Method HandleFrameCheckSequence

pcsx2/DEV9/pcap_io.cpp:411–446

* Strips the Frame Check Sequence if we manage to capture it. * * On Windows, (some?) Intel NICs can be configured to capture FCS. * * Linux can be configure to capture FCS, using `ethtool -K rx-fcs on` on supported devices. * Support for capturing FCS can be checked with `ethtool -k | grep rx-fcs`. * if it's `off [Fixed]`, then the interface/driver dosn't support c

 * Packets sent by another application via packet injection also won't have FCS and may not match the adapter MAC.
 */
void PCAPAdapter::HandleFrameCheckSequence(NetPacket* pkt)
{
	EthernetFrameEditor frame(pkt);
	if (frame.GetSourceMAC() == hostMAC)
		return;

	// There is a (very) low chance of the last 4 bytes of payload somehow acting as a valid checksum for the whole Ethernet frame.
	// For EtherTypes we already can parse, trim the Ethernet frame based on the payload length.

	int payloadSize = -1;
	if (frame.GetProtocol() == static_cast<u16>(EtherType::IPv4)) // IP
	{
		PayloadPtrEditor* payload = frame.GetPayload();
		IP_Packet ippkt(payload->data, payload->GetLength());
		payloadSize = ippkt.GetLength();
	}
	if (frame.GetProtocol() == static_cast<u16>(EtherType::ARP)) // ARP
	{
		ARP_PacketEditor arpPkt(frame.GetPayload());
		payloadSize = arpPkt.GetLength();
	}

	if (payloadSize != -1)
	{
		// Minumum frame size is 60 + 4 byte FCS.
		// Virtual NICs may omit this padding, so check we arn't increasing pkt size.
		payloadSize = std::min(std::max(payloadSize, 60 - frame.headerLength), pkt->size);

		pkt->size = payloadSize + frame.headerLength;
		return;
	}

	// Ethertype unknown, rely on checking for a FCS.
	if (ValidateEtherFrame(pkt))
		pkt->size -= 4;
}

bool PCAPAdapter::ValidateEtherFrame(NetPacket* pkt)
{