On abrupt disconnect, server keeps repeating ACK messages

huitema commented 12 months ago

Client (on a MAC) is connected to a local server using loopback. The client drops abruptly. We would expect to see a few retransmission attempts before the server gives up on the connection, but instead we see the servers sending ACK messages in a loop.

huitema commented 12 months ago

In my tests of PR #1545, I saw that issue happen briefly. There were two reasons:

a bug in loss recovery that caused picoquic_retransmit_needed that caused it to return "empty" packet, with length set to the header length, when there was no packet ready to be repeated.
a bug in ACK generation that caused ACK to be generated even when not needed, thus bumping the packet length above header length and causing the packet to be send through picoquic_prepare_packet-ready.

The header-only packet bug from loss recovery is being fixed in PR #1545. We need to add a unit test of ACK generation to ensure that if something else causes a similar issue, only a small number of ACK will be generated.

huitema commented 11 months ago

Perhaps related, but work on PR #1545 also discovered "too many ACK sent when using simple multipath", which could probably fixed at the same time as this "ACK loop" problem.

huitema commented 11 months ago

Reported as not reproducing after PR #1545.

Added tests and coding safeties in Pr #1568.

private-octopus / picoquic

On abrupt disconnect, server keeps repeating ACK messages #1558