Jetty 12 - Remove WriteFlusher.Listener

[sbordet]

Jetty version(s)
12

Description
WriteFlusher.Listener was introduced to compute the response data rate.
This was necessary because for HTTP/2 or HTTP/3 we do not know often before hand how many bytes are flushed (because we use objects that are serialized just before hitting the network).
Furthermore wrapping with TLS complicates things because of the added wrapping.

However, I think it should now be possible to remove this (expensive) listener mechanism in favor of callbacks.

For HTTP/2, for example, a [Control|Data]Entry knows how many bytes it has generated, and upon completion of its write it can update the number of bytes written (for statistics), and check the minResponseDataRate in the callback inHttpStreamOverHTTP2.send().

This will only take into account clear-text writes (the overhead of a wrapping protocol such as TLS is not counted).

Note that we cannot move the bytes counting to EndPoint because for multiplexed protocols we want to check the minResponseDataRate per-stream, not per-session.

[sbordet]

@gregw thoughts?

[gregw]

@sbordet the less listeners the better

[github-actions]

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