tree 5618351437dfd1c0c8bb2ad35f986b43e853bdb6
parent 7acb9c7d627a2ee9b786946f32c37eb6317e1c00
author Alessandro Ghedini <alessandro@ghedini.me> 1591011047 +0100
committer Alessandro Ghedini <alessandro@ghedini.me> 1594648785 +0100

recovery: retransmit frames from 2 oldest unacked packets on PTO

In 39905083 we implemented support for retransmitting unacked data in
PTO probes if no new data is available.

However after discussion it seems that prioritizing new data is not
actually necessary, and simply retransmitting old data first might be
the better strategy (if anything it's easier to implement).

This reverts the changes from the previous commit, and simply implements
logic to reschedule the frames from the 2 oldest sent packets when the
PTO expires.

Besides having a much simpler implementation, this also has the
advantage of allowing other frames to be sent in the probe packet (e.g.
ACKs), without risking that the original data frame wouldn't fit in the
output packet, since we won't retransmit CRYPTO and STREAM frames as-is
but will go through the normal packetization procedure (including e.g.
respecting STREAM priorities).

This also means that we won't retransmit the same data in both probe
packets. Though if there aren't enough packets with data frames
available we might still end-up sending a PING frame only in the second
probe packet.