LND sends an incoming HTLC which would exceed local `maxHtlcValueInFlightMsat`

[akumaigorodski]

Background

BLW user attempted to send and receive a number of HTLCs through a channel with LND node and some of outgoing HTLCs got stuck, a bit later LND attempted to fulfill one of BLW's payment requests but doing so exceeded a local maxHtlcValueInFlightMsat.

BLW maxHtlcValueInFlightMsat is set to 4000000 SAT, LND maxHtlcValueInFlightMsat is set to 14850000 SAT, BLW has 7 stuck outgoing HTLCs with total sum of 5783057 SAT which already exceeds local in-flight limit, which is fine since when sending we only take into account a remote limit (right?).

As far as I understand LND should not attempt to fullfill any of BLW's requests until total in-flight sum gets below 4000000 SAT but it does.

Your environment

0.5.1-beta commit=v0.5.1-beta-rc4

[akumaigorodski]

On a slightly related note, I've just tried to remove local maxHtlcValueInFlightMsat check to let an incoming HTLC get fulfilled but LND sends a commit_sig which BLW thinks is invalid. I guess we can deal with that once this one is settled.

[cfromknecht]

@btcontract thanks for the report!

which is fine since when sending we only take into account a remote limit (right?).

Yes it will only apply the remote limit.

As far as I understand LND should not attempt to fullfill any of BLW's requests until total in-flight sum gets below 4000000 SAT but it does.

The limits are directional; BLW can only offer 14850000 sat in-flight, and LND can only offer 4000000 sat. If the final payment from LND to BLW was below 4000000 sat, I think this is expected?

[cfromknecht]

From BOLT 02:

if the sum of total offered HTLCs would exceed the remote's max_htlc_value_in_flight_msat:

• MUST NOT add an HTLC.

[akumaigorodski]

Indeed, thanks for explanations. BLW gets it wrong here by checking a total in-flight amount.