TsgcWSPClient_MQTT › Events › OnMQTTConnect

OnMQTTConnect Event

Fires after CONNACK is received; reports the Session flag, ReasonCode and MQTT 5 ConnectProperties.

Syntax

property OnMQTTConnect: TsgcWSMQTTConnectEvent;
// TsgcWSMQTTConnectEvent = procedure(Connection: TsgcWSConnection; const Session: Boolean; const ReasonCode: Integer; const ReasonName: String; const ConnectProperties: TsgcWSMQTTCONNACKProperties) of object

Default Value

—

Remarks

Raised when the broker acknowledges the CONNECT with a CONNACK. This is the first moment at which the MQTT session is fully usable — it is safe to call Subscribe / Publish from inside this handler. Parameters:

• Session — broker-side session state. With CleanSession = True the broker must reply with Session = False. With CleanSession = False, Session = True means the broker still had stored state for this ClientIdentifier, Session = False means it did not.
• ReasonCode (MQTT 5) — numeric CONNACK reason (0 = Success).
• ReasonName (MQTT 5) — human-readable description of ReasonCode.
• ConnectProperties (MQTT 5) — broker capabilities and negotiated limits: SessionExpiryInterval, ReceiveMaximum, MaximumQoS, RetainAvailable, MaximumPacketSize, AssignedClientIdentifier, TopicAliasMaximum, ReasonString, UserProperties, WildcardSubscriptionAvailable, SubscriptionIdentifiersAvailable, SharedSubscriptionAvailable, ResponseInformation, ServerReference, AuthenticationMethod and AuthenticationData.

Example

procedure TForm1.MQTTConnect(Connection: TsgcWSConnection;
  const Session: Boolean; const ReasonCode: Integer;
  const ReasonName: String;
  const ConnectProperties: TsgcWSMQTTCONNACKProperties);
begin
  if ReasonCode <> 0 then
  begin
    Memo1.Lines.Add('Connect rejected: ' + ReasonName);
    Exit;
  end;

  Memo1.Lines.Add(Format('Connected. Session=%s MaxQoS=%d',
    [BoolToStr(Session, True), ConnectProperties.MaximumQoS]));

  // now it is safe to subscribe and publish
  MQTT.Subscribe('sensors/#', mtqsAtLeastOnce);
end;

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