TCP: Zero window probing not correct

[BartVolkaerts]

Flow:
we <--------- SYN ------------- pico
we ---------- SYN, ACK -----> pico
we <--------- ACK ------------- pico (connection established)
we <----- PSH, ACK, data --- pico
we ------- ACK, window=0 --> pico (we advertise our window is zero)
Now, when pico wants to send more data it is going to probe our window first, but in an incorrect way. (It sends a segment with only PSH flag, a seq nr. and no data)

There are 2 correct ways of window probing.

• 'normal' way
  • send a packet with PSH,ACK flags on
  • seq and ack numbers incrementing in normal way
  • data = one byte
• keep-alive way (suggested and linux-like)
  • send a packet with PSH,ACK flags on
  • seq = -1
  • no data needed

pcap:
Faulty: https://dl.dropboxusercontent.com/u/49342572/faultywindowprobe (packet 9)
Correct: https://dl.dropboxusercontent.com/u/49342572/correctwindowprobe (keep-alive packets)

[BartVolkaerts]

Testcase:
sudo ./run.sh --test zerowindowprobing testcases/hardware/tcp_talk_dut_bench.txt