private void TryPublishQueuedMessage(MqttManagedMessage message)
{
Exception transmitException = null;
try
{
_mqttClient.PublishAsync(message.ApplicationMessage).GetAwaiter().GetResult();
lock (_messageQueue) //lock to avoid conflict with this.PublishAsync
{
//While publishing this message, this.PublishAsync could have booted this
//message off the queue to make room for another (when using a cap
//with the DropOldestQueuedMessage strategy). If the first item
//in the queue is equal to this message, then it's safe to remove
//it from the queue. If not, that means this.PublishAsync has already
//removed it, in which case we don't want to do anything.
_messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
}
_storageManager?.RemoveAsync(message).GetAwaiter().GetResult();
}
catch (MqttCommunicationException exception)
{
transmitException = exception;
_logger.Warning(exception, $"Publishing application ({message.Id}) message failed.");
if (message.ApplicationMessage.QualityOfServiceLevel == MqttQualityOfServiceLevel.AtMostOnce)
{
//If QoS 0, we don't want this message to stay on the queue.
//If QoS 1 or 2, it's possible that, when using a cap, this message
//has been booted off the queue by this.PublishAsync, in which case this
//thread will not continue to try to publish it. While this does
//contradict the expected behavior of QoS 1 and 2, that's also true
//for the usage of a message queue cap, so it's still consistent
//with prior behavior in that way.
lock (_messageQueue) //lock to avoid conflict with this.PublishAsync
{
_messageQueue.RemoveFirst(i => i.Id.Equals(message.Id));
}
}
}
catch (Exception exception)
{
transmitException = exception;
_logger.Error(exception, $"Unhandled exception while publishing application message ({message.Id}).");
}
finally
{
ApplicationMessageProcessed?.Invoke(this, new MqttMessageProcessedEventArgs(message, transmitException));
}
}
