Eclair sends out HTLC that pushes peer below channel reserve resulting in a force close

[DerEwige]

I had 2 force closes with LND nodes that were triggered by “internal error”.
I don’t have any logs on my side leading up to the issue other than:

2023-05-07 16:37:21,481 ERROR f.a.e.c.fsm.Channel n:020ca6f9aaebc3c8aab77f3532112649c28a0bfb1539d0c2a42f795fb6e4c363b2 c:ebe6bd43f9ee41617fcc455c869eaba86a5edc98a0e4bd25ac698b2054bc508e - peer sent error: ascii='internal error' bin=696e7465726e616c206572726f72
2023-05-07 16:37:21,511 INFO  f.a.e.c.p.TxPublisher n:020ca6f9aaebc3c8aab77f3532112649c28a0bfb1539d0c2a42f795fb6e4c363b2 c:ebe6bd43f9ee41617fcc455c869eaba86a5edc98a0e4bd25ac698b2054bc508e - publishing commit-tx txid=76a55a85d7c8ea382d2de31dc3e5de0191f0e52f94d5eee260a9e19379da5720 spending 8f50bc54208b69ac25bde4a098dc5e6aa8ab9e865c45cc7f6141eef943bde6eb:1 with id=940b27af-fd2e-41e4-afa0-7251f0db4238 (0 other attempts)

The reason is: I run that class in “WARN” log level because of the amount of logs my rebalances cause

I recently started to try to get in touch with all my peers that have a force close triggered by “internal error” from LND to figure out what really happened.

I managed to get hold for the logs of both these cases an believe that this might actually be eclairs fault or an incompatibility problem:

In short:
In both cases most of the liquidity (98+%) was on my side in the channel. I tried to sent a payment through the channel but my peer returned an error, which then caused a force close.
This is the log from the LND sides

2023-05-07 16:37:21.363 [ERR] HSWC: ChannelLink(8f50bc54208b69ac25bde4a098dc5e6aa8ab9e865c45cc7f6141eef943bde6eb:1): failing link: unable to update commitment: commitment transaction dips peer below chan reserve: our balance below chan reserve with error: internal error

I already opened a case when I encountered the first FC in the LND repo:

lightningnetwork/lnd#7657

There they think it might be an issue with fee calculation. That somewhat is different on Eclair vs LND
That leads to the situation in which Eclair thinks it is ok to add the HTLC but LND refuses.

eclair version: version=0.8.0 commit=0077471

[t-bast]

Let's follow this in lightningnetwork/lnd#7657, I've asked for some data to be able to reproduce the issue and see who is incorrectly computing the reserve.

[t-bast]

Closing this issue as the issue is on the lnd side (see lightningnetwork/lnd#7657 (comment)). We will ignore lnd's "internal error" messages in the next release, which will hopefully help avoid force-closing such channels (see #2659).