funding: fund channel with selected utxos #7516

hieblmi · 2023-03-15T20:57:38Z

This PR implements feature #6955.

Background

It extends the ways in which the user can instruct the OpenChannel RPC to allocate funds when opening a channel. Specifically, it adds the ability to select individual utxos from the user's wallet as the basis for funding. Besides funding via psbts, there are currently two ways in which the user can define the amount a channel is funded with, local_amt and fundmax. The former selects coins until the amount is reached and creates the funding output and a change output with the excess. The later uses up all available funds towards a channel opening. Both source from lnd's internal wallet.

This PR allows both these funding options to instead source from a set of defined utxos.

Examples

To see how this works lets consider two examples:

lncli openchannel --utxo=A --utxo=B --local_amt 100000
Instead of considering the entire available wallet balance only two utxos from our wallet are taken into account for funding a 100k cap channel.
lncli openchannel --utxo=A --utxo=B --fundmax
Instead of spending the entire wallet balance on a channel opening fundmax only consumes the specified utxos for it.

Wallet reserve considerations

In both examples we have to ensure that our wallet keeps enough funds to cover for the anchor reserve requirement.
For example, in the fundmax case, if the remaining wallet balance is less than the anchor reserve requirement, we have to carve out the remaining sats from the specified utxo set. Similarly this has to be handled for the local_amt case.

Roasbeef

Nice work! Super useful feature to make it easier to do coin control/selection funding on the CLI.

Did an initial pass with a few comments that jumped to mind.

lnwallet/chanfunding/assembler.go

lnwallet/chanfunding/wallet_assembler.go

rpcserver.go

lnwallet/wallet.go

itest/lnd_channel_funding_utxo_selection_test.go

cmd/lncli/cmd_open_channel.go

ziggie1984

Solid contribution 🤓, good structure, very nice itests.

Keep up the good work :)

rpcserver.go

lnwallet/wallet.go

itest/lnd_channel_funding_utxo_selection_test.go

ziggie1984 · 2023-05-24T22:10:19Z

itest/lnd_channel_funding_utxo_selection_test.go

+			localAmt:           btcutil.Amount(210_337),
+			chanOpenShouldFail: true,
+			expectedErrStr: "not enough witness outputs to " +
+				"create funding transaction, need 0.00210337 " +


q: does this error msg account for the reserve it the wallet tho, doesn't look like it ?

No it doesn't, in this test case the user chooses too much local_amt for what they have in their wallet. And it's not an anchor but a static remote key channel, so no reserve.

itest/lnd_channel_funding_utxo_selection_test.go

ziggie1984 · 2023-05-24T22:24:59Z

lnwallet/chanfunding/wallet_assembler.go

+					// manually selected coins can be spent
+					// entirely on the channel funding.
+					reserve = 0
+				}


shouldn't we decrease the reserve requirement by the reserve = reserve - (sumAll-sumManuel) amount here to let non selected coins also account for the reserve ?

Yeah right, but only if sumAll-sumManual < reserve. I thought about something like:

excess := sumAll - sumManual if excess >= reserve { reserve = 0 } else { reserve -= excess }

cmd/lncli/cmd_open_channel.go

hieblmi · 2023-05-25T11:11:26Z

Appreciate the review @ziggie1984, I will get to your comments in a bit.

lnwallet/chanfunding/wallet_assembler.go

shaurya947

Very nice feature! I was wondering if reordering the commits would make reviewing easier:
cli -> RPC(protobuf) -> rpcserver.go -> chanfunding -> lnwallet -> itest

lnwallet/chanfunding/wallet_assembler.go

itest/lnd_channel_funding_utxo_selection_test.go

ziggie1984

Almost ready had a final question regarding concurrent safety when manual utxo selection and allCoins selection happens in different places.

