Update fee after channel becomes active

rkfg commented 1 week ago

Change Description

See #8790, PR recreated for several reasons. The fee update timer is initially set to zero to trigger the fee update check right after the channel becomes active, the next update interval will be random (between 10 and 60 minutes) as usual.

Steps to Test

Have a low commitment fee, make the estimated fee high and reconnect the peer. The commitment fee should update.

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Roasbeef commented 3 days ago

Approved CI run.

rkfg commented 1 day ago

This is very interesting, some lock-up is triggered if this timer is set to a small value. Couldn't that be a sign of a bigger issue somewhere? If it's set to 10-60 minutes as it is by now then the tests work fine. If I set it to less than 10 minutes it hangs. Could be a race condition between the tests?

rkfg commented 1 day ago

So the actual failing test is TestChannelLinkCancelFullCommitment, the update there blocks it from progressing. If I change the initial 0 to time.Second it starts running but since it takes a long time to settle all the HTLCs the fee update times out with failing link: unable to complete dance with error: remote unresponsive (I enabled log output for this test to see what's wrong). Normally that shouldn't be a problem I suppose, if we ever need to settle ≈483 HTLCs and then need to update the fee and it fails because it took us longer than pending-commit-interval to finish, the link would be dropped after that. Then we should reconnect and continue normally. So one solution would be to fix the test so that the update doesn't get in the way and break the link like this:

    n.aliceChannelLink.updateFeeTimer.Reset(time.Minute * 10)
    n.bobChannelLink.updateFeeTimer.Reset(time.Minute * 10)

as well as setting the original PR line to l.updateFeeTimer = time.NewTimer(time.Second * 1). In this case the test passes and doesn't hang indefinitely. I'll check the other unit tests, if there are too many that needs such a fix maybe it wasn't a good idea in the first place.

rkfg commented 1 day ago

Many tests seem to rely on update fee never happening unless explicitly requested. It either breaks their expectations or the link. Since the tests usually complete in under 2 minutes and the default fee update interval is at least 10 minutes those tests have never broken before. Not sure how to fix it reliably, I'd like the fee update to happen in 1-10 seconds after the link is established but then too many tests break so I set it to 1 minute now.

Another way could be patching the mock links like this:

diff --git a/htlcswitch/test_utils.go b/htlcswitch/test_utils.go
index 9a72197ec..70e8e71f0 100644
--- a/htlcswitch/test_utils.go
+++ b/htlcswitch/test_utils.go
@@ -1185,7 +1185,7 @@ func (h *hopNetwork) createChannelLink(server, peer *mockServer,
                        }
                }
        }()
-
+       link.(*channelLink).updateFeeTimer.Reset(time.Minute * 10)
        return link, nil
 }

and then adding a separate test to check for this short interval working as expected. Please tell me what solution is better for the project.

rkfg commented 1 day ago

Yes, I tried this before and the tests failed in the same way. Changing the timer period is better in this case because we can delay the fee update if needed. Currently the update period is 10-60 minutes, all tests are faster than that, no test accounts for a random fee update in the middle of the run (in production it can happen of course in a similar scenario). If we make a fee update soon after a channel becomes active, the test gets an unexpected update and misbehaves. Either many tests should be fixed (other issues could be discovered during that but idk tho) or we pretend nothing changed and test the short update period separately.

lightningnetwork / lnd