libpcap has a bug on Linux which leads to incorrect BPF generation for our
capture filter. This commit changes the filter expression on Linux such that
correct BPF is generated.
Fixes#354
Tx/Rx stream stats related threads no longer have a direct reference to the
port's stream stats - instead they have their own copy that they keep and
return (in a reset-on-read fashion) when asked for. Each copy also has it's
own lock to prevent contention for read/update/clear.
PcapPort now fetches Tx(Transmitter) and Rx(Poller) stats on demand and
updates the port's stream stats - under protection of a lock.
There are 2 changes -
1. Encode txPort in ttag packets and use it at TxTtagStats and
RxPcapStats to identify Tx and Rx packets respectively
2. Don't use pcap_sendqueue_transmit() if stream timing is in use -
since we can't modify TTAG packets inside that API
The problem happens for bidirectional flows. The sequence of events is
as follows when you start Tx on Ports p1, p2 with the current code -
1. Clear stream stats on p1
2. Start tx on p1
3. Clear stream stats on p2
4. Start tx on p2
By the time #3 is executed, it may have already rx packets from p1 which
are being incorrectly cleared, this will cause these number of packets
to show up as dropped instead - incorrectly.
The fix is to change the order like this -
1. Clear stream stats on p1
2. Clear stream stats on p2
3. Start tx on p1
4. Start tx on p2
Unidirectional flows will not see this problem - as long as startTx is
done only on the Tx port and not the Rx port.
This bug is a regression caused due to the code changes introduced for the
stream stats rates feature implemented in 1.2.0
On some platforms and/or some libpcap verisons, libpcap doesn't support a
timeout which makes interactive stop not possible. So we now use a UNIX
signal to break out. Obviously this works only on *nix platforms - which
includes MacOS. For now the problem is not seen on Windows with WinPCAP,
so we should be fine. May need to revisit when we add Npcap support.
Fixes#215, #234