Some other remarks also in regards of the discussion during the review club:

We went by the idea, if we selected more than what is needed we just neglect the other inputs? No consolidation option?
Is the coin-selection strategy now part of this PR or is this still not influenced?

ziggie1984 · 2023-06-13T08:00:14Z

lnwallet/chanfunding/wallet_assembler.go

+				if excess >= reserve {
+					reserve = 0
+				} else {
+					reserve -= excess


ziggie1984 · 2023-06-13T08:02:49Z

lnwallet/chanfunding/wallet_assembler.go

+				// the excess of coins cover the reserve
+				// partially then we have to provide for the
+				// rest during coin selection.
+				excess := sumAll - sumManual


can we be sure that sumAll and sumManuel don't run in any race condition so that this always stays positive ?

now that the selection happens in one place it is guaranteed that we do not run into a race condition so this is fine here 👍

lnwallet/wallet.go

cmd/lncli/cmd_open_channel.go

itest/lnd_channel_funding_utxo_selection_test.go

hieblmi · 2023-07-12T09:01:55Z

@ziggie1984 thanks for your review. I placed the coin availability checks within the coin lock so to avoid a race here.

As to the coin selection and consolidation strategy discussed in the review club - this seems like an optimization that I want to address in a separate PR, once the basic functionality here is merged.

ziggie1984

LGTM 🎉

Had some minor nits but this looks very good, tested it locally and works perfect ! This feature is really cool.

ziggie1984 · 2023-07-12T12:03:02Z

rpcserver.go

@@ -2145,6 +2145,15 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 			"exceeds %d", in.Memo, len(in.Memo), maxMemoLength)
 	}

+	// Check if manually selected outpoints are present to fund a channel.


I think this comment is not what the below code does. It does not really check if outpoints are present imo? Just converts these to types ?

ziggie1984 · 2023-07-12T13:50:45Z

lnwallet/chanfunding/assembler.go

@@ -84,6 +84,13 @@ type Request struct {
 	// e.g. anchor channels.


Nit: Commit Msg: adds ability to fund a channel with a selected set of coins?

ziggie1984 · 2023-07-12T14:02:06Z

lnwallet/chanfunding/wallet_assembler.go

+			// selected coins that should be considered available
+			// for funding a channel.
+			manuallySelectedCoins []Coin
+			err                   error


Nit: We could still use := in the line and it would not redeclare the manuallySelectedCoins variable, or is this the style we have to adhere in such a case ? If so maybe an entry in the code_formatting_rules.md file

ziggie1984 · 2023-07-12T14:05:06Z

lnwallet/chanfunding/wallet_assembler.go

 			r.MinConfs, math.MaxInt32,
 		)
 		if err != nil {
 			return err
 		}

+		// Ensure that all manually selected coins remain unspent.
+		unspent := make(map[wire.OutPoint]struct{})


ziggie1984 · 2023-07-12T14:15:30Z

lnwallet/chanfunding/wallet_assembler.go

+				// the excess of coins cover the reserve
+				// partially then we have to provide for the
+				// rest during coin selection.
+				excess := sumAll - sumManual


now that the selection happens in one place it is guaranteed that we do not run into a race condition so this is fine here 👍

ziggie1984 · 2023-07-12T14:21:22Z

lnwallet/chanfunding/wallet_assembler.go

+					reserve = 0
+				}
+			}
+


Could you elaborate more, do you mean adding new external inputs as well when the internal ones do not suffice?

itest/lnd_channel_funding_utxo_selection_test.go

lightninglabs-deploy · 2023-07-19T19:01:54Z

@Roasbeef: review reminder
@hieblmi, remember to re-request review from reviewers when ready

Roasbeef

LGTM 🍾

Roasbeef · 2023-07-23T14:48:06Z

lnwallet/chanfunding/wallet_assembler.go

+		for _, coin := range allCoins {
+			unspent[coin.OutPoint] = struct{}{}
+		}
+		for _, coin := range manuallySelectedCoins {


Alternatively, we could also assert that the coins are locked as well at this stage. Though, if things proceed as expected here (final transaction actually broadcast), then this'll happen eventually.

