cnct: anchor output sweeping and fee bumping #3758

joostjager · 2019-11-25T10:50:44Z

LND supports an experimental commitment format that produces anchor outputs (#3829, lightning/bolts#688). Anchor outputs allow users to increase the fee of their commitment txes after they've been published. It allows timely confirmation even if the miner fee of the commitment tx itself is insufficient.

This PR adds the functionality required to do so. When the commitment tx isn't confirming, the BumpFee rpc can be used to increase the fee of the total package. Anchor outpoints that are available can be discovered via the PendingChannels and PendingSweeps rpcs.

To make the experience more friendly towards users, a composite lncli command bumpclosefee is added.

For channels in the waiting_close_channels stage, this command can be used as follows:

lncli wallet bumpclosefee 2b66cf489298b5b4a9305127413e4124e385588178e4b0fc4cec2d28c277b17d:0 --sat_per_byte 15

Notes:

lnd needs to be built with the walletrpc subserver enabled.
The channel that is closed needs to be an anchor channel. Anchor channels are created automatically with OpenChannel when both sides run lnd with --protocol.anchors
The anchor commitment format is experimental. It doesn't have the reliability track record of the regular commitment format and therefore carries more risk. There is also still a chance of breaking changes in future releases. In that case, lnd will most likely require anchor channels to be closed before upgrading.

Important implementation changes made:

Keeping certain anchor inputs in separate sweep transactions always. When the commitment transaction hasn't confirmed yet, we don't know which of the three versions (local, remote, remote pending) will confirm. We attempt to sweep all three anchors, but batching those together would always create an invalid tx.
A dedicated bucket for sweeping at the minimum fee rate. Anchor outputs are very small and if they would be batched in a higher fee rate bucket, they are unlikely to be economical.
Try to sweep anchors before and after commit confirms
Report status of anchor sweep

joostjager · 2020-03-16T12:44:25Z

One more issue found. Recording commit a9c08ab as base for comparison (git range-diff).

This issue was that when NewAnchorResolutions was called, there was no fresh copy of the channel state obtained from the db.

Co-authored-by: Joost Jager <[email protected]>

Exclusive group is a static property that doesn't need to be updated. Requiring the exclusive group to be passed into UpdateParams creates a burden for the caller to make sure they supply the existing group. This change will be beneficial for users that bump anchor sweeps that have exclusive groups set.

halseth

Great work, LGTM ✅ Only non-blockinng comments.

contractcourt/channel_arbitrator.go

input/size.go

contractcourt/anchor_resolver.go

rpcserver.go

Prior to this change, the trigger height for closed channels was set to the current best block height. As this height is in some cases used as a height hint, the spend may have been missed.

Allows unit testing of the channel arbitrator with fewer dependencies. This is a preparation for the addition of anchor sweeping.

Relay fee is needed later to sweep anchors at the minimum fee rate.

joostjager · 2020-03-17T18:12:31Z

Need to fix restore_from_backup_file_anchors itest after rebase

Start anchor sweep attempts immediately after the commitment transaction has been published. This makes the anchor known to the sweeper and allows the user to bump the fee on it to get their commitment transaction confirmed in case the fee committed too is insufficient for timely confirmation.

Preparation for the anchor resolver which does not have persistent state.

Preparation for anchor resolver. The recovered anchor amount should still be included in the pending channel report even after it has been resolved. This also fixes an existing bug that in some cases caused the recovered amount from an htlc resolver not to be included in the total.

Sweeping anchors and being able to bump the fee was already added in a previous commit. This commit extends anchor sweeping with an anchor resolver object that becomes active after the commitment tx confirms. At that point, the anchors do not serve the purpose of getting the commitment tranaction confirmed anymore. It is however still possible to reclaim some of their value if using a low fee rate.

To make it easier to determine which pending sweep to bump in order to get your anchor commitment tx confirmed.

