qlog, AckFrame, and ack_delay

[Damien Neil <[e-mail]>]

The qlog AckFrame type includes the ack delay as a float32 number of
milliseconds:

AckFrame = {
    frame_type: "ack"

    ; in ms
    ? ack_delay: float32
    ; ...
}

https://www.ietf.org/archive/id/draft-ietf-quic-qlog-quic-events-06.html#section-8.12.3

Given a serialized ack frame, determining the delay as a duration requires
knowing the ack_delay_exponent. In some cases, the logging endpoint may not
have this available (if receiving an ack before transport parameters have
been received). Even when available, it may not be easily accessible at the
point of logging. For example, in my own implementation, I'd like to be
able to convert a packet payload to a series of qlog event frames without
needing to reference persistent connection state.

I think there should be an alternative to log the raw value of the ACK
Delay field:

AckFrame = {
    frame_type: "ack"

    ; in ms
    ? ack_delay: float32

    ; integer value of the ACK Delay field, not scaled by the
ack_delay_exponent
    ? unscaled_ack_delay: uint64

    ; ...
}

- Damien