Add TLVs required for splicing taproot channels#1324
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t-bast wants to merge 3 commits intolightning:masterfrom
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Add TLVs required for splicing taproot channels#1324t-bast wants to merge 3 commits intolightning:masterfrom
t-bast wants to merge 3 commits intolightning:masterfrom
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Splicing allows spending the current funding transaction to replace it with a new one that changes the capacity of the channel, allowing both peers to add or remove funds to/from their channel balance. Splicing takes place while a channel is quiescent, to ensure that both peers have the same view of the current commitments. We don't want channels to be unusable while waiting for transactions to confirm, so channel operation returns to normal once the splice tx has been signed and we're waiting for it to confirm. The channel can then be used for payments, as long as those payments are valid for every pending splice transactions. Splice transactions can be RBF-ed to speed up confirmation. Once one of the pending splice transactions confirms and reaches acceptable depth, peers exchange `splice_locked` to discard the other pending splice transactions and the previous funding transaction. The confirmed splice transaction becomes the channel funding transaction. Nodes then advertize this spliced channel to the network, so that nodes keep routing payments through it without any downtime.
When sending `tx_add_input`, we previously required transmitting the entire transaction being spent to prevent malleability issues where attackers replace a `p2wpkh` input by a `p2pkh` input after signing. When both participants of the interactive-tx protocol sign a taproot input, this malleability issue disappears. We thus allow transmitting only the utxo amount and script in that case. For simplicity, we only allow this when splicing a taproot channels (where both participants sign the previous funding output) or when *all* inputs are using taproot (we could be less strict, but being too smart here may risk losing funds, so we err on the cautious side).
We add musig2 nonce fields in various `interactive-tx` messages to allow using taproot channels with dual funding and splicing.
Roasbeef
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Mar 9, 2026
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Nice to have this follow up!
| transaction | ||
| - MUST set `sequence` to be less than or equal to 4294967293 (`0xFFFFFFFD`) | ||
| - If the transaction splices an existing taproot channel or only uses taproot inputs: | ||
| - MAY omit `prevtx` (and set `prevtx_len` to `0`) and provide the amount and script |
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Prob too late to also make prevtx a TLV given already deployed?
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Yeah, unfortunately this shipped has sailed, but it's only two bytes wasted so it's probably fine even though it isn't very elegant...
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We add support for splicing and dual-funding taproot channels. Each commit adds a specific feature that leverages taproot and splicing:
prevtxfield when using taproot: there are caveats because of malleability issues (see https://delvingbitcoin.org/t/malleability-issues-when-creating-shared-transactions-with-segwit-v0/497 for more details)This PR will be moved out of draft after #1160 and #995 are merged.