TsgcWSPClient_MQTT is a native MQTT 3.1.1 and MQTT 5.0 client. Publish and subscribe with QoS 0, 1 and 2, retained messages, a Last Will and Testament, persistent sessions, and the MQTT 5 additions: reason codes, user properties, topic aliases, shared subscriptions and enhanced authentication. The same component and the same API in Delphi and C++ Builder.
Assign a TsgcTCPClient to Client, pick the protocol version with MQTTVersion, wire OnMQTTConnect and OnMQTTPublish, then call Subscribe and Publish.
TsgcWSPClient_MQTT
OASIS MQTT 3.1.1 and MQTT 5.0
TCP (1883) or TLS (8883)
Delphi, C++ Builder
Transport: plain TCP and TLS. sgcMQ connects over plain TCP and TLS. If you need MQTT over WebSocket, that requires a sgcWebSockets package, which provides the WebSocket client.
A TsgcTCPClient on the Client property puts MQTT straight on the TCP socket. Switch on TLS and point the port at 8883 for an encrypted broker.
uses
sgcTCP_Client_WS, sgcWebSocket_Classes, sgcWebSocket_Types,
sgcWebSocket_Protocols, sgcWebSocket_Protocol_MQTT_Client,
sgcWebSocket_Protocol_MQTT_Message;
var
TCPClient: TsgcTCPClient;
MQTT: TsgcWSPClient_MQTT;
begin
TCPClient := TsgcTCPClient.Create(nil);
TCPClient.Host := 'broker.example.com';
TCPClient.Port := 1883;
TCPClient.WatchDog.Enabled := True;
MQTT := TsgcWSPClient_MQTT.Create(nil);
MQTT.Client := TCPClient;
MQTT.MQTTVersion := mqtt5;
MQTT.Authentication.Enabled := True;
MQTT.Authentication.UserName := 'sgc';
MQTT.Authentication.Password := 'sgc';
MQTT.LastWillTestament.Enabled := True;
MQTT.LastWillTestament.Topic := 'devices/sensor-01/status';
MQTT.LastWillTestament.Message := 'offline';
MQTT.LastWillTestament.QoS := mtqsAtLeastOnce;
MQTT.LastWillTestament.Retain := True;
MQTT.OnMQTTConnect := MQTTConnect;
MQTT.OnMQTTPublish := MQTTPublish;
TCPClient.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', mtqsAtLeastOnce);
MQTT.Publish('devices/sensor-01/status',
'online', mtqsAtLeastOnce, True);
end;
procedure TForm1.MQTTPublish(Connection: TsgcWSConnection;
aTopic, aText: string;
PublishProperties: TsgcWSMQTTPublishProperties);
begin
Memo1.Lines.Add(aTopic + ' = ' + aText);
end;// include: sgcTCP_Client_WS.hpp, sgcWebSocket_Protocols.hpp,
// sgcWebSocket_Protocol_MQTT_Client.hpp
TsgcTCPClient *TCPClient = new TsgcTCPClient(this);
TCPClient->Host = "broker.example.com";
TCPClient->Port = 1883;
TCPClient->WatchDog->Enabled = true;
TsgcWSPClient_MQTT *MQTT = new TsgcWSPClient_MQTT(this);
MQTT->Client = TCPClient;
MQTT->MQTTVersion = mqtt5;
MQTT->Authentication->Enabled = true;
MQTT->Authentication->UserName = "sgc";
MQTT->Authentication->Password = "sgc";
MQTT->OnMQTTConnect = MQTTConnect;
MQTT->OnMQTTPublish = MQTTPublish;
TCPClient->Active = true;
void __fastcall TForm1::MQTTPublish(TsgcWSConnection *Connection,
UnicodeString aTopic, UnicodeString aText,
TsgcWSMQTTPublishProperties PublishProperties)
{
Memo1->Lines->Add(aTopic + " = " + aText);
}
// In the OnMQTTConnect handler:
MQTT->Subscribe("sensors/+/temperature", mtqsAtLeastOnce);
MQTT->Publish("devices/sensor-01/status",
"online", mtqsAtLeastOnce, true);The members you reach for most often.
Client takes the TsgcTCPClient that owns the socket. Its Host, Port, TLS, TLSOptions and WatchDog decide how the bytes travel.
MQTTVersion selects mqtt311 or mqtt5. The MQTT 5 properties and reason codes only appear on the wire when version 5 is selected.
Authentication.Enabled, UserName and Password fill the CONNECT packet. For MQTT 5 challenge/response schemes use Auth together with OnMQTTAuth.
Publish(topic, text, qos, retain) sends a message, with a TStream overload for binary payloads. PublishAndWait blocks until the broker acknowledges the packet.
Subscribe(topic, qos) takes a single filter or a TsgcWSTopics list, and UnSubscribe mirrors it. Wildcards are + for one level and # for the remainder.
OnMQTTPublish delivers an inbound message. The QoS 2 handshake surfaces as OnMQTTPubRec, OnMQTTPubRel and OnMQTTPubComp, with OnMQTTPubAck for QoS 1.
LastWillTestament carries the topic, message, QoS and retain flag the broker publishes on your behalf if the connection drops without a clean DISCONNECT.
ConnectProperties sets MQTT 5 session expiry and limits. HeartBeat drives the keep-alive PINGREQ, with OnMQTTPing on the response.
The QoS property controls how outbound QoS 1 and 2 messages are stored and retried while the acknowledgement is outstanding.
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