TsgcWSPClient_MQTT › Events › OnMQTTBeforeConnect

OnMQTTBeforeConnect Event

Fires before the CONNECT packet is sent; lets the app override CleanSession and ClientIdentifier.

Syntax

property OnMQTTBeforeConnect: TsgcWSMQTTBeforeConnectEvent;
// TsgcWSMQTTBeforeConnectEvent = procedure(Connection: TsgcWSConnection; var aCleanSession: Boolean; var aClientIdentifier: String) of object

Default Value

—

Remarks

Last chance to tweak the CONNECT packet just before it is written to the wire. The component raises this event after the WebSocket / TCP transport is up but before serializing CONNECT, so the handler can override:

• aCleanSession (var, Boolean) — when True (default) the broker discards any previous session and starts fresh; set False to resume a stored session (MQTT 5 exposes this more finely through SessionExpiryInterval on ConnectProperties).
• aClientIdentifier (var, String) — the unique client id. The component auto-generates a GUID-based value; replace it here if your broker requires a specific id (for example to match an access-control rule or to reconnect and resume a persistent session).

Any other connection state (credentials, LastWillTestament, ConnectProperties) should be configured on the component itself before Activate, not inside this handler.

Example

procedure TForm1.MQTTBeforeConnect(Connection: TsgcWSConnection;
  var aCleanSession: Boolean; var aClientIdentifier: String);
begin
  // resume the stored session if the broker still has it
  aCleanSession     := False;
  aClientIdentifier := 'sensor-gateway-01';
end;

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