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Implement option_simple_close #2747

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Implement option_simple_close #2747

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@t-bast t-bast commented Sep 20, 2023

Implement option_simple_close as defined in lightning/bolts#1096

Hopefully this is the last time we change the mutual close protocol! And at some point that will let us entirely remove all the code supporting the two previous mutual close protocols (this is why I kept the code as separate as possible instead of trying to fit into the existing NEGOTIATING state).

Note that this is a prerequisite for taproot channels: this protocol allows nodes to safely exchange nonces in shutdown and closing_complete to spend a musig2 channel output.

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codecov-commenter commented Sep 20, 2023

⚠️ Please install the 'codecov app svg image' to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 87.41497% with 37 lines in your changes missing coverage. Please review.

Project coverage is 86.18%. Comparing base (b8e6800) to head (3708ab9).
Report is 4 commits behind head on master.

Files with missing lines Patch % Lines
...in/scala/fr/acinq/eclair/channel/fsm/Channel.scala 83.84% 21 Missing ⚠️
...c/main/scala/fr/acinq/eclair/channel/Helpers.scala 88.88% 6 Missing ⚠️
...la/fr/acinq/eclair/channel/fsm/ErrorHandlers.scala 40.00% 6 Missing ⚠️
...la/fr/acinq/eclair/transactions/Transactions.scala 94.87% 2 Missing ⚠️
...n/scala/fr/acinq/eclair/balance/CheckBalance.scala 0.00% 1 Missing ⚠️
...la/fr/acinq/eclair/io/OpenChannelInterceptor.scala 0.00% 1 Missing ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files
@@            Coverage Diff             @@
##           master    #2747      +/-   ##
==========================================
- Coverage   86.30%   86.18%   -0.13%     
==========================================
  Files         224      224              
  Lines       19867    20326     +459     
  Branches      795      805      +10     
==========================================
+ Hits        17147    17517     +370     
- Misses       2720     2809      +89     
Files with missing lines Coverage Δ
...core/src/main/scala/fr/acinq/eclair/Features.scala 100.00% <100.00%> (ø)
...in/scala/fr/acinq/eclair/channel/ChannelData.scala 100.00% <100.00%> (ø)
...in/scala/fr/acinq/eclair/channel/Commitments.scala 96.84% <100.00%> (+0.01%) ⬆️
...a/fr/acinq/eclair/channel/fsm/CommonHandlers.scala 89.36% <100.00%> (+4.06%) ⬆️
...inq/eclair/channel/fund/InteractiveTxBuilder.scala 92.82% <100.00%> (+0.21%) ⬆️
...n/scala/fr/acinq/eclair/io/PeerReadyNotifier.scala 71.75% <100.00%> (+0.21%) ⬆️
...n/scala/fr/acinq/eclair/json/JsonSerializers.scala 96.42% <ø> (ø)
...ire/internal/channel/version4/ChannelCodecs4.scala 98.53% <100.00%> (+0.06%) ⬆️
...ala/fr/acinq/eclair/wire/protocol/ChannelTlv.scala 100.00% <100.00%> (ø)
.../eclair/wire/protocol/LightningMessageCodecs.scala 99.47% <100.00%> (+0.01%) ⬆️
... and 7 more

... and 9 files with indirect coverage changes

This feature adds two new messages:

- `closing_complete` sent after exchanging `shutdown`
- `closing_sig` sent in response to `closing_complete`
The spec allows the closer to use an OP_RETURN output if their amount is
too low when using `option_simple_close`.
We introduce a new `NEGOTIATING_SIMPLE` state where we exchange the
`closing_complete` and `closing_sig` messages, and allow RBF-ing previous
transactions and updating our closing script.

We stay in that state until one of the transactions confirms, or a force
close is detected. This is important to ensure we're able to correctly
reconnect and negotiate RBF candidates.

We keep this separate from the previous NEGOTIATING state to make it
easier to remove support for the older mutual close protocols once we're
confident the network has been upgraded.
Whenever one side sends `shutdown`, we restart a signing round from
scratch. To be compatible with future taproot channels, we require
the receiver to also send `shutdown` before moving on to exchanging
`closing_complete` and `closing_sig`. This will give nodes a message
to exchange fresh musig2 nonces before producing signatures.

On reconnection, we also restart a signing session from scratch and
discard pending partial signatures.
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