Question about PacketFilterBase canPushPacket implementation

[haug-den-lucas]

Hello,

I'm currently working with some Per-Stream Filtering and Policing in INET and stumbled upon the following lines of code:

inet/src/inet/queueing/base/PacketFilterBase.cc

Lines 65 to 71 in 61410b4

	bool PacketFilterBase::canPushPacket(Packet *packet, const cGate *gate) const
	{
	if (backpressure)
	return matchesPacket(packet) && consumer != nullptr && consumer.canPushPacket(packet);
	else
	return !matchesPacket(packet) || consumer == nullptr || consumer.canPushPacket(packet);
	}

In the no-backpressure case, this code accepts all packets in case its consumer accepts all packets.
However, if the consumer does not accept packets, canPushPacket returns true iff the packet criteria does not match, meaning it accepts all packets it will immediately filter out.
I cannot think about any scenario why this implementation would be useful.

Could you please clarify why it is implemented like this?