Add `maxFeeRatio` parameter to sanityCheckFee in psbt coin selection by GeorgeTsagk · Pull Request #8600 · lightningnetwork/lnd

GeorgeTsagk · 2024-03-28T16:47:19Z

Description

With the introduction of new template options for WalletKit.FundPsbt (see related PR) we made use of chanfunding.CoinSelect which introduces a slight change in behavior compared to the other template options, it performs a "fee sanity check" which will error out if the total fees exceed the 20% of the total outputs amount.

While this makes sense for channel funding, it may be a limitation the user won't always desire when manually funding PSBTs via the RPC.

Solution [Updated]

This PR simply adds a float parameter to the chanfunding.CoinSelect named maxFeeRatio which controls the maximum allowed fee to total output amt ratio. Any other path other than the WalletKit.FundPsbt rpc uses the default ratio of 0.2 (20% of total output amount). When calling this function from the RPC we use the value provided by the RPC, or the default if it wasn't set.

References

Tapd PR that exposed this behavior

coderabbitai · 2024-03-28T16:47:24Z

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guggero

Change makes sense. Didn't think about very small amounts when adding the fee sanity check.

guggero · 2024-04-02T11:35:23Z

 		changeAmt, needMore, err := chanfunding.CalculateChangeAmount(
 			inputSum, outputSum, packetFeeNoChange,
-			packetFeeWithChange, changeDustLimit, changeType,
+			packetFeeWithChange, changeDustLimit, changeType, true,


I think adding this flag makes sense, as you might want to be able to craft a 1-in-1-out transaction that pays more than 20% fees when it's a small input amount. But I think we should also expose this to the RPC and not just set this to true statically here.
So a new bool RPC parameter, for example allow_high_fees which by default is false.

Ok, very happy to see that you agree with this approach.

I didn't expose this on RPC only because of "bloating" concerns, as I didn't want this extra flag to reach the user-facing params.
But I also think a psbt related call is the place to be specific and have fine control, on the other hand. So will change it as per your suggestion 👌

dstadulis · 2024-05-16T15:26:10Z

!lightninglabs-deploy mute 720h30m

litbot-9000 · 2024-07-08T01:55:11Z

@GeorgeTsagk, remember to re-request review from reviewers when ready

guggero · 2024-07-08T08:08:11Z

!lightninglabs-deploy mute

dstadulis · 2024-09-18T13:04:31Z

There's renewed interest in shipping these features.

Will unmute to try to merge the code. If alerts are bothersome for a long time, we can remute

!lightninglabs-deploy unmute

ziggie1984 · 2024-09-19T16:22:30Z

hmm, I think rather than adding a ratio, what about skipping the sanity_fee check, because I think the ratio idea is basically the same as skipping it, at least that's how I envision it will be used.

instead of a ratio, just add maybe a flag to skip the fee-check

guggero

Needs some commit massaging, otherwise looks pretty good.

GeorgeTsagk · 2024-10-15T16:23:19Z

@guggero all commits can compile now

guggero

Linter and commit check still fails.
Other than that looks good to me.

Helper command to make sure each commit compiles individually:

git rebase -i origin/master --exec "make unit pkg=... case=_NONE_"

GeorgeTsagk · 2024-10-28T17:56:52Z

Linter and commit check still fails. Other than that looks good to me.

Helper command to make sure each commit compiles individually:
git rebase -i origin/master --exec "make unit pkg=... case=_NONE_"

Ah yes, the first commit that updates the func didn't have the unit tests calling the funcs with all args, used dummy values just for the commit to compile, should be good now

GeorgeTsagk · 2024-11-04T13:13:08Z

Forgot to update the cmd command, doing now

guggero

Just nits, otherwise LGTM 🎉

ziggie1984

Still not convinced about the ratio approach but i am open to hear your side of the argument why we should not just instead go with a boolean here ?

I think the use-case will look like this:

User funds psbt, and gets the error that the fee exceeds 20%
Probably we currently also return the acutaly ratio with would be needed
User just selects this ratio, however because we use a > maxFee, he will probably do it twice

So I would favour just a skipFee boolean, which imo does exactly the right thing.

GeorgeTsagk · 2024-11-05T14:09:20Z

Still not convinced about the ratio approach but i am open to hear your side of the argument why we should not just instead go with a boolean here ?

I think the use-case will look like this:

User funds psbt, and gets the error that the fee exceeds 20%

Probably we currently also return the acutaly ratio with would be needed

User just selects this ratio, however because we use a > maxFee, he will probably do it twice

So I would favour just a skipFee boolean, which imo does exactly the right thing.

Yeah I agree that a skipFee bool could be simpler for a manual user-driven story

Although this is also meant for external automated software that uses lnd for the funding of psbts

Could have a protocol/wallet that needs to craft PSBTs, and depending on what the application is I might want to select a certain ratio across all my calls to FundPsbt. One application may want to pick a protective ratio, another one maybe a more aggressive/relaxed ratio.

