bwtester: enhancements #210

Possible bwtester enhancements, extracted from discussion in #209:

• Improve parameter parsing to allow to properly specify zero duration tests (currently, can only specify zero bandwidth). At the same time, support for fractional seconds should be added by using time.Duration types throughout.

• Infinite test duration; at the moment we can only pick <= MaxDuration (now 5 minutes)

• Fine tune reporting: report inter packet delays over certain threshold.

• Instant reporting. Configure reporting every N seconds.

• Allow to specify pattern for packets to easily identify them in packet traces etc. More generally, do not require each packet to be full of AES counter mode PRG data. This is overkill (and not "secure" anyway as the key is transmitted in plaintext). Suggested structure for a test data packet:

  • session identifier (not strictly necessary, but might be helpful)
  • packet index
  • user chosen pattern
  • a fixed, repeated byte value (e.g. 0xca) to detect truncation

  Possibly, including a timestamp could also be useful to correlate send with receive times.

• Require round trip confirmation before starting test -- it's a bit too easy for a client to spoof its source address and so abuse the bwtestserver to blast at a different host. Maybe even better / simpler would be to just use quic for the control channel.