Allow coop closing a channel with HTLCs on it via lncli by ziggie1984 · Pull Request #9491 · lightningnetwork/lnd

ziggie1984 · 2025-02-09T11:31:25Z

This PR adds the possibility to coop close a channel which has still HTLCS on it. Moreover it makes sure we do not exceed the max-fee-rate we specify.

This change is

coderabbitai · 2025-02-09T11:31:34Z

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yyforyongyu

I guess this is a followup of #8167?

cmd/commands/commands.go

docs/release-notes/release-notes-0.18.5.md

cmd/commands/commands.go

rpcserver.go

yyforyongyu

Reviewed 3 of 4 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: 4 of 5 files reviewed, 4 unresolved discussions (waiting on @starius)

itest/lnd_coop_close_with_htlcs_test.go line 263 at r2 (raw file):

	// Wait for Bob to understand that the channel is ready to use.
	ht.AssertChannelInGraph(bob, chanPoint)

use ht.CreateSimpleNetwork instead?

itest/lnd_coop_close_with_htlcs_test.go line 270 at r2 (raw file):

	// Have alice attempt to close the channel but we the expected fee rate
	// exceeds the max fee rate so we fail the closing process.
	closeClient := alice.RPC.CloseChannel(&lnrpc.CloseChannelRequest{

nit: can use ht.CloseChannelAssertErr instead

cmd/commands/commands.go line 1036 at r2 (raw file):

			Name: "block",
			Usage: `block will wait for the channel to be closed,
			"meaning that it will wait for the channel tx to get 1

should be close tx or channel close tx, not sure what channel tx is

rpcserver.go line 2876 at r2 (raw file):

		).FeePerKWeight()

		if maxFee != 0 && maxFee < feeRate {

I'm not sure about this approach, either should it abort the flow, or cap the value. Since right now, the chan closer will always use the maxFee instead when it's set.

starius

I added several questions.

cmd/commands/commands.go

rpcserver.go

starius · 2025-02-13T03:32:12Z

cmd/commands/commands.go

 		MaxFeePerVbyte:  ctx.Uint64("max_fee_rate"),
+		// This makes sure that a coop close will also be executed if
+		// active HTLCs are present on the channel.
+		NoWait: true,


The effect of waiting for HTLCs is documented in rpcserver.go, but not in the schema.

// If true, then the rpc call will not block while it awaits a closing txid. // Consequently this RPC call will not return a closing txid if this value // is set. bool no_wait = 8;

// If the user hasn't specified NoWait, then before we attempt // to close the channel we ensure there are no active HTLCs on // the link. if !in.NoWait && len(channel.ActiveHtlcs()) != 0 {

I propose to add this important detail to the schema as well and maybe rename the flag to coop_with_htlcs or wait_for_htlcs or something to make it clear that it affects the closing transaction (making it coop instead of force close), not only for how long it executes.

Looking at the current name and the description of NoWait I thought originally, that it is a flag similar to --block before I read the code of rpcserver.go.

we cannot rename it because of backwards comp. issues. I think with a proper description we can keep it like this.

The description is great! Thanks!

Is it possible to decouple it into two flags? So NoWait only affects RPC behavior (whether or now to wait in RPC for transaction being broadcasted and return its txid) and a new flag would define what to do if there is a pending HTLC (force-close or wait-and-coop-close).

In that case NoWait can be removed, since it can be implemented on the client side similar to --block. The former will wait on gRPC stream for a transaction being broadcast, while the later waits on gRPC stream for confirmation of the transaction.

What do you think?

yeah I think resolving this with 2 distinct flags is the way to go, but I keep it low priority for now.

cmd/commands/commands.go

docs/release-notes/release-notes-0.19.0.md

ziggie1984

Reviewable status: 1 of 12 files reviewed, 12 unresolved discussions (waiting on @starius and @yyforyongyu)

rpcserver.go line 2876 at r2 (raw file):

Previously, yyforyongyu (Yong) wrote…

I'm not sure about this approach, either should it abort the flow, or cap the value. Since right now, the chan closer will always use the maxFee instead when it's set.

Could you elaborate, we only want to abort if the user specified a feerate which is lower than the estimate for the first intial fee rate ?

cmd/commands/commands.go line 1036 at r2 (raw file):

Previously, yyforyongyu (Yong) wrote…

should be close tx or channel close tx, not sure what channel tx is

👌

itest/lnd_coop_close_with_htlcs_test.go line 270 at r2 (raw file):

Previously, yyforyongyu (Yong) wrote…

nit: can use ht.CloseChannelAssertErr instead

ok but had to change the func signature for that, now I pass in the req instead of the single arguments.

rpcserver.go

lnrpc/lightning.proto

lnwallet/chancloser/chancloser.go

yyforyongyu

Looks like the CI failed

Reviewed 9 of 11 files at r3.
Reviewable status: 10 of 12 files reviewed, 11 unresolved discussions (waiting on @starius and @ziggie1984)

rpcserver.go line 2876 at r2 (raw file):

Previously, ziggie1984 (ziggieXXX) wrote…

Could you elaborate, we only want to abort if the user specified a feerate which is lower than the estimate for the first intial fee rate ?