If we had the skipFee version here we would force all the external software to do the fee check on their end, while now they can rely on LND's internal fee calculations by exposing max_fee_ratio

I don't really have better arguments than this, and that I'd rather have a bit more expressiveness by default

ziggie1984

Ok agree, the ratio idea can make sense for external software 👍

Had some final comments.

ziggie1984

LGTM

GeorgeTsagk · 2024-11-05T15:24:37Z

Fixed some more unit tests which expected the old err format, waiting for CI

guggero

Some last minute changes made it into the wrong commit.

GeorgeTsagk · 2024-11-05T18:57:28Z

Thanks for the last second nits @guggero 💪

guggero

Nice, LGTM 🎉

GeorgeTsagk self-assigned this Mar 28, 2024

guggero requested changes Apr 2, 2024

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GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch from 129145c to 1f32b5f Compare September 19, 2024 14:21

GeorgeTsagk changed the title ~~Omit fee sanity check on chanfunding.CoinSelect when coming from RPC FundPsbt~~ Add maxFeeRatio parameter to sanityCheckFee in psbt coin selection Sep 19, 2024

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch from 1f32b5f to 155d1a0 Compare September 19, 2024 15:02

GeorgeTsagk requested a review from guggero September 19, 2024 15:03

guggero reviewed Oct 14, 2024

View reviewed changes

Comment thread lnrpc/walletrpc/walletkit_server.go

Comment thread lnrpc/walletrpc/walletkit.proto Outdated

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch from 155d1a0 to 0e487e4 Compare October 15, 2024 16:23

GeorgeTsagk requested a review from guggero October 15, 2024 16:23

guggero mentioned this pull request Oct 24, 2024

chanfunding: improve sanityCheckFee error message for clarity #9219

Merged

guggero reviewed Oct 28, 2024

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Comment thread lnwallet/chanfunding/coin_select.go Outdated

Comment thread lnwallet/chanfunding/coin_select.go

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch from 0e487e4 to 5eda335 Compare October 28, 2024 17:55

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch 2 times, most recently from 909891c to e138fa7 Compare November 4, 2024 10:16

GeorgeTsagk requested a review from guggero November 4, 2024 13:03

guggero approved these changes Nov 4, 2024

View reviewed changes

Comment thread lnwallet/chanfunding/coin_select.go Outdated

Comment thread docs/release-notes/release-notes-0.19.0.md Outdated

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch 2 times, most recently from ca72f74 to 582fe81 Compare November 5, 2024 09:24

ziggie1984 self-requested a review November 5, 2024 10:58

ziggie1984 reviewed Nov 5, 2024

View reviewed changes

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch 2 times, most recently from 51d09d5 to 33320ba Compare November 5, 2024 14:41

ziggie1984 reviewed Nov 5, 2024

View reviewed changes

Comment thread lnrpc/walletrpc/walletkit_server_test.go

ziggie1984 reviewed Nov 5, 2024

View reviewed changes

Comment thread lnwallet/chanfunding/coin_select.go

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch from 33320ba to b19fac1 Compare November 5, 2024 15:03

ziggie1984 approved these changes Nov 5, 2024

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GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch from b19fac1 to 6116039 Compare November 5, 2024 15:21

ziggie1984 reviewed Nov 5, 2024

View reviewed changes

Comment thread lnrpc/walletrpc/walletkit_server_test.go

guggero reviewed Nov 5, 2024

View reviewed changes

Comment thread lnwallet/chanfunding/coin_select.go Outdated

Comment thread lnwallet/chanfunding/coin_select.go

Comment thread lnrpc/walletrpc/walletkit_server.go Outdated

GeorgeTsagk added 5 commits November 5, 2024 19:55

lnwallet: use new maxFeeRatio for sanityCheckFee func

a72dae3

lnrpc: add maxFeeRatio to FundPsbtRequest

f2b7632

lnwallet+lnrpc: use maxFeeRatio across coin selection tests

55c3da3

cmd: expose max_fee_ratio to fundpsbt command

b51dde7

docs: update release notes for fundpsbt max_fee_ratio

c1f5908

GeorgeTsagk force-pushed the chanfunding-coinselect-nofeecheck branch from 6116039 to c1f5908 Compare November 5, 2024 18:56

GeorgeTsagk requested a review from guggero November 5, 2024 18:57

guggero approved these changes Nov 5, 2024

View reviewed changes

guggero merged commit e3cc4d7 into lightningnetwork:master Nov 5, 2024

GeorgeTsagk mentioned this pull request Mar 10, 2025

[bug]: Small Anchor Output Amounts Trigger False Positive in Fee Tolerance Check lightninglabs/taproot-assets#1417

Closed

guggero mentioned this pull request May 10, 2025

[feature]: Make Fee Floor Configurable for Outbound Transfers lightninglabs/taproot-assets#1524

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Description

Solution [Updated]

References

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