[Lightning-dev] Making (some) channel limits dynamic

[Bastien TEINTURIER]

Good evening list,

Recent discussions around channel jamming [1] have highlighted again the
need to think twice when
configuring your channels parameters. There are currently parameters that
are set once at channel
creation that would benefit a lot from being configurable throughout the
lifetime of the channel
to avoid closing channels when we just want to reconfigure them:

* max_htlc_value_in_flight_msat
* max_accepted_htlcs
* htlc_minimum_msat
* htlc_maximum_msat

Nodes can currently unilaterally udpate these by applying forwarding
heuristics, but it would be
better to tell our peer about the limits we want to put in place (otherwise
we're wasting a whole
cycle of add/commit/revoke/fail messages for no good reason).

I suggest adding tlv records in `commitment_signed` to tell our channel
peer that we're changing
the values of these fields.

Is someone opposed to that?
Are there other fields you think would need to become dynamic as well?
Do you think that needs a new message instead of using extensions of
`commitment_signed`?

Cheers,
Bastien

[1] https://twitter.com/joostjgr/status/1308414364911841281
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