a more feature-rich MQTT library if available.

   Always check the documentation of the libraries you use and ensure compatibility with your Delphi version. Additionally, consider checking for more recent MQTT libraries or updates to existing ones.