yeah nvm, was thinking we should cap it since it could cause the coop negotiation to fail, but maybe it's easier to just abort it here.

rpcserver.go line 2899 at r3 (raw file):

	if in.NoWait {
		rpcsLog.Trace("[closechannel] sending instant update")
		activeHtlcs := len(channel.ActiveHtlcs())

I think this value is already obtained above.

lnrpc/lightning.proto

lnwallet/chancloser/chancloser.go

starius

LGTM! 🌴
The proposal to decouple the flag is for another PR if you decide to implement it.

cmd/commands/commands.go

starius · 2025-02-13T16:03:45Z

cmd/commands/commands.go

 		MaxFeePerVbyte:  ctx.Uint64("max_fee_rate"),
+		// This makes sure that a coop close will also be executed if
+		// active HTLCs are present on the channel.
+		NoWait: true,


The description is great! Thanks!

Is it possible to decouple it into two flags? So NoWait only affects RPC behavior (whether or now to wait in RPC for transaction being broadcasted and return its txid) and a new flag would define what to do if there is a pending HTLC (force-close or wait-and-coop-close).

In that case NoWait can be removed, since it can be implemented on the client side similar to --block. The former will wait on gRPC stream for a transaction being broadcast, while the later waits on gRPC stream for confirmation of the transaction.

What do you think?

ziggie1984

Reviewable status: 6 of 12 files reviewed, 11 unresolved discussions (waiting on @starius and @yyforyongyu)

rpcserver.go line 2899 at r3 (raw file):

Previously, yyforyongyu (Yong) wrote…

I think this value is already obtained above.

Done.

cmd/commands/commands.go

yyforyongyu

Looking good, only a few typos.

itest/lnd_coop_close_with_htlcs_test.go

htlcswitch/switch.go

docs/release-notes/release-notes-0.19.0.md

yyforyongyu · 2025-02-20T15:39:46Z

itest/lnd_coop_close_with_htlcs_test.go

+	// Set the fee estimate for one block to 10 sat/vbyte.
+	ht.SetFeeEstimateWithConf(chainfee.SatPerVByte(10).FeePerKWeight(), 1)
+
+	// Have alice attempt to close the channel but we the expected fee rate


Suggested change

// Have alice attempt to close the channel but we the expected fee rate

// Have alice attempt to close the channel but we expect the fee rate

Changed the structure even more.

lnrpc/lightning.proto

rpcserver.go

For the lncli cmd we now always initiate the coop close even if there are active HTLCs on the channel. In case HTLCs are on the channel and the coop close is initiated LND handles the closing flow in the background and the lncli cmd will block until the transaction is broadcasted to the mempool. In the background LND disallows any new HTLCs and waits until all HTLCs are resolved before kicking of the negotiation process. Moreover if active HTLCs are present and the no_wait param is not set the error msg is now highlightning it so the user can react accordingly.

yyforyongyu

LGTM🌹 - looks like forward_interceptor_restart is extremely flaky these days, will investigate.

ziggie1984 self-assigned this Feb 9, 2025

ziggie1984 force-pushed the closechannel-rpc branch from a978a6c to 6ce096d Compare February 9, 2025 11:53

ziggie1984 marked this pull request as ready for review February 9, 2025 11:54

ziggie1984 force-pushed the closechannel-rpc branch 2 times, most recently from 6f66e70 to 1e9cbc8 Compare February 9, 2025 12:33

yyforyongyu reviewed Feb 10, 2025

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ziggie1984 force-pushed the closechannel-rpc branch 2 times, most recently from 67122b4 to 9e289f7 Compare February 10, 2025 08:05

ziggie1984 requested a review from yyforyongyu February 10, 2025 08:17

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ziggie1984 force-pushed the closechannel-rpc branch 2 times, most recently from 7f47e31 to 83bc0b9 Compare February 12, 2025 15:35

ziggie1984 requested review from starius and yyforyongyu February 12, 2025 19:07

yyforyongyu requested changes Feb 13, 2025

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ziggie1984 force-pushed the closechannel-rpc branch from 83bc0b9 to ad10e21 Compare February 13, 2025 12:21

ziggie1984 commented Feb 13, 2025

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saubyk added this to the v0.19.0 milestone Feb 13, 2025

starius approved these changes Feb 13, 2025

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ziggie1984 force-pushed the closechannel-rpc branch from ad10e21 to 1400bbe Compare February 13, 2025 18:45

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yyforyongyu reviewed Feb 20, 2025

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ziggie1984 added 4 commits February 20, 2025 17:43

lnd: add max fee rate check to closechannel rpc

f458844

htlcswitch: fix log output

f994c2c

docs: add release-notes

8017139

ziggie1984 force-pushed the closechannel-rpc branch from 6b7cbac to 8017139 Compare February 20, 2025 16:43

ziggie1984 requested a review from yyforyongyu February 20, 2025 16:45

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guggero merged commit 1227eb1 into lightningnetwork:master Feb 21, 2025
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	// Have alice attempt to close the channel but we the expected fee rate
	// Have alice attempt to close the channel but we expect the fee rate

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ziggie1984 commented Feb 9, 2025 •

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