Roasbeef · 2023-07-23T14:55:19Z

itest/lnd_channel_funding_utxo_selection_test.go

+}
+
+// runTestCase runs a single test case asserting that test conditions are met.
+func runUtxoSelectionTestCase(ht *lntest.HarnessTest, t *testing.T, alice,


Mismatch in godoc name: runTestCase -> runUtxoSelectionTestCase

itest/lnd_channel_funding_utxo_selection_test.go

Roasbeef · 2023-07-23T14:56:34Z

rpcserver.go

@@ -2145,6 +2145,15 @@ func (r *rpcServer) parseOpenChannelReq(in *lnrpc.OpenChannelRequest,
 			"exceeds %d", in.Memo, len(in.Memo), maxMemoLength)
 	}

+	// Check if manually selected outpoints are present to fund a channel.


hieblmi marked this pull request as draft March 15, 2023 20:59

hieblmi changed the title ~~funding: pass selected utxos to the OpenChannel RPC~~ funding: fund channel with selected utxos Mar 15, 2023

hieblmi force-pushed the utxo-funding branch from 22e3474 to c790d57 Compare March 15, 2023 21:07

saubyk linked an issue Mar 15, 2023 that may be closed by this pull request

Add argument to OpenChannel rpc to input UTXOs #6955

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saubyk assigned hieblmi Mar 15, 2023

hieblmi force-pushed the utxo-funding branch 4 times, most recently from 0d9ac8b to 625234d Compare March 20, 2023 20:53

hieblmi force-pushed the utxo-funding branch from 625234d to bdaaed1 Compare March 27, 2023 18:29

guggero changed the base branch from master to 0-16-1-staging March 28, 2023 07:35

hieblmi force-pushed the utxo-funding branch from bdaaed1 to 95f3417 Compare March 31, 2023 11:41

Roasbeef requested changes Apr 6, 2023

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hieblmi changed the base branch from 0-16-1-staging to master April 7, 2023 08:38

hieblmi force-pushed the utxo-funding branch from 95f3417 to e0b2308 Compare April 11, 2023 07:51

hieblmi mentioned this pull request Apr 11, 2023

Add argument to OpenChannel rpc to input UTXOs #6955

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hieblmi force-pushed the utxo-funding branch 5 times, most recently from b03a52e to 50b2658 Compare June 10, 2023 20:56

hieblmi marked this pull request as ready for review June 10, 2023 21:12

hieblmi requested review from Roasbeef and ziggie1984 June 10, 2023 21:12

hieblmi force-pushed the utxo-funding branch from 50b2658 to 03e904b Compare June 10, 2023 21:16

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ziggie1984 approved these changes Jul 12, 2023

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Roasbeef approved these changes Jul 23, 2023

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Roasbeef modified the milestones: v0.17.1, v0.17.0 Jul 23, 2023

hieblmi added 3 commits July 24, 2023 12:10

chanfunding: adds ability to fund a selected set of coins

ac523f9

lnrpc: adds field Outpoints to fund a selected set of coins

50acd49

lnwallet: adds selected Outpoints for funding

d327c92

hieblmi force-pushed the utxo-funding branch from 0c112a7 to 23467cb Compare July 24, 2023 11:06

hieblmi added 5 commits July 24, 2023 13:06

lnd: handles selected outpoints in parseOpenChannelReq

e4f0e58

lncli: add flag utxos for openchannel

f0579cc

chanfunding: fix typo

baa1419

itest: anchor reserve test for SendOutputs

396cffc

docs: update release notes

23467cb

Roasbeef merged commit 9ed064b into lightningnetwork:master Jul 25, 2023

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funding: fund channel with selected utxos #7516

funding: fund channel with selected utxos #7516

hieblmi commented Mar 15, 2023 •

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		@@ -84,6 +84,13 @@ type Request struct {
		// e.g. anchor channels.

funding: fund channel with selected utxos #7516

funding: fund channel with selected utxos #7516

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hieblmi commented Mar 15, 2023 • edited Loading

Background

Examples

Wallet reserve considerations

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hieblmi commented May 25, 2023

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hieblmi commented Mar 15, 2023 •

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