Add support for zero-fee commitment format #3192
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We add support for the zero-fee commitment format specified in lightning/bolts#1228. Channels using this commitment format benefit from better protection against pinning attacks (thanks to TRUC/v3 transactions), don't need the `update_fee` mechanism, have less dust exposure risk, and use an overall simpler state machine. In this commit, we simply introduce the commitment format and create the corresponding transactions.
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Now that we mostly use anchor channels where HTLC txs have a feerate of `0 sat/byte`, we don't benefit from the output "trimming" mechanism anymore: we must set a `dust_limit` that ensures that we only create outputs when they are economical to spend on-chain.
It isn't delayed anymore for v3 transactions. We could use static wallet public key, but in most cases it wouldn't work and adds extra complexity so we don't do it. We add a comment in the documentation of this class to explain why we're always making a 2nd-stage transaction.
We apply slightly different validation for zero-fee commitments: - the commit feerate must be `0 sat/byte` - the max number of accepted HTLCs must be at most 114 - `update_fee` cannot be used We verify those requirements during channel creation and add tests for normal channel operation.
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## master #3192 +/- ##
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+ Coverage 86.43% 88.95% +2.51%
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Files 242 218 -24
Lines 22607 20538 -2069
Branches 832 810 -22
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- Hits 19541 18270 -1271
+ Misses 3066 2268 -798
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We add support for the zero-fee commitment format specified in lightning/bolts#1228.
Channels using this commitment format benefit from better protection against pinning attacks (thanks to TRUC/v3 transactions), don't need the
update_feemechanism, have less dust exposure risk, and use an overall simpler state machine.This isn't ready to review yet, important details and tests are missing.