[bug]: lnwallet's DustLimitForSize doesn't consider p2tr outputs precisely

[hieblmi]

Calls to lnwallet.DustLimitForSize(input.P2TRSize) generate a dust limit based on input.GenerateUnknownWitness() which assumes a maximum witness size of 40 bytes.

Similar to GenerateP2PKH, we should provide a function GenerateP2TR to account for the exact taproot witness size.

See:

lnd/lnwallet/parameters.go

Line 46 in bb9c680

func DustLimitForSize(scriptSize int) btcutil.Amount {

[ziggie1984]

Hmm not sure if we want to fix it, because we overestimate just by 8 bytes and currently the BOLT spec also does classify all other Pk_Script with a StackElement > OP_0 as unknown witness: https://github.com/lightning/bolts/blob/master/03-transactions.md#dust-limits

If we go that route we would also need to maybe adjust the input script (witness) assumption which is currently after discountn 107.

So not sure if we wanna go this route.

[Crypt-iQ]

input.P2TRSize is identical to input.P2WSHSize so it doesn't hit the unknown case

[hieblmi]

input.P2TRSize is identical to input.P2WSHSize so it doesn't hit the unknown case

True, both are 34, maybe a clarifying comment on the case input.P2WSHSize will suffice then.