[bug]: sweep: LinearFeeFunction off by one about lnd HOT 6 OPEN

@saubyk add to 18.0?

from lnd.

@saubyk add to 18.0?

makes sense. added.

from lnd.

cc: @yyforyongyu

from lnd.

But in the extreme case of a next-block deadline, LinearFeeFunction will return the min feerate instead of the max, which is quite bad.

What do you mean by saying next-block deadline? That we only have 1 block left till it times out? What is this min feerate?

from lnd.

What do you mean by saying next-block deadline? That we only have 1 block left till it times out? What is this min feerate?

Here's an example graph of the LinearFeeFunction. The min feerate is the starting feerate. The max feerate is the ending feerate.

Now imagine we call SweepInput with a deadline 1 block away. The fee function will be initialized with a width of 1 and starting feerate at the minimum of the feerate line. After 1 block (i.e. deadline missed), the feerate will be immediately bumped to the maximum of the feerate line.

But for this next-block deadline case, we really don't want a sloped line at all -- we want to start right at the maximum.

from lnd.

func (l *LinearFeeFunction) feeRateAtPosition(p uint32) chainfee.SatPerKWeight {
if p >= l.width - 1 {
return l.endingFeeRate
}
...
}
does this suggestion fix the issue located in /sweep/fee_function.go

from lnd.