At a glance

MQTT subprotocol client

Lightweight publish-subscribe messaging for IoT and constrained devices. Full MQTT 3.1.1 and MQTT 5.0 support, over WebSocket or raw TCP.

Component class

TsgcWSPClient_MQTT

Protocol

MQTT 3.1.1 & MQTT 5.0

Platforms

Windows, macOS, Linux, iOS, Android

Edition

Standard / Professional / Enterprise

QuickStart

Drop the component, set a few properties, go

Pair a TsgcWebSocketClient with TsgcWSPClient_MQTT, wire OnMQTTConnect / OnMQTTPublish, then Subscribe and Publish.

uses
  sgcWebSocket, sgcWebSocket_Protocol_MQTT_Client,
  sgcWebSocket_Protocol_MQTT_Message;

var
  WSClient: TsgcWebSocketClient;
  MQTT: TsgcWSPClient_MQTT;
begin
  WSClient := TsgcWebSocketClient.Create(nil);
  WSClient.Host := 'www.esegece.com';
  WSClient.Port := 15675;

  MQTT := TsgcWSPClient_MQTT.Create(nil);
  MQTT.Client := WSClient;
  MQTT.Authentication.Enabled  := True;
  MQTT.Authentication.UserName := 'sgc';
  MQTT.Authentication.Password := 'sgc';

  MQTT.OnMQTTConnect := MQTTConnect;
  MQTT.OnMQTTPublish := MQTTPublish;

  WSClient.Active := True;
end;

procedure TForm1.MQTTConnect(Connection: TsgcWSConnection;
  const Session: Boolean; const ReasonCode: Integer;
  const ReasonName: string;
  const ConnectProperties: TsgcWSMQTTCONNACKProperties);
begin
  MQTT.Subscribe('sensors/temperature/#');
end;

procedure TForm1.MQTTPublish(Connection: TsgcWSConnection;
  aTopic, aText: string;
  PublishProperties: TsgcWSMQTTPublishProperties);
begin
  Memo1.Lines.Add(aTopic + ': ' + aText);
end;

// Publish a retained QoS 1 message
MQTT.Publish('sensors/temperature/room1',
  '{"value":22.5,"unit":"C"}', mtqsAtLeastOnce, True);

// uses: sgcWebSocket, sgcWebSocket_Protocol_MQTT_Client
TsgcWebSocketClient *WSClient = new TsgcWebSocketClient(this);
WSClient->Host = "www.esegece.com";
WSClient->Port = 15675;

TsgcWSPClient_MQTT *MQTT = new TsgcWSPClient_MQTT(this);
MQTT->Client = WSClient;
MQTT->Authentication->Enabled  = true;
MQTT->Authentication->UserName = "sgc";
MQTT->Authentication->Password = "sgc";

MQTT->OnMQTTConnect = MQTTConnect;
MQTT->OnMQTTPublish = MQTTPublish;

WSClient->Active = true;

void __fastcall TForm1::MQTTPublish(TsgcWSConnection *Connection,
    UnicodeString aTopic, UnicodeString aText,
    TsgcWSMQTTPublishProperties PublishProperties)
{
  Memo1->Lines->Add(aTopic + ": " + aText);
}

MQTT->Publish("sensors/temperature/room1",
  "{\"value\":22.5,\"unit\":\"C\"}", mtqsAtLeastOnce, true);

using esegece.sgcWebSockets;

var WSClient = new TsgcWebSocketClient();
WSClient.Options.Parameters = "/ws";

var MQTT = new TsgcWSPClient_MQTT();
MQTT.Client = WSClient;
MQTT.Authentication.Enabled  = true;
MQTT.Authentication.UserName = "sgc";
MQTT.Authentication.Password = "sgc";
MQTT.HeartBeat.Enabled  = true;
MQTT.HeartBeat.Interval = 5;

MQTT.OnMQTTConnect += (conn, session, code, name, props) => MQTT.Subscribe("sensors/temperature/#");
MQTT.OnMQTTPublish += (conn, topic, text, props) => Console.WriteLine(topic + ": " + text);

WSClient.Host = "www.esegece.com";
WSClient.Port = 15675;
WSClient.Active = true;

MQTT.Publish("sensors/temperature/room1",
  "{\"value\":22.5,\"unit\":\"C\"}", TmqttQoS.mtqsAtLeastOnce, true);

Technical features

What's inside

10 published properties, 9 methods and 13 events — matched against the TsgcWSPClient_MQTT reference.

Protocol versions

MQTTVersion selects the level advertised in the CONNECT packet — MQTT 3.1.1 or MQTT 5.0. ConnectProperties carries the MQTT 5 session-expiry, receive-maximum, packet-size, topic-alias and extended-auth fields.

WebSocket or raw TCP

Plug the Client property into a TsgcWebSocketClient to run MQTT over WebSockets, or into a TsgcWSMQTTBroker via Broker to use the native TCP transport on port 1883/8883.

QoS & retain

Publish at QoS 0, 1 or 2 with optional retain. QoS property controls default level, retry interval and timeout. PublishAndWait blocks until the broker acknowledges — useful for transactional publishes.

Last Will & Testament

LastWillTestament registers the topic, payload, QoS and retain flag the broker will publish on this client's behalf if the connection drops ungracefully — a clean way to signal device disconnects.

Subscriptions & events

Subscribe / UnSubscribe accept topic filters with + and # wildcards. OnMQTTPublish delivers incoming messages; OnMQTTPublishEx gives raw bytes / stream. Full QoS 2 handshake exposed via OnMQTTPubRec, OnMQTTPubRel, OnMQTTPubComp.

Keep-alive & auth

HeartBeat sends PINGREQ on a timer and detects silent broker drops. Authentication sends a UserName/Password in CONNECT. MQTT 5 enhanced auth: call Auth and handle OnMQTTAuth for SCRAM-style challenges.

Standards

Specifications & references

Authoritative sources for the protocols this component implements.

OASIS MQTT 3.1.1 — Standard
OASIS MQTT 5.0 — Standard
RFC 6455 — WebSocket transport binding

Resources

Documentation & Demos

Deep-link to the component reference, grab the ready-to-run demo project, and download the trial.

	Online Help — Protocol_MQTT Full property, method and event reference for this component.	Open
	Demo Project — Demos\Protocols\MQTT Ready-to-run example project. Ships inside the sgcWebSockets package — download the trial below.	Open
	Technical Document (PDF) Features, quick start, code samples for Delphi, C++ Builder and .NET and primary-source references — this component only.	Open
	User Manual (PDF) Comprehensive manual covering every component in the library.	Open

MQTT Protocol