TsgcWSPClient_MQTT › Events › OnMQTTSubscribe

OnMQTTSubscribe Event

Fires when a SUBACK is received in response to Subscribe; exposes per-topic reason codes and MQTT 5 SubscribeProperties.

Syntax

property OnMQTTSubscribe: TsgcWSMQTTSubscribeEvent;
// TsgcWSMQTTSubscribeEvent = procedure(Connection: TsgcWSConnection; aPacketIdentifier: Word; aCodes: TsgcWSSUBACKS; SubscribeProperties: TsgcWSMQTTSUBACKProperties) of object

Default Value

—

Remarks

Raised when the broker replies with a SUBACK to a SUBSCRIBE request. The broker can accept, partially accept or reject individual topic filters in the request, so the event delivers a code per filter. Parameters:

• aPacketIdentifier — 16-bit packet id of the original SUBSCRIBE.
• aCodes — a TsgcWSSUBACKS array with one entry per topic filter. Values 0x00/0x01/0x02 mean the subscription was accepted with the granted maximum QoS; values 0x80 and above (MQTT 5 also adds 0x83, 0x87, 0x8F, 0x91, 0x97, 0x9E, 0xA1, 0xA2) indicate the filter was rejected. Inspect each code to confirm which filters succeeded.
• SubscribeProperties (MQTT 5) — ReasonString and UserProperties returned by the broker.

Example

procedure TForm1.MQTTSubscribe(Connection: TsgcWSConnection;
  aPacketIdentifier: Word; aCodes: TsgcWSSUBACKS;
  SubscribeProperties: TsgcWSMQTTSUBACKProperties);
var
  i: Integer;
begin
  for i := 0 to Length(aCodes) - 1 do
    if aCodes[i] < $80 then
      Memo1.Lines.Add(Format('subscription %d accepted (QoS %d)',
        [i, aCodes[i]]))
    else
      Memo1.Lines.Add(Format('subscription %d rejected (code $%x)',
        [i, aCodes[i]]));
end;

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