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BOLT#02: clarify coop close requirements #970

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Jul 18, 2022
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BOLT#02: clarify coop close requirements #970

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21 changes: 13 additions & 8 deletions 02-peer-protocol.md
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Original file line number Diff line number Diff line change
Expand Up @@ -604,8 +604,9 @@ A sending node:
- MUST NOT send a `shutdown`.
- MUST NOT send multiple `shutdown` messages.
- MUST NOT send an `update_add_htlc` after a `shutdown`.
- if no HTLCs remain in either commitment transaction:
- MUST NOT send any `update` message after a `shutdown`.
- if no HTLCs remain in either commitment transaction (including dust HTLCs)
and neither side has a pending `revoke_and_ack` to send:
- MUST NOT send any `update` message after that point.
- SHOULD fail to route any HTLC added after it has sent `shutdown`.
- if it sent a non-zero-length `shutdown_scriptpubkey` in `open_channel` or `accept_channel`:
- MUST send the same value in `scriptpubkey`.
Expand Down Expand Up @@ -637,10 +638,13 @@ shutdown starts, the question of how to behave if it wasn't is avoided:
the sender always sends a `commitment_signed` first.

As shutdown implies a desire to terminate, it implies that no new
HTLCs will be added or accepted. Once any HTLCs are cleared, the peer
may immediately begin closing negotiation, so we ban further updates
to the commitment transaction (in particular, `update_fee` would be
possible otherwise).
HTLCs will be added or accepted. Once any HTLCs are cleared, there are no commitments
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HTLCs will be added or accepted. Once any HTLCs are cleared, there are no commitments
HTLCs will be added or accepted. Once any HTLCs are cleared, there are no commitments

for which a revocation is owed, and all updates are included on both commitment
transactions, the peer may immediately begin closing negotiation, so we ban further
updates to the commitment transaction (in particular, `update_fee` would be
possible otherwise). However, while there are HTLCs on the commitment transaction,
the initiator may find it desirable to increase the feerate as there may be pending
HTLCs on the commitment which could timeout.

The `scriptpubkey` forms include only standard segwit forms accepted by
the Bitcoin network, which ensures the resulting transaction will
Expand All @@ -659,8 +663,9 @@ The `shutdown` response requirement implies that the node sends `commitment_sign

### Closing Negotiation: `closing_signed`

Once shutdown is complete and the channel is empty of HTLCs, the final
current commitment transactions will have no HTLCs, and closing fee
Once shutdown is complete, the channel is empty of HTLCs, there are no commitments
for which a revocation is owed, and all updates are included on both commitments,
the final current commitment transactions will have no HTLCs, and closing fee
negotiation begins. The funder chooses a fee it thinks is fair, and
signs the closing transaction with the `scriptpubkey` fields from the
`shutdown` messages (along with its chosen fee) and sends the signature;
Expand Down