This command allows users to easily bump the fee on their unconfirmed closing transactions.

joostjager · 2020-03-18T14:27:31Z

Anchors itest failure fixed as part of 'cnct: pre-confirmation anchor sweep'

joostjager force-pushed the anchor-output-poc-joost branch 5 times, most recently from 3a906e6 to bb94988 Compare December 2, 2019 11:28

joostjager force-pushed the anchor-output-poc-joost branch 2 times, most recently from 79e8375 to 6df6c0e Compare December 3, 2019 10:32

halseth added the anchors label Dec 5, 2019

joostjager force-pushed the anchor-output-poc-joost branch 4 times, most recently from 338b1f2 to 7f4ecde Compare December 12, 2019 12:38

joostjager force-pushed the anchor-output-poc-joost branch 4 times, most recently from ef5d3c6 to f4ac679 Compare January 7, 2020 16:20

Roasbeef mentioned this pull request Jan 14, 2020

Feature Request: Specify the lowest CSV delay we're willing to accept #2426

Closed

Roasbeef added the v0.10 label Jan 14, 2020

joostjager mentioned this pull request Jan 14, 2020

anchor wip #3599

Closed

joostjager force-pushed the anchor-output-poc-joost branch 5 times, most recently from aaac70c to bec3316 Compare January 24, 2020 11:32

joostjager mentioned this pull request Jan 24, 2020

[anchors] anchors resolutions #3920

Closed

joostjager force-pushed the anchor-output-poc-joost branch 3 times, most recently from e6c5a18 to c72e852 Compare January 27, 2020 10:33

joostjager force-pushed the anchor-output-poc-joost branch 2 times, most recently from cf266e3 to 8c9717c Compare February 12, 2020 09:03

joostjager force-pushed the anchor-output-poc-joost branch 2 times, most recently from e36eccc to a6784a4 Compare March 16, 2020 16:55

joostjager and others added 4 commits March 17, 2020 14:19

lnwallet/test: pass in test channel type

30fc03d

lnwallet+channeldb: add anchor resolutions

dc6c463

Co-authored-by: Joost Jager <[email protected]>

sweep: isolate min fee rate bucket

1c93e9e

joostjager force-pushed the anchor-output-poc-joost branch from a6784a4 to 64c60f2 Compare March 17, 2020 13:21

halseth reviewed Mar 17, 2020

View reviewed changes

halseth approved these changes Mar 17, 2020

View reviewed changes

joostjager added 6 commits March 17, 2020 16:25

cnct: always set trigger height to close height

c0b1b3b

Prior to this change, the trigger height for closed channels was set to the current best block height. As this height is in some cases used as a height hint, the spend may have been missed.

cnct: create channel interface for arbitrator

7f3d4e7

Allows unit testing of the channel arbitrator with fewer dependencies. This is a preparation for the addition of anchor sweeping.

cnct: persist anchor resolutions

dd77d92

input: add anchor witness type

c376cdb

cnct+sweeper: give contract court access to relay fee

3b51739

Relay fee is needed later to sweep anchors at the minimum fee rate.

cnct: simplify channel arbitrator state logging

e8e99c6

joostjager force-pushed the anchor-output-poc-joost branch from 64c60f2 to 2cd26d0 Compare March 17, 2020 15:34

joostjager force-pushed the anchor-output-poc-joost branch 2 times, most recently from b01923b to afc5023 Compare March 18, 2020 08:08

joostjager added 7 commits March 18, 2020 12:26

cnct: do not persist stateless resolvers

07a39b1

Preparation for the anchor resolver which does not have persistent state.

cnct+lnrpc: report anchor resolution

ab451f6

lnrpc: expose commit hashes for waiting close channels

d60303b

To make it easier to determine which pending sweep to bump in order to get your anchor commitment tx confirmed.

lncli: add bumpchannelclose command

fa115b5

This command allows users to easily bump the fee on their unconfirmed closing transactions.

joostjager force-pushed the anchor-output-poc-joost branch from afc5023 to fa115b5 Compare March 18, 2020 11:27

joostjager merged commit e2052f7 into lightningnetwork:master Mar 18, 2020

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cnct: anchor output sweeping and fee bumping #3758

cnct: anchor output sweeping and fee bumping #3758

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cnct: anchor output sweeping and fee bumping #3758

cnct: anchor output sweeping and fee bumping #3758

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