tapchannel: add a 1msat per HTLC extra tolerance to invoice acceptor #1639
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When converting an mSAT amount to units and vice versa we frequently get an off-by-1-unit result. This is already accounted for in our invoice acceptor by adding the value of as many asset units as HTLCs in the invoice. What we didn't account for is that the UnitsToMilliSatoshi calculation for the margin can also be off by 1 msat.
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guggero
approved these changes
Jul 4, 2025
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Description
When converting an mSAT amount to units and vice versa we frequently get an off-by-1-unit result. This is already accounted for in our invoice acceptor by adding the value of as many asset units as HTLCs in the invoice. What we didn't account for is that the UnitsToMilliSatoshi calculation for the margin can also be off by 1 msat.
So the result of
UnitsToMilliSatoshifor thetotalUnits - 1can itself be off by 1mSAT, compared to the result ofUnitsToMilliSatoshifor a single unit